双语教学实例-Meteorology.ppt

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1、双语教学实例-Meteorology Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望The Earths Global Energy Balance Solarradiationisthedrivingpowersourceforwind,waves,weather,rivers,andoceancurrents.Theearthsenergybalance,whichincludeslandandoceansurfacesandtheatmosphere,con

2、trolstheseasonalanddailychangesintheearthssurfacetemperature.Electromagnetic Radiation Wavelength describesthedistanceseparatingonewavecrestfromthenextcrest.Theunittomeasurewavelengthisthemicrometer.Radiantenergycanexistatanywavelength.Radiation and Temperature Thereisaninverserelationshipbetweenthe

3、radiationthatanobjectemitsandthetemperatureoftheobject.Hotobjectsradiatemoreenergy,andatshorterwavelengths,thancoolerobjects.Solar radiation TheSunisaballofconstantlychurninggasesthatareheatedbycontinuousnuclearreactions.It has a surface temperature ofabout 6000oC.Like all objects,it emitsenergy in

4、the form of electromagneticradiation.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 Thesundoesnotemitallwavele

5、ngthsofradiationequally TheintensityofsolarenergyisstrongestinvisiblewavelengthsLongwave radiation from the Earth Theearthssurfaceandatmospherearemuchcolderthanthesunssurface,sotheenergyfromtheEarthhaslongerwavelengthThe global radiation balance Theearthconstantlyabsorbssolarshortwaveradiationandemi

6、tslongwaveradiation.Thesunprovidesanearlyconstantflowofshortwaveradiationtowardearth.Theatmosphere,land,andoceanalsoemitenergyintheformoflongwaveradiation.Figure1GlobalEnergyBalanceInsolation over the GlobeInsolation(incomingsolarradiation)dependsontheangleofthesunabovethehorizon.The Path of the Sun

7、 in the Sky Thesunspathintheskychangesgreatlyinpositionandheightabovehorizonfromsummertowinter.Atequinox,thesunrisesdirectlytotheeastandsetsdirectlytothewest.Thenoonsunispositionedatanangleof50oabovethehorizoninthesouthernsky.Thesunisabovethehorizonforexactly12hours.Atnoonitwillbe73.5oabovethehorizo

8、n.Thesunisabovethehorizonforabout15hourDaily Insolation Through the YearDailyinsolationdependsontwofactors:theangleatwhichthesunsraysstriketheearth thelengthoftimeofexposuretotheraystheequatorhastwoperiodsofmaximumdailyinsolation,theseperiodsoccurneartheequinoxes.Therearealsotwominimumperiodsnear th

9、e solstices,when the subsolarpoint moves farthest north and southfromtheequator.Alllatitudesbetweenthe tropic of cancer 23.5oN and thetropic of Capricorn 23.5oS have twomaximumandminimumvalues.Seasonalpatternofdailyinsolationisdirectlyrelatedtolatitude.Annual Insolation by LatitudeAnnualinsolationva

10、riessmoothlyfromtheequatortothepoleTheannualinsolationvalueatthepoleisabout40%ofthevalueattheequator.Thetiltingoftheearthsaxisredistributesasignificantportionoftheearthsinsolationfrom the equatorial regions toward thepoles.World Latitude ZonesTheequatorial zoneencompassestheequatorandcoversthelatitu

11、debeltroughly10oNto10oSSpanningthetropicsofcancerandCapricornarethe tropical zones,rangingfromlatitudes10oto25onorthandsouthMovingtowardthepolesfromeachofthetropicalzonesaretransitionalregionscalledthesubtropical zones,rangingfromlatitudes25oto35onorthandsouthThemidlatitude zonesliebetween35oand55ol

12、atitudesinthenorthernandsouthernhemispheresBorderingthemidlatitudezonesonthepolewardsidearethesubarctic zoneandsubantarctic zone,55oto60onorthandsouthlatitudesAstridethearcticandAntarcticcirclesfromlatitudes60oto75oNandSliethearcticandAntarctic zones The polar zones,northandsouth,arecircularareasbet

