Commission for Instruments Methods of Observation

WORLD METEOROLOGICAL ORGANIZATION

COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION

ABRIDGED FINAL REPORT OF THE FOURTH SESSION

Tokyo, 4th -15th October 1965

PRICE: Sw. fro 10.50

I WMO-No. 185. RP. 68 I

Secretariat of the World Meteorological Organization - Geneva • Switzerland 1966 , C" CONTENTS

Page List of representatives attending the session • VI Agenda IX General sunllllary of the work of the session 1 Resolutions adopted by the ses-sion 26

Final Session No. No. 1 2.1/1- Rapporteur on duration of leaf wetness 26

~ 3/1 Working Group on Measurement of Precipitation 26 3 4/1 Working Group on Evaporation Measurement 27 4 5/1 Working Group on Hygrometry • • • • • • • 27 5 5/2 Rapporteur on measurement of temperature 28 6 7/1 Working Group on Instruments and Methods of Observation on Aerodromes • • • • • 29 7 8/1 Working Group on Use of Meteorological Radar for Aeronautical Purposes • • . • • • • • • • • • • • 30 8 9/1 Working Group on Radiation Instruments and Qbservations for General Use . • • • . • . . . • • • . • • • • • 31 9 9/2 Working Group on Special Radiation Instruments and Observations • • • • • • • • • 32 10 10.1/1 Working _Group on Radiosonde and Radiowind Measurements 32 11 10.2/1 Rapporteur on radiowlnd observations on board merchant sllips . . • . . . . . • ...... • • • . • • 33 12 10.4/1 Rapporteur on radiosonde and radiowind computation tecl'm.iques • • • • • • • • • • • • • • • • • • 34 13 10.5/1 Rapporteur on instrumental aspects of dropsonde observations ...... • 35 14 10.7/1 Working Group on Sensors and Telemetry for Meteorological Rockets ••• 35 15 10.8/1 Rapporteur on meteorological instrumental requirements for supersonic transport aircraft operations • • • • • • 16 12/1 Working Group on Measurement of Atmospheric Electricity • 17 13/1 Rapporteur on lower troposphere soundings • 18 14/1 Rapporteur on accuracy of measurements 19 16/1 Executive Working Group of-CIMO •••••• 20 18/1 rtapPQrteur on measurement of atmospheric radioactivity and Working Group on Standardization and Int~rcoropar~son of Radioactivity Measurements ••••••••••••••• 39 IV CONTENTS

Final Session (continued) No. No. 21 19/1 Working Group on Observations in Polar Regions • • • 40 22 23/1 Working Group on Training in Instruments and Methods of Observation. •••••••••••••••• 40 23 24/1 Revision of the resolutions and reoommendations of CIMO 41

Recommendations adopted by the seqsion 42

Final Session No. No. 1 9/1 National and regional radiation centres. . 42 2 9/2 World radiation centre 42 3 9/3 Comparisons of pyrheliometers 43 4 10.1/1 Comparison of radiosondes • . 44 5 11/1 Radio frequency allocations 44 6 13/1 Lower troposphere soundings . . . . 46' 7 17/1 Comparisons of instruments 46 8 17/2 Inter-regional comparisons of barometers 47 9 21/1 Revision of Te.ohnical Regulations • . 47 10 22/1 Terms of reference of the Commission 49 11 24/1 Revision of resolutions of the Executive Committee based on previous recommendations of CIMO ...... 49

Annexes I Annex to paragraph 5.1 of the General Summary Reference hygrometers covering a wider range than obtainable with the psychrometer ...... f. . . • • • • . • • • . • . • • • 51 II Annex to paragraph 8.3 of the General Summary Note on the feasibility of determining the height of convective cloud tops • ...... • " ...... 60 III Annex to paragraph 20.2 of the General Summary Proposal for a standard layout for chapters of'the Guide to Meteorological Instrument and Observing Practices • • • • • 62 IV Annex to paragraph 20.3 of the General Summary Amendments to the Guide to Meteorological Instrument and Observing Practices ...... V Annex to Recommendation 1 (CIMO-IV) Regional and national radiation centres ...... VI Annex to Recommendation 4 (CIMO-IV) Accuracy requirements stated by technical commissions ...... 69 CONTENTS v

Annexes (continued) VII Annex to Recommendation 7 (CIMO-IV) Programme of international comparisons of meteorological instruments. 70

List of documents 71 VI

LIST OF REPRESENTATIVES ATTENDING THE SESSION

L Officers of the session L. S. Mathur president M. Yoshitake vice-president

2. Representatives of Members of WMO A.G. Maenhout principal delegate Belgium M.E. Etienne delegate L.J. Koenigsfeld delegate J.M. dos Santos principal delegate Brazil K.E. Potter principal delegate British Caribbean Territories and British Guiana H.H. Bindon principal delegate Canada R.E. Vockeroth delegate M. Clerebaut principal delegate Congo (Dem.Rep. of) A. Kadima delegate J.W. O'Byrne adviser V. VliisaHi principal delegate Finland Y. I. Toivola delegate V. Marc principal delegate France C. Perrin de Brichambaut delegate A. Rouaud delegate H. Treussart delegate M. Hinzpeter principal delegate Germany (Federal Republic of) J. Grunow delegate L.S. Mathur principal delegate India Miss A.M. Mani delegate M. Thaller principal delegate Israel G. Cena principal delegate Italy M. Yoshitake principal delegate Japan M. Ito delegate N. Arizumi delegate S. Ohta delegate T. Kitaoka delegate M. Sanuki adviser I. Oyama adviser H. Fujiwara expert I. Imai expert J. Kobayashi expert K. Otani expert I. Shimizu expert K. UChikawa expert LIST OF REPRESENTATIVES

Ch. Kim principal delegate Korea

B. Azmy principal d~legate Morocco C.M. Wierda principal delegate Netherlands J.H. Rietman delegate J. Knudsen principal delegate Norway R.L. Kintanar principal delegate Philippines H. de la Cruz delegate H.M. Siraj principal delegate Saudi Arabia A.A. Salih principal delegate Sudan M. Aronsson principal delegate Sweden S. Suwanpong principal delegate Thailand B.G. Rozdestvenski principal delegate U.S.S.R. N.P. Rusin delegate V.I. Shlyakhov delegate Miss E.S. Bocieva interpreter Mrs. N.Ju. Vajl interpreter A.L. Maidens principal delegate United Kingdom N.E. Rider delegate W.R. Linton delegate Ch. Harmantas principal delegate U.S.A. V.D. Rockney delegate V.S. Hardin delegate R.M. Marchgraber delegate D.T. Acheson adviser L.M. Polan adviser V. Figuera principal delegate Venezuela A. Garant6n observer

3. Observers (a) ~Dt~~=~9Y§~9W§Dt~1_g~g~!~~~!9D§ O. Suschny International Atomic Energy Agency

(b) 9~h§~_g~g~Di~~~igD§_ H. Hatakeyama Pacific Scienoe Assooiation A. Kimpara International Scientifio Radio Union D.E. Bertin InternaUonal Air Transport Assooiation T. ';['akeda International Air Transport Assooiation

4. Representatives of WMO Seoretariat K. Le,nglo Representative of Secretary-General O.M. Ashford Permanent Seoretary of CIMO

5. Seoretariat of the session M. Yoshitake Chief M. Ito Exeoutive Seoretary S. Tajima Exeoutive Seoretary VIII LIST OF REPRESENTATIVES

Secretariat of the session (continued) S. Ono Assistant Secretary (Administration) K. Takeuchi Assistant Secretary (Documentation) N~ Suzuki Assistant Secretary (Documentation) Y. Oka Assistant Secretary (Social events)

I "'" IX

AGENDA

Agenda Relevant Res. Rec. item Documents No. 1. Organization of the session 1.1 Opening of the session 1.2 Report on credentials 1.3 Adoption of the agenda I, Add, I, 2 2, Add. I, 2, 3 1.4 Election of a vice-president for the session 1.5 Establishment of committees .1.6 Programme of work of the session

2. Reports 2.1 Report by the president of 31, Add. 1, 2; 70 1 the Commission 2.2 Reports by chairmen of 4; 5; 6; 7; 8; 10; working groups 11; 17; 18; 19; 24; 40; 46; 50; 52 2.3 Reports by rapporteurs 3; 55

3. Precipitation 24; 29; 46; 81 2

4. Evaporation 6, Corr. 1; 68 3 5. Surface temperature and humidity 17; 28; 62; 101 4,5

6. Barometer comparisons 43; 56. Add. 1; 69 7. Instruments and methods of II, Add. 1, Corr. 1; 6 observation on aerodromes 51; 63; 94

8. Uses of radar in meteorology 30; 45; 52; 64; 83 7

Radiation 4, Add. 1; 40; 41; 8,9 I, 2, 3 42; 61; 80

10. Upper-air measurements 10.1 Radiosondes 19; 36; 58; 60; 92 10 4 10.2 Radiowind measurements on 7; 76 11 board merchant ships 10.3 Radiosonde hygrometry 50; 57; 77 x AGENDA

Agenda Relevant item Documents Res. Rec. No. 10.4 Computation techniques 79 12 10.5 Dropsonde observations 27; 67; 13 10.6 Horizontal soundings 16; 66 10.7 Meteorological rockets 32; 93 14 10.8 Instrumentation for supersonic 48;·54; 78 15 transport (SST) aircraft

11. Radio-frequency allocations 23, Add. 1; 88 5 12. Atmospheric electricity 18; 74 16 13. Lower troposphere soundings 8, Add. 1·• 75 17 6 14. Accuracy of measurements 5; 25; 35; 38; 18 47; 84 15. Instrument standards 14; 26; 95

16. Instrument development 10, Add. 1; 33; 39; 19 44; 49; 51; 65~ 71 17. Comparisons of instruments 20, Add. 1; 53; 98 7, 8 18. Atmospheric radiQactivity 3; 34; 59; 87 20 19. Observations in Antarctica 55; 72 21

20. Guide to Meteorological Instrument 22, Add. 1; 97 and Observing Practices

21. Technical Regulations 21, Add. 1, 2·• 99 9 22. Terms of reference of the 12, Add. 1·• 86 10 Commission

23. Training in instrumehts and methods 13;. 85 22 of observation

24. Review of previous resolutions and 15; 96 23 11 recommendations of the Commission and relevant Executive Committee decisions

25. Establishment of working groups 9; 73; 91

26. Election of officers 82; 90

27. Date and place of the fifth session

28. Scientific lectures and discussions 37; 100 GENERAL SUMMARY OF THE WORK OF THE SESSION

1. ORGANIZATION OF THE SESSION (Agenda item 1)

At the invitation of the Government of Japan, the fourth session of the Commission for Instruments and Methods of Observation (CIMO) was held in Tokyo from 4 to 15 October 1965. The meeting took place at the Takanawa Prince Hotel, where excellent accommodation and equip ment was provided for carrying out the work of the session. The Commission held six plenary meetings and the proceedings were greatly facili tated by the simultaneous interpretation in English and French both during the plenaries and during the meetings of the two main working committees.

1.1 Opening of the session (Agenda item 1.1) The session opened at 11.00 a.m. on 4 October 1965 with the president of the Commission, Dr. L.S. Mathur, in the chair. In welcoming the delegates and guests as the Permanent Representative with WMO of the host country, Dr. Yoshizi Shibata referred to the importance of the applications of meteo rology and stressed the need for more knowledge of the Earth's atmosphere. He expressed the hope that the results of the session would contribute to the development of meteorological services in the world. Mr. Bunshichi Hoshi, Director of the United Nations Bureau, Ministry of Foreign Affairs, then addressed the session on behalf of the Minister of Foreign Affairs. He indi cated that the Ministry provided support for the activities of the United Nations specialized agencies in their efforts to advance scientific technology and thus to benefit humanity. He mentioned the recent rapid progress in the field of meteorological observations, including the use of weather satellites, and concluded by expressing his best wishes for a fruitful session. The representative of the Secretary-General of WMO, Dr. K. Langlo, expressed the regrets of the Secretary-General at not being able to be present in person. On his behalf, Dr. Langlo oonveyed greetings to all participants and good wiShes for the success of the session. Dr. Langlo then referred to the planning of the World Weather Watch and ment,ioned that many of the items on the agenda for the session were of great importance in this connex tion. He considered that the Commission could make an important contribution by advising the countries of the world on how the new observational requirements could best be met. He also stressed the importance of the role of the Commission in the field of standardization. In conclusion, Dr. Langlo conveyed the thanks of WMO to the Government of Japan for making the session possible. The meeting was then addressed by Mr. Herbin, Director of the United Nations Information Center in Tokyo. In conveying the best wiShes of the United Nations, he referred to the value of international co-operation on the technical level during a period of troubled international relationships. In his presidential address, Dr. Mathur spoke of Tokyo as an ideal venue for this session. He was sure that many delegates who were visiting Japan for the first time would wish to return again. He then outlined the history of international co-operation in the field of standardization of instruments and methods of observation, with special reference to the role of WMO and the activities of CIMO. Recent developments such as the introduction of meteorological satellites and planning of the International Hydrological Decade provided 2 GENERAL SUMMARY incentives for developing improved instrumentation and represented a challenge to the spe cialists in this field. Dr. Mathur was pleased to note the growing number of members of the Commission and paid special tribute to his colleagues who had contributed by serving on work ing groups of the Commission. He also spoke of the support which he received from the WMO Secretariat and concluded witha tribute to the excellent arrangements made for the session by the Director General of the Japan Meteorological Agency and his colleagues, particularly Dr. M. Yoshitake, chief of the local secretariat. The final remarks at the opening ceremony were made by Dr. M. Yoshitake who ex pressed cordial thanks on behalf of the local secretariat to all the partiqipants at the session. There were 67 participants at the session. These included representatives from 25 countries and 4 international organizations. The WMO Secretariat was represented by Dr. K. Langlo and Mr. O.M. Ashford. A complete list of delegates and observers is given at the beginning of this report.

1.2 Report on credentials (Agenda item 1.2) At the second plenary meeting the representative of the Secretary-General presented a list of participants based on the credentials received. This report was accepted unanimously and it was therefore decided that it would not be necessary to set up a credentials committee.

1.3 Adoption of the agenda (Agenda item 1.3) The president reported that two new items had been suggested for inclusion in the agenda. The provisional agenda thus amended was adopted at the first plenary meeting. The fjnal agenda is given at the beginning of this report. Lists of relevant documents and de cisions are also provided.

1.4 Election of a vice-president for the duration of the session (Agenda item 1.4) The death of Mr. A. Hauer had left vacant the post of vice-president of the Commission. Dr. M. Yoshitake was unanimously elected to serve as vice-president for the duration of the session.

1.5 Establishment of committees (Agenda item 1.5)

1.5.1

Two working committees were set up to examine in detail the various agenda items: (a) Committee A to deal with agenda items 2.1, 3, 4, 5, 6, 9, 14, 15, 16, 17, 19, 20 and-25~--i5f;. M. Hinzpeter (Federal Republic of Germany) and Mr. H.H. Bindon (Canada) were elected chairman and vice-chairman respectively and Mr. O.M. Ashford (WMO Secretariat) served as secretary to this committee. (b) Committee B to deal with agenda items 2.1, 8, 10, 11, 12, 13, 18, 20, 21, 22, 23, 24~-25-and-28. Mr. V.D. Rockney (United States of America) was elected chairman and Dr. K. Langlo (WMO Secretariat) acted as secretary to this committee. Committee A reported to plenary on the three common items, i.e., 2.1, 20 and 25.

1.5.2 Co-ordination Committee In accordance with Regulation 26 of the General Regulations of WMO, a Co-ordina tion Committee consisting of the president, the vice-president, the representative of the Secretary-General of WMO and the chairmen of Committees A and B was established. GENERAL SUMMARY 3

1.5.3 Nomination Committee In accordance with Regulation 22 of the General Regulations of WMO, a Nomination Committee was established consisting of Messrs H.H. Bindon (Canada), chairman; M. Clerebaut (Democratic Republic of the Congo), J.M. dos Santos (Brazil), B. Rozdestvenski(U.S.S.R.), S. Suwanpong (Thailand), G. Cena (Italy) and R.L. Kintanar (Philippines). Mr. H.H. Bindon unfortunately had to return home before the end of the session owing to illness and his place as chairman of the committee was then taken by Mr. Ch. Harmantas (U.S.A.).

1.5.4 A committee for nominating members of working groups and rapporteurs was also established. It consisted of the presiden~, the vice-president, the chairmen of Committees A and B, and in addition Messrs. B. Rozdestvenski (U.S.S.R.), V. Marc (France), and V. Figuera (Venezuela) •

1.6 Programme of work of the session (Agenda item 1.6) As already mentioned, the Commission held in all six plenary meetings. The minutes of the first three meetings were adopted at subsequent plenary meetings and the president was authorized to approve the remaining minutes on behalf of the Commission.

2. REPORTS (Agenda item 2)

2.1 Report by the president of the Commission (Agenda item 2.1)

2.1.1 The report of the president was noted with satisfaction. Delegates were particularly appreciative of the six-monthly progress reports which the president had prepared regularly since the third session of the Commission. It was also felt that the very sub stantial achievements of the working groups owed much to the leadership of the president.

2.1.2 Most of the matters raised in the president's report were the subject of documents under other items of the agenda and were accordingly discussed under these respective items. With regard to the comparisons being carried out in India and the U.S.A. of instru ments for measuring the duration of leaf wetness, it was agreed that the period of trial had been too short for valid conclusions to be drawn and that this work should therefore be con tinued. In order to keep the Commission informed about these activities it was decided to nominate a rapporteur with the terms of reference given in Resolution 1 (CIMO-IV).

2.2 Reports by chairmen of working groups (Agenda item 2.2) The reports submitted by the chairmen of the working groups were first presented to plenary and then studied in detail by the working committees under the corresponding item of the agenda. The action taken by the Commission on these reports will therefore be found under agenda items 3, 4, 5, 7, 8, 9, 10.1, 10.2, 10.3, 12, 13, 14, 16.

2.3 Reports by rapporteurs (Agenda item 2.3) The reports submitted by rapporteurs were first presented to plenary and then studied in detail by the working committees under the corresponding item of the agenda. The action taken by the Commission on these reports will therefore be found under agenda items 18 and 19. 4 GENERAL SUMMARY

3. PRECIPITATION (Agenda item 3)

3.1 The Commission noted with satisfaction the report of the Working Group on Snow Measurements. Although it had not been possible for the group to meet, a chapter had been drafted for the Guide to Meteorological Instrument and Observing Practices on the IIMeasure ment of- Solid Precipitation and Snow Gover". The members of the group present at Tokyo held an informal meeting and reached agreement on the final version of the chapter, the text of which was handed over to one of the WMO Secretariat representatives at the session. The Commission decided to request the Secretary-General to arrange for this chapter to be published after taking into account any suggestions made -by the presidents o~ CRy and CCI. to whom it should be submitted for comment. The nomenclature for snow structure used in the chapter should also be brought into line with the nomenclature published in August 1954 by the Com mission on Snow and Ice of the International Association of Hydrology. 3.2 The working group had also studied the various sources of error involved in measuring solid precipitation. The errors due to wetting of the surface of the gauge and to evapo ration were much smaller than those due to the effects of wind. The Commission decided that these investigations should be continued. with special reference to wind effects. 3.3 The CIMO representative on the CRy Working Group on Instruments and Methods of Observation reported on the activities of the group. He considered that there was need for continued close collaboration between ClMO and CRy and it was agreed that the president of CRy would be welcome to designate representatives to serve on any CIMO working group whose terms of reference were of direct interest to CRy. 3.4 After the untimely death of the chairman of the Working Group on International Comparisons of Precipitation Gauges, the files of the group had been transferred temporarily to the Secretariat. A report on the activities of the group submitted by the Secretary General indicated that the main achievement had been the successful launching of the compa risons of national precipitation gauges against the International Reference Precipitation Gauge (IRPG). OWing to various delays in the ordering and production of the lRPG, the com parisons had only started in some countries in 1964 and 1965, and it had therefore not been possible for the group to report on the results of the comparisons. 3.5 In order to obtain results of statistical significance. the Commission considered that the comparisons should continue until the end of 1968. Some delegates believed that a sunken gauge would give a higher absolute accuracy than the IRPG, but it was reported that tests in India had shown that two IRPGs installed side by side gave very consistent results, with differences of only 0.1 to 0.2 per cent. 3.6 In Resolution 2 (CIMO-IV) it was decided to establish a Working Group on Measure- ment of Precipitation to report on the results of precipitation gauge comparisons and to study further the sources of error in measuring both solid and liquid preoipitation.

4. EVAPORATION (Agenda item 4)

4.1 The Commission noted with satisfaction the report of the Working Group on Evapo- ration Measurement and recommended that Appendix III of the report be published as a WMO Technical Note. The working group had also drafted a separate chapter on the measurement of evaporation to replace the existing section 7.6 of the Guide to Meteorological Instrument and Observing_ Practices. The Secretary-General was requested to undertake the final editing of this chapter in the light of suggestions made during the session and of any comments re ceived from the presidents of CAgM and CRy. If necessary he should consult the chairman of the Working Group on Evaporation Measurement, which was re-established by Resolution 3 (ClMO-IV). 4.2 As the the comparisons of various types of evaporation pans being conducted by Members in response to Recommendation 4 (elMO-III) had not been completed, the former, working GENERAL SUMMARY 5 group had not been able to discharge fully the relevant items of its terms of reference. The new working group was accordingly requested to continue these studies.

5. SURFACE TEMPERATURE AND HUMIDITY (Agenda item 5)

5.1 The Commission noted with satisfaction the report of the Working Group on Psy- chrometry and examined in particular the proposals concerning the design of a portable refer ence psychrometer. The group1s very thorough approach to this problem was greatly appre ciated but some doubts were expressed as to whether the psychrometers proposed might not prove to be too costly to serve as portable reference instruments. In Resolution 4 (CIMO-IV) it was decided to establish a Working Group on Hygrometry to continue the work on the portable reference psychrometer and to give further attention to ways of improving the accuracy of routine measurements of humidity below freezing point, for which purpose a psychrometer is not really suitable. In this connexion, the Commission decided that the seQtion of the working group1s report entitled llReference hygrometers covering a wider range than obtainable with the psychrometerll should be reproduced as Annex I to the Abridged Final Report of the session. The Commission also recommended that WMO should provide funds for experiments on hygrometers required in implementing the terms of reference of the Working Group on Hy grometry.

5.2 Under this item, the Commission also considered the design and exposure of thermometer screens. In response to requests for advice on the best form of screen for use in the tropics, the president had encouraged Members to conduct some experiments on various types of screens. The results reported at the session indicated that differences of tempe rature between different types of screens could amount to 2° or even 3°C in extreme cases. It was stressed that many investigations of this problem had been carried out in the past and it was agreed that it would be useful to carry out a critical survey of the results al ready available. It was accordingly decided in Resolution 5 (CIMO-IV) to designate a rappor teur to make this survey.

