WORLD METEOROLOGICAL ORGANIZATION THE EFFECT OF THERMOMETER SCREEN DESIGN ON THE OBSERVED TEMPERATURE by W. R. ~~!A!iKS CIMO Rapporteur on Measurement of Surface Temperature I WMO • No. 315 I .Secretariat of the World Meteorological Organization - Geneva • Switzerland 1972 .: s \. s ~.) :~·., . : ~:· r 1.• s· 2 Y l_ s P~s FOREWORD The fact that a thermometer screen creates its own micro-environment has been realized since temperature measurements were first taken on a systematic basis. The magnitude of the effects of the screen and screen design have thus been studied by investigators in many parts of the world. Mr. W. R. Sparks has reviewed a large number of published studies to identify the aspects of thermometer screen design, exposure and use that affect the tempera­ ture measured inside the screen. In addition he has compiled an extensive biblio­ graphy and completed a survey of the types of thermometer screens currently used by meteorological services. I believe that the present report will be welcomed as a very thorough review of this subject and it gives me great pleasure to extend my appreciation, on behalf of the WMO, to Mr. Sparks for the time and effort he has put into its preparation. ~· D. A. Davies Secretary-General SUMMARY The author has stated that the purpose of this publication is to identify, through a review of existing literature, those aspects of thermometer screen design, exposure and use that affect the temperature measured in a screen. In carrying out this comprehensive review he has referred to a large number of published studies, the earliest dating back to 1869, the most recent being published in 1969. They include comparisons made on board ships at sea as well as at land stations, in equatorial and polar regions as well as in temperate zones. In sections 1 and 2, Mr. Sparks outlines the scope of his study and discusses the WMO standards for temperature measurement. He points out that differences in measurement due to differences in screen height may occur even though heights are within the range specified in WMO publications. Sections 3; 4 and 5 deal with comparisons of "identical in~truments" and dis­ cuss the characteristics of forced ventilated screens in comparison with the traditional naturally ventilated screens. Section 6 contains a review of the various types of thermometer screens which have evolved in the course of time through attempts to improve performance and reduce weight and costs of construction. The performance of the tropical screen is discussed and compared with the standard wooden Stevenson screen. Other types of screens of various sizes and materials are also described. Section 7 examines the factors affecting temperatures measured in screens, such as colour, exposure, thermal inertia and temperature distribution within a screen. Section 8 summarizes the essential features of a well-designed screen and section 9 contains recommendations for further work. A comprehensive list of reference publications is given in sections 10 and 11. The Annex contains descriptions of thermometer screens in current use in various / countries. RESUME Cette publication, comme I•indique son auteur, a pour but de d'terminer, par une analyse des travaux publi's sur cette question, les aspects de la conception, de !'exposition et de !'utilisation de l'abri m,t,orologique qui exercent une influence sur la temp,rature mesur'e sous abri. Pour mener ~ bien cette analyse approfondie du probleme, l'auteur s'est r'f'r' a un grand nombre d''tudes publHes dont les plus anciennes remontent ~ 1869, tandis que les plus recentes furent publi,es en 1969. Parmi ces 'tudes figuraient notamment des comparaisons faites a bard de navires en mer et ~ des stations terrestres, dons des r'gions 'quatoriales et polaires, aussi bien que dons des zones temp'r'es. Dons les sections 1 et 2, M. Sparks d'finit la port'e de son 'tude et examine les normes 'tablies par 1 'OMM pour mesurer la temp,rature. Il fait remarquer que des diff,rences de mesures peuvent se produire du fait de diff,rences dons la hauteur de l'abri, meme si cette hauteur est comprise dons la gamme de valeurs prescrites dons les publications de l'OMM. Les sections 3, 4 et 5 traitent des comparaisons "d'instruments identiques" et examinent les caract,ristiques des abris ~ ventilation forc'e par rapport ~ celles des abris classiques a ventilation na.turelle. La section 6 passe en revue les divers modeles d'abris m,t,orologiques que les sp,cialistes ont mis au point au cours des ann,es en s'efforc;:ant d'am,liorer les performances des abris, d'en r'duire le poids et le cout de