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§4地面、大气及地气系统的辐射平衡〔1〕地面辐射差额地面获得的能量：太阳直接辐射、太阳散射辐射、大气逆辐射地面失去的能量：地面发射的长波辐射、地面对太阳辐射的反射因此，影响地面辐射差额的因子：昼夜变化和季节变化白天为正，夜晚为负；夏季为正，冬季为负地理纬度低纬度以及大局部中高纬度地区为正，极区为负地面反照率反照率大的地方为负〔2〕大气辐射差额大气获得的能量太阳短波辐射的吸收、地面有效长波辐射大气失去的能量大气上界的有效长波辐射一般而言，整层大气的辐射差额为负值，大气的热量平衡要依靠其它的热传输渠道来维持，如：潜热输送等。因此，大气辐射差额为〔3〕地-气系统的辐射差额如果把地面和大气看做一个整体，其辐射能的净收入为地面辐射差额与大气辐射差额的总和：地-气系统的辐射差额在不同的季节可以有正有负；地-气系统的辐射差额在不同的纬度可以有正有负〔以35度为界线〕：赤道地区全年为正，两极全年为负，其余大局部地区夏季为正，冬季为负；对整个地-气系统来说，其辐射差额多年平均值为0。地-气系统净辐射的季节变化〔4〕全球热量平衡本节给出太阳短波辐射进入地气系统后，能量传输和能量平衡的总体图象以下给出的是ERBE的观测分析结果EarthRadiationBudgetExperiment(ERBE)November1984-February1990Inthe1970's,NASArecognizedtheimportanceoftheradiationbudgetanditseffectsontheEarth'sclimate.LangleyResearchCentrewaschargedwithdevelopinganewgenerationofinstrumentationtomakeaccurateregionalandglobalmeasurementsofthecomponentsoftheradiationbudget.TheGoddardSpaceFlightCentrebuilttheEarthRadiationBudgetSatellite(ERBS)onwhichthefirstERBEinstrumentswerelaunchedbytheSpaceShuttleChallengerin1984.ERBEinstrumentswerealsolaunchedontwoNationalOceanicandAtmosphericAdministration(NOAA)weathermonitoringsatellites;NOAA9andNOAA10,in1984and1986.TheEarthRadiationBudgetExperimentisdesignedaroundthreeEarth-orbitingsatellites:theNASAEarthRadiationBudgetSatellite(ERBS),andtwoNOAAsatellites.Thedatafromthesesatellitesisbeingusedtostudytheradiationbudget；Itcanbeusedtoestimatetheinsulatingeffectoftheatmosphere(thegreenhouseeffect)；Itisalsoausefulindicatorofcloudamountandactivity.ConsequentlytheERBEhashelpedscientistsworldwidebetterunderstandhowcloudsandaerosols,aswellassomechemicalcompoundsintheatmosphere(greenhousegases),affecttheEarth'sdailyandlong-termweather(theEarth'sclimate).Inaddition,theERBEdatahashelpedscientistsbetterunderstandhowtheamountofenergyemittedbytheEarthvariesfromdaytonight.Thesediurnalchangesarealsoveryimportantaspectsofourdailyweatherandclimate.TheERBEinstrumentaboardERBS,launchedfromtheSpaceShuttleChallengerinOctober1984(STS-41G),hadthemainaimofprovidingaccuratemeasurementsofincomingsolarenergyandshortwaveandlongwaveradiationreflectedoremittedfromtheEarthbackintospace.TheothergoalsoftheEarthRadiationBudgetExperiment(ERBE)are:tounderstandtheradiationbalancebetweentheSun,Earth,atmosphereandspacewhichdrivesourweatherandclimatesystem.toestablishanaccurate,long-termbaselinedatasetforstudyingclimatesystemchanges.太阳短波辐射100地表吸收51大气吸收16云吸收3大气反射6云反射20地表反射4总吸收70总反射30GlobalRadiationBudgetShortwaveCascadeIncomingsolarradiation100%(1365W/m2)GlobalRadiationBudgetLongwaveCascade70%地表吸收51大气吸收16云吸收3直接发射到空间6传导和对流到大气7潜热携带到云和大气23辐射到大气15通过大气和云发射到空间6470%
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