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1、MeteorologyGeography Department East China Normal UniversityShu JiongThe Earths Global Energy Balance Solarradiationisthedrivingpowersourceforwind,waves,weather,rivers,andoceancurrents.Theearthsenergybalance,whichincludeslandandoceansurfacesandtheatmosphere,controlstheseasonalanddailychangesintheear
2、thssurfacetemperature.Electromagnetic Radiation Wavelength describesthedistanceseparatingonewavecrestfromthenextcrest.Theunittomeasurewavelengthisthemicrometer.Radiantenergycanexistatanywavelength.Radiation and Temperature Thereisaninverserelationshipbetweentheradiationthatanobjectemitsandthetempera
3、tureoftheobject.Hotobjectsradiatemoreenergy,andatshorterwavelengths,thancoolerobjects.Solar radiation TheSunisaballofconstantlychurninggasesthatareheatedbycontinuousnuclearreactions. It has a surface temperature ofabout 6000oC. Like all objects, it emitsenergy in the form of electromagneticradiation
4、.electromagnetic spectrum Shortwave radiation Ultraviolet radiation(0.2 to 0.4 m) Visible lightradiation(0.4 to 0.7m) Shortwave infrared radiation(0.7 to 3m) Longwave radiation Thermal infrared wavelengths(3m)Characteristics of solar energy Thesundoesnotemitallwavelengthsofradiationequally Theintens
5、ityofsolarenergyisstrongestinvisiblewavelengthsLongwave radiation from the Earth Theearthssurfaceandatmospherearemuchcolderthanthesunssurface,sotheenergyfromtheEarthhaslongerwavelengthThe global radiation balance Theearthconstantlyabsorbssolarshortwaveradiationandemitslongwaveradiation.Thesunprovide
6、sanearlyconstantflowofshortwaveradiationtowardearth.Theatmosphere,land,andoceanalsoemitenergyintheformoflongwaveradiation.Figure1GlobalEnergyBalanceInsolation over the GlobeInsolation(incomingsolarradiation)dependsontheangleofthesunabovethehorizon.The Path of the Sun in the Sky Thesunspathintheskych
7、angesgreatlyinpositionandheightabovehorizonfromsummertowinter.Atequinox,thesunrisesdirectlytotheeastandsetsdirectlytothewest.Thenoonsunispositionedatanangleof50oabovethehorizoninthesouthernsky.Thesunisabovethehorizonforexactly12hours.Atnoonitwillbe73.5oabovethehorizon.Thesunisabovethehorizonforabout
8、15hourDaily Insolation Through the YearDailyinsolationdependsontwofactors: theangleatwhichthesunsraysstriketheearth thelengthoftimeofexposuretotheraystheequatorhastwoperiodsofmaximumdailyinsolation,theseperiodsoccurneartheequinoxes.Therearealsotwominimumperiodsnear the solstices, when the subsolarpo
9、int moves farthest north and southfromtheequator.Alllatitudesbetweenthe tropic of cancer 23.5oN and thetropic of Capricorn 23.5oS have twomaximumandminimumvalues.Seasonalpatternofdailyinsolationisdirectlyrelatedtolatitude.Annual Insolation by LatitudeAnnualinsolationvariessmoothlyfromtheequatortothe
10、poleTheannualinsolationvalueatthepoleisabout40%ofthevalueattheequator.Thetiltingoftheearthsaxisredistributesasignificantportionoftheearthsinsolationfrom the equatorial regions toward thepoles.World Latitude ZonesTheequatorial zoneencompassestheequatorandcoversthelatitudebeltroughly10oNto10oSSpanning
11、thetropicsofcancerandCapricornarethe tropical zones,rangingfromlatitudes10oto25onorthandsouthMovingtowardthepolesfromeachofthetropicalzonesaretransitionalregionscalledthesubtropical zones,rangingfromlatitudes25oto35onorthandsouthThemidlatitude zonesliebetween35oand55olatitudesinthenorthernandsouther
