Effective terrestrial radiant energy atthe ground at...
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MAUSAM. 49 , 2 (April 19'18), 203 ·210 551.521.32 (547.1) Effective terrestrial radiant energy at the ground at Pune V. DESIKAN and V.R. CHIVATE M, u orologicaI Offi cr. Pun,-411005, India (Received 3 September 1993. Modifi ed 4 Decembe r 1996 ) llIt - '1 <WI iii ll'ftq iii .fr'l'I llT<r.li Ii 3!R qffi qftmf;ij <i1 'it>fT 'liT Il'Wfl f.r\lr-fT 3WIl m I 3WIl iii l«lm 'If'ii il> . 3I11T'I Ii FolWUT llT<r.li it 'IR Ii 'IT'll "IT m I 3WIl Ii l:('fi 3itmI f<-I Ii 85 qtf l('l . l('l . iJ; ' 3IJiIl'I Ii 1Ii'fT 3mit I 3IJiIl'I . 3!lr.f Ii 1253 'l'i l('l . iI . l('l . iW I "fIO'I3!"T!<l Ii 3.87 'l'i l('l . 'IT!I1 'T<I1 I li 3l lT'fl iJq; m 'lTC: m I omlQ qq - 3!R qffi <r<ri iii fm!roT om Ii 'fIfT 'liT '11m 'P. f.W , All STRA C T. Tbe effective outgoing f:khanl ene rgy controls the vananons in OInc:r ue teorologrcal parameters near the ground surface. In the absence of direct mca. suremerus of chis energy. the values an: derived from otber radrenon .Ihat an: being measured 31 Pure . On an average day the loss of this terrestrial energy is ul lhc order of MJm"· . Tbe maximum of 12.53 MJrn- 2 is reached In AJlfl I and the mmrmum of .l .87 MJm"z dunng .. 1. The daily maximum occurs ar noon or juseafter that Yecrao-yccr variations bowever depend on ther.unf311 distnbunon and the moisture in the air. Key words - Terrestrial radiation. Radian t exposure. Radian! energy. Pyreoo rrerer. I. Introducti on Allhough solar irradiance is Ille primary source of all energy transactions in the earth-atmosphere system, a wide variety of interactions is largely controlled by the eart h's radiance.The changes in the ambie nt temperature, humidit y, evaporation etc. are affected by variations in this eart h's radiance. Because of the low temperatures (compared to that of the sun) at which the emission lakes place. the radiance occurs at wavelengths of terrestri al radia nt energy. The interaction between this energy and the atmosphere, whose tem perature is not significantly different, is quite complex . The net so lar irrad iance is available for heating, direc tly and indirect ly, the earth and the atmusphere. The thermal radia- tion is one of resulting transformations of the solar irradi- ancc after absorption by the eart h's surface. The radiative heating of each successive layer of the atmosphere by this therm al radiation is equally importa nt. One of the important effects of this thermal radiation lies on the thennodynamical aspects leading to the various changes in the atmospheri c parameters, like, temperature, pressure, air now and cloud [ormation. The regular and co ntinuous measurement of the effective outgoing radiant energy is. however, difficult and carried out only at limited centres. The present paper deals with the data deduced from other regular radiation measure- mcnts being made at Pune and the variations that lake place over a time. 2. Data collection In the terrestrial region of electromagnetic spectrum, the entire environment. including the instrumen t itself. is emitting the radiant energy in the same wavelengths moni- tored. An instrument which will direc tly measu re the terres- trial radiant energy must be insensitive to the wavelengths of solar irradiance. Most of the window materials that are suitabl e for such selective transmission do not. however, have sufficient hardness and are generally hygroscopic in nature. resulting in abrup t change s in the transmi ssion char- actcristics of the window materials. Added to this, the win- dow material itself participates in the energy transac tions . The very few materials which are impervi ous to the solar irr adiance and weather resistant as well as are prohibitive ly costly. Thus the measureme nt of the effective outgoing terrestrial radia tion is not made on a large network scale. The measurements are agai n highly vitiated by the dust deposits and water depos ition due to dew, fog and precipitation. It is more convenient to deduce the effective outgoing terrestrial radiation (Hi ) from the measurements of glooal and re- fleeted solar radiant exposures and the nCI total radiant
Transcript of Effective terrestrial radiant energy atthe ground at...