6. BAROMETER COMPARISONS (Agenda i tern 6 )

6.1 Under this item the Commission reviewed the results of trials conducted by Members on the use of aneroid barometers and hypsometers as travelling standards for barometer com parisons. It was agreed that the following text should be incorporated in section p.5 of the Guide to Meteorological Instrument and Obs~rving Practices. Precision aneroid barometers may be used as travelling standards provided they have the necessary stability and accuracy. It is recommended that two or more such instru ments be used at a time so that any change in any one can be detected immediately. An ane roid barometer which is used for this purpose must not suffer from hysteresis effects. Fur ther it should have a negligible temperature coefficient. These features can only be obtained by the use of special materials and design. An essential feature of a suitable instrument is that the aneroid capsule should not be loaded by the indicating mechanism.

7· INSTRUMENl'S AND METHODS OF OBSERVATION ON AERODROMES (Agenda item 7) 7.1 The Commission examined the report of the Working Group on Instruments and Methods of Observation on Aerodromes and noted with satisfaction the progress achieved. Attention was given in particular to the working group1s proposals with regard to Recommendations 2/1, 2/2, 2/3, 2/4, 2/8, and 5/3 of the third session of CAeM, held simultaneously with the Meteo rology and Operations Divisional Meeting of ICAO. The working group had drafted amendments for the Guide to Meteorological Instrument and Observing Practices, to take account of the above recommendations. The Commission approved these amendments with some modifications and 6 GENERAL SUMMARY

the final text was handed to the representative of the Secretary-General for appropriate action.

7.2 With regard to Recommendations 2/3 and 2/4, the Commission considered that the note to Recommendation 2/4 cannot be reconciled with good observing practices. Any given anemometer using direct energy transfer can have the proper relationship at only one speed and it is unlikely that there are any anemometers in existence that approximate to the cha racteristics required by the note.

7.3 With regard to Recommendation 2/8, the Commission considered that the required accuracy of ± 1 knot for wind speeds up to 10 knots is not attainable in practice because of the highly variable character of the wind speed and direction in light wind conditions.

7.4 With regard to Recommendation 5/3. some delegates were not in favour of specifying wind in longitudinal and lateral components but the majority view was that although such in formation could not, in general, be provided at the present time, this information is likely to become an operational necessity in the future and efforts should therefore be made to de velop appropriate instruments. The Secretary-General was requested to communicate the working group's comments on Recommendation 5/3 and a report on the above discussions to the rapporteur on accuracy requirements.

7.5 At the suggestion of ICAO, the Commission agreed that the proposed amendments to the Guide to Meteorological Instrument and Observing Practices regarding visibility para meters should not be PUblished in the Guide until action on Recommendations 5/8 and 5/9 of the MET/OPS/CAeM-III meeting has been completed.

7.6 In view of the need for continuing the work on. instruments and methods of observation on aerodromes, it was decided in Resolution 6 (CIMO-IV) to re-establish the working group for this purpose.

8. USES OF RADAR IN METEOROLOGY (Agenda item 8)

8.1 The Commission noted with appreciation the report of the Working Group on Uses of Radar in Meteorology. It was informed that a revised version of Technical Note No. 27 had recently been submitted to the Secretary-General for publication and that the Note would be published both in English and French. The Commission noted that the revised Note will contain two additional chapters, one c~vering measurements of rainfall rate and the other radarscope photography. On the other hand, the chapter on use of radar in research has been omitted because it was considered that the Note is mainly intended for operational purposes. The Commission had no comments to offer on these changes.

8.2 The working group also submitted to the session a draft chapter on observations of precipitation for inclusion in the Guide to Meteorological Instrument and Observing Prac tices. This chapter was accepted with only a few editorial corrections and the approved draft was handed over to the representative of the WMO Secretariat at the session.

8.3 Under this item the Commission considered the request from Regional Association VI at its fourth session (paragraph 12.2.3 of the General Summary) about the feasibility of de termining the height of tops of convective clouds for the safe operation of supersonic air craft. The Commission had some difficulty in determining the exact meaning of the above re quest but agreed that the best way of handling the matter would be to draft a note explaining the present possibilities for determining the heights of tops of convective clouds. This note is reproduced as Annex II to this report. The president of CIMO was requested to convey these views to the president of Regional Association VI and also to the presidents of CAeM and CSM. GENERAL SUMMARY 7

8.4 During the discussion of this item and also of item 10.8~ Instrumentation for Supersonic Transport Aircraft, it was felt that there was a need for further studies of the use of radar for the purposes of safe operation of supersonic aircraft. This applies both to ground-based radar and to airborne radar. It was also pointed out that there was a need for guidance material for training personnel in the use of airborne radar. The Commission agreed that the above task could best be carried out by a working group which could deal with all questions ~e1ated to the use of meteorological radar for aeronautical purposes. The terms of reference of this working group are given in Resolution 7 (CrMO-IV).

9. RADIATION (Agenda item 9)

9.1 The Commission noted with satisfaction the reports of the Working Group on Radia tion Instruments and Observations for General Use and the Working Group on Special Radiation Instruments and Observations. Delegates spoke with appreciation of the close collaboration between these two groups and of the pUblication of the revised Chapter 9 of the Guide to Meteorological Instrument and Observing Practices~ which contained the agreed termino"logy of radiation quantities and measuring instruments.

9.2 There was general agreement that further encouragement should be given to the establishment of national and regional radiation centres. This point is covered in Recommend ation 1 (CIMO-IV)~ which specifies the functions and requirements of these centres. It was also felt that it would be very useful if one or two world radiation centres could be estab lished: and designated as such by WMO - see Recommendation 2 (CIMO-IV).

9.3 Reports were given on the progress achieved in comparing various types of radia tion instruments and it was agreed that this work should continue. Several suggestions re garding steps which ought to be taken to improve the accuracy of pyrhe1iometers were incor porat€d in Recommendation 3 (CrMO-IV).

9.4 The Commission considered that the WMO Technical Regulations should give more details regarding networks of various kinds of radiation stations and the observing programmes at these stations. The decisions on this matter were incorporated in Recommendation 9 (CIMO-IV) •

9.5 Fina11y~ it was decided in Resolutions 8 and 9 (CrMO-IV) to re-establish both radiation working groups with revised terms of reference.

10. UPPER-AIR MEASUREMENTS (Agenda item 10)

10.1 Radiosondes (Agenda item 10.1)

10.1.1 The Commission noted with appreciation the report of the Working Group on Radio- sondes. It f1.U'ther noted with interest the considerable progress made in the development of a reference radiosonde, as exemplified by the fine~ire thermometer in the Federal Republic of Germany~ the vibrating wire thermometer in France, the whirling arm thermometer in the U.S.S.R. and the fine-wire thermometer in Finland. It was the consensus that a reference radiosonde for temperature, a requirement of high priority, is almost at hand.

10.1.2 The Finnish delegation described the.ir study on heating of the balloon by sunlight and the warming of the air environment. The temperature indicated by a radiosonde suspended as far as 65 metres below the balloon did not differ much from that at a distance of 15 metres. They concluded that the measured day-night temperature differences were not due exclusively to radiation error of the sonde nor to diurnal temperature changes of the atmosphere. 8 GENERAL StlMMARY

10.1.3 The Commission noted the increasing concern of other commissions of WMO that the amount and quality of radiosonde data at high levels should be increased. Research in balloon development has progressed to the point where a height of 30 km or more can be reached quite dependably with balloons that are not excessively expensive. But there still remain problems of early bursting when temperatures are exceedingly low, as in the tropical tropopause. It was agreed that much progress has been made in developing instruments whose solar radiation corrections at high altitudes are either known and can be allowed for, or are insignificant. But it is now also evident that at very high altitudes new factors must be considered, such as : (a) long-wave radiation from the sensor itself and the sonde; (b) variable long-wave radiation from the earth and clouds under the radiosonde; (0) special problems of heat trans fer between sensors and ambient air; and (d) warming effects in day-time on an ascending sonde which is in the wake of a balloon that has been heated by solar radiation.

10.1.4 The Commission also noted that at high altitudes and in tropical regions measurement of the winds aloft is of particular importance to meteorological analysis. Jt was agreed that there is need for CIMO to increase its efforts to achieve improved international com patibility of radiowind observations.

10.1.5 It was noted that action toward improvement of data from high altitudes is also being taken under several other agenda items, such as 10.4 and 10.7.

10.1.6 The Commission Qoncluded that the entire field of radiosonde and radiowind observat ions is of great importance and decided to establish a new Working Group on Radiosonde and Radiowind Measurements. The terms of reference of this workine; group are given in Resolu ~ion 10 (CIMO-IV).

10.1.7 In view of the improved equipment now available, both for making measurements at high altitudes and for comparing the results obtained by various kinds of radiosonde systems, the Commission adopted Recommendation 4 (CIMO-IV) encouraging Members to make further compa risons of radiosondes.

]0.2 Radiowind measurements on board merchant ships (Agenda item 10.2)

10.2.1 The report of the Working Group on Radiowind Measurements on Board Merchant Ships was noted with appreciation. As an introduction to this item the chairman of the working group expanded slightly on the report to describe additional work in progress in the U.S.A. towards a solution of the problem of obtaining accurate measurements from a moving" merchant ship.

10.2.2 Several delegates ~eported on theoretical and practical studies they are making in this field. Some suggestions were made regarding problems of stabilization of antennae and automatic correction for pitch and roll of the ship.

10.2.3 There were a number of questions as to whether the working group's statement regarding the requirements for system accuracy should not also include statements as to the maximum pitch, roll and yaw of the ship, and the range of wave periods that should be accept able to the system without serious deterioration of accuracy. I r= 10.2.4 With regard to these questions it was suggested that any equipment developed for the purpose should have the following capability, or better : Azimuth angle: ± 0.5° Elevation angle + 0.25° Slant range : + 50 metres Ability to track targets up to at least 80° elevation Maximum slant range : at least 75 km GENERAL SUMMARY 9

The-above tolerances should be realized. at least until the ship experiences pitch ·and roll of':!: 5°', :t.'lOo,· .respectively, and-a wave .period·as 'short as 8-12 seconds •.

10.2.5 In view of the fact that many problems in measuring winds aloft from merchant ships coptinue to call urgently for solution; auditakiilg into .account,other activities of WMO in ,this fie1das part of theWo:r'ld,Weather Watch plarining,' the Commission decided ,to appoint a rapporteur.on·radiowind observations on board merchant ships. with the terms: of reference laid down in Resolution 11 (CIMO-IV).

10.3 Radiosonde hygrometry (Agenda. 'item 10.3) .,' . 'lO.3.1 TheContrnission noted 'with interest the 'report of the W,orking Group on Review of ,Radiosonde Hygrometry _and also a document· submitted by Japan on the comparison of 'a hair. '. hygrometer with. a dew-'point meter.

10.3.2 The Commission took note of the view expressed by the working group that, in view of the papers presented at the International. Symposium on Humidity and. Moisture 'held at Washington in May 1963, little action was called for on the part of the group itself. The proceedings of this symposium. are published in four volumes of which the first, tlPrinciples and Methods of Measuring Humidity in Gaseslf , 'edited by Robert E. Ruskin, contains material ~'of :interest. for radiosonde applications • The .. editor-in-chief of this.publication is Arnold We~ler.,·National BUreau of Standards,. U.S.A., and the prOCeedings are published by Reinhold Publishtng Cor.poration, New. York. (Chapman &.HallLtd.,London). An additional publication of interest is tllnvestigations on Hygrometrylf by J. Kobayashi in If Papers on Meteorology and Geophysicstl , Volume XI, Numbers 2 - 4, 1960, published by the Meteorological Research Insti tute'; Japan.

10.3.3.· ,The Commissi~na:gree'd that :tn view of thecomplEiteness,of the infoi'maticmin the above-mentioned' pu};)l;Lcatipns and since no "ne,v{ s,ensors have been fo~d to' date, a WMO TecbDi cal Note at this time would not be required.

10.3.4 The Commission, agreed. that it, was .. necessaryfor Members to increase their research efforts to .improve. the radiosonde humidity measurements, and action to this effect was taken under agenda ' items 10.1 and" 13.

10.4· Computation techniques (Agenda; item.·10.. .4).

··10,.4.1' . The . Commission' noted that at its flourteenth session the Executive Committee had requested CIMO to accelerate the study of standardization of computation techniques for radiosonde and radiowind observations. It was informed that the Working Group on Radiosondes had not had sufficient time to consider this question in detail: It was therefore decided to:appoint a rapporteur to examine the.matter on the basis of an inquiry to be carried out among Members of WMO; . The terms of ref~rence of the rapporteur are .given in Resolution 12 . (CIMO-IV).

10.5 Dropsonde observations(Agenda item 10.5)

10.5.1 At.the suggestion of. the president: of ClMO, the Commission examined the instrumental aspects of· dr.opsondeobservations from c.ommercial aircraft as the first step towards exploring the possibility of a practical s.oheme.

10.5.2 The representative' of, the'Secretary-General;de,scribedstudies, at present under eonsideration as·part.of the planning of the World Weather. Watch, .on the possibility of ex tending the·observatiorrsCur';J:'ently be.ir.lg made from commercii'll aircraft. rt was noted that 10 GENERAL SUMMARY one of these projects would include a long-term investigation of the possibility of dropsonde observations from commercial aircraft, and the view was expressed that the Commission should be kept currently informed of the results.

10.5.3 On request, the observer from lATA indicated that the airlines operating in the Pacific area were very interested in obtaining additional observations from areas of sparse observations and, if such observations were found feasible, lATA would consider the possibi lity of co-operating.

10.5.4 It was further noted that, as part of the World Weather Watch planning, Members would be encouraged to undertake research on the development of suitable techniques for drop sonde observations from commercial airqraft. The appropriate action for CIMO at the present stage would therefore be to appoint a rapporteur to keep abreast of the instrumental aspects of these questions and to report to the next session of ClMO. Resolution 13 (CIMO-IV) was adopted to this effect.

10.6 Horizontal soundings (Agenda item 10.6)

10.6.1 The Commission considered in some detail the document presented by the Secretary- General. on the subject of horizontal soundings. It noted that as part of the planning of the World Weather Watch consideration is being given to the PQssible use of horizontal sound ing techniques as a means of obtaining additional meteorological observations, especially over areas where the density of aerological stations cannot readily be increased to provide the necessary observations.

10.6.2 It was further noted that some Members of WMO have already developed plans for' detailed experiments using horizontal sounding techniques and that the first of these ex periments will be conducted in the very near future. The Commission expressed great interest in· these experiments and it was agreed that, suitable machinery should be established to keep the president of the Commission informed of important developments in this field.

10.6.3 The Commission was informed that the Secretary-General would, as part of the World Weather Watch activities, collect information on the results of experiments with horizontal soundings and it was stressed that these reports would be of particular interest to CIMO if they contained full information about the instrumental and communication aspects of the ex periments. Consequently the Commission decided to request the Secretary-General to keep the president of CIMO informed of all the studies in this field and in particular to request the countries concerned to include in their reports complete information on the experience ac quired in the field of instrumentation and communication techniques during these experiments.

10.7 Meteorological rockets (Agenda item 10.7)

10.7.1 The Commission noted the interest of several Commissions in increasing the amount and quality of meteorological data in the layer from 30 to 70 km. Note was also taken of the interest in this matter as expressed by the WMO Advisory Committee at its second session in February 1965.

10.7.2 The Commission considered that the accuracy of conventional radiosondes in measuring pressure and temperature at pressures lower than 10 mb is questionable. The consequence of errors in pressure -of 1 or 2 millibars in determining the absolute height becomes serious at high altitudes. The effects caused by the inadequate transfer of heat by conduction from the ambient atmosphere to bimetallic temperature elements or rod-type thermistors at the'se pressures and by the long-wave radiation from these sensors are largely unknown. The measure ment of moisture parameters, generally unsatisfactory at temperatures below OOC, is believed to be completely unreliable below -20°C. The low density of the air at pressures 'less than GENERAL SUMMARY 11

10 mb results in the descent of parachute-borne devices at a rate such that lag in instrument response has to be considered. Furthermore, devices such as parachutes and falling inflated spheres will not respond completely to the wind at very high levels.

10.7.3 The need for research on safety aspects of the falling parts of the rocket system was discussed. In some cases the spent motor is returned to earth by a parachute; in some countries research is under way on combustible and/or frangible parts.

10.7.4 The Commission concluded that in this rapidly-developing field of activity there is urgent need for additional work toward achieving internationally compatible results. It therefore decided to form a Working Group on Sensors and Telemetry in Meteorological Rockets. The terms of reference of this working group are given in Resolution 14 (CIMO-IV).

10.7.5 In addition, the Commission recommended that the Secretary-General should keep Members informed of developments in the various countries on sensors, telemetry, data reduc tion and safety as applied to rockets used for meteorological purposes.

10.8 Instrumentation for supersonic transport (SST) aircraft (Agenda item 10.8)

10.8.1 The Commission considered this item on the basis of documents submitted by India and the United States. The question of improvements in radiosonde and radiowind-finding techniques raised in the document submitted by India was discussed under agenda item 10.1. A number of other questions raised in the same document, such as turbulence measurements, detection of hail, and the determination of heights of tops of clouds, involve the use of either ground-based radar or airborne radar and were discussed under agenda item 8. The pro blem of advanced detectlon of clear-air turbulence raised in the document submitted by the U.S.A. was also consid~red under agenda item 8. The question of measuring low-level wind profiles was considered under agenda item 13.

10.8.2 In addition to the action mentioned above, the Commission felt that it would be useful to appoint a rapporteur on meteorological instrumental requirements for supersonic aircraft operations. This rapporteur should seek information and give advice on questions relating to instrumentation for surface and upper-air observations of importance for super sonic aircraft operations. The terms of reference of the rapporteur are contained in Resolu tion 15 (CIMO-IV).

11. RADIO FREQUENCY ALLOCATIONS (Agenda item 11)

11.1 This item was discussed on the basis of documents submitted by the Secretary-General and by Finland. In reviewing this question the Commission took due account of the anticipated increase of radiosonde stations envisaged by the global observation system of the World Weather Watch. It was further stressed that there was a clear need for providing frequency allocations not only for radiosondes, but also for radar, automatic weather stations and for meteorological satellites.

11.2 With reference to the decisions made by CIMO at its third session, the Commission did not wish to retain its request for allocation of a frequency band between 45 and 70 Mc/s, in view of the comments made by the International Frequency Registration Board of the ITU.

11.3 On the other hand, the Commission expressed a requirement for frequen~y allocations in the radar bands for locating, indirect sensing and controlling. A request was also made for additional radio frequencies for watch on atmospherics as a "silent" band, ;that is without transmissions at any time. These decisions are recorded in Recommendation 5 (CIMO-IV). 12 GENERAL SUMMARY

12. ATMOSPHERIC ELECTRICITY (Agenda item 12)

12.1 The Commission noted with appreciation the report presented by the Working Group on Measurement of Atmospheric Electricity. The Commission also noted with interest the various comparisons of atmospheric electricity sondes which had been carried out during the last few 'years. Although a considerable amount of useful information has been derived from these comparisons, the Commission agreed with the conclusion of the working group that the development of atmospheric electricity sondes is still in its very early stages. Many pro blems remain to be solved, such as the effect of the radioactive probes on the electric field; speed of response; influence of the shape of the sondes on the reduction factor; insulation of the sonde in cloud or fog; electricity charging through high humidity, etc. It was there fore agreed that the working group should be re-established and ResolutioR 16 (CIMO-IV) was adopted to this effect.

13· LOWER TROPOSPHERE SOUNDINGS (Agenda item 13)

13.1 The Commission noted with appreciation the report presented by the Working Group on Lower Troposphere Soundings. The draft Techn~cal Note o~ lower troposphere soundings pre pared by the working group was examined by a sub-committee and the Commission recommended that this text be published as a WMO Technical Note subject to some minor amendments made at the session. The amended text was handed over to the Secretariat representative at the ses sion.

13.2 The Commission agreed to the main recommendations of the working group and in par ticular to the need for early development of more precise humidity measuring devices and also for urgent research on the development of indirect probing techniques to provide profiles of wind, temperature and humidity in the lowest 1500 metres above the surface. These recommen dations are embodied in Recommendation 6 (CIMO-IV).

13.3 The Commission considered that our present knowledge of spatial-temporal variabi lity in the lowest 1500 metres is too sparse to permit optimum design of a sORde system. It therefore agreed to encourage further studies and data compilations of : (a) Temporal variability over time intervals of 0.1 to 10 hours; (b) Spatial variability over distances of 1 to 100 kilometres for temperature and hu midity in the lowest 1500 metres. It was felt that such studies and compilations could most appropriately be under taken by the Commission for Aerology, and it was therefore agreed to request the president of CIMO to refer this matter to the president of CAe (a) with a request that the results of these studies be communicated as soon as possible to the president of eIMO, and (b) with the suggestion that CAe might appoint a rapporteur who could work in close consultation with the CIMO rapporteur on this subject.

13.4 The Commission noted the view~ expressed by the working group that it had been I unable to acquire sufficient information on their requirements from the various users of lower <= r troposphere soundings. For instance, no universal views were available on the specifications of accurac1' frequency of observations, required height intervals, the spatial density of soundings, etc. The Commission therefore agreed that it would be necessary to assemble, from all available sources, quantitative requirements from the various users of lower troposphere data. The Commission also agreed that it would be necessary to collect descriptions of the lower level sounding deviJes developed by Members and to study the best way of making such information available to all Members. It was agreed that these tasks could best be carried out by a rapporteur assisted by the WMO Secretariat and these conclusions are embodied in Resolution 17 (CIMO-IV). GENERAL SUMMARY 13

14. ACCURACY OF MEASUREMENTS(Agenda item 14)

14.1 The Commission noted with satisfaction the report of the Working Group on Accuracy Requirements. The first task of this group had been to prepare definitions of terms such as lf "observation", "reading", "tolerance , and these definitions had since been published in sec tion 1.8 of the Guide to Meteorological Instrument and Observing Practices. The group had then invited all the other technical commissions to submit statements of accuracy require ments, following the above definitions. The report of the group consisted largely of a sur vey of the replies received from the other commissions. It was felt that the information con tained in the report was ·of permanent value and that the main findings should be published in the ·Guide to Meteorological Instrument and Observing Practides. In Resolution 18 (ClMO-IV) it was accordingly decided to designate a rapporteur to prepare a suitable text for inclusion in the guide. In carrying out his task the.rapporteur should take account of information which had been received subsequent to the preparation of the working group's report, and the Secretary-General was requested to ensure that he received all the necessary material.

14.2 The Commission also examined some questions which had been raised at the fourth session of the Commission for Climatology and discussed in particular a request for advice on the best method of observing minimum temperature at the surface of the earth. As it was not possible to answer this request during the .session, it was decided to refer the problem to the rapporteur on .measurement of temperature for further study.

14.3 The Commission for Climatology had also indi9ated the desirability of preparing a Technical Note on the methods for assessing the elements of the heat balance and it was decided to request the president of CIMO to offer assistance to the president of CCl on this matter as required.

15. INSTRUMENT STANDARDS (Agenda item 15).

15.1 The Commission considered the two documents submitted by the Secretary-General and the president of CIMO on terminology o~ standard instruments and suggestions for permanent arrangements to ensure standardization of measuring techniques and the comparisons of stan dards maintained by Members.

