遥感物理遥感物理柳柳 钦钦 火火工作单位：工作单位： 中国科学院遥感应用研究所中国科学院遥感应用研究所 遥感科学国家重点实验室遥感科学国家重点实验室联系电话：联系电话：6484984064849840（O O）Email: Email: qhliuirsa.ac.cnqhliuirsa.ac.cn20112011年年11-1211-12月月中国科学院研究生课程中国科学院研究生课程遥遥感感物物理理1.1.绪论绪论2.2.第一章第一章 基本概念基本概念3.3.第二章第二章 植被遥感模型植被遥感模型4.4.第三章第三章 土壤与冰雪遥感模型土壤与冰雪遥感模型5.5.第四章第四章 海色遥感海色遥感6.6.第五章第五章 大气效应及其纠正大气效应及其纠正7.7.第六章第六章 热红外遥感热红外遥感8.8.第七章第七章 地表通量遥感模型地表通量遥感模型第五章第五章大气效应及其纠正大气效应及其纠正 前言前言Introduction第一节第一节 大气组成与大气的基本特性大气组成与大气的基本特性ATMOSPHERECONTENTANDBASICPROPERTIES第二节第二节 辐射与大气的相互作用辐射与大气的相互作用INTERACTIONOFRADIATIONWITHATMOSPHERE第三节第三节 大气效应纠正大气效应纠正ATMOSHPHERICEFFECTCORRECTION第四节第四节 大气的遥感探测大气的遥感探测ATMOSHPHERICREMOTESOUNDING前前言言u大大气气：是是介介于于遥遥感感传传感感器器与与地地球球表表层层之之间间的的一一层层由由多多种种气气体体及及气气溶溶胶胶等等组组成成的的介介质质层层，当当电电磁磁波波由由地地球球表表层层传传至至遥遥感感传传感感器器时时，大气是必经的通道；，大气是必经的通道；u大大气气对对电电磁磁波波的的作作用用：主主要要可可以以归归纳纳为为两两种种物物理理过过程程，即即吸吸收收与与散散射射，对对地地表表遥遥感感来来说说，大大气气的的吸吸收收与与散散射射作作用用均均可可使使电电磁磁波信息受到削弱；波信息受到削弱；u遥遥感感图图像像的的大大气气纠纠正正：如如何何依依据据遥遥感感图图像像直直接接或或间间接接获获得得的的大大气气参参数数，消消除除大大气气对对电电磁磁波波属属性性量量的的影影响响，恢恢复复其其在在地地球球表表层层的的“本来面目本来面目”，就成为定量遥感不可回避的问题；，就成为定量遥感不可回避的问题；u大大气气属属性性参参数数的的遥遥感感反反演演：无无论论是是置置于于地地面面的的传传感感器器还还是是星星载载的的传传感感器器，当当它它接接收收到到从从大大气气作作用用后后的的电电磁磁波波时时，它它必必然然带带有有大大气气的的特特征征信信息息，因因此此我我们们可可以以设设法法从从中中反反演演出出表表征征大大气气属属性性的的参数，如大气气溶胶与大气水汽等。参数，如大气气溶胶与大气水汽等。第五章第五章大气效应及大气纠正大气效应及大气纠正前言前言Introduction第一节第一节大气组成与大气的基本特性大气组成与大气的基本特性ATMOSPHERECONTENTANDBASICPROPERTIES第二节第二节辐射与大气的相互作用辐射与大气的相互作用INTERACTIONOFRADIATIONWITHATMOSPHERE第三节第三节大气效应纠正大气效应纠正ATMOSHPHERICEFFECTCORRECTION第四节第四节大气的遥感探测大气的遥感探测ATMOSHPHERICREMOTESOUNDING5.1.1大气成分大气成分5.1.2描述大气状态的基本参量描述大气状态的基本参量5.1.3大气静力学方程大气静力学方程5.1.4大气压力和密度的垂直廓线大气压力和密度的垂直廓线5.1.5大气温度和湿度的垂直廓线大气温度和湿度的垂直廓线5.1.6大气气溶胶大气气溶胶5.1.7大气水汽大气水汽5.1.8水圈与水文循环水圈与水文循环5.1.9云与降水云与降水第一节第一节大气组成与大气的基本特性大气组成与大气的基本特性Thecompositionoftheatmosphereisimportantinanyunderstandingoftherolewhichtheatmosphereplaysinremotesensingandininteractionswithelectromagneticradiation.Theatmosphereislargelyamixtureofgases混合气体,somewithfairlyconstantconcentrations,othersthatarevariableinspaceandtime.Inadditiontherearesuspendedparticles悬浮颗粒(e.g.aerosol,smoke,ashetc.)andhydrometeors水汽凝结体(e.g.clouddroplets,raindrops,snow,icecrystals,etc).About99%ofthemassliesbelowanaltitudeof30km.Table1belowshowsthecompositionoftheatmospherebelow100km.5.1.1大气成分大气成分CompositionTable1:Mainconstituentsoftheearthsatmosphere*aconcentrationneartheearthssurface氮、氧、氩、二氧化碳、氖、氦、氪、氙、氢、甲烷、氧化氮、一氧化碳氮、氧、氩、二氧化碳、氖、氦、氪、氙、氢、甲烷、氧化氮、一氧化碳水汽、臭氧、氨、二氧化硫、二氧化氮、痕量气体、气溶胶、尘埃水汽、臭氧、氨、二氧化硫、二氧化氮、痕量气体、气溶胶、尘埃Nitrogen氮氮,oxygen氧氧andargon氩氩accountforabout99.99%ofthepermanentgases.Ofthevariableconstituents,carbondioxide二氧化碳二氧化碳canbesomewhatvariableinconcentrationonalocalizedbasisatlowlevels.Watervapor水汽水汽contentmayvaryfromabout0to4%ozone臭氧臭氧concentrationsalsovarymarkedly.Inadditiontothesevariableconstituentstherearealsoaerosols气溶胶气溶胶andhydrometeors水颗粒水颗粒whichcanvarywidelyinspaceandtime.