12、nhemispheresBorderingthemidlatitudezonesonthepolewardsidearethesubarctic zoneandsubantarctic zone,55oto60onorthandsouthlatitudesAstridethearcticandAntarcticcirclesfromlatitudes60oto75oNandSliethearcticandAntarctic zones The polar zones,northandsouth,arecircularareasbetweenabout75olatitudeandthepoles
13、Composition of the Atmosphere Theearthsatmosphereconsistsofair-amixtureofvariousgasessurroundingtheearthtoaheightofmanykilometers.Almostalltheatmosphere97%lieswithin30kmoftheearthssurface.Theupperlimitoftheatmosphereisata height of approximately 10,000kmabove the earths surface, a distanceapproachin
14、gthediameteroftheearthitself.Pure,dryairconsistslargelyofnitrogen,about78%byvolume,andoxygen,about21%.Othergasesaccountfortheremaining1%WatervaporisanimportantcomponentoftheatmospherethatvariesinconcentrationfromplacetoplaceandtimetotimeOzone in the Upper Atmosphere Ozone(O3)isfoundmostlyintheupperp
15、artoftheatmosphere,inalayertermedthestratosphere.OzoneinthestratosphereabsorbsultravioletradiationfromthesunasthisradiationpassesthroughtheatmosphereAt both polar regions, climate and chemistry combine to deplete ozone during spring months. Dark blue indicates lowest ozone amounts. Arctic total ozon
16、e amounts seen by TOMS in March 2003 (above, left) were among the lowest ever observed in the northern hemisphere. The Antarctic ozone hole of 2003 (above, right) was the second largest ever observed.Sensible Heat and Latent Heat Transfer Sensible Heat-thequantityofheatheldbyanobjectthatcanbesensedb
17、ytouchingorfeeling When two objects of unlike temperaturecontact each other, heat energy moves byconduction fromthewarmertothecooler.This type of heat flow is referred to assensible heat transferThe Global Energy System InsolationlossesintheAtmosphereAlbedoCounterradiationandtheGreenhouseEffectGloba
18、lEnergyBudgetoftheAtmosphereandSurfaceNetRadiation,Latitude,andtheEnergyBalanceWinds and the Pressure Gradient Force Windisairmotionwithrespecttotheearthssurface,anditisdominantlyhorizontal. Barometric pressurefallswithincreasingaltitudeabovetheearthssurface.Thechangeinbarometricpressureacrossthehor
19、izontalsurfaceofamapconstitutesapressure gradient.Thegradientisinthedirectionfromhigherpressuretolowerpressure.Whereapressuregradientexists,airmoleculestendtodriftinthesamedirectionasthatgradient.Thistendencyformassmovementoftheairisreferredtoasthepressure gradient force.Sea and Land Breezes Duringt
20、hedaytime,morerapidheatingofthelowerairlayeroverthelandthanovertheoceancausesapressuregradientfromseatoland.Airmovinglandwardinresponsetothisgradientfromhighertolowerpressureconstitutesthesea breeze.Athigherlevels,areverseflowsetsin.Togetherwithweakrisingandsinkingairmotions,acompleteflowcircuitisfo
21、rmed.Duringthenight,whenradiationalcoolingofthelandisrapid,thelowerairbecomescolderoverthelandthanoverthewater.Higherpressurenowdevelopsoverlandandthebarometricgradientisreversed.Airnowmovesfromlandtoseaasaland breeze.Figure 2 Sea breeze and land breezeCyclones and Anticyclones A center of low press
22、ure is called acyclone;acenterofhighpressureisananticyclone.Winds in a cyclone in the northern hemisphere show an anticlockwiseinspiral. In an anticyclone, there is aclockwiseoutspiral.Thesurfacewindsspiralinwardonthecenterofthecyclone,sotheairisconvergingonthecenterandmustalsorisetobedisposedofathi
23、gherlevels.Fortheanticyclone,bycontrast,surfacewindsspiraloutfromthecenter.Thismotionrepresentsadivergingofairflowandmustbeaccompaniedbyasinkingofairinthecenteroftheanticyclonetoreplacetheoutmovingair.Figure 3 Surface winds in cyclones and anticyclonesGlobal Distribution of Surface Pressure Systems