15.2 The Commission examined the relevant extracts from the Draft Classification of Standards of the International Organization for Legal Meteorology (IOLM).It was felt that it was not suitable for immediate us.e within WMO where two different definitions are normally required, one based on the physical principles involved (for example primary and secondary standards) and the other on the geographical distribution of the standards (for example inter national, regional, national and travelling standards). As it was not possible to complete the draft of the necessary definition before the end of the session it was decided to request the Executive Working Group of CIMO to pursue the matter. Account should be taken of the proposals of the sub-committee which discussed this item during the session, and every effort should be made to avoid any differences between WMO definitions and those adopted by other international organizations, including IOLM.

15.3 The suggestion of the president of CIMO concerning a permanent arrangement to ensure standardization of measuring techniques was discussed. The recommendations of the Commission on this matter are recorded under section 17 of this report.

16. INSTRUMENT DEVELOPMENT (Agenda item 16)

16.1 The Commission noted with satisfaction the report of the Working Group on Instru- ment Development. The chairman of the group mentioned that he had experienced some difficul ties in obtaining information from some countries and he expressed the hope that in future 14 GENERAL SUMMARY

Members would report regularly on their instrument d.evelopment work. There was general agreement that this was one of the most important working groups of the Commission and it was accordingly decided that it should be re-established. It was however felt that in future the terms of reference of the working group could be combined with those of the Executive Working Group, discussed under agenda item 25; this decision is taken into account in the terms of reference of the new working group,. given in Resolution 19 (CIMO-IV).

16.2 The New Zealand Meteorological Service had reported several instances of hydrogen- filled balloons exploding and had suggested that it would be useful for Members to exchange information about their current practices designed to minimize such explosions. The general feeling at the session was that balloon explosions were very infrequent. provided that normal precautionary measures were taken. It would be interesting to know if the special precautions introduced in the New Zealand Meteorological Service had resulted in a decrease in the number of explosions. The president of CIMO was requested to correspond further about the matter with the director of the New Zealand Meteorological Service and, if it seemed desirable, to arrange for some further guidance to be published in section 11.3.3 of the Guide to Meteo rological Instrument and Observing Practices.

16.3 Under this item the Commission also discussed certain aspects of automatic weather stations, based on a report by the CIMO representatives on the CSM Working Group on Minimum Performance Characteristics of Automatic Weather Stations. Discussion centred mainly on the desirability of having a special code for these stations. The present SYNOP code was not suitable for the direct transmission of data from automatic stations, and in view of the in creasing use of these stations the Commission agreed to recommend that the development of a special code should be considered by the Commission for Synoptic Meteorology. The president of CrMO was requested to inform the president of CSM of this proposal and to offer to provide the services of a representative of CIMO if CSM decided to follow up the suggestion. It was stressed that there was no question of imposing a particular form of telemetering for auto matic weather stations. Countries developing these stations could decide for themselves whether to arrange for the stations to code their messages directly in the final form or whether the final coding should be done by an editing station or by a human operator.

17. COMPARISONS OF INSTRUMENTS (Agenda item 17)

17.1 The Commission considered in some detail the documents presented by the Secretary- General and the Netherlands on the subject of comparisons of instruments. It noted that in the past the international comparisons of meteorological instruments had been carried out on an ad hoc basis. The Commission welcomed the opportunity provided by the Executive Committee for making an overall assessment of the international comparisons of instruments already made and for preparing comprehensive proposals for future comparisons.

17.2 In accordance with paragraph c (ii) of its terms of reference, CIMO had for many years promoted the international comparison and standardization of meteorological instruments in an effort to determine the systematic differences between the various types under field conditions. The Commission noted with satisfaction the great importance attached by the WMO Advisory Committee to international comparisons of instruments, both those used for routine· observations and those used for research programmes. It also made a broad review of the present situation, noting with appreciation the work already done on the international com parisons of radiosondes and working standard pyrheliometers, and those which have been organ ized on a long-term basis between various types of radiation instruments, precipitation gauges, evaporimeters and leaf-wetness recorders.

17.3 There was general agreement that the comparisons should be classified under two broad headings, short-period and long-period. Among short-period comparisons the Commission considered the following : GENERAL SUMMARY 15

17.3·1 ------Radiosondes It was felt that an international comparison of all types of radiosonde in current use was not feasible at present, but that, in view of the importance of improved radiosonde data, comparisons should be encouraged between two or more instruments which could be used as interim reference sondes leading to the choice of a standard high-level radiosonde. To improve the comparability of measurements made in different countries the WMO Advisory Com mittee had recommended WMO sponsorship for the design of a standard high-level radiosonde. This had been endorsed by the Executive Committee at the sixteenth session. The Commission decided that in addition to the twin soundings envisaged in Recommendation 4 (CIMO-IV), the comparison described above should be conducted by the Working Group on Radiosonde and Radio wind Measurements. -----Barometers Procedures for international comparisons of barometers were laid down by CIMO-II and many bilateral and multilateral comparisons had been made within regions of the WMO during the last few years. In paragraph "2.3.2.4 of the report of its seventeenth session, the Exe cutive Committee had suggested that WMO should finance inter-regional comparisons. It was accordingly decided to invite Members to arrange for the inter-regional comparisons of baro meters. The decisions on this matter were incorporated in Recommendation 8 (CIMO-IV).

17·3.3 The first and second international comparisons of working standard pyrheliometers were carried out at Davos in 1959 and 1964. The Commission approved the recommendation of the Working Group on Radiation Instruments and Observations for General Use that such compa risons be made every five years. The Commission's decision on the subject is incorporated in Recommendation 3 (CIMO-IV).

17.3.4 Radiometersondes Comparisons of different types of radiometersondes were made under WMO auspices in the U.S.A. in 1965. Support for such comparisons had been expressed by the WMO Advisory and Executive Committees, and the Commission felt that a second comparison might with advan tage be carried out sometime during 1967-1968. It was decided to entrust the task to the Working Group on Special Radiation Instruments and Observations.

17.3.5 A series of comparisons between various potential gradient sondes in use were made during 1963-1965. The results were discussed under agenda item 12 and the decisions of the Commission incorporated in Resolution 16 (CIMO-IV). It was felt that the next comparisons should be held during 1968 at Weissenau in the Federal Republic of Germany, where the neces sary instrumental and other facilities are available. ------Ozone-sondes The first international comparison of ozone-sondes was made in 1962. The fourth session of CAe recommended that WMO should continue to sponsor or co-sponsor comparisons of ozone-sondes already in regular use. Interest in ozone data had also been expressed in Recommendation 8/16 (CAeM-III/ICAO/MET/OPS). It was felt that since many ozone-sondes have been developed and brought into regular use since 1962 a second international comparison should be organized by WMO at a central station in Europe during 1967-68. The Commission expressed its readiness to assist in this work (see section 20.4). 16 GENERAL SUJ.VJMARY

17·3· 7 !2.e!!B.£r~ !.oE. !!!e,!e.£r.£l.£g!c2:,l_r.£c!,e,!s Under item 10.7, the Commission noted the importance of the comparability of high altitude measurements Using meteorological rockets and established a Working Group on Sen sors and Telemetry for Meteorological Rockets. It was also recommended that the inter-com parison of the various sensors be carried out at an international rocket launching facility during 1968-1969.

17.4 Among long-period comparisons, the Commission noted with satisfaction the action taken by the relevant working groups in organizing and conducting various comparisons •. It was agreed that there was no need to alter the existing arrangements whereby comparisons were mainly carried out under the supervision of CIMO working groups. Appreciation was also expressed for the close support of the Members concerned, which had made the comparisons possible without any expense to WMO.

17.4.1 Sunshine recorders - ...... ------The comparisons were started in 1964 under the auspices of the CIMO Working Group on Radiation Instruments and Observations for General Use; they are expected to continue until 1967-1968. WMO has already allotted $JOOfor analysis of data during 1965. The Com mission recommended that additional funds required by the working group should be provided in order that the analysis could be completed and the final report submitted to its fifth session. 17.4.2 Comparisons are being conducted under the auspices of the CIMO Working Group on Radiation Instruments and Observations for General Use and in close collaboration with the CIMO Working Group on Special Radiation Instruments and Observations and the Radiation Com mission of IAMAP. The WMO Advisory Committee at the second session noted that investigations into the influence of radiative processes in the atmosphere and at ground level were seriously hampered by the absence of instruments of known reliability. The committee was of the opinion that there was a pressing need for a reliable standard net pyrradiometer and strongly recom mended that special attempts should be made to co~struct one. It also wished to endorse all efforts directed towards further comparisons of net pyrradiometers and felt that WMO should give whatever support it could to such activities. I~ was felt that the present comparisons in progress at four stations would lead to the selection of an interim reference standard and stimulate the interest of Members in the construction of a reliable standard. Resolutions 8 and 9 (CIMO-IV) incorporate the decisions of the Commission.

Under the auspices of the CIMO Working Group on Radiation Instruments and Obser vations for General Use four types of pyranometer are being compared at three stations. The comparisons, which began in 1965, will continue till 1968, and a small sum has been earmarked for the analysis of data during 1966. It was recommended that additional funds required by the working group should be provided in order that the analysis of the data could be completed and the final report submitted before the fifth session of the Commission.

I <= t 17.4.4 Comparisons between national gauges and IRPGs were started in many countries during 1962-1965 under the auspices of the CIMO Working Group on International Comparisons of Pre cipitation Gauges. The Commission considered this item and decided that the comparisons should continue until the end of 1968. The decisions are incorporated in Resolution 2 (CIMO-IV) • GENERAL SUMMARY 17

17.4.5 Under the auspices of the CIMO Working Group on Evaporation Measurement. compari sons of various types of evaporation pans are being conducted by Members in response to Re commendation 4 (CIMO-III). WMO has also allotted $700 for the analysis of the results during 1965. It was felt that the necessary financial assistance should be continued in order that the work could be completed before the fifth session of the Commission. The relevant deci sion of the Commission is incorporated in Resolution 3 (CIMO-IV).

17.4.6 Leaf-wetness recorders Comparisons of four different types of leaf-wetness recorders are being carried out in India and the U.S.A. A rapporteur has been appointed (see Resolution 1 (ClMO-IV) ) to review the results of comparisons of these instruments and to submit a report before 1 January 1969.

The Executive Committee (see para. 2.2.12 of the report of the sixteenth session) invited the president of CIMO to examine the question of standardization of radioactivity measurements and arrangements for international comparisons of the relevant instruments and methods of observation. The Commission therefore decided in Resolution 20 (CIMO-IV) to set up a working group for the purpose.

17.4.8 ------Tower instrumentation Recommendation 17 (CAe-IV) proposed that efforts should be made to perform inter national comparisons of micrometeorological tower instrumentation in order to achieve stan dardization of techniques for the study of boundary-layer effects. It was felt that while such comparisons were important. they should only be conducted after all available informa tion on micrometeorological instrumentation had been collected. In-Recommendation 6 (CIMO-IV) the Commission expressed its willingness to assume responsibility for this work.

17.4.9 In Resolution 4 (CIMO-III) and Recommendation 5 (CIMO-III) the Commission had established a working group for the selection of an interim portable reference hygrometer and recommended that it be used for comparing national psychrometers by Members. It was felt that the work should be continued and Resolution 4 (eLMO-IV) incorporates the decisions of the Commission on this matter. 17·4.10 ------Transmissometers and ceilometers The Commission considered the need for comparisons of meteorological instruments used at aerodromes. Particular account was taken of the views of the representative of the International Air Transport Association (lATA) about comparisons of various types of trans missometers. It was felt that. in view of the importance of this work. the comparisons should be organized ona long-period basis by the newly appointed Working Group on Instruments and Methods of Observations on Aerodromes (see Resolution 6 (CIMO-IV)).

17.5 The Commission also considered the need for comparisons of spherics equipment, thermometers for measuring sea-surface temperature. precipitation gauges for use on board ship, aircraft meteorological instruments. hydrological instruments, soil thermometers and soil moisture meters. The general feeling was that while there was a need for comparison of these instruments the matter might be considered after the comparisons of instruments listed in paras. 17.3 and 17.4 had been organized. 18 GENERAL SUMMARY

17.6 The above proposals are incorporated in Recommendations 7 and 8 (CIMO-IV). In the light of the Executive Committee's decision on Recommendation 7 (CIMO-IV), the president of CIMO should give the necessary directives to the various working groups of the Commission.

18. ATMOSPHERIc RADIOACTIVITY (Agenda item 18)

18.1 The Commission noted with appreciation a draft summary of contents of a WMO Tech- nical Note on the measurement of atmospheric r.adioactivity prepared by the rapporteur, Dr. O. Suschny of the International Atomic Energy Agency.

18.2 There was some discussion on the main objectives of the proposed Technical Note. The consensus of opinion was that more emphasis should be placed on the third objective men tioned in the draft, viz. the scientific use of the measurements of atmospheric radioactivity.

18.~ It was finally decided to request the rapporteur to continue his work and.to prepare a draft Technical Note on the basis of the sUJlllllary of contents presented and of the discussion of this subject at the session (see Resolution 20 (CIMO-IV)).

18.4 The Commission noted that the Executive Committee at its sixteenth session (see para. 2.2.12 of the report of EC-XVI) had invited t):J.e president of CIMO to examine the ques tion of standardization of radioactivity measurements and arrangements for international comparisons of the relevant instruments and methods of observation. In view of this, the Commission decided to set up a working group for this purpose, the terms of reference of which are given in Resolution '20 (CIMO-IV).

18.5 The Commission noted that radiosondes for measurement of atmospheric radioactivity have been in use in several countries for Some years, in particular in Japan, France, Finland, and the U.S.A. A suggestion was made that international comparis9ns of these instruments should be arranged, and the Commission felt that such comparisons on at least a bilateral basis would be useful.

19. OBSERVATIONS IN ANTARCTICA (Agenda item 19)

19.1 Following a request from the Scie~tific Committee for Antarctic Research (SCAR), the president of t.he Commission had requested Dr. V.I. Shlyakhov of the U.S.S.~. to prepare a report on the diffic1).li;ies. encOUJl.tered when making meteorological observations in the Antarctic. The session. examined Dr. Shlyakhov's report and there,was an exchange of views about the special instrumental problems arising from the strong winds, low temperatures, intense radiation and heavy snow encountered in Polar regions. Delegates reported that some of these problems had.beensolved and that investigations on the remaining problems were under way.

19.2 From the above discussion the Commission concluded that further work was required in this field, but that sufficient material was already available for the preparation of a report to meet the request from SCAR at least partially. In view of the fact that the diffi culties encountered in the Antarctic were also experienced in the Arctic it was felt that work on this. question should cover both. It was accordingly decided in Resolution 21 (CIMO-IV) to establish a Working Group on Observations in Polar Regions to draft a suitable chapter for the Guide to Meteorological Instrument and Observation Practices.

20. GUIDE TO METEOROLOGICAL INSTRUMENl' AND OBSERVING PRACTICES (Agenda item 20)

20.1 The session discussed the various chapters of the guide under the respective agenda items and the decisions are recorded in the corresponding sections of this report (see para graphs 3.1, 4.1, 6.1, 7.1, 7.5, 8.2, 9.1, 14.1, 16.2, 19.2). Under item 20, the Commission GENERAL SUMMARY 19 reviewed the guide as a whole, with particular reference to some proposals from the U.S.S.R. concerning a standard chapter layout and amendments to existing chapters.

20.2 It was decided that a standard chapter layout was desirable but that it would not be worthwhile to revise the whole guide simply in order to achieve greater uniformity of pre sentation. The Commission adopted the chapter layout given in Annex III to this report and requested all concerned to endeavour to follow this layout when existing chapters are being substantially revised and when new chapters are being drafted.

20.3 The specific amendments to the guide proposed by the U.S.S.R. were examined in detail and the conclusions are recorded in Annex IV to this report.

20.4 The Commission noted that the chapter on measurement of atmospheric ozone, being drafted by CAe, is not yet ready. This led to a discussion about the role of CrMO with re gard to ozone measurements. Hitherto the Ozone Commission of IAMAP and CAe have covered all aspects of this question, but as ozone data are now of interest to more than one technical commission, it was felt that CIMO.shoUJd be .·prepared to accept responsibility for the relevant aspects of ozone measurements. The president was requested to discuss this matter with the president of CAe and to take any necessary subsequent action. It should be noted that the question of comparisons of ozone-sondes is dealt with in section 17.3.6.

20.5 In· view of the existence of the Guide to Hydrometeorological Practices, it was agreed that it would not be necessary to have a separate chapter in the Guide to Meteorologi cal Instrument and Observing Practices on hydrometeorological instruments. Where necessary, cross-references should be made between the two guides.

20.6 At previous sessions of CIMO it had been decided to amend paragraph 12.1.2 of the guide regarding the application of corrections to height measurements for upper-wind obser vations to take account of the Earth's curvature. As regards the purely geometric correc tions, it was agreed that the present text of paragraph 12.1.2 was adequate. With regard to corrections to allow for refraction, however, the Commission decided that as work was still proceeding on this very complicated matter it would not be possible to deal with it adequate ly in the guide at the present time. It seemed in any case questionable whether the effort required to apply corrections for errors due to refraction would be justified by any signi ficant increase in the accuracy of the measured winds.

20.7 The session considered a request from the Executive Committee concerning the need for guidance material on how activities relating to meteorological instruments and methods of observation can best be organized at the national level. It was agreed that this matter could well be dealt with in the Guide to Meteorological Instrument and Observing Practices on the lines of section 1.2 of the Guide to Agricultural Meteorological Practices. The Executive Working GroUp of elMO established by Resolution 19 (CIMO-IV) was requested to ar range for a suitable text to be prepared.

20.8 There was some support for a suggestion to have a separate chapter in the guide on measurements of soil moisture. It was agreed to request the president to discuss this with the presidents of CAgM and CRy and to take any necessary subsequent action.

21. TECHNICAL REGULATIONS (Agenda item 21)

21.1 The revised contents of Part I of the Technical Regulations were reviewed. Note was taken of the revised version of paragraph 3.4.4.1 of the Technical Regulations.

21.2 The following new text is suggested for paragraph (5) of Appendix A of the Technical Regulations : 20 GENERAL SUMMARY

n(5) Determination of local acceleration of gravity. The value of g~H required for reducing barometer readings to standard gra vity shall be based on the most accurate determination of the acceleration of gravity g available. In the event that the local value of the accele ration of gravity has not been determined on the basis of some method consi dered to be more accurate in the absolute sense than the methods outlined in Appendix B, it shall be ascertained in accordance with the provisions of Appendix B. n

21.3 It was further agreed that the request by the Commission for Aerology (para. 9.6.2 of the general summary of the report of the fourth session)regarding the necessity of instruc tions in the Technical Regul~tions for correcting aerological soundings for effects of lag and radiation should be referred to the new Working Group on Radiosonde and Radiowind Measure ment.

21.4 The Commission discussed at length the views of the various commissions on the definitions for various kinds of automatic stations. It was noted that at this time Chapter 1 of the Technical Regulations only contains definitions of' certain instruments which are refer red to in the text of the Technical Regulations. The Commission therefore felt it would be inappropriate to include such definitions on the Technical Regulations at the present time. The existence of a working group of the Commission for Synoptic Meteorology on the subject, on which CIMO has a member, was also noted and it was decided to leave the matter in the hands of that working group.

21.5 The Commission discussed Recommendation 19 (CAe-IV) that certain appendices to the Technical Regulations should be put in a recommended rather than a mandatory category in order to facilitate amendment of these appendices as new values of physical functions and constants are approved for world-wide use. The Commission agreed that these arguments were applicable also to Appendices A and B of the Technical Regulations and this conclusion is incorporated in Recommendation 9 (CIMO-IV).

21.6 The Commission finally agreed to a recommendation of the Working Group on Radia tion Instruments and Observations for General Use that the Technical Regulations should in clude a detailed clas.sification of radiation stations. The proposed amendments to Chapters 1, 2 and 3 of the Technical Regulations are included in Recommendation 9 (CIMO-IV).

22. TERMS OF REFERENCE OF THE COMMISSION (Agenda item 22)

22.1 The Commission examined the request of Fourth Congress (general, summary paragraph 5.2.5) to study whether the wording of paragraph (0) (iv) of the Terms of Referenoe of CIMO could not be improved by omitting the reference to,nfinanoial estimates," It was agreed that the present wording of this paragraph might be misinterpreted but on the other hand the Com mission felt that it would be useful for tho Executive Committee and Congress if relevant proposals of the Commission be accompanied by tentative cost estimates of the proposals. The Commission consequently adopted Recommendation 10 (CIMO-IV). i 22.2 The Commission considered the d~cision of the Executive Committee recorded in F paragraph 5.3.4 of the general summary of 't-he report of its seventeenth sessiorl, requesting CIMO to establish a list of the instruments and measuring teohniques for whioh it is res ponsible. The consensus was that it would be a formidable task to list in detail all indi vidual instruments and all possible measuring techniques for which the Commission is res ponsible. It was noted that CIMO, in acoordanoe with paragraph (c) of its terms of reference, is responsible for internation~l aspeots of meteorological instruments and methods .of obser vation which are the conoern of more than one Teohnioal Commission and furthermore that CIMO, according to paragraph (e) of its terms of reference, may also deal with instruments and methods of observation whioh are the sole conoern of another Commission. GENERAL SUMMARY 21

22.3 In view of the above, and since ClMO has the overall responsibility for these questions within WMO, the Commission felt it would be advisable to request the other Tech nical Commissions, in particular CHy, CAgM and CMM, to specify, if necessary, the specialized instruments and techniques, or particular aspects of them, which these Commissions wish to be responsible for. The Commission wishes to add that there appears to be no difficulty at the present time in handling these matters within WMO and it suggested that, if necessary, the question could be discussed at the next meeting of presidents of Technical Commissions which will take place in May 1966.

23. TRAINING IN INSTRUMENTS AND METHODS OF OBSERVATION (Agenda item 23)

23.1 The Commission examined in detail the document presented by the Secretary-General on the subject of training in instruments and methods of observation. It noted that such training is highly desirable if the success of the World Weather Watch is to be assured and that the need for such training is not confined to the developing countries.

23.2 Several members, however, had doubts about the utility of a universal programme of training in instruments and methods of observation, in view of the diversity of types of instruments used in different countries. A number of members drew attention to the fact that in certain countries recruitment to courses in these fields would be difficult unless the candidates were assured that on successful completion they would receive diplomas equi valent to those given in other fields of training.

23.3 The Commission concluded that a working group should be formed to study the question of training in instruments and methods of observa~ion, and that this group should take into account the views expressed in the above paragraphs. These decisions are recorded in Resolution 22- (CIMO-IV).

24. REVIEW OF PREVlOUSRESOLUTIONS AND RECOMMENDATIONS OF THE- COMMISSION AND RELEVANT EXECUTIVE COMMITTEE DECISIONS (Agenda item 24)

24.1 The Commission examined the resolutions and recommendations adopted prior to its fourth session and also the Executive Committee resolutions relevant to the field of activity of the Commission.