氧气占地球大气质量的氧气占地球大气质量的23%23%，除，除游离游离存在的氧气以外，氧还以存在的氧气以外，氧还以硅酸硅酸盐、氧化物和水化物盐、氧化物和水化物等形式存在，在高空中还有臭氧与原子氧。氧占等形式存在，在高空中还有臭氧与原子氧。氧占包括海洋和大气在内的地壳质量的包括海洋和大气在内的地壳质量的49.5%49.5%。光合作用：光合作用： nCO2+nH2OCH2On+nO2水汽的水汽的光解作用：光解作用：2H2O2H2+O2（太阳紫外辐射）（太阳紫外辐射）氧的分解作用氧的分解作用：O2+hO+O（短于（短于0.24微米的紫外辐射）微米的紫外辐射）复合作用：复合作用：O+O+MO2+MO2+O+MO3+M臭氧分解作用：臭氧分解作用：O3+hO2+O*（臭氧分子吸收短于（臭氧分子吸收短于0.32微米的紫外辐射）微米的紫外辐射）O3+O*2O2（太阳紫外辐射）（太阳紫外辐射）其中其中M是第三种分子（是第三种分子（N2、O2或其它分子），吸收反应中释放的化学能。或其它分子），吸收反应中释放的化学能。大气中的氧与臭氧大气中的氧与臭氧（oxygenandOzone）Theconcentrationofozoneishighlyvariableinspace(latitudeandaltitudeforexample)andtime.Mostozoneisgeneratedanddestroyedbyphotochemicalreactionsinthelayerbetween20kmand60km.Ozonetendstoaccumulateinthelowerstratosphereataltitudesbetween15and25km.Smallamountsofozonearealsoproducedbyelectricaldischargesandinphotochemicalsmogovercities.Atthesurface,ozoneisdestroyedrapidlybyreactingwithplantsanddissolvinginwater,whereasinthestratospherethelifetimeisontheorderofmonths.OzonehascharacteristicpronouncedabsorptionatUV,IRandmicrowavewavelengths.TheabsorptionofUVradiationmakeshumanlifepossibleontheearthssurface.DepletionoftheearthsozonelayerhasbecomeaveryseriousissuefollowingdetailedobservationalandtheoreticalstudieswhichhavefocusedprimarilyontheAntarcticozonehole.臭氧（臭氧（Ozone）Carbondioxidehasarelativelyconstantmixingratiowithheightintheatmosphere,thatis,itisfairlyevenlydistributedonaverage.Themainsources源源:burningoffossilfuels化石燃料化石燃料,humanandanimalrespiration呼吸呼吸,theoceansandvolcanicactivity火山活动火山活动.Themainsinks汇汇:photosynthesis光合作用光合作用andtheproductionofcarbonates(limestones)intheocean/landsystem.Therateofremovalofcarbondioxide,agreenhousegas,isobservedtobelessthanthegeneration(fromfossilfuelburning)becausetheconcentrationofcarbondioxideintheatmospherehasbeenrisingsteadilysincetheearlypartofthelastcentury.About99%oftheearthscarbondioxideisdissolvedintheoceans.Thesolubilityistemperaturedependent.Itisestimatedthattheannualamountofcarbondioxideenteringorleavingtheairbyallmechanismsisaboutonetenthofthetotalcarbondioxidecontentoftheatmosphere.二氧化碳二氧化碳（CarbonDioxide）硫化合物硫化合物二氧化硫二氧化硫SO2+硫化氢硫化氢H2S占硫化合物总量的占硫化合物总量的80-90%氮化合物氮化合物氮气是大气中最丰富的气体，性质稳定，仅有极少量的氮气是大气中最丰富的气体，性质稳定，仅有极少量的N2能被微能被微生物固定在海洋和土壤里，变成有机化合物。