13、weenabout75olatitudeandthepolesComposition of the Atmosphere Theearthsatmosphereconsistsofair-amixtureofvariousgasessurroundingtheearthtoaheightofmanykilometers.Almostalltheatmosphere97%lieswithin30kmoftheearthssurface.Theupperlimitoftheatmosphereisata height of approximately 10,000kmabove the earth

14、s surface,a distanceapproachingthediameteroftheearthitself.Pure,dryairconsistslargelyofnitrogen,about78%byvolume,andoxygen,about21%.Othergasesaccountfortheremaining1%WatervaporisanimportantcomponentoftheatmospherethatvariesinconcentrationfromplacetoplaceandtimetotimeOzone in the Upper Atmosphere Ozo

15、ne(O3)isfoundmostlyintheupperpartoftheatmosphere,inalayertermedthestratosphere.OzoneinthestratosphereabsorbsultravioletradiationfromthesunasthisradiationpassesthroughtheatmosphereAt both polar regions,climate and chemistry combine to deplete ozone during spring months.Dark blue indicates lowest ozon

16、e amounts.Arctic total ozone 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-thequantityofheatheldbyanob

17、jectthatcanbesensedbytouchingorfeeling 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 InsolationlossesintheAtmosphereAlbedoCounterradiationandtheGr

18、eenhouseEffectGlobalEnergyBudgetoftheAtmosphereandSurfaceNetRadiation,Latitude,andtheEnergyBalanceWinds and the Pressure Gradient Force Windisairmotionwithrespecttotheearthssurface,anditisdominantlyhorizontal.Barometric pressurefallswithincreasingaltitudeabovetheearthssurface.Thechangeinbarometricpr

19、essureacrossthehorizontalsurfaceofamapconstitutesapressure gradient.Thegradientisinthedirectionfromhigherpressuretolowerpressure.Whereapressuregradientexists,airmoleculestendtodriftinthesamedirectionasthatgradient.Thistendencyformassmovementoftheairisreferredtoasthepressure gradient force.Sea and La

20、nd Breezes Duringthedaytime,morerapidheatingofthelowerairlayeroverthelandthanovertheoceancausesapressuregradientfromseatoland.Airmovinglandwardinresponsetothisgradientfromhighertolowerpressureconstitutesthesea breeze.Athigherlevels,areverseflowsetsin.Togetherwithweakrisingandsinkingairmotions,acompl

21、eteflowcircuitisformed.Duringthenight,whenradiationalcoolingofthelandisrapid,thelowerairbecomescolderoverthelandthanoverthewater.Higherpressurenowdevelopsoverlandandthebarometricgradientisreversed.Airnowmovesfromlandtoseaasaland breeze.Figure 2 Sea breeze and land breezeCyclones and Anticyclones A c

22、enter of low pressure is called acyclone;acenterofhighpressureisananticyclone.Winds in a cyclone in the northern hemisphere show an anticlockwiseinspiral.In an anticyclone,there is aclockwiseoutspiral.Thesurfacewindsspiralinwardonthecenterofthecyclone,sotheairisconvergingonthecenterandmustalsoriseto

23、bedisposedofathigherlevels.Fortheanticyclone,bycontrast,surfacewindsspiraloutfromthecenter.Thismotionrepresentsadivergingofairflowandmustbeaccompaniedbyasinkingofairinthecenteroftheanticyclonetoreplacetheoutmovingair.Figure 3 Surface winds in cyclones and anticyclonesGlobal Distribution of Surface P

24、ressure Systems Overtheequatorialzoneisabeltofsomewhatlowerthannormalpressure,between1011and1008mb,whichisknownastheequatorial trough.Lowerpressureisconspicuousbycontrastwithbeltsofhigherpressurelyingtothenorthandsouthandcenteredataboutlat.30NandS.Thesearethesubtropical belts of high pressure,inwhic

25、hpressureexceed1020mb.Inthesouthernhemisphere,southofthesubtropicalhigh-pressurebelt,isabroadbeltoflowpressure,extendingfromthemidlatitudezonetothearcticzone.The axis of low pressure iscenteredataboutlat.65S.Thispressuretroughiscalledthe subantactic low-pressure belt.LyingoverthecontinuousexpanseofS

26、outhernOcean,thistroughhasaveragepressureaslowas984mb.OverthecontinentofAntarcticaisapermanentcenterofhighpressureknownasthepolar high.The Global Pattern of Surface WindsFromthetwosubtropicalhigh-pressurebeltsthepressuregradientisequatorward,leading down to theequatorial trough of low pressure.Airmo

27、ving from high to low pressure isdeflected by the Coriolis effect.As aresult,two belts of trade windsareproduced.Meetingofthetradestakesplacewithinanarrowzonecalledtheintertropical convergence zone.Alongpartsoftheequatorialtroughoflowpressureatcertaintimesofyear,thetradesdonotcometogetherinconvergen

28、ce.Instead,abeltofcalmsandvariblewinds,calledthedoldrums,forms.Betweenlat.35and60NandSisthebeltofprevailing westerly winds,or westerlies.Awindsystemcalledthepolar easterliesischaracteristicofthearcticandpolarzones.Figure 4 Surface windsMonsoon Winds of Southeast Asia In summer southern Asia develops

29、 acycloneintowhichthereisstrongflowofair.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 pres

30、sure fromwhichthereisanoutwardflowofairreversingthatofthesummermonsoon.Blowingsouthwardandsoutheastwardtoward the equatorial oceans,thisairflowconstitutesthewinter monsoonandbringsdryweatherforaperiodofseveralmonths.Mountain winds and valley windsDuringthedaylighthourstheairalongtheslopesofthemounta

31、insisheatedmoreintenselythantheairatthesameelevationoverthevalleyfloor.Thiswarmairglidesupalongtheslopeandgeneratesavalley wind.Aftersunsetthepatternisreversed.Rapidradiationheatlossalongthemountainslopesresultsincoolairdrainageintothevalleybelowandcausesthemountain wind.Global Circulation The Hadle

32、y Cell CirculationInthezonebetweentheequatorandroughly30latitude,thesurfaceflowisequatorwardwhiletheflowaloftispoleward.NeartheequatorthewarmrisingairthatreleaseslatentheatduringtheformationofcumulustowersisbelievedtoprovidetheenergytodrivethiscellThecirculationbetween30and60latitudeisjustoppositeth

33、atoftheHadleycell.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 heat

37、,tends to lower thetemperatureofawetsurface.Measurement of air temperatureAirtemperaturesarenowautomaticallyrecordedbythermometersatauniformheightabovetheground.The daily cycle of air temperature Because the earth rotates on its axis,incomingsolarenergyatalocationcanvarywidelythroughoutthe24-hourper

38、iod.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.m.),rise

39、s 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 is positiv

40、e,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 temperatureThe minim

41、um 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 sunriseandhighestinmidafternoon.Ur

42、ban and rural temperature contrastsUrbansurfaceslackmoistureandsoarewarmerthanruralsurfacesduringthe day.At night,urban materialsconductstoredheattothesurface,alsokeepingtemperatureswarmer.The urban heat islandAsaresultoftheaboveeffects,airtemperaturesinthecentralregionofacity are typically several

43、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,city temperatures are ra

44、isedthroughtheuseofairconditioning.Temperature structure of the Atmosphere TroposphereThetroposphereisthelowestatmospheric layer,in which temperaturedecreaseswithincreasingelevation.Everyday weather phenomena,such ascloudsorstorms,occurmainlyinthislayer.The troposphere contains significantamountsofw

45、atervaporandcountlesstinydustparticles.Stratosphere Above the troposphere lies thestratosphereinwhichtheairbecomesslightlywarmerasaltitudeincreases.Thestratosphereextendstoaheightof roughly 50km above the earthssurface.It is the home of strong,persistentwindsthatblowfromwesttoeast.Oneimportantfeatur

46、eofthestratosphere 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 temperature inversionsoftenoc

47、curoversnow-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 plants during the growingseason,

48、this temperature condition iscalledakillingfrost.The annual cycle of air temperaturelTheannualcycleofnetradiation,whichresultsfromthevariationofinsolationwiththeseasons,drivestheannualcycleofairtemperatures.Land and water contrastsLand-watercontrastskeepairtemperaturesat coastal locations more const

49、ant 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 temperature cyclelP62Figure3.15Thea

50、veragedailycycleofairtemperature 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.The seasonal effect on overalltempera