24.2 It was found that all resolutions and recommendations of the Commission were either obsolete, redundant or taken account of in the resolutions and recommendations of the fourth session or in the Executive Committee resolutions.

24.3 The Commission made the decisions recorded in Resolution 23 (CIMO-IV) and proposed action by the Executive Committee in Recommendation 11 (ClMO-IV) .•

25. ESTABLISHMENT OF WORKING GROUPS (Agenda item 25)

25.1 At the request of the Executive Committee, the Commission discussed the desirability of establishing an executive working group to advise the president as required on urgent matters referred to him between sessions, wjth special reference to international programmes. It was agreed that such a working grotp would be extremely useful, especially if it could hold a session each year prior to the session of the Executive Committee. This question was further discussed under agenda item 16 and the final decision is reported in paragraph 16.1 above.

25.2 To carry out its programme between the fourth and fifth sessions, the Commission established an Executive Working Group and 13 other working groups and appointed 9 rapporteurs. The subjects to be dealt with by the working groups are as follows: 22 GENERAL SUMMARY

Measurement of precipitation; evaporation measurement; hygrometry; instruments and methods of observation on aerodromes; use of meteorological radar for aeronautical pur poses; . radiation instruments and observations for general use; special radiation instru ments and observationsl radiosonde and radiowind measurements; sensors and telemetry for meteorological rockets; measurement of atmospheric electricity; standardization and inter comparison of radioactivity measurements; observations in polar regions; and training in instruments and methods of observation. Rapporteurs were appointed to study the following topics: duration of leaf wet ness; measurement of temperature; radiosonde and.radiowind computation techniques; radio wind observations on board merchant ships} instrumental aspects of dropsonde observations; meteorological instrumental requirements for supersonic transport aircraft operations; lower troposphere soundings; accuracy of measurements; and measurement of atmospheric radioacti vity. So far as possible the chairmen and members of the working groups, as well as the rapporteurs, were designated by name at the session. The tasks of the rapporteurs and the terms of reference and composition of the working groups are given in Resolutions 1-22 (CIMO-IV) •

26. ELECTION OF OFFICERS (Agenda item 26)

Dr. L.S. Mathur (India) was elected president and Mr. V.D. Rockney (U.S.A~ was elected vice-president.

27. DATE AND PLACE OF THE FIFTH SESSION (Agenda item 27)

The delegate of Brazil indicated that his Government might be willing to invite the Commission to hold its fifth session in Rio de Janeiro. It was decided that the date and place of the fifth session should be determined by the president· in consultation with the Secretary-General.

28. SCIENTIFIC LECTURES AND DISCUSSIONS (Agenda item 28)

28.1 The Commission not~d with appreciation the Executive Committee1s request that CIMO should indicate aspects of its work of suffioient importance to be considered as sub jects for symposia and/or d;l.scussion in soientific meetings at ClMO-V.

28.2 The Commission was informed by the representative of the Secretary-General that WMOIS support of such' symposia cQuld be (a) in the form of substantial financial support to symposia organized by WMO in co operation with other interested organizations, or (b) merely a co-sponsoring by WMO of symposia organized by other organizations and involving only insignificant WMO funds.

28.3 The Commission expressed its full support of the prinoiple that symposia in the I F" field of instruments and methods of observation should,be organized as far as possible jOintly with other interested organizations, in particular with the relevant bodies of lUGG.

28.4 It was realized that the programme of WMO symposia for 1966 in category (a) had already been established and the Commission therefore requested the Secretary-General to consider co-sponsoring additional symposia in 1966 in category (b) and to consider organizing or co-sponsoring symposia in subsequent years taking into account the following list : GENERAL SUMMARY 23

(a) Radar instrumentation (perhaps joint co-sponsorship with the American Meteorolo gical Society in 1966). Tentative programme : (i) Radar equipment, general. (ii) Techniques and accessory equipment to radar, for quantitative measurements. (iii) Radar remoting equipment. (iv) Radar data processing equipment. (v) Advanced radar equipment development. (vi) Radar interpretation and observational techniques. (b) Automatic weather stations including telemetry (possibly to be organized in con junction with the planned WMO conference on such stations in 1966). Tentative programme: (i) Methods of telemetry for surface observations. (ii) Automatic land stations. (iii) Automatic marine stations. (iv) Satellite interrogated stations. (c) Radiosonde and radiowind instrumentation for high altitudes (possibly to be organized in co-operation with CAe and CAeM). Tentative programme ( i) Balloons. ( ii) Sensors. ( iii) Telemetry. ( iv) Tracking. (v) Meteorological rockets. (vi) Data reduction.

(d) Instrumentation for measurements and methods of observation in the boundary layer (possibly to be organized in co-operation with IAMAP. SCOR. CAe, CMM. CAgM. CAeM, CSM, etc.)

28.~ A series of scientific discussions in the field of instruments and methods of observation was organized at the Japan Meteorological Agency from 18 to 20 October 1965 following the fourth session of the Commission.

The topics discussed an~ the names of the speakers are given below : 18 October (afternoon) - Chairman: Mr. A.L. Maidens (1) Mesure de la temperature pour les Mr. Ch. Perrin de Brichambaut radiosondes de reseau jusqu1a 35 km and Mr. A. Valentin (France) d1altitude

(2) Physical ch~racteristics of measur Dr. M. Hinzpeter (Federal Republic of ing techniques in connexion with Germany) radiosondes up to an altitude of 30 km 24 GENERAL SUMMARY

(3) On various methods of measuring the Dr. J. Kobayashi (Japan) vertical distribution of ozone (4) Recent developments in high-altitude Mr. V.p. Rockney (U.S.A.) meteorological soundings in the U.S.A. 19 October (morning) - Chairmen: Mr. A.L. Maidens and Mr. V.S. Hardin (5 ) Observations concerning the daily Dr. V. Wisl:l.ll:l. (Finland) variation of temperature and the balloon component of the radiation error at high altitude (6) The Finnish high' altitude radio Mr. Y.I. Toivola (Finland) sondes Instruments de mesure mete orologiques Dr. L. Facy and Mr. M. Petit (France) pour fusees 19 October (afternoon) - Chairman: Mr. V.S. Hardin (8) On the measurement of wind and Mr. N. Arizumi (Japan) temperature in the stratosphere by means of rocket-sondes in Japan (9) A rocket dropsonde system for tem Dr. N.E. Rider (U.K.) perature and wind determination to about 65 km (10) Meteorological satellite instrumen Mr. H.I. Butler and Mr. H.S. Moore tation (U.S.A. ) 20 October (morning) - Chairman : Dr. M. Yoshitake (11) A chemical ozonesonde for the de Miss A.M. Mani (India) termination of the vertical distribu tion of ozone in the atmosphere (12) Radar studies in India Dr. L.S. Mathur (India)

28.6 The question of organizing similar scientific discussions in connexion with the fifth session of CIMO was briefly considered but it was concluded that it would be premature to determine the subjects for such discussions four years ahead. The president of CIMO was requested to make arrangements for scientific lectures and discussions at CIMO-V preferably in such a way that these discussions could be organized during the session itself. The Commission felt that the duration of a session of CIMO should not be less than 2 1/2 weeks.

29. ACTION TO BE TAKEN ON THE DECISIONS OF THE SESSION

As there were no decisions requiring to be submitted to the President of the Or ganization for urgent consideration, the resolutions and recommendations of the session will be submitted direct to the Executive Committee at its eighteenth session.

30. METEOROLOGICAL INSTRUMENT EXHIBITION

An exhibition of meteorological instruments was held at the headquarters of the Japan Meteorological Agency. GENERAL SUMMARY 25

31. CLOSURE OF THE SESSION

The session ended on the evening of 15 October 1965. In his closing remarks, the president expressed his thanks to the Government of Japan and to the director-general of the Japan Meteorological Agency for their hospitality during the session. He also thanked·the local secretariat, the chairmen of the working com mittees and the representatives of the Secretary-General for their help in assuring its suc cess. On behalf of the Japanese delegation, Dr. Yoshitake thanked the president for the tri"[)tit'es paid,'· and Mr. Harmantas and Mr. Marc expressed on behalf of all the delegates their appreciation of the work done by the president both before and during the session' and also of the perfect organization of the session in Tokyo •

. ,. Dr. Langlo,' on behalf of the Secr~tary-:-General, thanked the local secret1;triat and ment':L

.. -<.!} :-...,j <~-' •• - 26

RESOLUTIONS ADOPTED BY THE SESSION

. Res. 1 (CIMO-tv) ~ RAPPORTEUR ON DURATION OF LEAF WETNESS

THE COMJIIIISSION FOR INSTRUMENTS AND METHODS OF OESERVATION,

NOTING pa~agraph 8.2 of the general summary of. the third session of the Commission for Instrqments and Methods of Observation, and

CONSIDERING that measurement of the duration of leaf wetness is a matter of con siderable importance arid that so far the comparisons of iristruments for this purpose have been· carried out oV'er·too short a period to permit valid conclusions to be drawn,

DECIDES (1) To invite Mr. M. Gangopadhyaya (India) to serve as rapporteur on the dura tion of leaf wetness with the following tasks (a) To keep abreast of developments in the field of instruments for measuring the duration of leaf wetness; (b) To review the results of comparisons of these instruments now being conducted in Poona and at the University of Iowa;

(2) To request the rapporteur to submit his report with appropriate recommenda tionsto the president of the Commission not later than 1 January 1969.

Res. 2 (CIMO-IV) - WORKING GROUP ON MEASUREMENT OF PRECIPITATION

THE COMJIIIISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING with satisfaction the reports of the Working Groups on International Comparisons of Precipitation Gauges and on Snow Measurements, and

CONSIDERING (1) The need for continuing the comparisons of national precipitation gauges against the International Reference Precipitation Gauge (IRPG), and (2) The need for further investigations of the sources of error in measuring both solid and liquid forms of precipitation,

DECIDES (1) To establish a Working Group on Measurement of Precipitation with the follow ing terms of reference : = (a) To review and report on the results obtained from the IRPG comparisons; (b) To co-ordinate and collect information on investigations relating to sources of error in the measurement of both solid and liquid forms of precipitation, with special reference to aerodynamic effects; RESOLUTIONS 3~ 4 27

(2) To invite the following individuals to serve on the working group N.P. Rusin (U.S.S.R.) (chairman) J. Grunow (Federal Republic of Germany) V. Kalyansundaram (India) C. Levert (Netherlands) R. Sneyers (Belgium)

(3) To request the working group to submit periodical reports on item (a) of its terms of reference and to submit its final report to the president of the Commissio.n not later than 1 January 1969.

R.e9, :3 (CIJIlO-ry) - WORKING GROUP ON EVAPORATION MEASUREMENT

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING with satisfaction the report of the Working Group on Evaporation Measure ment,; and

CONSIDERING that the working group cannot complete all its tasks until the results of comparisons of evaporation pans now being conducted by several Members are available#

DECIDES

:.J ... : ; (l) . To re-establish the Working Group on Evaporation Measurement with the follow ing terms of reference : (a) To make recommendations for the selection of an interim international reference e'Vaporimeter taking into account the results reported by Members· on comparisons of evaporimeters; (b) To consider the role of evaporation pans in the study of evaporation and evapo transpiration;

(c) To consider and advise whether the evaporation pan might be supe~seded by the measurement of definable meteorological elements;

(2) . To invite the .following individuals to serve on the working group M. Gangopadhyaya (India) (chairman) T. Nordenson (U.S.A. ) V. A. Uryvaev (U.S.S.R. )

(3) To request the working group to report to the president of the Commission not later than 1 January 1969 •

. Res •. 4 (CIMO-IV) - WORKING GROUP ON HYGROMETRY

THE COMMISSION FOR INSTRUMENrS AND METHODS OF OBSERvATION,

NOTING with satisfaction the report :Jf the Working Group on Psychrometry,

ENDORSES the conclusions concerning the fundamentals for the design of an interim reference psychrometer; and 28 RESOLUTION 5

CONSIDERING (1) The continuing need for a precise instrument for the measurement of humidity over the whole meteorological range near the ground, (2) That the interim reference psychrometer can be used satisfactorily only at temperatures above freezing, (3) That it is imperative to insure improved compatibility of hygrometric measure- l'J1ents~

DECIDES (1) To establish a Working Group on Hygrometry with the following terms of referenae: (a) To continue the study of the properties of the psychrometer suggested by the pre vious Working Group on Psychrometry; (b) To propose other reference hygrometers capable of operating in one or more ranges .of environm~ntal temperatures and humidities; (c) To study the problems of radiation shielding of hygrometers in close co-ordination with the rapporteur on measurement of temperature; (d.) '1:0 recommend. inexpensive M.d st!j.ble hygrometers for routine netwc;>rk measurements; (e) To recommend the installation, operation and maintenance procedures for such in struments; (f) Through the president of CIMO, to arrange for the selected hygrometers to be tested and calibrated in one or more national laboratories;

(2) To invite the following individual,s to serve on the working group: R.G. Wylie ( Australia) (chairman) H.B. B1p.don (Canada) M. Thaller (Israel) P. Viton (France) M. Yoshitake (Japan) A member to be designated by the U.S.A.

(3) To request the working group to submit its report to the president of the Commission not later than 1 January 1969.

Res. 5 (CIMO-IV) - RAPPORTEUR ON MEASUREMENT oir TEMPERATURE

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

CONSIDERING (1) That there is a variety of thermometer Screens in use in different countries, (2) That the use of different types of screens may result in systematic differen ces in the results obtained, (3) That many investigations have already been made on the effects of different types of screens, (4) That the method of measuring "grass minimum" temperature' described in section 4.4.5 of the Guide to Meteorological Instrument and Observing Practices does not always give satisfactory results, RESOLUTION 6 29

DECIDES (1) To invite the Permanent Representative of the United Kingdom to des"ignate ,a rapporteur on the measurement of temperature with the following terms of reference: (a) To review the existing literature on the design of thermometer screens and the effects of the different types of screens on the observed temperature; "(b) " To; prepare a report in a form" suitable for publication as a WMO Technical Note containing a critical survey of the results which have been published and recom mendations for any necessary future investigations; " (c) To recommend the best method for measuring minimum temperature at the earth1s suri~ce;

(2) To request the rapporteur to submit his report to the president of the Commission not later than 1 January 1969.

Res. 6 (CIMO-IV) - WORKING GROUP ON INSTRUMENrS AND METHODS OF OBSERVATION ON AERODROlVIES

"THE COMMISSION"FOR INSTRUMENrS AND METHODS OF OBSERVATION,

NOTING with satisfaction the report of the Working Group on Instruments and Methods of Observation on Aerodromes, and

~ .,' i -.' _.' CONSIDERING that many problems in this field require additional study,

.:. " DECIDES- (1) To re-establish the working group with the following terms of reference : (a) To study and make recommendations, as appropriate, on the most suitable types of meteorological instruments for aerodromes~ on their exposure and on methods of observation to meet the requirements of aviation,; ""3:: (B}" 'In particular, to determine standards for calibration of transmissometers, light scatter meters, and optical wedge meters, whereby such data as runway visual range, ~u~wayvisibility, meteorological optical range, etc., would each have a -u,niqtie value fo1;' e?,ch value of the parameter involved (atmosph~ric transmission, etc.) and tl<:tUs'"in all cOuntries be directly comparable to the median of values that observation by expert human observers would assign to the value of the para meter in;"question under a wide range of observing conditions,; (c) To prepare an appropriate text for insertion in Chapter 8 of the Guide to Meteo rological Instrument and Observing Practices which properly reflects the stan dards of calibration of such meters; "(d) To study--and recommend instruments and methods of observation whereby the orthogo nal components of the wind may be determined with sufficient accuracy to satisfy the stated ICAQ requirements;

(2) To invite the fbllowing individuals to serve on the working group C. Perrin de Brichambaut (France) (chairman) D.T. Acheson (U.S.A. ) G. Cena (Italy) W. Olbers (Federal RePublic of Germany) M.S. Sternzat (U.S.S.R.) A.A. Worthington (U.K. ) 30 RESOLUTION 7

(3) To invite the president of CAeM to nominate a suitable expert to serve on the working group; (4) To request the working group to report to the president of the Oommission not later than 1 January 1969.

Res. 7 (CIMO-IV) - WORKING GROUP ON USE OF METEOROLOGICAL RADAR FOR AERONAUTICAL PORPOSES

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING the report of the Working Group on Uses of Radar in Meteorology and the various instrumental requirements related to the operation of supersonic transport air craft,

OONSIDERING (1) The need for an overall study of the various uses of meteorological radar f9.r aeronautical purposes, and (2) The need for guidance material for training of personnel in the use of airborne radar,

DECIDES (1) To establish a Working Group on Use of Meteorological Radar for Aeronautical Purposes with the following terms of reference : (a) To study in general all information useful for aeronautical purposes which could be obtained by ground-based or airborne radar; (b) To study in particular : (i) The possibilities of hail detection by means of one or another of the above types of radar; (ii) The possible location of zones of turbulence situated in zones of precipi tation;

~ii) Techniques for determining, by means of groUnd-based radar, the heights of the zones containing water droplets with a sufficiently great diameter to be of importahce for supersonic airc~aft. operation;

~v) Interpretation of the echoes as a function of the characteristics of the radar used (influence of attenuation, emitted beamwidth, etc.); (v) The progress in instrumental techniques most likely to increase the practical efficiency of the observations made with airborne and ground-based radar, including instruments and techniques used for transmitting information from ground-based radar to aircraft in flight and in connexion with air traffic control problems; (c) To prepare a Technical Note aimed at guiding and facilitating the task of meteo rological services charged with training of personnel in the interpretation of echoes obtained by airborne radar; (2) To invite the following individuals to serve on the working group : H. Treussart (France) (chairman) S.G. Bigler (U.S.A.) R.F. Jones (U.K. ) V.V. Kostarev (U.S.S.R. ) T. Kume (Japan) RESOLUTION 8 31

(3) To invite the president of CAeM to nominate a suitable expert to serve on the working group; and

(4) To request the working group to report to the president of the Commission not later than 1 January 1969.

Res. 8 (CIMO-IV) - WORKING GROUP ON RADIATION INSTRUMENTS AND OBSERVATIONS FOR GENERAL USE

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING with satisfaction the report of the Working Group on Radiation Instruments and Observations for General Use,

CONSIDERING (1) That Members would welcome guidance as to the most suitable types of instru mentsto be 'used in networks of radiation stations, taking into account all components of the radiation balance, (2) That further work is needed on international comparisons of national stan dard radiation instruments, (3) That comparisons of pyranometers and net pyrradiometers have been organized and the studies to date have been of too short duration to permit valid conclusions to be drawn, (4) That the comparisons of interim reference sunshine recorders (IRSR) with national sunshine recorders have been in progress for some time and the study of the results has to be completed,

DECIDES (1) To re-establish the Working Group on Radiation Instruments and Observations for General Use with the following terms of reference : (a) To make recommendations on instruments which are most suitable at the present time for use in networks of radiation stations, taking into account all compo nents of the radiation balance; (b) To assist in the co-ordination of international comparisons of national standard radiation instruments and to study the results of such comparisons; (c) To study and report on the results of the comparisons of sunshine recorders, pyranometers and net pyrradiometers;

(2) To invite the following individuals to serve on the working group Miss A. Mani (India) (chairman) R.H. Collingbourne (U.K. ) Mrs. T.V. Kirillova (U.S.S.R. ) G. Lamboley (France) R. Latimer (Canada) C. Levert (Netherlands) J.M. dos Santos (Brazil) W. SchUepp (Switzerland)

(3) To request the working group to report to the president of the Commission . not later than 1 January 1969. 32 RESOLUTIONS 9, 10

Res. 9 (CIMO-IV) - WORKING GROUP ON SPECIAL RADIATION INSTRUMENTS AND OBSERVATIONS

THE COMMISSION FOR INSTRT.JMENl'S AND METHODS OF OBSERVATION,

CONSIDERING (1) That there is a need for improved standard radiation instruments for measur ing all components of the radiation balance.

(2J That such improved instruments can only be developed t~ough a better under standing of the principles of operation and knowledge of the materials used in their construction,

DECIDES (1) To re-establish the Working Group on Special Radiation Instruments and Obser vations with the following terms of reference : (a) To define the requirements for standard instruments for the measurement of solar radiation; (b) To evaluate tb,e measuring procedures used with standard instruments and their associated readout instrumentation with special attention to possible sources of error and their elimination, and to factors paramount for long-term-stability; (c) To study the influence of circumsolar radiation on pyrheliometers with different apertures and to propose a standard turbidity for calibration purposes; (d) To study the propertieS of materials which have a paramount influence on the per formance characteristics of radipmeters, such as receiver surfaces (absorbing blacks), filter domes and compensating components; (e) To prepare a report on the findings of the study and suggest precautions to be taken to insure optimum accuracies of measurements;

(2) To invite the following individuals to serve on the working group R. M. Marchgraber (U.S.A.) (chairman) R. Dogniaux (Belgium) R. Schulze (Federal Republic of Ge:r'ml:).ny) K. Sekihara (Japan) A member to be designated by India A member to be designated by U.S.S.R.

(3) To request the working group to report to the president of the Commission not later than 1 January 1969.

Res. 10 (CIMO-IV) - WORKING GROUP ON RADIOSONDE AND RADIOWIND MEASUREMENTS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING with satisfaction the report of the Working Group on Radiosondes, and

CONSIDERING (1) The many problems that still remain unsolved in the fields of radiosounding (such as hygrometry), in improvement of measurement at high altitudes, in concurrently measuring the winds aloft by electronic means and in speeding up and improving the accu racy of the calculations, RESOLUTION 11 33

(2) The importance of improved radiosonde data to the work of other commissions of WMO,

DECIDES (1) To establish a Working Group on Radiosonde and Radiowind Measurements with the following terms of reference : (a) To do everything possible to stimulate programmes for radiosonde comparisons as outlined in Recommendation 4 (CIMO-IV); (b) To study and report on new developments in radiosounding, particularly as regards (i) radiosonde hygrometry; (ii) fast-rising and/or high-altitude balloons, including the effects of tempe rature and ozone on balloon performance; (iii) heating effects of the balloons; (iv) improved sensors for measurements up to a height of approximately 30 kilo metres; (v) techniques and equipment, both airborne and ground-based, for measuring the winds aloft by electronic means, up to a height of approximately 35 km; (vi) sensors for pressure and humidity that can be used for reference purposes in sondes; (vii) calibration of sondes and ground equipment; (viii) improvement of radiosonde and radiowind calculation; and (ix) any relevant information contained in documents presented to CIMO-IV;

(2) To invite the following individuals to serve on the working group : A. Valentin (France) (chairman) N. Arizumi (Japan) C. Harmantas (U.S.A. ) M. Hinzpeter (Federal Republic of Germany) V.I. Shlyakhov (U.S.S.R.) V. WisM.IM. (Finland)

(3) To request the working group to report to the president of the Commission by 1 January 1969 on action taken as a result of (a) above and the findings derived .from the studies enumerated in (b).