24、Overtheequatorialzoneisabeltofsomewhatlowerthannormalpressure,between1011and1008mb,whichisknownastheequatorial trough. Lowerpressureisconspicuousbycontrastwithbeltsofhigherpressurelyingtothenorthandsouthandcenteredataboutlat.30NandS.Thesearethesubtropical belts of high pressure,inwhichpressureexceed
25、1020mb. Inthesouthernhemisphere,southofthesubtropicalhigh-pressurebelt,isabroadbeltoflowpressure,extendingfromthemidlatitudezonetothearcticzone. The axis of low pressure iscenteredataboutlat.65S.Thispressuretroughiscalledthe subantactic low-pressure belt.LyingoverthecontinuousexpanseofSouthernOcean,
26、thistroughhasaveragepressureaslowas984mb.OverthecontinentofAntarcticaisapermanentcenterofhighpressureknownasthepolar high.The Global Pattern of Surface WindsFromthetwosubtropicalhigh-pressurebeltsthepressuregradientisequatorward, leading down to theequatorial trough of low pressure. Airmoving from h
27、igh to low pressure isdeflected by the Coriolis effect. As aresult, two belts of trade windsareproduced.Meetingofthetradestakesplacewithinanarrowzonecalledtheintertropical convergence zone.Alongpartsoftheequatorialtroughoflowpressureatcertaintimesofyear,thetradesdonotcometogetherinconvergence.Instea
28、d,abeltofcalmsandvariblewinds,calledthedoldrums,forms.Betweenlat.35and60NandSisthebeltofprevailing westerly winds,or westerlies.Awindsystemcalledthepolar easterliesischaracteristicofthearcticandpolarzones.Figure 4 Surface windsMonsoon Winds of Southeast Asia In summer southern Asia develops acyclone
29、intowhichthereisstrongflowofair. From the Indian Ocean and thesouthwestern Pacific, warm, humid airmoves northward and northwestward intoAsia.Thisairflowconstitutesthesummer monsoon and is accompanied by heavyrainfallinsoutheasternAsia. In winter, Asia is dominated by astrong center of high pressure
30、 fromwhichthereisanoutwardflowofairreversingthatofthesummermonsoon.Blowingsouthwardandsoutheastwardtoward the equatorial oceans, thisairflowconstitutesthewinter monsoonandbringsdryweatherforaperiodofseveralmonths.Mountain winds and valley windsDuringthedaylighthourstheairalongtheslopesofthemountains
31、isheatedmoreintenselythantheairatthesameelevationoverthevalleyfloor.Thiswarmairglidesupalongtheslopeandgeneratesavalley wind. Aftersunsetthepatternisreversed.Rapidradiationheatlossalongthemountainslopesresultsincoolairdrainageintothevalleybelowandcausesthemountain wind.Global Circulation The Hadley
32、Cell CirculationInthezonebetweentheequatorandroughly30latitude,thesurfaceflowisequatorwardwhiletheflowaloftispoleward.NeartheequatorthewarmrisingairthatreleaseslatentheatduringtheformationofcumulustowersisbelievedtoprovidetheenergytodrivethiscellThecirculationbetween30and60latitudeisjustoppositethat
33、oftheHadleycell.Thenetsurfaceflowispoleward,andbecauseoftheCorioliseffect,thewindshaveastrongwesterlycomponent. About the circulation in the highlatitudes, it is generally believed thatsubsidencenear the poles produces asurface flow that moves equatorwardandisdeflectedintothepolareasterliesofbothhem
34、isphere.Theregionwherethe cold polar winds and the warmerwesterlyflowofthemidlatitudesclashhasbeennamedthepolarfront.The global Circulation and Mans Environment Inlowlatitudes,theHadleycelloperateslikeasimpleheatenginetotransportheatfromtheequatorialzonetothesubtropicalzone.Upper-airwavestakeupthetr
