Diurnal variation of Upper Air Temperatures over India...
9
." 5.,) \ ' 524 ' 7 :551'50 8'9 (M) Diurnal variation of Upper Air Temperatures over India S. HANGAHAL\.N and n, H. SI K KA Meteoro!?gic ll Office, Poona (Rectitoed 31 .1" :1""1 1962) A RST R:\ f"r . A Rtat i", tical et udy of the diur na l variation of upper air tempe ra tu res over Ind ia j ", made uttlistng radiosonde da ta of fo ur lltationfl for four Rta netard liuUl'g of the day and covering (our repn'M'ntati\"l' months. A marked dtffercn ce in the pattern or diurnal "ariation is found between & co ntinental »t a t io n like Xew Delhi end the three co lloi ta l tlta t io nM- Humha \" . Calc utta and )I adraa. dinrnnl variations art' foun d over X f'W I'k-lbi unl".. upt o J to 3 km jf' p;'ndingon th e scescn, UIO mt'an daily range ht·in.'t abou t I to 2° C in meet Ca H" lI. On the e ther hand. diurnal variation s at the eoeste l !!I talions exten d higher u pto 4·6 km, the ampli tudes being nf the me order. Apparent diumal v. ril - tinn" found at "till bight'f level ... a rt" probab ly due to inadequacy or rad iation eoerect tons. Xocturnal coo ling of t he a tmos phe re bet ween 600 and ,J(H)· m b leve l- found to be in the range 0( 0 · 1 to 0 · 15' per hour. -. 1. Introdu ction Experimental determinationsof the diurnal vari at ion of upper air temperatures provide valuable information on (I) the magni tud e of the of the free at mosphere by di- rect absorption of solnr radia tion du ring the day , (2) t he mngn itud cof the radiative cool- ing of tho atmosphere (luring the night r,llIl (3) the height upto which the surface diurnal temperature wave is propagated upwards due to eddy conduction and turbulence. The determination is a somewhat diffi cult problem. Firstly. the magnitude of the trne diurnal hC lltin .a or cooling between about 3 km and the tro popause is small and sometimes the radiosonde instruments have probable errors of the ...me order. Secondly, the prob- lem of app lying ra diat ion corrections to upper air temperatu re s observed with rad io- sonde inst ruments under varyi ng cond itio ns of the atmosphere, is a \'Cry diffic ult one. The general pract ice is to determine eorrec- tions by simula ted laboratory expe riments with certain assumed standard condi t ions and to apply them to the act ual flight d ata, The only variable factor made use of in th e actual application of radiation correction is the solar elevat ion angle. This assumption is not always justified because the magnitude of correction would also depend on varying factors, e.g.. cloud cover, the swinging of the instrument, etc. Studies 0 11 diurnal variation of upper air temperatures have been made mainly by two methods. In the first method, special rad io- sonde observations are taken at short inter- vals of time, say or 3 hours for a limited number of days and the d at a analysed. In the second method, a statiatical analys is of routine radiosondedata pertaining to different synoptic hours covering hoth day and ni ght is made and appropriate conclusions drawn. Among the first category may be mentioned the work of Riehl (1917) who investigated the diurnal variation of upper air tempera- tures over the Caribbean Sea. fly analysing special rad iosond e asce nts taken at three- hourly intervals taking into account approxi- m at e corrections for solar radiation effects (t hese corrections were later found to be under.stirnated) he found diurnal tempe rature ranges of nbont 1 to 2°C upto 6 how and 2 to 3' 0 aloft upto 16 km. The maximum rise in the temperature was found to occur with the rise of solar elevation angle and the maximum fall with t he decrease of solar elevation. R iehl found two distinct effects, t;z ., (I) an effect d ue to t urb ulent exchange of heat with the !(round which was confined to a layer of about 1·5 km and (2) an effcct due to
Transcript of Diurnal variation of Upper Air Temperatures over India...