Res. 11 (CIMO-IV) - RAPPORTEUR ON RADIOWIND OBSERVATIONS ON BOARD MERCHANT SHIPS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING the report of the Working Group on Radiowind Measurements on Board Merchant Ships,

CONSIDERING that the problem of measurements of winds aloft by electronic means on merchant ships continues to be urgently in need of solution, and

NOTING the interest of the Executive Committee and other constituent bodies of the WMO in the subject, 34 RESOLUTION 12

DECIDES (1) To invite Mr. V.D. Rockney (U.S.A.) to serve as rapporteur on radiowind observations on boara merchant ships with the following terms of reference (a) To review possible new techniques for making radiowind observations on board merchant ships; (b) To keep in touch with new instrumental developments made in this field by Members;

(2) To request the rapporteur to make an interim report on his findings to the president of the Commission by 1 January 1967 and a final report by 1 January 1969;

(3) To request the Secretary-General to obtain information from Members on in strumentaldevelopments in their countries that are relevant to the problem of electroni cally measuring the winds aloft from merchant ships.

Res. 12 (CIMO-IV) RAPPORTEUR ON RADIOSONDE AND RADIOWIND COMPUTATION TECHNIQUES

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING the request in paragraph 5.13.1 (a) of the general summary of the report of the fourteenth session of the Executive Committee,

CONSIDERING (1) The multiplicity of types of instruments being used for radiosonde and radiowind observations, and (2) The desirability of assuring the comparability of radiosonde and radiowind observations and the significance of computational procedures in achieving that end,

DECIDES (1) To invite Mr. R.E. Vockeroth (Canada) to serve as rapporteur on radiosonde and radi0win~ computation techniques with the following terms of reference : (a) To prepare a questionnaire whereby (i) the computation techniques for radiosonde and radiowind data transmitted in synoptic reports of all Members can be compared; (ii) the iag and radiation corrections, the effects of smoothing and level selec tion procedures, corrections for refraction and curvature of the earth, etc. used by Members, may be determined and evaluated; (b) To propose action to promote and co-ordinate the exchange of information on this subject between Members; (c) To review the results of these determinations and to recommend any changes deemed desirable in the Guide to Meteorological Instrument and Observing Practices;

(2) To request the rapporteur to report to the president of the Commission not later than 1 January 1968. RESOLUTION 11 33

(2) The importance of improved radiosonde data to the work of other commissions of WMO,

DECIDES (1) To establish a Working Group on Radiosonde and Radiowind Measurements with the following terms of reference : (a) To do everything possible to stimulate programmes for radiosonde comparisons as outlined in Recommendation 4 (CIMO-IV); (b) To study al1d report on new developments in radiosounding, particularly as regards (i) radiosonde hygrometry; (ii) fa$t-rising and/or high-altitude balloons, including the effects of tempe rature and ozone on balloon Performance; (iii) heating effects of the balloons; (iv) improved sensors for measurements up to a height of approximately 30 kilo metres; (v) techniques and equipment, both airborne and ground-based, for measuring the winds aloft by electronic means, up to a height of approximately 35 kIn; (Vi) sensors for pressure and humidity that can be used for reference purposes in sondes; (vii) calibration of sondes and ground equipment; (viii) improvement of radiosonde and radiowind calculation; and (ix) any relevant information contained in documents presented to CIMO-IV;

(2) To invite the following individuals to serve on the working group : A. Valentin (Franoe) (chairman) N. Arizumi (Japan) C. Harmantas (U.S.A. ) M. Hinzpeter (Federal Republic of Germany) V. I. Shlyakhov (U.S.S.R. ) V. Wisl:tll:t (Finland)

(3) To request the working group to report to the president of the Commission by 1 January 1969 on action taken as a result of (a) aoove and the findings derived f'rom the studies enumerated in (b).

Res. 1],. (CIMO-IV) - RAPPORTEUR ON RADIOWIND OBSERVATIONS ON BOARD MERCHANT SHIPS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING the report of the Working Group on Radiowind Measurements on Board Merchant Ships,

CONSIDERING that the problem of measurements of winds aloft by electronic means on merchant ships continues to be urgently in need of solution, and

NOTING the interest of the Executive Committee and other constituent bodies of the WMO in the subject, 34 RESOLUTION 12

DECIDES (1) To invite Mr. V.D. Rockney (U.S.A.) to serve as rapporteur on radiowind observations on boaru merchant ships with the following terms of reference (a) To review possible new techniques for making radiowind observations on board merchant ships;

(b) To keep in touch with new instrumental developments made ~n this field by Members;

(2) To request the rapporteur to make an interim report on his findings to the president of the Commission by 1 January 1967 and a final report by 1 January 1969;

(3) To request the Secretary-General to obtain information from Members on in strumenta1developmehts in their cOl:lllt:riies that are relevant to the problem of electroni cally measuring the winds aloft from merchant ships.

Res. 12 (ClMO-IV) RAPPORTEUR ON RADIOSONDE AND RADIOWIND COMPUTATION TECHNIQUES

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING the request in paragraph 5.13.1 (a) of the general summary of the report of the fourteenth session of the Executive Committee,

DECIDES (1) To invite Mr. R.E. Vockeroth (Canada) to serve as rapporteur on radiosonde and radiowind computatoion techniques with the following terllls of reference : (a) To prepare a questionnaire whereby (i) the computation techniques for radiosonde and radiowind data transmitted in synoptic reports of all Members can be compared; (ii) the lag and radiation corrections, the effects of smoothing and level selec tion procedures, corrections for refraction and curvature of the earth, etc. used by Members, may be determined and evaluated; (b) To propose action to promote and co-ordinate the exchange of information on this subject between Members; (c) To review the results of these determinations and to recommend any changes deemed desirable in the Guide to Meteorological Instrument and Observing Practices;

(2) To request the rapporteur to report to the ~resident of the Commission not later than 1 January 1968. RESOLUTIONS 13, 14 35

Res. 13 (CIMO-IV) - RAPPORTEUR ON INSTRUMENl'AL ASPECTS OF DROPSONDE OBSERVATIONS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NarING the various studies planned to be undertaken by WMO in the framework of the World Weather Watch, in particular a study of the possible use. of dropsonde obser vations from commercial aircraft,

CONSIDERING the importance of the instrumental problems involved in such obser vations,

DECIDES (1) To invite Mr. V.S. Hardin (U.S.A.) to serve as rapporteur on instrumental. aspects of dropsonde observations with the tasks of keeping abreast of all studies made on the taking of dropsonde observations from commercial aircraft and of keeping the president of CIMO iIll'ormed; (2.) To request the rapporteur to report to the president of the Commission not later than 1 January 1968.

Res. 14 (CIMO-IV) - WORKING GROUP ON SENSORS AND TELEMETRY FOR METEOROLOGICAL ROCKETS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

CONSIDERING (1) The rapid developments in recent years in methods for sounding the atmo sphere by means of meteorological rockets above the levels that can be reached by meteo rological balloons, and .(2-) The importance of accurate meteorological data above these levels to several of the ·other constituent bodies of WMO,

DECIDES (1) To set up a Working Group on Sensors and Telemetry for Meteorological Rockets, with the following terms of reference: (a)· To assemble and exchange information on the techniques used for atmospheric sensing and telemetry by meteorological rockets, for reduction of data obtained by these devices, and on methods that would allow rockets to be used safely in networks, particularly with regard to the safe disposal of the rocket motor and associated heavy parts; (b) To study the need for comparisons of the observational results obtained by the various sensors and techniques and. if such comparisons are found to be desirable and necessary. to arrange for them to be made. the objective being to obtain international compatibility of·data at heights up to 65-70 km; (2) To invite the following individuals to serve on the working group : L.S. Mathur (India) (chairman) N. Arizumi (Japan) L. Facy (France) A member to be designated by U.K A member to be designated by U.S.A. A member to be designated by U.S.S.R. ~SOLUTIONS 15, 16

OJ To request the working group to rePort to the president of the Commissioh by 1 January 1969.

Res. 15 (CIMO-IV) - RAPPORTEUR ON MIDI'EOROLOGICAL INSTRUMENTAL REQ,UIREJ.'vlENTS FOR SUPERSONIC TRAWSPORT AIRCRAFl' OPERATIONS

THE COJVJlVlISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING that Meteorological Services will soon be required to provide services for operations of supersonic transport aircraft,

CONSIDERING that the design and operation of supersonic aircraft may involve special meteorological instrumentation and observation techniques,

DECIDES (1) To invite Mr. A.A. WOrthington (U.K.) to serve as rapporteur on meteorologi cal instrumental requirements for supersonic transport aircraft operations with the following terms of reference : (a) To ascertain the problems in the design and operation of supersonic aircraft which may involve special meteorological instrumentation and observation tech niques; (b) To seek information as to the progress of development of instruments for surface and upper-air observations which may have applications in this field; (c) To advise, as requested, the proper authorities developing such instrumentation as to the special requirements of supersonic aircraft operations;

(2) To request the rapporteur to report on the current position in this field to the president of the Commission at agreed intervals and, at an appropriate time, to advise on the need for setting up working groups on any aspect of the problem and also on the names of experts suitable to serve on such groups.

NOTE: In undertaking the above-mentioned duties the rapporteur should be'ar in mind that separate problems may arise in regard to observaticins for high and low altitude flight, together with the meteorological conditions for landing and take-off. The attention of the rapporteur is also invited to the relevant documents submitted to the fourth session of CIMO under this agenda item.

Res. 16 (CIMO-IV) - WORKING GROUP ON MEASUREMENT OF ATMOSPHERIC ELECTRICITY

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERvATION,

NOTING the report by the Working Group on Measurement of Atmospheric Electricity, and

CONSIDERING

(1) That it is important that measurements of atmospheric elect~icity in the free atmosphere made at various places around the world should be comparable, (2) That the instruments and techniques now used for measurement of atmospheric electricity parameters require further study and development, and RESOLUTION 17 37

(3) That new problems arising from the work of the previous Working Group on Measurement of Atmospheric Electricity require elucidation and further study,

DECIDES (1) To re-establish the Working Group on Measurement of Atmospheric Electricity with the following terms of reference : -(a): To study and analyse the results of the comparisons made during the last three years, together with any associated problems; (b) To study and recommend improved techniques for the measurement of atmospheric electricity in :the free atmosphere; (c) To study the influence of the environment on the measurement of atmospheric electricity parameters; (d) To prepare guidance material for Members wishing to make atmospheric electricity -soundings; (e) To investigate techniques and instruments for the measurement of other parameters of atmospheric _electricity in the free atmosphere such as conductivity and air -earth current, to compare relevant instruments and to study the results; (2) -To invite the following individuals to serve on the working group : J.L. Koenigsfeld (Belgium) (chairman) H.W. Kasemir (U~S.A. ) Miss A.M. Mani (India) R. MUhleisen (Federal Republic of Germany) K. Uchikawa (Japan) (3) To request the working group to report to the president of the Commission by 1 January 1969.

Res. 17 (CIMO-IV) - RAPPORTEUR ON LOWER TROPOSPHERE SOUNDINGS

THE COMMISSION FOR INSTRUMENTS-AND METHODS OF OBSERVATION,

NOTING the report by the Working Group on Lower Troposphere Soundings,

CONSIDERING the need for further information to be collected and distributed in the field of low-level soUnding devices,

DECIDES -(1) To invite the Permanent Representative-of the U.S.A. to designate a rappor teur on lower troposphere soundings with the following tasks : (a) With the assistance of the Secretariat to assemble from all available sources quantitative requirements including, but not limited to, accuracies and frequency of observation in time and space (including the vertical dimension) for the various current and potential applications of low-level sounding data; (b) To study and make recommendations on the best way of keeping Members1nformed of new developments in low-level sounding devices, for instance by such means as regular reviews of developments, blbliographiesp and selected articles describing the current state of low-level sounding systems and data; (2) To request the rapporteur to present a final report to the president of the Commission by I-January 1968. RESOLUTIONS 18, 19

Res. 18 (CIMO-IV) - RAPPORTEUR ON ACCURACY OF MEASUREMENTS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING (1) The report of the Working Group on Accuracy Requirements, (2) The statements subsequently provided by various constituent bodies of WMO, and

CONSIDERING the desirability of including in the Guide to Meteorological Instru ment and Observing Practices more information about the accuracy required for various purposes,

DECIDES (1) To invite Mr. N.E. Rider (U.K.) to serve as rapporteur on accuracy of measure ments with the following task : On the basis of the statements provided by various·technical commissions and the report of the Working Group on Accuracy Requirements, to draft a section for the Guide to Meteorological Instrument and Obgerving Practices on the accuracy required for various purposes; (2) To request the rapporteur to submit his report to the president of the Commission not later than 1 January 1967.

Res. 19 (CIMO-IV) - EXECUTIVE WORKING GROUP OF CIMO

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION ..

NOTING the request of the Executive Committee(in paragraph 6 of Annex XVI to the report of EC-XVII) to consider the establishment of a working group of the Commission to deal with urgent tasks submitt.Gd to the Commissi0I.l between sessions and. to advise on internation~~ programmes, and

CONSIDERING that the tasks of this proposed working group can be,cQmbined with those of the former·Working Group on Instrument Development,

DECIDES (1) To establish an Executive Working Group of CIMO with the following terms of reference : (a) To assist the president of the Commission in providing advioe or taking action on urgent matters referred to the Commis~ion which cannot be dealt with by the regular working groups or by correspondence; (b) To assist the president of the Commission in reviewing the progress of the work of the Commission and in planning its future programme; (c) To collect information on instrumental development work in Member countries with special reference to the operational experience gained; (d) To provide advice as required on instrument development questions; RESOLUTION 20 39

(2) To invite the following individuals to serve on the working group President of CIMO (chairman) Vice-president of CIMO M. Hinzpeter (Federal Republic of Germany) A.L. Maidens (U.K.) V. Marc (France) M. Yoshitake (Japan) A member to be designated by U.S.S.R. (3) To request the president of CIMO to prepare six-monthly reports for distri bution to members of the Commission on the activities of the Executive Working Group and to report on these activities also to the fifth session of the Commission.

NOTE: Invitations to sessions of the working group should be decided by the president of CIMO in consultation with the Secretary-General taking into account the items to be discussed and the financial implications.

Res. 20 (CIMO-IV) - RAPPORTEUR ON MEASUREMENT OF ATMOSPHEiRIC RADIOACTIVITY AND WORKING GROUP ON STANDARDIZATION AND INTERCOMPARISON OF RADIOACTIVITY MEASUREMENTS THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION

NOTING th~ summary of contents' of a WMO Technical Note on Measurement of A~mo spheric Radioactivity prepared by the rapporteur, INVITES the rapporteur, Dr. O. Suschny, to continue his work and prepare a draft Technical Note on Measurement of Atmospheric Radioactivity; . . NOTING FURTHER the request of. the Executive Committee in paragraph 2.2.12 of the Gener.al Summary' of EO-XV! •. DECIDES

(1) ~o set up a Working Group on Standardization and Intercomparison of Radio activity Measurements with the following terms of reference : (a) To review existing practices in radioactivity measurements in air and precipi tation; (b) To advise on techniques which lead to the greatest consistency; (c) To advise on intercomparisons between instruments and techniques used at moni toring stations; (d) To review the draft Technical Note prepared by the rapporteur on measurement of atmospheric radioactivity; (2) To invite the following individuals to serve on the working group J. Grandjean (Belgium) (chairman) M. Hinzpeter (Federal Republic of Germany) N. Murayama (Japan) K. G. Vohra (India) O. Suscbny (IAEA) (rapporteur) (3) To request the working group to report to the president of the Commission on items (a), (b) and (c) of its terms of reference by 1 January 1969, and to implement paragraph (d) as soon as practicable. 40 RESOLUTIONS 21, 22

Res. 21 (CIMO-TV) - WORKING GROUP ON OBSERVATIONS IN POLAR REGIONS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING (1) The request from the Scientific Committee for Antarctic Research (SCAR) for guidance material on meteorological instruments and methods of observation in the Antarctic, and (2) The report of the rapporteur on observations in the Antarctic,

DECIDES (1) To establish a Working Group on Observations in Polar Regions with the following terms of reference : (a) To study the special problems enc.ountered in making meteorological observations in polar regions and the ways of solving these problems; (b) To draft a chapter on instruments and methods of observation in polar regions for the Guide to Meteorological Instrument and Observing Practices; (c) To recommend further investigations which should be made to solve the outstand ing problems of making meteorological observations in polar regions; (2) To invite the following individuals to serve on the working group : V.I. Shlyakhov (U.S.S .R. ) (chairman) H. Gerger (Canada) K. Morita (Japan) C.L. Roberts (U.S~A. ) (3) To request the working group to submit to the president of the Commission the draft chapter for the guide by 1 January 1968 and its final report by 1 January 1969.

Res. 22 (CIMC-TV) - WORKING GROUP ON TRAINING IN INSTRUMENTS AND METHODS OF OBSERVATION

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING with satisfaction the interest demonstrated by the Secretariat concerning the needs for training in instruments and methods of observ~tion,

EXPRESSES its enthusiastic support for such activities;

CONSIDERING (1) The attention that must be given to the training of meteorological personnel in instruments and metho~s of observation because of the increasing complexity of meteo rological equipment, (2) That the successful development of the World Weather Watch will depend on the availability of a sufficient number of meteorological personnel in all countries, with an adequate knowledge of instruments and observational techniques, (3) That all Members, but more especially the developing countries, have a common interest in the establishment of a basic programme of training in instruments and methods of observation, RESOLUTION 23 41

D:::!:CIDES (1) To establish a Working Group on Training in Instruments and Methods of Observation with the following terms of reference : (a) To draw up special syllabi and a list of textbooks and other training aids suitable for the various grades of personnel required for meteorological instru ment development, calibration, comparisons, and maintenance; (b) To study and comment on the relevant parts of WMO Technical Note No. 50; (c) To recommend any further action which might be needed with regard to training in meteorological instruments and methods of observation; (d) To encourage and promote the establishment and operation of regional training centres for instruments and methods of observation, recogniziQg the particular requirements of the Members within each Region; (e) That the working group proceed immediately to the preparation of guidance ma terial in those domains which are of common interest to the greatest number of Members;

(2) To invite thefollowingipdividuals to serVe on the working group J .M. dos Santos (Brazil) (chairman) B. Azmy (Morocco) M. Clerebaut (Democratic Republic of Congo) K.E. Potter (British Caribbean Territories and British Guiana) A JIIernber to be designated by U.S.A. (3) To request the working group to submit its report to the president of the Commission not later than 1 January 1968.

Res. 23 (CIMO-IV) - REVISION OF THE RESOLUTIONS AND RECOMMENDATIONS OF THE COMMISSION FOR INSTRUMENl'S AND METHODS OF OBSERVATION

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

CONSIDERING that Resolutions 1 to 15 (elMO-III), adoptedprdor to its fourth session, are now obsolete,

NOTING the action taken on the recommendations adopted prior to its fourth session,

DECIDES (1) Not to keep in force Resolutions 1 to 15 (CIMO-III); (2) To note with satisfac,tion the action taken by the competent bodies on its Recommendations 1 to 12 (CIMO-III) which are now redundant. 42

RECOMMENDATIONS ADOPTED BY THE SESSION

Rec. 1 (CIMO-IV) - NATIONAL AND REGIONAL RADIATION CENTRES

. THE COMMISSION FOR INSTRillVJENl'S AND IVJETHODS OF OBSERVATION,

NOTING Recommendation 31 (CIfI'IO-I) and Recommendation 5 (CIMO-II), and

CONSIDERING (1) That many countries operating a network of radiation stations have not yet designated national radiation centres, (2) That some Regional Associations have not yet designated regional radiation centres, and- (3) That some clarification is necessary concerning the functions of regional radiation centres and the conditions which should be met before a centre is designated for this purpose,

RECOMMENDS (1) That Members which operate a network of radiation stations but have not yet designated national radiation centres should take steps to this end; (2) That Regional Associations which have not yet designated a regional radiation centre should designate one or more such centres as soon as possible; (3) That in designating national and regional radiation centres account should be taken of the factors given in the Annex* to this recommendation.

* See Annex V.

Rec. 2 (OIMO-IV) - WORLD RADIATION CENTRE

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING Recommendation 3 (CIMO-IV), and

CONSIDERING that there is an urgent need for the satisfactory maintenance of the International Pyrheliometric Scale (IPS) 1956 and for permanent facilities for inter-regional compari sons of standard radiometers,

CONSIDERS it necessary that one or two world radiation centres be established and officially designated as such by WMO;

RECOMMENDS that each of these world radiation centres should RECOMMENDATION 3 43

(a) Be equipped with (i) The most accurate standard pyrhe1iometer and its auxiliary measuring equipment; (ii) The standard radiometers and auxiliary measuring equipment necessary for the maintenance of the IPS 1956; (b) Serve as a centre for inter-regional and international comparisons of radiation instruments and maintain the standard instruments and have available the labo ratory and other facilities necessary for this purpose; (c) Be located in a climatic region with long uninterrupted periods of cloudless skies and stable radiative fluxes; (d) Have the necessary laboratory and outdoor facilities for the simultaneous com parison of large numbers of instruments and for the reduction of the data; (e) Follow closely all developments leading to 'improved standards and take all steps necessary to insure at all times the highest possible quality of its standards and testing equipment; (f) Have qualified scientists with wide experience in radiation; (g) Satisfy the above conditions before being designated as a world radiation centre and continue to fulfil them under WMO supervisiun after being so designated; and (h) Undertake training of specialists in radiation.

Rec. 3, (CIMO-IV) - COMPARISOl\fS OF PY.RHELIOMETERS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATIONr

NOTING Recommendation III adopted by the International Radiation Commission (Davos 1956), and

CONSIDERING (1) That an accuracy of ~ 1 per cent is desirable for routine measurements of direct solar radiation, (2) That this can only be attained if a higher degree of accuracy is achieved in national, regional and inter-regional comparisons of pyrh~liometers,

RECOMMENDS (1) That Members should endeavour to develop a standard pyrhe1iometer capable of achieving and maintaining an accuracy of measurement of at least ± 0.1 per cent; (2) That regional radiation centres should endeavour to achieve and maintain an accuracy of measurement of at least ± 0.25 per cent with the regional standard pyr heliometer; (3) That WMO should organize inter-regional cv;nparisons of regional standard pYrheliometers every five years; (4) That pyrheliometers used in national networks should be compared regularly against the national standard pyrheliometer; (5) That international comparisons of national standard pyrheliometers against the regional standard pyrheliometer should be carried out every five years. 44 RECOMMENDATIONs 4, 5

Rec. 4 (ClMO-IV) - COMPARISON OF RADIOSONDES

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING (1) With satisfaction the report of the Working Group on Radiosondes, and (2) The accuracy requirements stated by other technical commissions as indicated in the Annex* to this recommendation,

CONSIDERING (1) The importance to the science and practice of meteorology of increasing the number and accuracy of radtosonde opservations at altitudes of 30 kilometres and higher, (2) That improved equ;Lpment is now available, both for making me.asurements at these altitudes and for comparing the results obtained by various kinds of radiosonde systems, especially with regard to the measurements of temperature,

RECOMMENDS (1) That Members take into account the accuracy requirements stated by WMO Technical Commissions (see Annex*) when developing and operating radiosonde and radio wind instruments and equipment; (2) That Members,partioularly those in whose countries radiosonde systems of various kinds are manufactured, arrange to determine the comparability of results ob tained with identical systems when two radiosondes of the· same kind are flown on a single balloon (twin soundings); (3) That, as new instruments are developed which can serve as a reference for one or more meteorological parameters measured in the upper-air, Members, particularly thOSe in whose countries radiosondes are manufactured, arrange comparisons of their sondes with the reference sondes; (4) That all comparisons described above be conducted in each case in approxi mately equal numbers both by day and night, and that every possible effort be made to conduct the comparison to an altitude of 30 kilometres or higher; (5) That in all cases the results of the comparisons made in accordance with the above be published as quickly as possible and made available to the Secretariat for distribution to Members. * See Annex VI.