35、ansportandmovewarmairpolewardinexchangeforcoldair.Theglobalatmosphericcirculationalsotransportsheatinthelatentformheldbywatervapor.Windscarryalargeamountofwatervapor,whichisdepositedasprecipitationonthecoast.Windsalsotransportatmosphericpollutants,carryingthemtensandhundredsofkilometersfromthesource
36、sofpollution.Air temperature Temperature is a measure of thelevel of sensible heat of matter,whetheritisgaseous,liquid,orsolid. Conduction describes the flow ofheat from a warmer substance to acolderonewhenthetwoaretouching. Evaporation, the process by whichwaterchangesfromaliquidtoagasbyabsorbing h
37、eat, tends to lower thetemperatureofawetsurface.Measurement of air temperatureAirtemperaturesarenowautomaticallyrecordedbythermometersatauniformheightabovetheground.The daily cycle of air temperature Because the earth rotates on its axis,incomingsolarenergyatalocationcanvarywidelythroughoutthe24-hou
38、rperiod. Insolation is greatest in the middle of thedaylightperiod,whenthesunisatitshighestpositioninthesky,andfallstozeroatnight.Daily insolation and net radiation The daily cycle of temperature iscontrolled by the daily cycle of netradiation. At the equinox, insolation begins atabout sunrise (6 a.
39、m.),rises to a peakvalueatnoon,anddeclinestozeroatsunset(6p.m.).AttheJunesolstice,insolationbeginsabout two hours earlier (4 a.m.) andendsabouttwohourslater(8p.m.).AttheDecembersolstice,insolationbeginsabouttwohourslaterthantheequinoxcurve(8a.m.)andendsabouttwohoursearlier(4p.m.). When net radiation
40、 is positive, thesurfacegainsheat,andwhennegative,itlosesheat.Netradiationbeginsthe24-hourdayasa negative value-a deficit-at midnight.The deficit continues into the earlymorning hours. Net radiation shows apositive value- a surplus-shortly aftersunrise and rises sharply to a peak atnoon.Daily temper
41、atureThe minimum daily temperature usuallyoccurs about a half hourafter sunrise. Airtemperature rises sharply in the morninghours and continues to rise long after thenoonpeakofnetradiation.Airtemperaturerises as long as net radiation is positive.Temperatures are lowest just after sunriseandhighestin
42、midafternoon.Urban and rural temperature contrastsUrbansurfaceslackmoistureandsoarewarmerthanruralsurfacesduringthe day. At night, urban materialsconductstoredheattothesurface,alsokeepingtemperatureswarmer.The urban heat islandAsaresultoftheaboveeffects, airtemperaturesinthecentralregionofacity are
43、typically several degreeswarmerthanthoseofthesurroundingsuburbsandcountryside.Thisiscalledaheatisland. The heat island persists through thenight because of the availability of aheat stored in the ground during thedaytimehours.Anotherimportantfactorinwarmingthe city is fuel consumption. Insummer, cit
44、y temperatures are raisedthroughtheuseofairconditioning.Temperature structure of the Atmosphere TroposphereThetroposphereisthelowestatmospheric layer, in which temperaturedecreaseswithincreasingelevation.Everyday weather phenomena, such ascloudsorstorms,occurmainlyinthislayer. The troposphere contai
45、ns significantamountsofwatervaporandcountlesstinydustparticles.Stratosphere Above the troposphere lies thestratosphereinwhichtheairbecomesslightlywarmerasaltitudeincreases.Thestratosphereextendstoaheightof roughly 50km above the earthssurface. It is the home of strong, persistentwindsthatblowfromwes
46、ttoeast.Oneimportantfeatureofthestratosphere is that it contains theozonelayer.High-Mountain Environments At high elevations, air temperaturesaregenerallycoolerandshowagreaterday-to-nightrange.Temperature Inversion and Frost In a temperature inversion, airtemperatureincreaseswithaltitude. Low-level