气体氮化合物主要有：生物固定在海洋和土壤里，变成有机化合物。气体氮化合物主要有：氧化亚氮氧化亚氮N2O,一氧化氮一氧化氮NO,二氧化氮二氧化氮NO2,氨氨NH3大气中的其他微量成分大气中的其他微量成分（tracegases）Atmosphericgasescriticallyaffecttheearthsglobalenergybalance能量平衡能量平衡throughabsorptionandre-emissionandthroughtheroletheyplayinglobalgeophysicalcycles.Solarradiation太阳辐射太阳辐射reachingtheearthssurfaceisdeterminedbyatmosphericgases.ForexampleharmfulUVradiationisblockedbytheozonelayer.Also,“windows”大气窗口大气窗口inwhichatmosphericeffectsareminimalallowground-basedmeasurementsofcelestial(天体天体)objects,andsatellite-basedmeasurementsoftheearthssurfaceorcloudsforremotesensingapplications.Figure1:(a)Atmosphericabsorptionatgroundlevelfordiffuseterrestrialradiationandforsolarradiation,withazenithangleof50degrees.(b)Sameasinabutforthelayerofatmosphereabove11km.AfterWallaceandHobbs(1977),p332.Table2:FromSmith(1985),AtmosphericabsorptionfeaturesareshowninFigure1forgroundlevelandatanaltitudeof11km.Regionsofminimalabsorption(windows).Figure2:Solarirradianceatthetopandbottomoftheearthsatmosphere,forthesunatthezenith.Shadedareasindicateabsorptionbyatmosphericgases.AfterValley(1965).5.1.1大气成分大气成分5.1.2描述大气状态的基本参量描述大气状态的基本参量5.1.3大气静力学方程大气静力学方程5.1.4大气压力和密度的垂直廓线大气压力和密度的垂直廓线5.1.5大气温度和湿度的垂直廓线大气温度和湿度的垂直廓线5.1.6大气气溶胶大气气溶胶5.1.7大气水汽大气水汽5.1.8水圈与水文循环水圈与水文循环5.1.9云与降水云与降水第一节第一节大气组成与大气的基本特性大气组成与大气的基本特性气象要素：气象要素：大气中的物理现象和物理变化过程，可以用气温、气大气中的物理现象和物理变化过程，可以用气温、气压、湿度、能见度、风向、风速、云量、日照、辐射强度等物理量压、湿度、能见度、风向、风速、云量、日照、辐射强度等物理量来描述。其中气温、气压、湿度和能量等最为重要。来描述。其中气温、气压、湿度和能量等最为重要。气象台站的观测场通常设在空旷的平地上，并把温度表放入气象台站的观测场通常设在空旷的平地上，并把温度表放入离地面离地面1.5米的百页箱内，是温度不受阳光的直射，又能保持通风。米的百页箱内，是温度不受阳光的直射，又能保持通风。地面气温地面气温通常指百页箱温度。通常指百页箱温度。物理表面单位面积所受的大气分子的压力称为物理表面单位面积所受的大气分子的压力称为大气压强或气大气压强或气压压。空气可看成是混合气体，压强可写成：。空气可看成是混合气体，压强可写成：p=(2/3)*sum(n0iw)w=(3/2)*kT其中其中n为各气体成分的数密度，为各气体成分的数密度，w为分子平均动能，为分子平均动能，k为波尔为波尔兹曼常数。气压与分子数密度及温度成正比。兹曼常数。气压与分子数密度及温度成正比。饱和水汽压饱和水汽压混合比与比湿混合比与比湿水汽压水汽压水汽密度（绝对湿度）水汽密度（绝对湿度）相对湿度相对湿度露点与霜点露点与霜点虚温虚温湿度参量湿度参量5.1.1大气成分大气成分5.1.2描述大气状态的基本参量描述大气状态的基本参量5.1.3大气静力学方程大气静力学方程5.1.4大气压力和密度的垂直廓线大气压力和密度的垂直廓线5.1.5大气温度和湿度的垂直廓线大气温度和湿度的垂直廓线5.1.6大气气溶胶大气气溶胶5.1.7大气水汽大气水汽5.1.8水圈与水文循环水圈与水文循环5.1.9云与降水云与降水第一节第一节大气组成与大气的基本特性大气组成与大气的基本特性空气可以看作是有多种化学成分的混合气体。理想空气可以看作是有多种化学成分的混合气体。理想气体的状态方程为：气体的状态方程为：其中其中p为总压强，为总压强，V是容积，是容积，T为绝对温度，为绝对温度，m为气体为气体的总质量，的总质量，R*为普适气体常数为普适气体常数8.3143X*103J/kmol*K,为平均为平均mol质量。质量。