Rec. 5 (ClMO-IV) - RADIO FREQ.UENCY ALLOCATIONS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

CONSIDERING I ~ (1) The importance of meteorology to human safety and economic development, (2) The substantial anticipated increase in the use of the Meteorological Aids Service as the global observational system develops within the framework of the World Weather Watch, . (3) The necessity for dependable radio-frequency channels for telemetering, locating, indirect sensing and controlling, for the gathering of data to support the science and practice of meteorology, RECOMMENDATION 5 45

RECOMMENDS (1) That all Members, particularly in preparation for international telecommuni cation conferences, make representations to their appropriate national telecommunication administration, stressing the need for adequate and appropriate radio-frequency channels for the above-mentioned purposes; (2.) That, so far as national policy permits. Members seek to assure the avail ability of adequate and appropriate radio-frequency channels for operation of such in. struments~s radar sets, radiosondes, meteorological satellites, automatic weather sta tions and remote-reading sensors, and that, bearing in mind the widespread use of many of these instruments beyond. the bounds of any one Region, it is desirable that such radio frequencies should be of worldwide application and on a primary service basis; (3) That, in addition to action at the national level, the Secretary-General be requested to present the requirements of the Members for adequate and appropriate radio frequencies for meteorological purposes to the apPropriate international authorities; (4) That in taking this action, particular attention be paid to the need by various Members for : (a) The continuation of the current radio-frequency allocations by the ITU for Meteo rological Aids Service in the following bands : !lpical applicatiOns Radio treg,uencl band For telemetertng and similar applications over medium distances 2045 2065 kC/S For telemetering over distances not greatly exceeding !tline of sightli 27.5 28.0 .Me/s For telemetering and controlling, with minimum risk of interference, over "line of sightlt distances 151 154 Me/s For telemetering and/or locat~g 400.05- 406 MC/s For telemetering and/or locating with improved angular accuracy 1660 - 1700 Me/s (b) Additional radio frequencies in the following hands : For watch on atmospherics, as a "silent", non-transmitting band 8.5 kC/S For telemetering with or without location Two 50 kC/S bands adjacent to 24.0 and 25.6 MC/s respectively (5) That the Secretary-General be asked to ascertain the requirements of Members and to present these requirements additionally to those listed under paragraph (4). Particular attention should be paid to frequencies required for meteorological radars including allocations in the following spectra 2700 - 2900 MC/s, A spectrum in the C-band, 9300 - 9500 Me/ s, One or more spectra in the K-and Q.-bands. 46 RECOMMENDATIONS 6, 7

Rec. 6 (CLMO-IV) - LOWER TROPOSPHERE SOUNDINGS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING (1) The report of the Working Group on Lower Troposphere Soundings,

(2) Recommendation 17 (CAe~IV) - Meteorological observations from towers, (3) Recommendation 1/1 (CAeM-III/ICAO/MET/OPS), and

CONSIDERING (1) That the needs of the various users of low-level sounding data can best be met at present by a combined sounding system using a tall tower for rapid and pre cise measurement in th~ lowest 100-500 metres and a'tethered telemetry sonde to provide information to its maximum altitude, (2) The need for better humidity measurements, particularly in the critical accuracy range of 95-100% relative humidity, (3) The promising results of indirect ground-based probing techniques such as radiometry, optical lasers, doppler radar etc.,

RECOMMENDS (1) That Members be encouraged : (a) To arrange for the early development of more precise humidity-measuring devices suitable for lower troposphere sounding applications; (b) To undertake, as a matter of urgency, research on the-development of indirect probing techniques to provide profiles of wind, temperature and humidity in the lowest 1500 metres above the surface; (2) That elMO be entrusted with the study of techniques necessary for, and with the co-ordination of international comparisons o~ the meteorological tower instru mentation referred to in Recommendation 17 (CAe-IV).

Rec. 7 (CLMO-IV) - COMPARISONS OF INSTRUMENTS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

CONSIDERING (1) Paragraphs 5.2.3 and 5.3.4 of the Abridged Final Report of EC-XVII, (2) The importance of intercomparability of measurements made in various coun tries, particularly in investigations of a global nature, (?) The international comparisons already organized and the need for a compre hensive long-term programme of comparisonS of meteorological instruments,

RECOMMENDS (1) That arrangements be made for the international comparisons listed in the Annex*; (2) That WMO should provide the necessary financial support for the comparisons in consultation with the working groups concerned; RECOMMENDATIONS 8. 9 47

(3) That a consultant should prepare statistical guidance material for planning and making instrument comparisons so that they may be as fruitful and economical as possible; (4) That each international comparison should be preceded by an evaluation of the. consistency to be expected on the part of each instrument design submitted to the comparison.

* See Annex VII •

Rec. 8 (CIMO-IV) - INTER-REGIONAL COMPARISONS OF BAROMETERS

THE COMMISSION FOR INSTRUMENI'S AND METHODS OF OBSERVATION,

CONSIDERING (1) Paragraph 2.3.2.4 of the Abridged Final Report of EC-XVII, (2) Recommendation 2 (CIMO-II), and

NOTING the action taken by Members to carry out bilateral and multilateral comparisons of standard barometers within Regions of the WMO dl~ing the last few years,

RECOMMENDS (1) That Members be invited to carry out inter-regional comparisons of regional and national standard barometers; (2) That WMO should provide the necessary financial support for thesp. comparisons.

Rec.9 (CIMo-IV) - REVISION OF TECHNICAL REGULATIONS

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING (1) Resolution 19 (Cg-IV), (2) Resolution 21 (EC-XVI), (3) Resolution 22 (EC-XVI), (4) Recommendation 19 (CAe-IV), and

CONSIDERING (1) That discrepancies may arise between the future International Meteorological Tables and Appendices A and Bof the Technical Regulations considered as standard meteo rological practices, (2) That it is desirable to provide guidance to Members on the physical functions and constants used in meteorology,

RECOMMENDS (1) That paragraph 3.4.4.3 of the Technical Regulations be replaced by "Each Member should apply the International Barometer Conventions given in Appendix A."; 48 RECOMMENDATION 9

(2) That paragraph 3.4.4.4 of the Technical Regulations be replaced by "When ever it is necessary to compute the theoretical value of local g;ravity, each Member should follow the procedure given in Appendix B.";

WoTING FURTHER Resolution 25 (IV-RA VI), and

CONSIDERING the need for amending the existing Technical Regulations on the classification of radiation stations,

RECOMMENDS (1) That the following definitions be added to Chapter 1 (a) "Principal radiation station. A radiation station whose observing programme includes at ieast the continuous recoI'uwg of global.. solar and sky radiation on a horizontal surface and It'egular measurements of direct sol8.1:' radiation." (b) "Ordinary radiation station. A radiation station whope obse;rving programme includes at least the continuous recording of the global solar radiation on a horizontal surface." (c) "Radiation station.

A station at which observations of global I;lolar radiation ar~ made." (2) That the following paragraphs be added to Chapter 2 : "2.2.4.2 There should be at least one principal radiation station in each of the main climatic zones of every country." "2.2.4.3 The density of the network of ordihary radiation stations should be adequate for the study of the radiation climatology of the country." "2.3.6 Each radiation station should be sited with an adequate and unchanged exposure, where the observations can be made in representative conditions. The surroundings of the station should not alter in time to such ap extent as to affect the homogeneity of the series of observations. Each Member should maintain an up-to-date directory of radiation stations in its territory, giving- the following information for each station (a) Name and geographical co-ordinates. (b) Elevation of station. (c) A brief description of the local topography. (d) Category of station and details of observing programme. (e) Details of radiometers in use (type and serial humber,s of each instrument, cali bration factors, dates of any significant changes). (f) Exposure of radiometers, including heights above ground and nature of underlying surface. RECOMMENDATIONS 10, 11 49

(g) A station history (dates of beginning of records, removals, closing or interrup tion of records. changes in the name of tIle, station and important changes in the observing· programme) • (h) The name of the supervising organization or institution." (3) That the following amendments be made to ·Chapter :3.: 3.1.4.1 Amend to read : "At principal radiation stations the observing programme should include : (a) Continuous recording and publication of hourly totals of global solar radiation and of sky radiation, using pyranometers of the 1st or 2nd class (see Chapter 9 of the Guide to Meteorological Instrument and Observing Praotices). (b) Regular measurements of direct solar radiation. (c) Recording of duration of sunshine." "3.1.4.2 At ordinary radiation stations the observing programme should include : (a) Continuous recording and publication of daily totals of global solar radia tion, (b) Recording of duration of sunshine."

Rec. 10 (CIMO-IV) - TERMS OF REFERENCE OF THE COMMISSION

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION ..

N0rING Paragraph 5.2.5 of the general summary of the Abridged Final Report of Fourth Congress,

RECOMMENDS That paragraph (c) (iv) of the terms of reference of ClMO should read as follows "(c) (iv) Promote research and development projects relating to meteorological instruments and methods of observation including, where necessary, the preparation of appropriate technical plans and approximate estimates of oosts".

Rec. 11 (CIMO-IV) - REVISION OF RESOLUTIONS OF THE EXECUTIVE COMMITTEE BASED ON PREVIOUS RECOMMENDATIONS OF ClMO

THE COMMISSION FOR INSTRUMENTS AND METHODS OF OBSERVATION,

NOTING with satisfaction the aotion taken by the Executive Committee on the previous recommendations of the Commission for Instruments and Methods of Observation,

CONSIDERING that many of these recommendations have become redundant in the meantime, 50 RECOMMENDATION 11

RECOMMENDS (1) That Resolution 21 (EC-XIV) be no longer considered necessary;

(2) That Resolutions 22 to 25 (EC-XIV) be reconsidered by the Executive Committee in the light of their discussions on the recommendations adopted at CIMO-IV. 51

ANNEX I Annex to paragraph 5.1 of the General Summary

REFERENCE HYGROMETERS COVERING A WIDER RANGE THAN OBI'AINABLE WITH THE PSYCHROMETER

A summary of relevant information is here given with regard to several types of hygrometers which could satisfy the requirements over a wide range," or aJ least serve to pr.ovide useful auxiliary data. The following categories are discussed : (-a) Dew-point hygrometer and frost-point hygrometer (b) Pneumatic bridge hygrometer using critical flow (c) Electric hygrometer (d) Microwave hygrometer. Papers describing developments with relation to various categories of hygrometers have been recently published in the four-volume set of Proceedings of the 196) International SYmposium on Humidity and Moisture, Washington, D.C. We shall refer to this set as Ref. 1 (see Bibliography), and when we wish to refer to Volumes 1, 2, ), and 4 of these Proceedings, we shall cite Ref. 1-1, Ref. 1-2, Ref. 1-), and Ref. 1-4, respectively. Attention is also invited to a valuable annotated bibliography on humidity instruments published in December 1962 (Ref. 2). " - A fairly brief discussion follows with regard to each of the above-listed cate- "gories (a) Dew-point hygrometer and frost-point hygrometer The dew-point hygrometer and the frost-point hygrometer are capable of yielding reasonably accurate results provided that certain precautionary measures are taken, as ex plained below. It is important that the cooled mirror surface be devoid of contaminating substances and quantities of hygroscopic nuclei capable of inducing the formation of deposits on the mirror at temperatures significantly different from the_actual dew- or frost-point temperature pertinent to the water-vapour mixing ratio of the ambient air. In situations where the contaminants which are present, such as organic vapours or hygroscopic nuclei, " could produce deposits on the mirror under such conditions, it will be necessary to employ filtering for the removal of the contaminants before the sample is brought to the instrument, in order to enable the dew- and frost-point hygrometers to yield reliable, accurate results. The mirror surface will require cleaning at frequent intervals, especially if the sampled air contains dust, salts, and other contaminants. It is essential that the reference dew point or frost-point hygrometer be of such design as to permit the visual observation of the deposit on the mirror with the aid of a suitable optical magnifying device. Such a device serves at least two important purposes, for it enables the observer to determine the charac ter of the deposit and to investigate the conditions at the mirror surface. This proviSion is specified partly because there may be "uncertainty otherwise as to whether the deposit is dew or frost, bearing in mind that the difference between the dew-point and frost-point temperatures can be conSiderable, particularly at low values of these elements. Evidence is at hand that reliable results can be obtained by means of the dew-point and frost-point hy grometer when it is operated semi-automatically, where use is made of both visual and photo electric detection of the deposit, and special techniques are employed to observe the nature of the deposit and its changes under controlled conditions. The problems of precautions to be taken and proper techniques to be used have been discussed recently by a number of authors, for example, Wylie, Davies, and Caw (Ref. )); Brewer (Ref. 4); Martin (Ref. 5); and Paine and Farrah (Ref. 6). 52 ANNEX I

A possible source of error in dew-point hygrometry which should be taken into con sideration has been indicated in a paper by Yoshitake (Ref. 7). He has shown that the cool ing process and the condensation which occurs at the mirror surface of the instrument will produce gradients of temperature and aqueous vapour pressure normal to the surface. The gra dient in the latter case acts to cause the saturation vapour pressure es in equilibrium with the cooled surface to be slightly lower than the vapour pressure e which exists in the am bient undisturbed air. On these grounds it may be concluded that the dew-point temperature corresponding to es will be slightly lower. than the dew-point temperature corresponding to e. This difference would contribute an error which should be corrected if found to be signifi cant. An adequate ventilation rate for the airflow over the mirror surface is essential for accurate and precise determinations in order to. minimize the effect due to the vapour-pressure gradient and to standardize measures for the correction of the effect. Dew-point and 'frost-point hygrometers of good quality have been developed to operate' automatically by means of Peltier cooling which yields important advantages. When the hygro meters operate on the basis of Peltier cooling and are also equipped for visual detection and inspection of the deposit, they should serve well for the desired purpose, subject to the re servations indicated above (see Refs. 3-7).

(b) Pneumatic bridge h¥grometer using critical flow This type of hygrometer, based on the application of the critical flow nozzle, was only recently developed as a means of measuring 'the mixing ratio of samples ot moist air paSping through a cQntinuous flow system. A description of one form of this instrument was presented by Wildhack, Perlq, Kissinger, and Hayes (Ref. 8); and a description of another form was rendered by Greenqpan(Ref. 9). An essential part of the flow system at several points in the pneumatic bridge hy~ometer is the "critical flow nozzle". For each critical flow nozzle there exists a critical pressure ratio, denoted here by Rc, which depends upon the size and special shape characteristics of the nozzle. Rc represents a certain critical value of the ratio of the pressure in the throat of the nozzle to the absolute entrance (inlet) pressure. The critical flow nozzle is characterized by the following property: when the ratio of the actual pressure in the throat of the nozzle to the absolute entrance pressure under any existing flow condition is less than the critical pressure ratio Rc for the given nozzle, the gas flow in the nozzle occurs at the speed of sound. So long as this condition prevails the mass flow rate through the nozzle is proportional to the absolute upstream (inlet) pressure and is independent of the actual value of the downstream pressure. The mass flow rate is then a known function of the mixing ratio, the absolute temperature of the gas, the entrance pressure, the compressibility factor of the moist air, and some other parameters of the gas and nozzle Which can be determined by means of calibration. In the pneumatic' bridge hygrometer use is made of four'critical flow nozzles connected by tubing so that two sets of two nozzles are located in separate series, arranged in four arms analogous to those of the well-known Wheatstone bridge employed in electrical measurements. That is, each nozzle is analogous to an electrical resistance in the Wheatstone bridge. Moist air in a continuous flowing stream (analogous to an electric current in the bridge) is introduced at one of the junctures of the arms of the hygrometer bridge. One of the arms on the upstream side inciudes a vessel which contains a desiccant for the purpose of absorbing all of the water vapour passing through the arm under consideration. The mois ture-absorbing action of this drying agent, which is located on the downstream side of the nozzle in the given arm, causes the pressure in the stream to be less after the stream of moist gas has passed through the nozzle than it was at the entrance of the nozzle. A sensitive manometer is included in tubing which connects two of the juncture points of the arms; that is, the manometer is installed in a manner analogous to that of the galvanometer in the Wheat stone bridge. The manometer serves to measure the pressure differential (~P)x which deve lops across the bridge due to the fall in pressure resulting from the water-vapour absorption by the desiccant in one of the arms (say x), while the adjacent arm (say y) connected to the inlet orifice of the bridge does not have a desiccant. In the form of pneumatic bridge ANNEX I 53

hygrometer designed by G~eenspan (Ref. 9), the vessel containing the desiccant can be switched from the ,arm x to the arm y; and in that case the manometer serves to measure the pressure differential ~P)y which occurs because of the fall i~ pressure resulting from the absorption of the vapour by the desiccant in arm,y, while the arm x does not contain a desic cant. A barometer is employed to measure the absolute pressure within the tubing at the exits of arms x and,y when the vessel containing the desiccant is not present, so that these pressure readings Px and, Py correspond to the entrance pressures at the downstream nozzles in the bridge when the d,esiccant is not present in the upstream arm for the respective switching arrange ments. The theory given by Greenspan (Ref. 9) shows that ,if the downstream critical flow nozzles are similar in shape and size, and if the entire bridge is immersed in a temperature controlled bath, the ratio (APh - (.AP)y)l /(Px + Py) is correlated with the mixing ratio of water vapour present in the sample of gas 1say air) passing'through the pneumatic bridge hy grometer. By using the standard gravimetric hygrometer of the u.s. National Bureau of stan dards asa calibration basis the phewriatic bridge hygrometer waS calibrated at a number of points over a range of mixing ratios from 0.15' to 19.1 mg of water vapour per gramme of dry air. The largest error measured was'0.025 mg of water vapour per gramme of dry air in this range, although it is est,itnated that the upper limit to the error due 'to random and systen atic errors might be about twice as much as the largest measured error. One manufacturing company has placed on the market for sale both a laboratory model and a portable model of a pneumatic bridge hygrometer operating on the principles de scribed in the paper by Wildhack, .PerIs, Kissinger, and Hayes (Ref. 8). The company claims that the portable instrument will yield the mixing ratio of the air to within an accuracy of ± 0.2 rug of water vapour pe~ gramme while operating ove; a temperatUre range from about 1.5° to 32°G. By virtue of the foregoing considerations, it is concluded that the pneumatic bridge hygrometer using 'critical flow nozzles can serve 'as a reference' instrument except at low temperatures and humid'ities:,: especially if it is calibrated from time to time against a national standard hygrometer.

(c) Electric hygrometer For a. number of years experience has been gained with the commercially manufac tured electric hygrometer of the Dunmo~e type designed for surface observations, and this experience has indicated that within certain limitations the instrument c~n .serve many useful purposes. One of the applications recommended is the use of the, electric hygJ;'ometer as a means of maintaining some degree of quality control on the indica.tions of the "interim port ab~reference hygrometer" while the latter is emplOYed in the field. In this Gonnexion the electric hygrometer can be applied to determine whether the "interim portable reference hy grometer" yields readings within specified tolerances, depending upon the combined tolerances of both instruments. For this purpose the electric hygrometer will be considered to play an auxiliary role in support of the reference hygrometer.

The following system of operations is .suggested: Six ide~tical, carefully selected electric hygrometers are accurately and precisely calibrated at a central laboratory by means of a national standard hygrometer or with reference to such an instrument. Three of the elec l tric hygrometers are tal$:en on every field trip with the "interim portable reference hygrometer • while the other three electric hygrometers are left behind in the central laboratory. When not in use, each of the electric hygrometers should be protected in accordance with the follow ing general directives recommended for guidance : (1) Do not expose the electric hygrometers to saturated atmospheres for prolonged pe riods; prevent, them from becoming wet in any manner and from suffering a deposit of moisture'by condensation. 54 ANNEX: I

(2) Keep the element under protective cover in order to prevent it from being attacked by deleterious substances, such as organic solvent vapours, salt sprays, or other possible contaminants. (3) Maintain the element at temperatures aQove - 20°C. steps (1) and (2) could be readily accomplished by keeping the electric hygrometers mounted in a sealed container with a salt solution which maintaihs a suitable average r'elative humidity, say, of the order of 50 per cent,' while provisions are made for assuring that the solution cannot make direct contact with the elements. Whenre!3.dings of the instrument are taken for comparat.ive purposes, the electric hygrometer should be maintained under steady state oonditions in respect to temperature and relative humiditufor a sufficient period of time to Permit equiliprium to be reached. This type of hygrometer should not be used for reliable readings at temperatures lower than _20°C, since the lag coefficient of the instrument is very high at extremely low temperatures. In order to take account of hysteresis, comparative readings 9f the electric hygrometer should be taken during steady conditions obtained as steps extending from increasing ~nd decreasing phases of a cycle of humidity variations. During the period when the electric hygrometers are being brought to equilibrium for the purpose of taking readings, it is des-irable that the elements be subjected to a steady ventilation current having a standard speed'of about 3 mVsec under normal sea-level pressure and temperature conditions.

The set of three electric hygrometers carried to the field should be compared both with the "interim portable reference hygrometer" and the station (or laboratory) hy grometer at each point, preferably over suitable ranges of temperature and relative humidity. Similar comparisons, but including the three electric hygrometers kept at the initial point, should be made upon return of the instruments to the point of departure (say, a'central labo ratory). If good agreement of the portable instruments is obtained for the comparative read ings at every point, it may be assumed that the hygrometers carried to the field and returned to the original central laboratory have maintained their calibration. If the agreement is poor or unsatisfactory, the matter should be investigated.

The instruments should be re-calibrated before each field trip, and ch~cked in a like manner upon return. Useful information relevant to the characteristics of several types of hygrometers, including the lithium chloride and carbon electric hygrometers, together with the dew-point hygrometer and the hair hygrometer, has been presented in a paper by Kobayashi (Ref. 10) based on his extensive' investigations. Other recent developments of great interest with respect to electric hygrometry and related matters have been described by various authors who reported in 1963 at the International Symposium on Humidity and Moisture. Details will be found in published reports (Refs. 1, 1-1, etc.). Although Dunmore-type electric hygrometers involving the use of lithium chloride in the humidity-sensitive film are conventional in meteorolpgical work, recent developments indicate that the employment of other ohemical substances in the film would lead to important advantages. For example, the investigations and developments by Jones and Wexler (Ref. 11), and Jones (Refs. 12, 13) have shown that electric hygrometers constructed in a certain manner with barium fluoride used in the humidity-sensitive film are highly sensitive to varia tions of ambient water-vapour content over wide ranges of temperature and humidity. The hyste resis effects in these elements are small. Another advantage is that when the barium-fluoride elements are exposed to high humidity or water spray they reveal no permanent harmful effects. In order to eliminate the influence of polarization on the elements they should be used in alternating~current circuits operating at low frequencies, but not lower than 2 cycles/sec, and with voltage drops across the element preferably of the order of 1 volt, root-mean-square. Because of changes in the structure and composition of the barium fluoride elements with time, and other possible factors, these instruments tend to age and their calibrations change, even ANNEX I 55

when they are kept in storage under fairly 90nstant humidity and temperatur~. On this account the barium-fluoride electric hygrometers, as presently constituted, should be used within one month after they are calibrated. An investigation by Jones (Ref. 14) of an electric hygrometer involving the use of lead iodide films has revealed that this type gives promise of yielding greater stability under storage than the barium-fluoride type.