47、temperature inversionsoftenoccuroversnow-coveredsurfacesinwinter. Inversions can also result when awarm air layer overlies a colder one.This type of inversion is often foundalong the west coasts of majorcontinents.Frost If the temperature of the lowermostairfallsbelowthefreezingpoint,forsensitive pl
48、ants during the growingseason, this temperature condition iscalledakillingfrost.The annual cycle of air temperaturelTheannualcycleofnetradiation,whichresultsfromthevariationofinsolationwiththeseasons,drivestheannualcycleofairtemperatures.Land and water contrastsLand-watercontrastskeepairtemperatures
49、at coastal locations more constant than atinteriorcontinentallocations. Oceans heat and cool more slowly thancontinents. The surface of any extensive, deepbodyofwaterheatsmoreslowlyandcoolsmoreslowlythanthesurfaceofalarge body of land when both aresubjected to the same intensity ofinsolation.Daily t
50、emperature cyclelP62Figure3.15Theaveragedailycycleofairtemperature for four different monthsshows the effect of continental andmaritimelocation.DailyandseasonalrangesaregreatatElPaso,astationinthe continental interior, but onlyweakly developed at North Head,Washington, which is on the Pacificcoast.
51、The seasonal effect on overalltemperaturesisstrongeratElPaso.Annual temperature cyclelP63figure3.16Annualcyclesofinsolation(a)andmonthlymeanairtemperature(b)for two stations at lat. 50N: Winnipeg,Canada,andScillyIslands,England.lInsolationisidenticalforthetwostations.Winnipeg temperatures clearly sh
52、ow thelarge annual range and earlier maximumandminimumthatarecharacteristicofitscontinentallocation.ScillyIslandstemperaturesshowitsmaritimelocationinthe small annual range and delayedmaximumandminimum.World Patterns of air temperature Isotherms: Lines drawn to connectlocationshavingthesametemperatu
53、re. Maps of isotherms show centers ofhighandlowtemperaturesaswellastemperaturegradients.Factors controlling air temperature patterns Global air temperature patterns arecontrolledprimarilybylatitude,coastal-interiorlocation,andelevation.World air temperature patterns for January and JulylP65figure Te
54、mperatures decrease from theequatortothepoles. Large landmasses located in thesubarctic and arctic zones developcentersofextremelylowtemperaturesinwinter. Temperatures in equatorial regionschangelittlefromJanuarytoJuly. Isotherms make a large north-southshift from January to July overcontinents in t
55、he midlatitude andsubarcticzones. Highlands are always colder thansurroundinglowlands.Areasofperpetualiceandsnowarealwaysintenselycold.The annual range of air temperatures The annual range increases withlatitude,especiallyovernorthernhemispherecontinents. The greatest ranges occur in thesubarcticand
56、arcticzonesofAsiaandNorthAmerica.Theannualrangeismoderatelylargeonlandareasinthetropicalzone,nearthetropicsofcancerandCapricorn.Theannualrangeoveroceansislessthanthatoverlandatthesamelatitude.Theannualrangeisverysmalloveroceansinthetropicalzone.Global warming and the greenhouse effect The temperatur
57、e of our planet iswarming.Mostscientistsagreethatthehuman-inducedbuildupofgreenhousegases has begun to affect globalclimate.However,naturalcycles,suchas variations in the suns output, stillprovidestronginfluences.Greenhouse gasesCarbonDioxide(CO2)Methane(CH4)Nitrousoxide(NO)Ozone(O3)Summery TheEarthsGlobalEnergyBalanceThePathoftheSunintheSkyWorldLatitudeZonesCompositionoftheAtmosphere Winds and the Global Circulation Airtemperature Thanks for attention !