MAUSAM. 49 , 2 (Apri l 19'18), 203·210
551.521.32 (547.1)
Effective terrestrial radiant energy at the ground at Pune
V. DESIKAN and V.R. CHIVATE
M, u orologicaI Offi cr. Pun,-411005, India
(Received 3 September 1993. Modifi ed 4 Decembe r 1996)
llIt - '1<WI iii ll'ftq iii~ .fr'l'I~ llT<r.li Ii 3!R qffi qftmf;ij <i1 'it>fT 'liT Il'Wfl f.r\lr-fT~ 3WIl~ m ~ I ~ 3WIl iii l«lm 'If'ii il> .3I11T'I Ii~ FolWUT llT<r.li it 'IR~
~ ~,~~ Ii 'IT'll "IT m ~ I ~~ 3WIl Ii l:('fi 3itmI f<-I Ii 85 qtf l('l . ~ . l('l . iJ; '3IJiIl'IIi 1Ii'fT 3mit ~ I .~ 3IJiIl'I .3!lr.f Ii 1253 'l'i l('l. iI . l('l. iW I "fIO'I3!"T!<l Ii 3.87 'l'i ~.
~. l('l . 'IT!I1 'T<I1 ~ I ~~.~~ li 3llT'fl iJq; m 'lTC: m ~ I omlQ qq - ~ 1 ,~
3!R qffi~ <r<ri iii fm!roT om ~ Ii 'fIfT 'liT '11m 'P. f.W~ ~ ,
AllSTRAC T. Tbe e ffect ive outgoing Ic~lnaJ f:khanl ene rgy controls the vananons in OInc:r ueteorologrca lparameters near the ground surface. In the absence of direct mca.suremerus of chis energy. the values an: derived from otberradrenon F'ncle~ .Ihat an: being measured 31 Pure. On an average day the loss of this terrestrial energy is ul lhc order of8.~ MJm"· . Tbe maximum of 12.53 MJrn-2 is reached In AJlflI and the mmrmum of .l .87 MJm"z dunng Aug~..1. The dailymaximumoccurs ar noon or juseafter that Yecrao-yccr variations bowever dependon ther.unf311 distnbunon and the moisturein the air.
Key words - Terres trial radiation. Radian t exposure. Radian! energy. Pyreoorrerer.
I. Introduction
Allhough solar irradiance is Ille primary source of allenergy transact ions in the earth-atmosphere system, a widevariety of interactions is largely controlled by the earth'sradiance.The changes in the ambie nt temperature, humidit y,evaporation etc. are affec ted by variations in this earth'sradiance. Because ofthe low temperatures (compared to thatof the sun) at which the emission lakes place. the radianceoccurs at wavelengths of terrestri al radiant energy. Theinteraction between this energy and the atmosphere, whosetemperature is not significantly different, is quite complex .The net solar irrad iance is available for heating, direc tly andindirect ly, the earth and the atmusphere. The thermal radiation is one of resulting transformations of the solar irradiancc after absorp tion by the earth's surface. The radiativeheating of each successive layer of the atmosphe re by thisthermal radiation is equally importa nt. One of the importanteffects of this thermal radiation lies on the thennodynamicalaspects leading to the various changes in the atmospheri cparameters, like, temperature , pressure, air now and cloud[ormation. The regular and co ntinuous measurement of theeffective outgoing radiant energy is. however, difficult andcarried out only at limited centres. The present paper dealswith the data deduced from other regular radiation measure-
mcnts being made at Pune and the variations that lake placeover a time.
2. Data collection
In the terrestrial region of electromagnetic spectrum,the entire environment. including the instrumen t itself. isemitting the radian t energy in the same wavelengths monitored. An instrument which will direc tly measure the terrestrial radiant energy must be insensitive to the wavelengthsof solar irradiance. Most of the window materials that aresuitable for such selective transmission do not. however,have sufficient hardness and are generally hygroscopic innature. resulting in abrup t changes in the transmission charactcristics of the window materials. Added to this , the window materia l itself participates in the energy transac tions .The very few materials which are impervi ous to the solarirradiance and weather resistant as wel l as are prohibitive lycostly. Thus the measureme nt of the effective outgoingterrestrial radia tion is not made on a large network scale. Themeasurements are again highly vitiated by the dust depositsand water depos ition due to dew, fog and precipitation. It ismore convenient to deduce the effective outgoing terrestrial
radiation (Hi ) from the measurement s of glooal and refleeted solar radiant exposures and the nCI total radian t