根据气体状态方程和道尔顿分压定律，可定义混合根据气体状态方程和道尔顿分压定律，可定义混合气体的平均气体的平均mol质量为质量为比气体常数为：比气体常数为：干空气的状态方程可以写为：干空气的状态方程可以写为：5.1.1大气成分大气成分5.1.2描述大气状态的基本参量描述大气状态的基本参量5.1.3大气静力学方程大气静力学方程5.1.4大气压力和密度的垂直廓线大气压力和密度的垂直廓线5.1.5大气温度和湿度的垂直廓线大气温度和湿度的垂直廓线5.1.6大气气溶胶大气气溶胶5.1.7大气水汽大气水汽5.1.8水圈与水文循环水圈与水文循环5.1.9云与降水云与降水第一节第一节大气组成与大气的基本特性大气组成与大气的基本特性VerticalstructureofpressureanddensityQuantitiessuchaspressure,densityandmeanfreepathvarydramaticallywithheightintheatmosphere.Thevariationcanbeovermanyordersofmagnitudeandisverymuchlargerthanhorizontalortemporalvariations.Meteorologiststhereforecommonlymakeuseofastandardatmosphereinwhichgeophysicalquantitieshavebeenaveragedhorizontallyandintime,andwhichvaryasafunctionofheightonly.5.1.4大气压力和密度的垂直廓线大气压力和密度的垂直廓线Figure3:VerticalvariationofpressureinhPa,anddensitying/m3,fortheUSextensiontotheICAO(InternationalCivilAeronauticsOrganization国际民用航空组织)standardatmosphere.AdaptedfromWallaceandHobbs(1977),p12.Generally,observedvaluesofatmosphericpressureanddensityarefairlyclosetothestandardatmospherevaluesforthesamelevel.TheICAOstandardatmosphereisspecifiedby:sealevelpressure(p)1013.2hPaSealeveltemperature(T)15degCfixedlapseratesforpandTdry我国有关部门将此标准与我国我国有关部门将此标准与我国60个台站的个台站的30公里以下部分的气球公里以下部分的气球探空资料进行比较后，认为与北纬探空资料进行比较后，认为与北纬45度的实际大气十分接近，低纬度度的实际大气十分接近，低纬度地区有较大偏差。地区有较大偏差。在建立我国自己的标准大气以前，可使用在建立我国自己的标准大气以前，可使用1976年美国标准大气，年美国标准大气，取其取其30公里以下部分作为国家标准。该模式假定大气是干燥的，在公里以下部分作为国家标准。该模式假定大气是干燥的，在86公里以下是均匀混合物，可以作为理想气体处理，处于静力学平衡和公里以下是均匀混合物，可以作为理想气体处理，处于静力学平衡和水平成层分布。在给定温度水平成层分布。在给定温度-高度廓线及边界条件后，通过对静力学方高度廓线及边界条件后，通过对静力学方程和气体状态方程求积分，就可以得到压力和密度数值。程和气体状态方程求积分，就可以得到压力和密度数值。海平面大气的部分特性如下：海平面大气的部分特性如下：空气空气Mol质量质量028.9644kg/kmol重力加速度重力加速度g09.80665m/s2压强压强P0101325Pa密度密度01.2250kg/m3温度温度T0288.15KTheverticalvariationofpressure(p)withheight(z)maybederivedasapproximately(seeWallaceandHobbs,1977pp12-13):p(z)=p(0)exp(-z/H)wherep(z)isthepressureatheightzabovesealevel,p(0)isthesealevelpressure,andHisaconstantcalledthescaleheight.PressuredecreasesbyafactorofeinpassingupwardthroughalayerofdepthH.Fortheearthsatmosphere,Hisabout8.4km.Asimilarapproximateexpressionmaybederivedfordensity asfollows: (z)= (0)exp(-z/H)Notethatdensityalsodecreasesrapidlywithheight.Itcanbeshownthathalfofthemassoftheearthsatmosphereisbelowthe500hPaleveloranaltitudeatabout5.5km.Atanaltitudeof50kmthepressure(iemassofparticlesaboveunitareaatthatlevel)isabout1hPasothatonlyabout0.1percentofthemassoftheatmosphereliesabovethatlevel.