GARP JOINT ORGANIZING COMMITTEE GARP PUBLICATION S SERIES No.' 4 INTERNATIONAL COUNCIL WORLD METEOROLOGICAL OF SCIENTIFIC UNIONS ORGANIZATION GLOBAL ATMOSPHERIC RESEARCH PROGRAMME (GARP) WMO-ICSU Joint Organizing Committee THE PLANNING OF . , .. \ GARP TROPICAL EXPERI'ME,.NTS GARP PUBLICATIONS SERIES No. 4 January 1970 03···SO-76 C"2 © 1970, World Meteorological Organization International Conncil of Scientific Unions CONTENTS Page FOREWORD . V SUMMARY (English, French, Russian, Spanish) VII LIST OF ABBREVIATIONS . XIII 1. INTRODUCTION..... 1 1.1 The place of tropical experiments within the context of GARP. 1 1.2 Earlier recommendations concerning experiments in the tropics 2 1.3 The JOC Study Group on Tropical Disturbances ...... 3 1.4 The Report of the JOC to the Executive Committees of WMO and ICSU. 3 1.5 The genesis of the present report. ................. 4 2. SCIENTIFIC REQUIREMENTS FOR TROPICAL EXPERIMENTS. 5 2. 1 General considerations. ............ 5 2.2 The scales of atmospheric motions in the tropics. 5 2.3 The problems to be solved. ..... 6 2.4 The relation with previous experiments ..... 7 3. A IDERARCHY OF GARP EXPERIMENTAL STUDIES IN THE TROPICS. ..... .. 8 3. 1 The concept of GARP experimental studies ............ .. 8 3.2 An experimental study to define the interactions between the large wave- scale and the cloud-cluster scale (Scales A and B) ......... .. 9 3.3 An experimental study to determine the interaction between the scale of the cloud cluster and the meso-convective scales (Scales Band C). .... .. 10 3.4 Auxiliary experimental studies on convection over a tropical land mass. " 10 3. 5 Auxiliary experimental studies on the planetary boundary layer in the equa- torial region .......................... .. 11 4. GENERAL CHARACTERISTICS OF THE OBSERVATIONAL SYSTEMS. 13 4. 1 The horizontal scales ..... 13 4.2 The vertical scales. ...... 13 4.3 The horizontal sampling scheme 13 4.4 The vertical sampling scheme. 13 4.5 Observing platforms. ... 15 5. THE OBSERVATIONAL SYSTEMS ........... 16 5.1 Basic assumptions of the proposed systems .... 16 5.2 Observational system for the large wave-scale (Scale A) 16 5.3 Observational system for the cloud-cluster scale (Scale B). 17 5.4 Observational systems for the meso-convective scale (Scale C) and convective cells (Scale D) ........................." 11 5.5 Observational system for an experiment of convection over a tropical land mass. ...............•............. .. 18 IV CONTENTS Page 6. THE STRATEGY OF IMPLEMENTATION •••••••• 19 6. 1 Factors influencing decisions in advanced planning . 19 6.2 Scientific considerations ............. 19 6.3 Considerations related to measuring techniques. .. 20 6.4 Considerations related to the availability of observational means. 20 6.5 Considerations related to the degree of international co-operation involved. 21 7. DATA COLLECTION, PROCESSING AND STORAGE. ••••••••• 23 7. 1 The planning of data processing in GARP tropical experiments . 23 7.2 Some general principles ................... 23 7. 3 An outline of requirements for the proposed large-scale tropical experiment in the western·Pacific 24 7.4 Storage. ............................ .. 27 Appendices I. Report on the first session ofthe JOC Study Group on Tropical Disturbances (Madison, 21 October - 8 November 1968). ............ .. 33 Il. First Report on the Planning of the First GARP Tropical Experiment (sub- mitted by the JOC to the Executive Committees of WMO and ICSU).. 41 Ill. Summary report on the session ofthe Ad Hoc Study Group on the Planning of Tropical Experiments (Miami, 5 -12 December 1969) 60 IV. Cloud-cluster census of the tropical Pacific 63 FOREWORD The investigation of tropical disturbances and the facts to be investigated in the GARP Tropical Sub­ evaluation of the net effect of organized tropical convec­ programme had now been clearly identified and that the tive processes on the energetics of the general circulation basic background information was already available to of the atmosphere have been singled out as one of the transform earlier proposals for a GARP tropical experi­ most important studies to be made under GARP. ment into concrete recommendations. The Report on The former ICSUjlUGG Committee on Atmospheric the Planning of the First GARP Tropical Experiment, Sciences already recommended that a tropical experiment reproduced as Appendix Il of the present publication be conducted at the earliest possible date. The WMOj (see also section 1.4), was accordingly prepared and ICSU Joint Organizing Committee on GARP (JOC), submitted to the Executive Committees of WMO and which succeeded the ICSUjIUGG CAS, endorsed this ICSU. It was emphasized that this report was only "a recommendation and assigned it the highest priority preliminary definition" of the type of experiment that within the GARP experiments. was required. Moreover, the report made only a single The problem of designing tropical experiments which proposal for a specific experiment, although it had been provide answers to those questions which are relevant to made clear from