construction. L'auteur compare les performances de l'abri tropical a celles du traditionnel abri Stevenson en bois. Il decrit egalement d'autres types d'abris, de tailles et de conceptions diverses. La section 7 est consacr'e aux facteurs qui exercent une influence sur les temperatures relevees sous abri : couleur, exposition, inertie thermique et distri- bution des temp,ratures drins l'abri. La section 8 r'sume les caract,ristiques essentielles d'un abri bien conc;:u, tandis que la section 9 contient des recommendations concernant les travaux ~ entre­ prendre dons ce domaine. Les sections 10 et 11 contiennent une liste bibliographique bien fournie et !'annexe comporte des descriptions d'abris m,t,orologiques utilis's dons les divers pays. PE3IOME ABTOp yKasa~, qTo ~e~:r:.ro GTol rry6~uKa~HH HB~HeTOH orrpe~e~eHue,rryTeM paooMOTpeHMH oym;eoTByrom;el ~HTepaTyphl, Tex aorreKTOB KOHOTPYK~HH TepMoMeT­ puqeoKol 6y~KH, ee 8KQIT03H~HH H HOITO~h30BaHHH, KOTOpbie B~HHIDT Ha TeMITepa­ Typy, H3MepHeMyro B 6y~Ke. llpH ooym;eOTB~eHHH OBOero o6sopa OH OCbmaeTOH Ha 6o~hmOe KO~HqeoTBO orry6~HKOBaHHhiX HOO~e~oBaHHH, OaMoe paHHee H3 KOTOpbiX OTHOOHTOH K 1869 r., a OaMOe IT03,ll;Hee 6bmO orry6~HKOBaHO B 1969 r. 3TH pa- 60Thl KaoaroTOH opaBHeHHH, rrpOBO,ll;HBillHXOH Ha 6opTy oy,n;oB B MOpe, a TaK~8 Ha Ha38MHbiX OTaH~MHX, B GKBaTOpHa~bHbiX H ITO~HpHbiX paloHax, a TaK~e B yMepeHHbiX soHax. B pas,n;e~ax 1 H 2 r-H CrrapKo us~araeT MaomTa6hr OBoero usyqeHHH H paooMaTpMBaeT oTaH~apThl BMO rro H3MepeHHID TeMrrepaTyphl.OH OTMeqaeT,qTo paoxo~­ ~eHHH B M3M8peHHHX B OBH3M 0 pa3~HqMHMM B BbiCOT8 6y,ll;KM MOryT Ha6~ro,n;aTbOH ,n;a~e B TeX O~yqaHX, KOr~a BbiCOTbi He BhiXO,ll;HT sa ITpe,n;e~hl, yoTaHOB~8HHbie B rry6~MKa~MHX BMO. B pas,n;e~ax 3, 4 M 5 pacoMaTpMBaiDTOH cpaBHeHMH "M,n;eHTMqHhiX rrpM6o­ poB" M xapaKTepHOTHKM 6y,n;OK C MCKYCOTBeHHOH Be:HTH~H~HeH ITO OpaBHeHHID 0 Tpa,n;M~MOHHbiMM 6y,n;KaMM 0 80T80TB8HHOH BeHTM~H~Mel. B pas~e~e 6 pacoMaTpMBaiDTCH pas~MqHhre. TMIJ:hi TepMoM:eTpMqeoKHX 6y~oK, rrpH KOHCTpyMpOBaHMM .KOTOpbiX. ~e~a~MOb ITOITbiTKM ycoBepmeHCTBOBaTh MX xapaKTepMO­ THKM M OOKpaTMTb MX B8C M CTOMMOOTh ITpOM3BO,ll;CTBa. TpOITHq8CKaH 6y,n;Ka o6oy~,n;aeTCH H cpaBHHBaelr.CH CO OTaH,n;apTHOH ~epeBHHHOH 6y,n;KOH CTHBeHCOHa. TaK~e OITMCbiBaiDTOH ,n;pyrMe TMIThi 6y,n;OK pa3~MqHbiX pa3M8pOB M O,ll;8~aHHbie M3 pa3~MqHbiX MaTepMa~OB. B pas,n;e~e 7 paocMaTpMBaiDTOH ~aKTOphl, B~HHrom;Me Ha TeMrrepaTypy B 6y,n;KaX, TaKMe ~a:KTOpbi, :KaK ~BeT, 8KOIT03M~MH, TeiT~OBaH MHep~MH H pacrrpe,n;e­ neHH8 TeMrrepaTyphl B 6y,n;Ke. B pas,n;e~e 8 o6o6m;aroTOH Ba~Hhre xapaKTepMCTMKH 6y,n;KM xopomel EOHOTpyK~MH, a B pas,n;e~e 9 co,n;ep~aTOH peKOMeH,n;a~MM OTHOOMT8~hHO ,n;a~bH8H­ mel pa6oThl. McqepiTbiBaiDm;MH OITMOOK rry6~MKa~MH ~~H CCbi~OE rrpHBO,ll;MTCH B pas,n;e~ax 10 H 11. B ITpM~0~8HMM oo,n;ep~MTCH OITMCaHM8 T8pMOM8TpMqeOEMX 6y~oK, KOTOpbie B HaCTOHm;ee Bp8MH MOITO~h3YIDTOH B pa3~MqHhiX OTpaHaX. RE SUM EN El outor monifiesta que el o~jeto de esta publicaci6n es determina~ median­ te el estudio de los textos actuolmente disponibles, los efectos que ejercen !as go­ ritos termometricos, os! como la instoloci6n y utilizoci6n del term6metro, en !os va­ lores de temperature medidos dentro de dichos goritas. Para realizar este completo estudio, el Sr. Sparks hace referencia a numerosas publicaciones, en la m6s ontiguo de los cuales se expone un trabajo realizodo en 1869, y la m6s reciente de las mis­ mos data de 1969. En estos estudios se resenon comporociones efectuodos en el mar a bordo de buques, os! como en !as estociones terrestres, en !as regiones ecuotoriales, polores y templodos. En los -Secciones 1 y 2,el Sr. Sparks explico el olconce de su estudio y ex­ pone los normos que la OMM ha fijado para la medida de la temperature. Indico que pueden producirse diferencias de medido con motivo de !as distintas alturas de la go­ rita incluso· cuando estos cumplen !os requisites especificados en !as publicaciones de la OMM. Los Secciones 3, 4 y 5 trotan de !os comparociones de "instrumentos identi­ cos" y en ellas se especifican los coracter!sticas de !as garitas de ventiloci6n for­ zodo, en comparoci6n con !os garitas tradicionoles de ventiloci6n natural. En la Secci6n 6 se hoce un estudio de !os distintos tipos de garitas termo­ metricos y de la evoluci6n que han experimentado 0 troves de los anos, con objeto de perfeccionar su funcionamiento y reducir su peso y gostos de construcci6n. Se estu­ dio tombien el funcionomiento de la gorito tropical en comporaci6n con la gorita nor­ malizado de Stevenson. Tombien se describen otros tipos de garitas de distintos ta­ manos construidos con diferentes materiales.