(d) Microwave hygrometer based on refractometer The index of refraction of moist air for electromagnetic waves of radio frequencies (microwaves) is represented by the expression n (1 + aP/T (1)

where

n = refractive index of moist air (}haracterized by the following physical properties (P,T, e); P barometric pressure; T absolute temperature; and e aqueous vapour pressure, while a, b, and g are empirical constants pertinent to air and water vapour.

The empirical constants ~, £, and ~ in the foregoing expression have the following values : a 7.76 x 10-5 oK/mb b 6 x 10-6 oK/ mb -1 2/ ~ 3.75 x 10 oK mb, when P is expressed in millibars, T in degrees Kelvin, and e in millibars. (See Smith and Weintraub, Ref. 15.) One can define the refractive index for waves of a specified frequency travelling in any given medium as the ratio n = c/v, where c = the velocity of electromagnetic waves through free space (a vacuum), and v = the velocity of electromagnetic waves of the specified frequency through the given medium. In the refractometer use is made of a suitably designed cavity, for example, a circular cylindrical hollow accurately formed in a metal such as Invar, which has a very small coefficient of linear thermal expansion (about 1 x 10-6 per °C). Elf employing elec tronic means electromagnetic waves are caused to oscillate in the cavity whose dimensions are so chosen that it will yield resonant frequencies in the spectral range corresponding to radio microwaves. The cavity is then used as a resonator for such waves, and the frequency f at which it resonates depends upon the size and shape of the hollow, and upon the refractive index n of its contents. If the dimensions of the cavity are maintained constant by keeping the metal in a constant-temperature bath, and by not subjecting it to mechanical stresses, the following relationship is applicable : fn K (2) where f the resonant frequency of the cavity n the index of refraction of the substance contained within the cavity K a constant which depends upon the radius and length of the cavity, and upon the mode of the electromagnetic wave vibrations within the 'caVity. (Note: Temperature and mechanical stress of metal could affect its size.)

Now, in order to develop a very accurate reference hygrometer on this basis, two circular cylindrical resonant cavities of the same size are constructed in a block of Invar ANNEX I

(Ref. 16). The block of material is kept in a constant-temperature bath, and the cavities are interconnected so that they are at the same barometric pressure. A sample of moist air whose humidity is to be determined will first pass through, a heat exchanger where the temperature of the sample will be brought to that of the constant-temperature bath. On emer gence of the air from the heat exchanger its temperature will be measured, and then the sam ple of moist air will flow into the first cavity at, say, temperature Tl , pressure Pl' and aqueous vapour pressure el' Thus, the first cavity will, yield a resonant frequency, say, fl, depending upon the refractive index nl, which characterizes the moist air under the spe cified conditions. After emerging from the first cavity the moist air is passed through a chamber packed with a suitable desiccant which removes essentially all of the water vapour present in the sample of air. The dry air which issues from the chamber is then transferred by means of tubing which is immersed in the constant-temperature bath, and in this manner the vapour-free air passes into the second cavity at, say, temperature T2, pressure P2' and aqueous vapour pressure e2 = O. In the second cavity the dry air will give rise to a reso nant frequency, say, f2 which is governed by the refractive index n2 pertinent to the dry air at these specified conditions with respect to temperature, pressure, and humidity. Owing to the action of the constant-temperature bath and the interconnecting tubing, the tempera tures tend to be the same in both cavities (say, at value T), while the pressures tend to be conserved (say, at value p) becaupe of the tubing. At the same time the pressure P is control led by venting the two cavities through a static-pressure head to the outside air, so that P is equal to the ambient barometric pressure. Since there are no sources or sinks of mois ture in the system, the mixing ratio of the moist air in the first cavity will be the same as that of the original sample taken from the ambient air. Then, because the mixing ratio and the pressure are conserved, the aqueous vapour pressure el in the first cavity will be the same as the aqueous vapour pressure e pertinent'to the ambient air at pressure P. By virtue of the foregoing considerations, one can assume the following relation ships to a high degree of approximation T

P (4) o (5 ) Owing to the conditions specified in Equations (3) and (4), it follows from Equation (2) that x n = K, a constant. (6) fl x nl f2 2 Under the conditions indicated the difference between the resonant frequencies will be (f - f ) 2 l (7) From Equation (1) and the given values of the parameters a, b, and g, it will be evident that at sea-level the values of n and n will be of the ;rd"6r of i:-0003; for example, when l 2 P = 1000 mb, T = 288°K, and e = l~ mb, tfie terms in the right-hand side of Eq. (1) are as follows : ap/T 0.0002694 ; belT 0.0000003 2 and ge/T = 0.0000678 • The aqueous vapour pressure in the cavity containing the dry air will be repre sented by e = O. Because of the fact that the terms ap/T, belT, and ge/T2 are small in 2 comparison with unity, one can write by virtue of Equations (1), (3), (4), and (5), 1 (1 - ap/T + belT - ge/T2), very closely, (8) n l ANNEx: I 57

1 (1 - aP/T), very closely. (9) n 2 When Equations (8) and (9) are substituted in Eq. (7) it follows that (f - f ) = (Ke/T)(g/T - b), very closely. (10) 2 l Thus, the difference of the resonant frequenci~s is very nearly proportional to e, the aqueous vapour pressure of the original sample of moist air, and is a function of the absolute tempe rature T of the air in both cavities. Equation (10) transforms to T(f - f ) 2 l e (11) K(i/T - b) This relation permits the determination of e on the basis of the measurement of the observed difference of resonant frequencies, (f - f ), and the observed temperature T. 2 l The quantity K can be determined by calibrating the microwave hygrometer with the aid of an absolute standard gravimetric hygrometer, and its value can also be calculated for a circular cylindrical cavity on the basis of the pertinent microwave theory. By installing sensitive temperature sensors at the entrance ports and exits of both cavities it would be possible to obtain temperature readings at those points and to compare them. If these readings had a common value, it could be regarded as representative of T. However, if there were disparities between them, some correction would be necessary as might be due, say, to the effect of the desiccant on the temperature of the dry air. The first-order theory given above with respect to the microwave hygrometer suggests that the behaviour of the instrument is independent of variations in the pressure P, but the involvement of P as a factor in Equations (1). (8), and (9) may suggest that this f~ctor plays at least a secondary role. In order to allow for this possibility it would be advisable to have a pressure transducer installed in the instrument for the purpose of indicating the pres sure within the vessel which contains the desiccant and connects the two resonant cavities. The instrument should then be calibrated over a sufficiently wide range of pressure in order to determine how the variations of P affect its response, and appropriate corrections to the results by Equation (11) could then be applied, if found necessary. From the foregoing discussion it can be inferred that the microwave hygrometer has interesting possibilities which should be investigated during the course of its develop ment, taking account of the results of calibrations under various conditions in respect to P, T, and e.

BIBLIOGRAPHY

1. Wexler, A. (Editor-in-Chief) "Humidity and Moisture Measurement and Control in Science and Industry" - In four volumes - Based on papers presented at the 1963 International Symposium on Humidity and Moisture, Washington, D.C. New York: Reinhold Publishing Corporation, 1965. 1-1. Ruskin, R.E. (Editor) "Principles and Methods of Measuring. Humidity in Gases". Volume One, op. cit.(Ref. 1). 1-2. Amdur, E.J. (Editor) "Applications". Volume Two, op.cit.(Ref. 1). 1-3. Wexler, A., and Wildhack, W.A. (Editors) "Fundamentals and Standards". Volume Three, op. cit.(Ref. 1).

1-4. Winn, P.N., Jr. (Editor) "Principles and Methods of Measuring Moisture in Liquids and Solids". Volume Four, op.cit. (Ref. 1). 58 ANNEX I

2. Sinha, E. (Compiler) "Bibliography on Humidity Measurement Instruments". Meteorological & Geoastrophysical Abstracts, vol.~, No. 12, )622-3717 (December 1962).

3. Wylie, R.G., Davies, D.K., and Caw, W.A. "The Basic Process of the Dew-Point Hygrometer".pp. 125-134 in Ref. 1-1.

4. Brewer, A.W. "The Dew- or Frost-Point Hygrometer". pp. 135-143 in Ref. 1-1.

5. Martin, S. "A Frost-Point Hygrometer for Use at Low Frost Points". pp. 144-148 in Ref. 1-1; and "A Laboratory Standard Manually Operated pew-Point Hygrometer Using 'rhermoelectric Cooling". pp. 149-154 in Ref. 1-1.

6. Paine, L.C. and Farr"ah, H.R. "Design and Applications of High-Performance Dew-Point Hygrometers ll • pp. 174-188 in Ref. 1-1.

7. Yoshitake, M. "On the Vapour Pressure Gradient in the Layer near the Cooled Surface of a Dew-Point Hygrometerll . Journal of the Meteorological Society, Japan, Series II, Volume 39, 97-102(June 1961).

8. Wildhack, W.A., Perls, T.A., Kissinger, C.W. and Hayes, J.W. "Continuous - Absorption Hygrometry with a Pneumatic Bridge Utilizing Critical Flow". pp. 552-570 in Ref. 1-1.

9. Greenspan, L. "A Pneumatic Bridge Hygrometer for Use as a Working Humidity Standardll .pp.433-444 in Ref. 1-3.

10. Kobayashi, J. IIInvestigations on Hygrometry". Papers in Meteorology and Geophysics, vol. 11, Nos. 2-4, pp. 213-338 (1960). Published by the Meteorological Research Institute, TOkYo, Japan.

11. Jones, F.E. and Wexler, A. ll "A Barium Fluoride Film Hygrometer Element • Journal of Geophysical Research, vol. £2, 2087-2095 (1960). 12. Jones, F.E. IIEvaporated-Film Electric Hygrometer Elements". Journal of Research, National Bureau of Standards, vol. 660, 209-216 (September 1962).

13. Jones, F.E. IIperformance of the Barium Fluoride Film Hygrometer Element on Radiosonde Flights". Journal of Geophysical Research, vol. --68. 2735-2751 (1963). 14. Jones. F.E. "A Study of the Variation of the Surface Electrical Resistance of Lead Iodide Films with Relative Humidity at Room Temperature". pp. 361-365 in Ref. 1-1. ANNEX I 59

15. Smith, E.K. and Weintraub, S. "The Constants in the Equation for Atmospheric Refractive Index at Radio Frequencies". Froc. LR.E., vol.41, 1035-1037 (1953). See also: Journal of Research, National Bureau of StandardS"; vol. ,22, 39-41 (1953).

16. McGavin, R.E. and Wetter, M.J. "Radio Refractometry and Its Potential for Humidity Studies", pp.553-560 in Ref. 1-2. 60

ANNEX II Annex to paragraph 8.3 of the General Summary

NOTE ON THE FEASIBILITY OF DETERMINING THE HEIGHT OF CONVECTIVE CLOUD TOPS

The purpose of this short paper is to define the difficulties of determining the height of convective cloud tops. It is by no means exhaustive since the matter will presu mably be studied by the Working Group on the Use of Meteorological Radar for Aeronautical Purposes. (1) Determination of the top of the cloud zone containing precipitating particles• The accuracy of this measurement depends mainly on the width of the beam transmitted in the vertical plane. That width being fixed by dimensions of the aerial and the frequency of the radar, the final accuracy varies according to these parameters. In the fir~t esti mate the width of the beam transmitted may be considered as proportional to the wavelength and inversely proportional to the size of the radar aerial in the vertical plane. The follow ing table gives some beam widths for various aerial diameters (d) and various wavelengths (~) Formula used : e 70~ (in degrees) Diameter (metres) 1.0 2.0 3·0 4.0 5.0 3.2 2.2 1.1 0·75 0.56 0.45 5.7 4.0 2.0 1.3 1.0 0.8 10.0 7.0 3.5 2·3 1.8 1.4

In electronical terminology each angle in the above table is defined as the angle delimited by straight lines representing radiation intensity equal to half the maximum intensity emitted. Therefore that angle does not include the total amount of power emitted by the radar; in the case of a target having an importarrt back-scatter cross-section it is not impossible for the power not included in the theoretical beam to produce an echo. As a result the aoouraoy of the measurements taken is often determined by a muoh wider angle than.that whioh is generally given for the width of the beam emitted. This reduotion in aoouraoy may also be aggravated by the aotion of seoondary lobes whioh may entail an important overestimate of the hei~t of the targets deteoted. Finally, it is advisable to mention that this reduotion depends also on the drop size distribution in the vertioal plane, on· the power emitted by the radar set, on its noise factor and receiver gain, on refraction phenomena, on the attenuation undergone by the signal between the radar set and the target and, finally, by the distanoe at whioh the measurement. is taken. (2) Determination of the height of the cloud top proper In view of the small diameter of drops, this determination can be oontemplated only by means of K-band radar. The comments made in the preceding paragraph also apply here. It is however likely that, in view of the ease of obtaining small beam widths, it will be possible to improve the measurement. Unfortunately it is beyond doubt that the ANNEX II 61 seriousness of the attenuation phenomena to which K-band radar is subject will restrict the useful range of sets operating in this band to an extremely low value. It may be mentioned that K-band radar equipment could prove useful in the case of aircraft flying over clouds, since the maximum range of detection is increased because the beam reaches the cloud tops without having to traverse cloud or precipitation zones. 62

ANN E X III Annex to paragraph 20.2 of the General Summary

PROPOSAL FOR A STANDARD LAYOUT FOR CHAPI'ERS OF THE GUIDE TO MEJrEOROLOGICAL INSTRUMENT AND OBSERVING PRACTICES

As was pointed out by the Soviet delegation at the CIMO session in New Delhi the Guide (2nd ed., WMO-No. 8. TP.3) is written very unevenly both from the viewpoint of the arrangement of the chapters and their contents. In so far as the Guide is intended for the workers of national services and scien tific centres to serve as the basis for their national regulations, the information in the Guide should, in our opinion, correspond to this task and make it possible to evaluate and select instruments and methods best suited for local conditions. In our opinion the draft standard chapter layout which we suggest meets these re quirements more fully. In drafting this layout we have tried to outline the necessary scope and character of information and to determine the order of presentation. We suggest that every chapter (excluding the first chapter dealing with the general principles and definitions) should contain a description on each point of the layout; when visual methods of observation are dealt with there will be no description of instruments. The first section of each chapter will contain general data on. the measured meteo rological element and the conditions of its measurement. This section will give more detailed and concrete information than the one given in the WMO Technical Regulations. The second section will give the description and evaluation of the recommended methods of observation (or measurement). The· aim of this section is to provide the basis for selecting the method best suited for local conditions. The third, fourth, etc. sections of the chapter deal with a particular method, in cluding the description of the principal features of instruments used. When a visual method is being described the section contains only the first two points. In order to indicate exactly what kind of information is meant every item in the proposed layout should cite as a reference example the number of the corresponding item of the present WMO Guide.

In the re-draftin~ of the Guide we suggest that all the chavters be given the same title: "Measurement of ••• " (followed by the measured meteorological element).

STANDARD LAYOUT for the chapters of the Guide to Meteorological Instrument and Observing Practices

No. Number and title of chapter No, 1 General No. 1.1 Definition and brief general information on the measured element. This should also contain the numeration of parameters to be measured (as was done for example in the present 3.1, 5.1.1, 6.1, 6.2.1, 8.1, 9.1, etc.). When necessary, a theoretieal basis should be given (as in 8.3.1). ANNEX III

ND, 1.2 Units of measurement, i.e. units recommended in accordance with the WMO Technical Regulations, as, for example, in 3.1.1, 5.1.2, etc. No, ••••• 1.3 The established conditions of the element measurement Indications as to the level (the height above ,ground level, or above sea-level) at whiCh measurements should be taken (as, for instance, in 4.1.3). to what level they refer or are reduced (for example, pressure, see 3.4, 5.1.1 (e) ). For some types of observations should be indicated the area or distance at which observations are to be taken (for 'example, cloud observations, as in 2.3; snow-pack observations, as in 7.4.2, the last paragraph; hydrometeor observations, etc.). The same division contains, when necessary, the description of standard conditions (as, for example, in 3.2.2), standard scales) or relation between values (as in 8.3).

No, 2. Methods of observation No, 2.1 The recommended methods and their description. The description of methods which could be recommended and their fiel~ of application (for example as in 4.4.4, 5.1.3~ ~.2.3, 7.6.2, 7.5.2, etc.), No, ••••• 2.2 The comparative estimate of errors. Errors of each method (including errors of instruments) are composed, the advantages and shortcomings of each metho~ or a group of methods are indicated (for example, as in 2.4.6, 3.2.7, 5.2.5). No, 3· Description of each method (This division, including all subsequent paragraphs, will be repeated each time a new method is described. The des~riptions of subsequent methods are given under No• ••••• 4, No .••••• 5, etc.). No, 3.1 Description of method No, 3.2 Basic requirements - general requirements or conditions involved in the applications of a given method, irrespective of the type of instruments used (See for example 4.2.1, 6.~.2, 7.1 - second part of the paragraph etc.).

N~ 3.3 Description and evaluation of different kinds of instruments used when a given method is applied.

No. 3.4 Requirements of scales and sensitive elements (see for example 3.2.3, 4.4.2, 7.2.2, 8.3 etc.). No, 3.5 Accuracy of readings. Whenever possible, the accuracy of readings ensuring that the error in the measurement by the given method does not exceed a maximum tolerable error (as in 3.2.5, the last paragraph, 4.5, 5.2.3.1, 5.2.5.4, 6.3.1 etc.). No, 3·6 Instruments and observations No, 3.6.1 Design of the instrument - description of the working principle of an in strument(or a series of instruments used in a given method) and their basic cha racteristics (see, for example, 2.5.2 - 2.5.3, 3.2.1, 3.3.1, 4.4.1, 4.4.3-4.4.6, 4.6.1-4.6.5, 6.3.3-6.3.4, 7.2.1 etc.), When describing visual (sensory) observation methods this item is omitted. • No. 3.6.2 Exposure and managemant - rules and location of the exposure, screens, management (see for example 3.2.4, 4.2.2 - 4.2.3, 5.2.2, 5.2.4, 5.3.2 - 5.3.4.4, 6.4, 7.2.3, etc.). When describing visual methods requirements of the point or area of observation are given instead. 64 ANNEX III

No 3.6.3 Conduct of observation - description of basic rules of observations (see for example 3.2.5, 3.5.2, 4.5, 5.2.3, 5.3.0, etc.). When necessary, the duration of observation should be specially indicated (see for example 2.2). NO 3.6.4 Sources of error - enumeration of causes of errors with approximate values of errors and their nature indicated (see for example 3.2.7, 3.3.4, 3.5.4, 5.2.5). No 3.6.5 Correction of reading - no explanation needed (see 3.2.6, 3.~.3, ~.5.4, 4.5 last part, etc.-). VariouR auxiliary tables, when necessary, could be described. No 3.6.6 Checking and control - description of methods of checking instruments at the point of observation (verification of zero, etc.) and methods of their control by comparison ~gainst reference instruments (see for example 4.6.6). 65

ANNEX IV Annex to paragraph 20.3 of the General Summary

AMENDMENTS TO THE GUIDE TO METEOROLOGICAL INSTRUMENT AND OBSERVING PRACTICES

Section 2.3 Cloud amount. The tabulation given on page II.2 should be amended to include scale in 1/10 which is in use in some Member countries. This scale should show the identity 8 oktas = 10/10. . (Note: There is however no intention of changing the cOde.)

Section 2.3 Insert after the sentence ending with " •••••••• blue sky." (line 7 of second para graph from the top): "Fog should be regarded as cloud at station level". Then continue with the text: "On occasions •••••• ".

Section 2.4.6 Replace the last two sentences beginning with "It is considered •••• " and ending with: " ••••• generally obtainable" "The accuracy of determining the cloud height by in strumental methods is better than ~ (20m + 0.1 h) where h = the height of the cloud base in metres."

Section 3.2.1 Add at the end of paragraph (f) the sentence "The scales should preferably be calibrated to give correct readings at ooC."

Section 3.2.7.3 Replace in line 6 the sentence beginning with : "This should ••••••• " by "This should not exceed 1.5 mm in diameter when the barometer is inclined."

Section 3.5.4 Amend the first sentence of the second paragraph (4th line from.below) as follows insert after ,,± 0.2 mb", "after corrections are applied,"; then continue with the text.

Section 5.1.1 The "Definitions and units" should form an appendix to this chapter. The format of this appendix should be that of the Appendix to Chapter 9.

Section 5.3.4.3 Add after" standard psychrometer." in line 2 : "To appraise the long-term stability, the presentation of the comparisons with the standard psychrometer in the form of correlation graphs is recommended." In lines 4 and 5 from the top of the paragraph replace : "in an ordinary room" by "indoors". The word "chambre" in the French version of the Guide should be replaced by the word "caisson". 66 ANNEX IV

Section 7.5.2 In lines 3 and 4 of the second paragraph delete "observe the appearance •••••• after exposure", and substitute: "and observe at or about sunrise the appearance of the dew on the surface after nocturnal exposure."

Section 10.1.2 Add the following sentence at the end of this paragraph : "Special precautions shall be taken in the exposure of the instruments sensing the various meteorological parameters to insure representative measurements. This may call for the use of remote indicating and/or recording instrumentation.

I ""; A N N-E X V Annex to Recommendation 1 (CIMO-IV)

REGIONAL AND NATIONAL RADIATION CENTRES

Regionai radiation centres 1. A regional radiation centre is a centre designated by a Regional Association to serve as a centre for international comparisons of radiation instruments within the Region and to maintain the standard instruments necessary for this purpose.

2. Each regional radiation centre should satisfy the following conditions before it is designated as such and should continUe to fulfil them after being designated. o (a) It should possess a set of at least three standard pyrheliometers of the Angstrom or silver disc type, one of which must have been compared at least once during the previous five years, against the international standard instruments, during an inter regional comparison conducted by WMO. One of the three standard pyrheliometers must have been used as a reference standard in the regional or national -network for at least five years. (b) It should possess measuring and checking equipment of which the accuracy is at least of the same order as that laid down for standard pyrheliometers in Chapter 9 of the Guide to Meteorological Instrument and Observing Practices. (c) It should have the necessary facilities and laboratory equipment for checking and maintaining the accuracy of the auxiliary measuring equipment. (d) It should provide the necessary facilities for international comparisons of nation al pyrheliometric standards within the Region. (e) The staff of the centre should provide for continuity and should include a qualified scientist with wide experience in radiation.