the outset that the complexity of pheno­ the GARP objectives did not, however, have a straight­ mena and their variation with respect to geographical forward solution. The number ofexperiments that would locations would require more than one type of experi­ be needed, as well as the nature of the experiment or ment. experiments, with reference to both the types of pheno­ The present publication contains a further elaboration menon to be investigated and the observational means to of the report reproduced in Appendix Il, in the light be used, had to be decided on the basis of supporting ofthe latest findings and on the basis ofthe recommenda­ facts and theoretical considerations, and these were by tions of the Study Group that met in Miami (5 - 12 De­ no means obvious at the time when the planning efforts cember 1969). Its genesis is described in section 1.5. for GARP were started. Since then, the amount of The first draft of the text, prepared by the JPS, was research that has been carried out and the evolution of circulated among all JOC members and the participants the thinking in this field have been, however, very at the Miami meeting. A revised version, which incor­ striking. porated the comments received by the JPS, was sub­ During this period the JOC has made every effort to mitted to the session of the JOC Officers in Rome bring together the results of new investigations and to (13 - 16 January 1970) and approved, with minor amend­ organize them in such a way as to present a consistent ments, as the text which is now published. picture which would provide more solid grounds for the As Chairman of the Joint Organizing Committee, and planning of GARP tropical experiments. In this regard on behalf of the Committee Officers, I have pleasure in the co-operation of a large number ofleading scientists in submitting this report for consideration by the Executive the field, who actively participated in the study groups Committees ofWMO and ICSU and as a basic document and the special meetings convened by the JOC, cannot for the Planning Conference on GARP to be held in be overestimated. The JOC is thus following the line Brussels from 16 to 20 March 1970. started by its predecessor, the ICSUjlUGG CAS, at the In its present form, the report contains a programme Study Conference on GARP (Stockholm, June - July that provides sufficient flexibility for approaching the 1967). It is worth emphasizing that this type of activity problem of implementation in more than one way. For (which also goes on in other GARP Sub-programmes) example, some small-size experiments (types III and IV is one of the most rewarding aspects of the JOC work. in the terminology of the report; see section 3.1) could A major step in these activities was the session of the be carried out earlier than the others. However, the JOC Study Group on Tropical Disturbances (Wisconsin, JOC Officers agreed with the main recommendation made October - November 1968). The report of this Study at the Miami meeting, giving highest priority to a large Group convinced the JOC that SOme of the fundamental experiment in the Western Pacific Over the MarshaU VI FOREWORD Islands region; this is substantially identical to the one cipating countries themselves have expressed their views proposed in the former Report on the Planning of the and have indicated the scope of their contributions. First GARP Tropical Experiment (see Appendix II). Should the Planning Conference on GARP show that there are insurmountable difficulties in implementing the proposed highest-priority experiment, a careful evaluation of possible alternatives would be required. The basis for BERT BOLIN such an evaluation is given in Chapter 6 of the present Chairman, report. But it cannot be carried out before the parti- Joint GARP Organizing Committee SUMMARY The first chapter, Introduction, contains a discussion Experiment oftype Ill: refers to an experimental study on the place of tropical experiments within the GARP on convection over a tropical land mass; Tropical SUb-programme and with reference to the over­ Experiment oftype IV: refers to an experimental study all objectives of GARP. The evolution of ideas concern­ on the planetary boundary layer in the equatorial ing the need for such experiments and their characteristics region. is briefly reviewed. Inthis connexion, reference is made to early recommendations of the ICSUjIUGG Committee The objectives and the characteristics ofthe observational on Atmospheric Sciences (April 1966); the WMO CAe programme, for each kind of experimental study, are Working Group on Tropical Meteorology (November indicated in this chapter. 1966); the Study Conference on GARP (June - July After a discussion on the general characteristics of the 1967); the JOC Study Group on Tropical Disturbances observational systems, in Chapter 4, the report describes, (April 1968); the Report of the JOC to the Executive in Chapter 5, each of the observational systems that may Committees of WMO and ICSU on the Planning of the be suitable for the proposed experimental studies.