(Recallthat1millibar=100hectoPascalsandthat1Pascal=1Newton/m2).Similarlybecausethepressureat90kmisabout0.001hPa,onlyaboutonemillionthofthemassoftheatmosphereliesabovethatlevel.5.1.1大气成分大气成分5.1.2描述大气状态的基本参量描述大气状态的基本参量5.1.3大气静力学方程大气静力学方程5.1.4大气压力和密度的垂直廓线大气压力和密度的垂直廓线5.1.5大气温度和湿度的垂直廓线大气温度和湿度的垂直廓线5.1.6大气气溶胶大气气溶胶5.1.7大气水汽大气水汽5.1.8水圈与水文循环水圈与水文循环5.1.9云与降水云与降水第一节第一节大气组成与大气的基本特性大气组成与大气的基本特性In1962theWorldMeteorologicalOrganizationadoptedadescriptionoftheatmosphereintermsoffourdistinctlayerscalledthetroposphere（对流层）（对流层）,stratosphere（平流层、同温层）（平流层、同温层）,mesosphere（中性层）（中性层）andthermosphere（热层）（热层）.Thetopsoftheselayersarecalledthetropopause,stratopause,mesopauseandthermopause,respectively.Thelayersarecharacterisedbydistinctmeanvariationsoftemperaturewithaltitude,asdefinedintheICAOStandardAtmosphere:Inthelowerpartofthestandardoraverageatmosphere,whichisassumedtobedry,thetemperaturelapserateis6.5degCperkm,upto11kmaltitude.Fromthereupto20kmaltitudethetemperaturelapserateis0degCperkm,butfromabout20kmto32kmthelapserateis-1.0degCperkm,inwhichcasetheatmospherictemperatureincreaseswithaltitude.5.1.5大气温度和湿度的垂直廓线大气温度和湿度的垂直廓线Figure4:VerticaltemperatureprofilefortheStandardAtmospherewiththemainatmosphericregionsasindicated.AdaptedfromButleretal(1987),p111.5.1.1大气成分大气成分5.1.2描述大气状态的基本参量描述大气状态的基本参量5.1.3大气静力学方程大气静力学方程5.1.4大气压力和密度的垂直廓线大气压力和密度的垂直廓线5.1.5大气温度和湿度的垂直廓线大气温度和湿度的垂直廓线5.1.6大气气溶胶大气气溶胶5.1.7大气水汽大气水汽5.1.8水圈与水文循环水圈与水文循环5.1.9云与降水云与降水第一节第一节大气组成与大气的基本特性大气组成与大气的基本特性Atmosphericaerosolsaresmallairborneparticlesofwidelydifferingchemicalcomposition.Theyareimportantforanumberofreasonsincluding:scatteringofaerosolswillbeusedbyanumberofnext-generationactiveremotesensinginstrumentsinderivationofgeophysicalparameters;manyaerosolsactascloudcondensationnucleiandarethereforeimportantintheformationofcloudsandprecipitation;aerosolcontentaffectstheearthsalbedoandthereforetheglobalenergybalanceandclimate.5.1.6大气气溶胶大气气溶胶(a)CompositionMostaerosolparticlesoriginatefromblowingsoil,smoke,volcanoes,andtheoceans.Particlesmadeofsodiumchloride氯化钠氯化钠ormagnesiumchloride氯化镁氯化镁arehygroscopic吸湿的吸湿的andthereforeactasgoodsitesforthecondensationofwatertoformclouddroplets.(b)ConcentrationsThesevaryconsiderablybutaretypicallyoforder103cm-3overoceans,104cm-3overrurallandand105overcities.Theconcentrationsgenerallydecreasewithaltitude.(c)SizespectrumAerosolparticlesareoftenclassifiedbysizeas:Aitkennuclei(about5x10-3to0.2microns);largenuclei(about0.2to1.0microns);giantnuclei(largerthan1.0microns).Theconcentrationsofnucleifalloffverysharplywithincreasingsizee.g.thevaluesaretypically103to105cm-3forAitkennuclei,100cm-3forlargenucleiand1orlesscm-3forgiantnuclei.