National radiation centres 1. A national radiation centre is a centre designated at the national level to serve as a centre for the calibration, standardization and checking of the instruments used in the national network of radiation stations and for maintaining the national standard instruments necessary for this purpose.

2. A national radiation centre should satisfy the following requirements : o (a) It should possess at least one working standard pyrheliometer of the Angstrom compensation or silver disc type for use as a national reference standard for the ca libration of radiation instruments in the national network of radiation stations. (b) The national working standard pyrheliometer should be compared with a regional work ing standard pyrheliometer at least once in 5 years. (0) The accuracy of calibration of the auxiliary measuring equipment should be of the same order as that of the pyrheliometer. (d) It should have the necessary facilities and equipment for checking and for the study of the operation and performance of instruments used in the network. 68 ANNEX V

(e) The staff of the centre should provide for continuity and should include a quali fied scientist with wide experience in radiation.

3. National radiation centres should be responsible for the preparation and keeping up-to-date of all necessary technical information for the operation and maintenance of the national network of radiation stations.

4. Arrangements should be made for the collection of the results of all radiation measurements made in the national network of radiation stations and for the regular scrutiny of these results with a view to ensuring their accuracy and reliability. If this wo~k is done by some other body~ the national radiation centre should maintain close liaison with this body. 69

ANN. E X VI Annex to RecOJI]Iilendatiol}. 4 (CIMO.,.JY)

ACCURAcY REQUIREMENTS STATED B¥~ .'l'ECHNICAL. COMMISSIONS

ELEMENT ACCURACY REQUIRED '. QOMMElI)TS

Upper-air observations Radio soundings

Pressure CSM : 1 mb - -- Temperature ., CSM : 0.5°C

CAe : in the troposphere·0.15°C in the stratosphere~0.300C , ,

Relative humidity CSM : up to the tropopause or 300 mb - ,.5% above - 10% ., -, Dew point CAe : lower layers - 0.5°C above - up to the tropopause '-. " ., if U high - 0.2°C if U low - 0.5°C

Wind direction CSM : if V> 25 m/s - 5° Mean va~ue-within a if V< 25 m/s - 10° layer # 3 to 400 m thick (CSl.'i!) Wind speed CSM : if V< 10 m/s - 1 m/s if V> 10 m/s - 10% "

CAe : 1 m/s 70

ANN E X VII Annex to-Recommendation 7 (crMO-IV)

PROGRAMME OF INTERNATIONAL COMPARISONS OF METEOROLOGICAL INSTRUMENTS

1. Short period Description Date

1. Radiosondes 1967 2. Barometers 1966-67 3· Pyrheliometers 1969 4. Radiometersondes 1967 5. Atmospheric electricity sondes 1968 6. Ozone-sondes 196'7-68 7· Sensors for meteorological rockets 1968 8. Radioactivity- sondes 1966

2. Long period Instruments compared Duration of comparison 1. Sunshine recorders 1964-68 2. Net pyrradiometers 1965-68 3· Pyranometers 1965-68 4. Precipitation gauges 1962-68 5. Evaporimeters 1965-68 6. Leaf-wetness recorders 1965-68 7. Instruments for measurement of radio- 1966-68 activity 8. Psychrometers 1967-68 9. Instruments for measuring visibility 1967-68 and height of cloud base

~ 71

LIST OF DOCUIVlENTS

Doc. Title Agenda item Submitted by No. 1 Provisional agenda Add. 1, 2 1.3 2 Explanatory memorandum concerning the provisional agenda 1.3 Add. 1, 2, 3 3 The measurement of atmospheric radioactivity - Draft summary of 18 Dr. O. Suschny, contents of a WMO Technical Note IAEA (rapporteur) 4 Report by the chairman of the Working Group on Radiation Instruments and 9 Chairman Observat.ions for General Use Add. 1 5 Report of.the chairman of the Working Group on Accuracy Requirements 14 Chairman 6 Report of the Working Group on Evaporation Measurement 4 Chairman Corr. 1 7 Report of the Working Group on Radiowind Measurements on Board 10.2 Chairman Merchant Ships 8 Report of the Working Group on Lower Troposphere Soundings 13 Chairman Add. 1 9 Establishment of Working Groups 25 Secretary-General 10 Report of the Working Group on Instrument Development 16 Chairman Add. 1 11 Report of the Working Group on Meteorological Instruments and Methods 7 Chairman of Observation on Aerodromes Add. 1, Corr. 1 12 Terms of reference of the Commission Add. 1 22 Secretary-General 13 Training in instruments and methods of observation 23 Secretary-General 14 Terminology of standard instruments 15 Secretary-General 15 Review of previous resolutions and recommendations of the Commission and 24 Secretary-General of relevant Executive Committee resolutions 72 LIST OF DOCUMENTS

~N~o~.~Doc. __~ ____~ ______Title Agenda item __ Submitted by

16 Horizontal soundings 10.6 Secretary-General 17 Report of the Working Group on Psychrometry 5 Chairman 18 Report of the Working Group on Measure- ment of Atmospheric Electricity 12 Chairman 19 Report of the Working Group on Radiosondes 10.1 Chairman 20 Comparison of Instruments Add. 1 17 Secretary-General 21 Technical Regulations Add. 1.2 21 Secretary-General 22 Guide to Meteorological Instrument and Observing Practices 20 Secretary-General Add. 1 23 Radio frequency allocations Add. 1 11 Secretary-General 24 Report of the Working Group on Snow Measurements 3 Chairman 25 Accuracies for meteorological obser vations at aerodromes President of CAeM 26 Suggestions for a permanent s~t-up to ensure standardization of measuring 15 President of CIMO techniques and the comparisons of standards maintained by Members

27 Dropsonde observations 10.5 President of CIMO 28 Design and exposure of thermometer screens 5 President of CIMO 29 Report of the CIMO representative on the CHy Working Group on Instruments 3 Dr. J. Grunow and Methods of Observation

30 Uses of airborne radar in meteorology 8 President of CIMO 31 Report of the president of the Com mission 2.1 President of CIMO Add. 1, 2 32 Sensors and telemetry for meteorolo gical rockets 10.7 U.S.A. 33 Automatic weather stations 16 Secretary-General 34 Views of CAe-IV on measurements of atmospheric radioactivity data 18 Secretary-General 35 Action taken by CAe-IV on accuracy requirements 14 Secretary-General LIST OF DOCUMENTS 73

Doc. Title Agenda item Submitted by No. Request by CAe-IV for CIMO expert to serve on CAe working group 10.1 Secretary-General 37 Scientific lectures and discussions 28 Secretary-General 38 Automatic weather stations 14 Secretary-General 39 Instrument development 16 Secretary-General 40 Final Report of the Working Group on Special Radiation Instruments and 9 Chairman Observations 41 The maintenance of the IPS 1956 pyrheliometric scale and the 9 Switzerland calibration of working standard pyrheliometers 42 Remarks on the improvement of radiation measurements with the 9 Switzerland compensation pyrheliometer Use of aneroid barometers as travelling standards 6 Secretary-General 44 Minimum performance characteristics of automatic weather stations 16 R.N. Brann and R. Treussart, CIMO representatives on theCSM Working Group 45 Feasibility of determining the height of tops of convective clouds 8 Secretary-General 46 Report of the Working Group on International Comparisons of 3 Secretary-General Precipitation Gauges 47 Questions raised by the Commission for Climatology 14 Secretary-General 48 Special instrumentation for meeting operational requirements of supersonic 10.8 India transport (SST) aircraft 49 Explosion of hydrogen filled balloons 16 New Zealand

50 Report of the Working Group on Review of Radiosonde HYgrometry Chairman 51 Preliminary report on runway visual range measurement trials 7 & 16 Belgium 52 Final Report of the Working Group on Uses of Radar in Meteorology 8 Chairman 53 Comparison of instruments - Statistical considerations 17 Netherlands '74 LIST OF DOCUMENTS

Doc. Title Agenda item Submitted by No. 54 Special instrumentation for meeting operational requirements of supersonic 10.8 U.S.A. transport (SST) aircraft 55 Review of meteorological observations in the Antarctic 19 Dr. V.I. Shlyakhov (rapporteur) 56 Barometer comparisons Add. 1 6 U.S.A. 57 Radiosonde humidity measurement - Comparison of hair hygrometer with 10.3 Japan dew-point meter 58 Calibration stability of Finnish radiosonde during one year1s storage 10.1 Finland 59 Radioactivity sonde 18 Finland. 60 Gas temperature of sounding balloons 10.1 Finland 61 The pyrheliometric standard instruments for securing the International 9 Sweden Pyrheliometric Scale of 1956 62 A comparison of dry-bulb and dew-point temperature as obtained by mercury-in- 5 United Kingdom glass thermometer in screens, Assmann psychrometers and whirling psychrometers 63 Instruments and methods of observation on aerodromes 7 ICAO 64 Simple equipment for the recording of PPI pictvres of·radars 8 France Combustion of hydrogen in the cylinder and the balloon 16 Japan 66 Horizontal soundings 10.6 Chairman, Committee B 67 Dropsonde observations 10.5 Chairman, Committee B 68 Evaporation 4 Chairman, Committee A 69 Barometer comparisons 6 Chairman, Committee A 70, Report by the president of the Commission 2.1 Chairman, Committee A 71 Instrument development 16 Chairman, Committee A 72 Observations in Antarctica 19 Chairman, Committee A 73 Establishment of working groups 25 Chairman, Committee A 74 Atmospheric electricity 12 Chairman, Committee B 75 Lower troposphere soundings 13 Chairman, Committee B LIST OF DOCUMENTS 75

Doc. Title Agenda item Submitted by No. 76 Radiowind measurements on board merchant ships 10.2 Chairman, Committee B 77 Radiosonde hygrometry 10·3 Chairman, Committee B 78 Instrumentation for supersonic transport (SST) aircraft 10.8 Chairman, Committee B 79 Computation techniques 10.4 Chairman, Committee B 80 Radiation 9 Chairman, Committee A 81 Precipitation 3 Chairman, Committee A 82 Report of the Nomination Committee 26 Chairman, Nomination Committee 83 Uses of radar in meteorology 8 Chairman, Committee B 84 Accuracy of measurements 14 Chairman, Committee A 85 Training in instruments and methods of observation 23 Chairman, Committee B 86 Terms bf reference of the Commission 22 Chairman, Committee B 87 Atmospheric radioactivity 18 Chairman, Committee B 88 Radio frequency allocations 11 Chairman, Committee B 89 General summary of the work of the session 1 Seeretary-General 90 Election of officers 26 Secretary-General 91 Draft proposals for establishment of working groups 25 Chairman, ad hoc Committee 92 Radiosondes 10.1 Chairman, Committee B 93 Sensors and telemetry for meteorological rockets Chairman, Committee B 94 Meteorological instruments and methods of observation on aerodromes 7 Chairman, Committee A 95 Instrument standards 15 Chairman, Committee A 96 Review of previous resolutions and recommendations of the Commission 24 Chairman, Committee B and relevant Executive Committee decisions 97 Guide to Meteorological Instrument 20 Chairman, Committee A and Observing Practices 98 Comparisons of instruments 17 Chairman, Committee A 99 Technical Regulations 21 Chairman, Committee B 100 Scientific lectures and discussions 28 Chairman, Committee B 101 Surface temperature and humidity 5 Chairman, Committee A WORLD MET E 0 R 0 LOG I CAL o R G A N I Z A T ION

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Supplement to WMO Publioation No. l85.RP.68

Decisions of the Executive Committee on the Agridged Final Report of the Fourth Session of the Commission for Instruments and Methods of Observation

This dooument should be oonsidered as a guide to the status of the deoisions adopted at the Fourth Session of the Commission for Instruments and Methods of Observation.

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A. DECISIONS RECORDED IN THE GEl\TE;RAL SUMIlIIARY OF THE WOliK DF EO-X:VII~"

_____Instruments - - - ______and -.---methods_._ ~ __of ~ observation...... ,....;r.. __ ._

5.5.4.1 The Committee examined the Abridged Final Report of the fourth session of the Commission for Instruments and Methods of Observation, with special attention to the recommendations. The main decisions of the Committee are incorporated in Resolutions 19 - 22 (EC-XVIII).

5.5.4.2 The Committee considered that the work of CHiO was of increasing importance in view of the new observational methods being introduced and of the development of the Global Observational System for the I"orld "leather Watch. The introduction of automatic weather stations meant that more attention must be paid to the accuracy and time resolution required from meteorological instruments. In this connexion, the Committee noted with satisfaction that in Resolution 18 (CI.ID-IV) a rapporteur had been desig nated to draft a section for the GUide to Meteorological Instrument and Observing Practices on the accuracy required for various purposes, taking into account the statements provided by various Technical Commissions.

5.5.4.3 ''lith regard to Recommendation 7 (CIMO-IV), dealing with compar isons of instruments, the Committee considered that the instruments for . which arrangements fo·r comparisons are to be made should be primarily those which are in general use, or about to be introduced for general use, and for which it is not possible to obtain the required information on accuracy by laboratory tests against an absolute standard instrument. The President of CIMO was requested to keep this in mind when making proposals for financial support for instrument comparisons.

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B. RESOLUTIONS

REPORT OF THE FOURTH SESSION OF THE C0M11ISSION FOR· HTSTRUMENTS MilD l\I[ETHOt)S OF OBSERVATION

. THE EXECUTIVE ,COM1YIITTEE,

: < HAVING CONSIDERED the report of the 'fourth session of the Commission for Instruments and MethQds of ObserY0tion,

DECIDES

(1) To note the repori; . ; .

(2) To" note without comments Resolutions 1 - 23 (GIMO-IV) 9

(3) To. embody the substance o:f th.e following reoommendations in resolutions of the ·Execu·tive CommJ.. ttee as :indica-ted 'g ,

~~::5:~~~~~.~j:~5:~_~;-~i~!~~:!:~O in ResolMtion 20 (EC~:x:VIII)

~~::::~~~::~~!~::~_~___ {~!~~~:X~~') in Resolution 21 (EC-XvIII)

~::~::~~::::~~!:!:5:~_1...:.:...{~~~~:~:~O in Resolution· 22 (BC-XVIII)·

Recommendat{on 11 (elMO-IV) in Resolution 44 (EC-XVIII)? ------.... ------~--'--... -.---.--- ..... - . ..' 0 To take action on the remaining recommendations as follows' g

Approves this recommendation in principle and requests ... ~he. Secr:e:!j~:.ry General to d,etermine whioh ?ountries would be able and willing to establish,;', viorld Radia1iion Centres and to report on this to EC-XIX;

Approves this reoommen~atiqn and requests the Secretary-General to take appropriate action with Members and other interested organizations, taking into aocount the views expressed in paragraph 7.10 of the General Summary of cmll-IV;;

Approves this recommendation and Reoommendation 17 (CAe-IV) and requests the Secretary-General to bring the relevant paragraphs of these - 6 -

two recommendations to the attention of Members and, in consultation with the President of CH10, to .. include the comparisons of meteorological tower instrumentation in the general programme for instrument comparisons;

Recommendation· 7 (CIMO:.:.tV)· - COmparisons of ins·trum(mts ------:"'"------.. ------.-~ ---- Approves this recommendation in principle and requests the Secretary-General, in consultation with the President of C1HO, to arrange for the programme of instrument comparisons to be carried out, subject to budgetary and other limitations;

Approves paragraph 1 of this recommendation and requests the Secretary-General to bring it to the attention of all concerned and, in consul tation wi th the President of CHIO, to consider any requests for financial assistance in the light of other needs for financial support for instrument comparisons;

Recommendation 9 (CIMO-IV) ·-Revision of Technical Regulations ------~--~-----~------Notes this recommendation and requests the Secretary-General to incorporate the proposed amendments in his consolidated .report .to Fifth Congress on the revision of the Technical Regulations;

Recommendation 10 (CINO-IV) - Terms of reference of the Commission ------~------Supports this recommendation and directs the Secretary-General to incorporate the proposed amendments in his report to Fifth Congress on the revision of the General Regulations.

Note This resolution replaces Resolution 21 (Ee-XIV) which is no longer in force. - 7 -

NATIONAL AND REGIONAL RADIATION CENTRES

THE EXECUTIVE COJl1HITTEE,

NOTING Recorrnnendation 1 (CHIO-IV),

CONSIDERING (1) That many countries operating a network of radiation stations have not yet designated national radiation centres,

(2) That some Regional Associations have not yet designated regional radiation centres, and

(3) That some clarification is necessary concerning the functions of regional radiation centres and the conditions which should be met before a centre is designated for this purpose,

REQUESTS

(1) Members which operate a network of radiation stations but have not yet designated national radiation centres to take steps to this end;

(2) Regional Assoc·iations which have not yet designated a regional radiation centre to designate one or more such centres as soon as possible; and

RECOMMENDS that in designating national and regional radiation centres account should be taken of the factors given ih the annex to this resolution.

Annex 1 :,',: 9 -

AnnHX to Resolution 20 (Ee-XVIII)

NATIONAL AND REGIONAL RADIATION CENTRES

Regional radiation centres

1. A regional radiation ~entre is a centre designated by a Regional Association to serve as a centre for international comparisons of radiation instruments within the Region and to maintain the standard instruments necessary for this purpose.

2. Each regional radiation centre should satisfy the following conditions before it is designated as such and should continue to fulfil them after being designated. (a) It should possess a set of at least three standard pyrheliometers of the Angstrom or silver disc type, one of which must have been compared at least once during the previous five years, against the international standard instruments, during an inter regional comparison conducted by WMO. One of the three standard pyrheliometerEi must have been used as a reference standard in the regional or national network for at least five years. (b) It should possess measuring and checking equipment of which the accuracy is at least of the same order as that laid down for standard pyrheliometers in Chapter 9 of the Guide to Meteorological Instrument and Observing Practices. (c) It should have the necessary facilities and laboratory equipment for checking and maintaining the accuracy of the auxiliary measuring equipment. (d) It should provide the necessary facilities for international comparisons of nation al pyrheliometric standards within the Region. (e) The staff of the centre should provide for continuity and should include a qualified scientist with wide experience in radiation.

National radiation centres 1. A national radiation centre is a centre designated at the national level to serve as a centre for the calibration, standardization and checking of the. instruments used in the national network of radiation stations and for maintain~ng the national standard instruments necessary for this purpose.

2. A national radiation centre should satisfy' the following re~lirements : o (a) It should possess at least one working standard pyrheliometer of th(~ Angstrom compensation or silver disc type for use as a national reference standard for the ca libration of radiation instruments in the national network of radiation stations. (b) The national working standard pyrheliometer 'should be compared with a regional work ing standard pyrheliometer at least once in 5. ·years. (c) The accuracy of calibration of the auxiliary measuring equipment should be of the same order as that of the pyrheliometer. (d) .It should have the necessary facilities and equipment for checking and for the study of the operation and performance of instruments used in the network. - 10 -

(e) The staff of the centre should provide for oontinuity and should include a quali fied scientist-with wideexperiehM ih l'adiatIon.

3. National radiation centres should be responsible for the preparation Hnd keep1rw up-to-date of all necessary technical information for the operation and maint-f'n'1nce of the national network of radiation stations.

4. Arrangements should be made for the collection of the results of all radlalton measurements made in the national network of radiation stations and for the rel':ular ['''1'111.1 I1V of these results with a view to ensuring their accuracy and reliability. If thls wor'k I:: done by some other body, the national radiation centre should maintain close liaison with this body. - 11 -

COMPARISONS OF PYRHELIQII'IETERS

THE EXECUTIVE COl'1nITTEE,

NOTING Recommendation 3 (CIMO-IV), and

CONSIDERING (1) That an accuracy of : 1 per cent is desirable for routine measurements of direct solar radiation, (2) That this can only be attained if a higher degree of accuracy is achieved in national, regional and inter-regional comparisons of pyrheliometers,

RECOr1MENDS (1) That Members should endeavour to develop a standard pyrhe-liometer capable of achieving and maintaining an accuracy of measure ment of at least! 0.1 per cent; (2) That regional radiation centres should endeavour to achieve and maintain an accuracy of measurement of at least ~ 0.25 per cent "Ii th the regional -standard pyrheliometer;

(3) That pyrheliometers used in national networks should be compared regularly against the national standard pyrheliometer; and

(4) That international comparisons of national standard pyrhe liometers against the regional standard pyrheliometer should be carried out every five years; and

DECIDES that WMO should organize inter-regional comparisons of regional standard pyrheliometers every five years. ( · . :. ;," - 13 -

R(~<101ution 22 (EC-XVIII] .,-_ ...... ___ u ,;:;e-_ -rlS -~...... -.

COMPARISON OF RADIOSONDES

THE EXECUTIVE COMMITTEE,

NOTING Recommendation 4 (CHrO-IV) j

CONSIDERING (1) The importance to the science and practice of meteorology of increasing the number and accuracy of radiosonde observations at altitudes of 30 kilometres and higher,

(2) That improved equipment is now available, both for making measurements at thesealti tudes and for cOi'i1paring the results obtained by various kinds of radiosonde systems, especially with regard to the measurements of temperature,

RECONMENDS

(1) That Hembers take into account the accuracy requirements stated by \~10 Technical Commissions (see Annex) when developing and operating radiosonde and radiowind instruments and equipment;

(2) That Members, particularly those in whose countries radio sonde systems of various kinds are manufactured,arrange to oetermine the comparabili ty of results obtained with identical systems vThen two radio sondes of the same kind are flown on a single balloon (t\vin soundings);

(3) That, as new instruments are developed '''hich can serve as a reference for one or more meteorological parameters measured in the upper-air, Members, particularly those in whose countries radioson des are manufactured, arrange comparisons of their sondes with the reference sondes;

(4) That all comparisons described above be conducted in each case in approximately equal numbers both by day and night, and that every possible effort be made to conduct the comparison to an altitude of 30 kilometres or higher; - 14--

(5) That in all cases. the res~lts of the comparisons made in accordance with the above be pubHsh"ed"'as' qui"ckly as possible and . made available to the Secretariat for distribution to Members.

Note This resolution replaces Resolution. 25 (EC-XIV), which is no longer in force.

Annex 1

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Annex to Resolution 22 (EC-XVIII)

COiTAPI SOH OF' RADIOSOITDES

Aocuracy re9.ui. r:.':"fi·3n- I.s state d by,- v[l\10 Technical Commies ions ELEMENT ACCURACY REQlJIRED COMfv1EmS

Upper-air observations Radio s01mdin~s

Pressure CSM : lOmb Temperature CSM : 0.5°C

CAe I in the troposphere-0.15°C in the stratosphere-0.300C Relative humidity COM . up to the tropopause or 300 mb - 5% above - 10%

Dew point CAe : lower layers - 0.5°C above - up to the tropopause if' U high - 0.2°C if' U low - 0.5°C

Wind direction CSM I if V> 25 mls - 5° Mean value within a if V< 25 m/s - 10° layer 3 to 400 m thick (CSM) Wind speed CSM : if' V< 10 m/s - 1 mls if' V'> 10 m/s - 10%

CAe : 1 m/s ,-