."5.,) \ ' 524 ' 7 :551'508'9 (M)
Diurnal variation of Upper Air Temperatures over IndiaS. HANGAHAL\.N and n, H. SI K KA
Meteoro!?gicll Office, Poona
(Rectitoed 31 .1":1""1 1962)
ARSTR:\f"r. A Rtat i",t ica l et udy of the diurna l variation of up per air tempera tu res over Ind iaj ", made ut tlistng radiosonde da ta of four llta t ionfl for four Rta netard liuUl'g of t he day and covering (ourrepn'M'ntati\"l' months. A marked dtffercn ce in the pattern or diurnal "ariat ion is found between &
continental »t at ion like Xew Delhi en d the t hree co lloi ta l tlta t ionM- Humha \". Calcutta a nd )Iadraa.~j liCnifi('atl t d inrn nl variations art' found over X f'W I'k-lbi unl".. upt o J to 3 km jf'p;'ndingon th e scescn, UIOmt'an dail y ra nge ht·in.'t about I to 2° C in meet CaH"lI. On the e ther hand. d iurn a l variations at the eoeste l!!I ta l ions extend higher u pto 4·6 km, the amplitudes being nf the me order. Apparent d iu m a l v. ril tinn" found at "till bight'f level ... a rt" probably due to inadequacy or rad iation eoerect tons. Xoct urnalcooling of t he atmos phere bet ween 600 and ,J(H)·m b leve l- i ~ found to be in the range 0( 0 · 1 to 0 · 15' perhour .
-.
1. Introduction
Experimental determina t ions of the diurnalvari at ion of upper air temperatures providevaluabl e informat ion on ( I) t he magnitudeof the heatin~ of th e free atmosphere by di rect absorpt ion of solnr radia tion du ring theday , (2) t he mngnitudc of th e radiative cooling of tho atmos phere (luring t he night r,llIl(3) th e height upto which the su rface diurna ltemperature wave is propagated upwardsdue to eddy conduction and turbulence.The determina tion is a somewhat difficultproblem. Fi rst ly. t he magnit ude of t he t rnediurnal hClltin.a or cooli ng between about 3km and th e tropopause is small and sometimesthe radiosonde instruments have probableerrors of th e ... me order. Secondly, t he problem of applying radiat ion corrections toupper air temperatu res observed with rad iosonde inst ruments under varyi ng cond itionsof t he atmosphere, is a \'Cry d ifficult one.The general pract ice is to dete rmine eorrections by simulated laboratory expe rimentswith certain assumed standard condi tionsand to apply them to the actua l flight data ,The only variable facto r made use of in theactual application of radiation correctionis t he solar elevat ion angle. This assumptionis not always just ified because t he magnitudeof correct ion would also depend on va rying
factors, e.g.. cloud cover, th e swinging of th einstrument, etc.
Studies 0 11 diurnal variation of upper airte mpera tures have been mad e mainly by twometh ods. In the first met hod, specia l rad iosonde observations are taken at short intervals of time, say ~ or 3 hours for a limitednu mber of days and t he data analysed . In th esecond method, a sta tiatical analys is ofroutine rad iosondedata pertainingto differentsynopt ic hours covering hoth day and nightis made and appropriate conclusions drawn.Among the first category may be mentionedt he work of Riehl (1917) who investigatedthe diurnal variation of upper air temperatures over the Caribbean Sea. fly analysi ngspecial rad iosonde ascents ta ken at threehourly inte rva ls tak ing into account approximate corrections for solar radiation effects(these corrections were later found to beunder. stirnated) he found diurnal temperatureranges of nbont 1 to 2°C upto 6 how and 2 to3' 0 aloft upto 16 km. The maximum rise inthe temperature was found to occur with therise of solar elevation angle and the maximumfall with t he decrease of solar elevation.R iehl found two dist inct effects, t;z., (I)an effect d ue to t urb ulent excha nge of heatwith t he !(round which was confined to alayer of about 1·5 km and (2) an effcct due to