(d)Effectonsolar,terrestrialandmicrowaveradiationThescatteringduetoaerosolsdependsonanumberoffactorsincludingthenatureoftheparticles,theirdiametersandthewavelengthofincidentradiation.Thisisdiscussedinmoredetaillater,butforthepresentitisnotedthat:atvisiblewavelengths,scatteringofsunlightbyaerosolscanbesignificantandisdominatedbylargeparticles0.2to2microns;atinfraredwavelengths(around10microns),scatteringalthoughpresent,isverysmallcomparedtothatatvisiblewavelengths;inthemicrowave,scatteringbyaerosolsisnegligible,astheparticlesizeisverysmallcomparedtothewavelength.Thishasveryimportantconsequencesforremotesensing.Althoughaerosolsabsorbandscatteronlyasmallfractionofincomingsolarradiationcomparedtocloudsandgases,variationsinglobalaerosolconcentrationcouldaltertheearthsenergybudget.Therearecompetingeffectsinthatabsorptionofradiationwouldraiseairtemperatures,butaerosolstendtodecreasetemperaturesbyscatteringsolarradiationbackintospace.5.1.1大气成分大气成分5.1.2描述大气状态的基本参量描述大气状态的基本参量5.1.3大气静力学方程大气静力学方程5.1.4大气压力和密度的垂直廓线大气压力和密度的垂直廓线5.1.5大气温度和湿度的垂直廓线大气温度和湿度的垂直廓线5.1.6大气气溶胶大气气溶胶5.1.7大气水汽大气水汽5.1.8水圈与水文循环水圈与水文循环5.1.9云与降水云与降水第一节第一节大气组成与大气的基本特性大气组成与大气的基本特性Watervapourisextremelyimportantinradiativeabsorptionandemissionprocessesintheatmosphere.Itsconcentrationishighlyvariable.Althoughalwayspresent,insomelocalitiesitisdifficulttomeasure,butinthetropicsitsconcentrationcanbeashighas3or4percentbyvolume.Watervapourcontentofairisastrongfunctionofairtemperature.Forexampleairat40degCcanholdupto49.8gramsofwaterperkgofdryair,whileat5degCthisreducesto5.5gramsperkgofdryair.5.1.7大气水汽大气水汽（Watervapour）Thereleaseoflatentheatfromcondensationofwaterintheatmosphereissignificantintheglobalenergybudgetandclimate.Relativelysmallamountsofwatervapourcanproducegreatvariationsinweather.Thisislargelyduetochangesinitsconcentrationandinlatentheatrelease,particularlybelowabout6kmwhereahighproportionofmoisturelies.Themajorsourcesofwatervapourareevaporationandtranspirationfromplantlife.Themainsinkiscondensationincloudswithresultingprecipitationoveroceansandland.Onaveragetheconcentrationofatmosphericwatervapourdecreaseswithaltitude,althoughthisdistributionmaybereversedfromtimetotime.5.1.7大气水汽大气水汽（Watervapour）5.1.1大气成分大气成分5.1.2描述大气状态的基本参量描述大气状态的基本参量5.1.3大气静力学方程大气静力学方程5.1.4大气压力和密度的垂直廓线大气压力和密度的垂直廓线5.1.5大气温度和湿度的垂直廓线大气温度和湿度的垂直廓线5.1.6大气气溶胶大气气溶胶5.1.7大气水汽大气水汽5.1.8水圈与水文循环水圈与水文循环5.1.9云与降水云与降水第一节第一节大气组成与大气的基本特性大气组成与大气的基本特性Atmosphericwatervapourcurrentlyaccountsforonlyasmallfraction(0.001%)ofthemassofwaterinthehydrosphere.Themaincomponents,bymass,aretheoceans(97%),ice(2.4%),groundwater(0.6%),andlakesandrivers(0.02%).Thetotalmassofthehydrosphereisabout1.4x1021kgorabout1400millioncubickilometresofliquidwater.Althoughonly0.001%ofthetotalmassisintheatmosphere,thisrepresentsabout13000cubickilometresofwater.Theevaporationamountsto250cubickilometresperday.5.1.8水圈与水文循环水圈与水文循环ThehydrosphereandthehydrologiccycleTable3:Theearthswaterbalance(fromMurphyetal(1987),p10.)Thereareanumberofatmosphericprocesseswhichareimportantinthehydrologiccycle.Theseincludethefollowing:evaporation;precipitation;scattering,absorptionandemissionofenergyintheformofsolarradiationwhichmaintainsthecycle,andinfraredradiationfromtheatmosphere,cloudsandtheearthssurface;atmosphericcirculationwhichresultsfromaheatsource(i.e.solarenergy)combinedwiththeeffectsofearthrotation.Thecirculationdistributesheatenergyovertheglobe;theeffectoflocalchangesintemperature,pressure,wind,watervapourcontentetcinducedbythemovementanddevelopmentofmeteorologicalsystems.Bothevaporationandprecipitationaffectthetransferofenergyovertheearthssurfaceandthroughouttheatmosphere.About65%ofthemoistureinprecipitationarisesfromoceanicevaporation,therestfromevaporationandtranspirationoverland.Thehydrologiccycleisrelevanttomanybranchesofsciencebutfromameteorologicalorhydrologicalperspectiveitreinforcestheconceptthattheatmosphere,oceansandlandformacloselycoupledphysicalsystem.5.1.1大气成分大气成分5.1.2描述大气状态的基本参量描述大气状态的基本参量5.1.3大气静力学方程大气静力学方程5.1.4大气压力和密度的垂直廓线大气压力和密度的垂直廓线5.1.5大气温度和湿度的垂直廓线大气温度和湿度的垂直廓线5.1.6大气气溶胶大气气溶胶5.1.7大气水汽大气水汽5.1.8水圈与水文循环水圈与水文循环5.1.9云与降水云与降水第一节第一节大气组成与大气的基本特性大气组成与大气的基本特性Cloudsarecomposedoftinywaterdropletsoricecrystalswhichformoncloudcondensationnuclei.Onlyasmallfractionofaerosolparticlesarecloudcondensationnuclei:about1%overland,about10to20%overoceans.Typicalconcentrationsofclouddropletsareoforder100droplets/cm3.Onaverage,dropletsofcontinentalcloudshavetypicalradiirangingfrom2to10microns,whereasmaritimeclouddropletsmaybelargerandrangefrom3to22microns.Therelativelyraregiantcondensationnucleimayproducedropsinthe20to30micronrangeorlarger.Anarbitrarydivisionbetweenclouddropletsandraindropsismadeataradiusof100microns.Beyondthisradiusthedropshaveterminalvelocitiesaboveabout1m/swhichexceedsupdraftsorverticalmotionintypicalclouds.5.1.9云与降水云与降水CloudsandPrecipitationCloudsscattervisibleradiationconsiderably.TheyemitIRandmicrowaveradiation.TheyarefairlyopaqueatIRwavelengthsbutarevirtuallytransparenttomicrowaveradiation.ThiscanbeseeninTable4.Table4:CloudTransmission(afterSmith1972)Thegrowthofclouddropletscanproceedinitiallyviacondensation.However,thisprocessinitselfdoesnotresultindropletradiilargerthanabout30microns.Inwarmclouds(whichliecompletelybelowthe0degCisothermandinwhichonlywaterdropletscanform)raindropsformbythecollisionandcoalescenceofclouddroplets,theefficiencyofwhichincreasesmarkedlyfordropletsaboveabout18micronradii.Incoldclouds,whichmaycontainsupercooledwaterdroplets,collisionandcoalescenceisalsoanimportantprocess.Howevermanycoldcloudsalsocontainicecrystalswhichgrowbyanumberofmechanismsincludingthefreezingofsupercooleddroplets,deposition,accretion(riming),aggregation,etc.PrecipitationInmixedclouds,whichcontainbothsupercooleddropletsandiceparticles,thereisanefficientmechanismfortheformationofprecipitationcalledtheBergeron-Findeisonprocess.Thisreliesonthefactthattherelativehumidityofairwithrespecttoanicesurfaceisgreaterthanwithrespecttoawatersurface.Whenanicecrystalisinthepresenceofsupercooledwaterdropletsthesituationisunstable,becausethewatervaporisunsaturatedwithrespecttowater,butsupersaturatedwithrespecttoice.Waterdropletsevaporateandwatervapoursublimesdirectlyontotheicecrystalswhichgrowattheexpenseofthesupercooledwaterdroplets.Collisionprocessesandaccretionaddtothegrowthoficecrystalsuntiltheirterminalvelocitiesexceedthecloudupdraftsandtheyfalloutasprecipitation.Iftheparticles(icecrystals,snowflakesetc)fallthroughasufficientdepthofairwarmerthan0degCtheprecipitationatthesurfacewillberain.Figure6:Comparisonbetweenclouddropletsandraindropsintermsofradius(r)inmicrons,concentration(n)innumberpercubiclitreofair,andterminalvelocity(v)incm/sec.Therearemanyformsofprecipitation,ofwhichraindrops,drizzleandsnowareperhapsthemostcommon.Whiletheconventionalborderlinebetweenclouddropletsandraindropsis100microns,dropsofradiilessthan250micronsareusuallycalleddrizzle.Drizzle细雨细雨frequentlyfallsfromstratiformcloud层云层云whichmaybeonlyafewhundredmetersthick.Raingenerallyarisesfromwidespreadascentofmoistairorfrommorelocalizedconvectivecloud局地对流云局地对流云.Raindropsmaytypicallybefromabout250to2500micronsradius,butlargedropsandhighrainfallratesareproducedinconvectivecloudwhichmaybeupto10kmthickwithstronginternalupdrafts(whichcansupportheavyprecipitationparticlessuchaslargeraindrops,icecrystalsorhail).Thermalradiationemittedfromthewaterinraindropsmaybemonitoredbysatelliteatmicrowavewavelengthstoestimaterainfallrates.Backscatteredmicrowaveradiationfromradarmayalsobeusedtoestimaterainfallrates.