气象科技英语翻译

1、Likeafishintheocean,manisconfined就像海洋中的鱼一样,人类被局限在大气中一of个非常狭窄的层次之内.虽然地球的大气层of在水平方向上的不均匀性比在垂直高度上的不均匀性要小得多.但它确确实实在水平和垂直两个方向上都是不均匀的.toaveryshallowlayeratmosphere.ThegaseousenvelopetheEarthisphysicallyinhomogeneousinboththeverticalandhorizontaldirections,althoughthehorizontalinhomogeneityismuchlessmarked

2、thantheverticalinhomogeneity.Variouscriteriahavebeendevisedfordividingtheatmosphereintolayers.Thisdivisioncanbebasedonthenatureoftheverticaltemperatureprofile,onthegaseouscompositionoftheairatdifferentaltitudes,andtheeffectoftheatmosphereonaircraftatdifferentaltitudes,etc.Thedivisionbasedonthevariat

3、ionoftheairtemperaturewithaltitudeisusedmostcommonlyinthemeteorologicalliterature.人们设计了各种各样的标准来划分大气的层次.有的基于垂直温度廓线的性质,有的根据空气在不同高度上的大气成分,有的根据大气在不同高度上对飞机的影响来划分等等.根据空气温度随高度的变化来划分大气的层次是气象文献中用得最普遍的一种划分方法.根据1961年世界气象组织大气学委会公布Accordingtoapublicationofthe的标准,地球大气被划分为5个主要层次:agrologicalcommissionoftheWorld对流层,

4、平流层,中层,热成层以及外逸层.MeteorologicalOrganization(WMO)in这些层次之间邻接着4个浅薄的过渡区域:1961,theEarth'satmosphere,isdivided对流层顶,平流层顶,中层顶以及热成层顶.intofivemainlayers:thetroposphere,thestratosphere,themesosphere,thethermosphereandtheexosphere.Theselayersareboundedbyfourthintransitionregions:thetropospause,thestratospaus

5、e,themesospause,thethermospause.对流层是介于地球外表和对流层顶之间的大气低层.在对流层中,温度以平均6.5C/kmThetroposphereisthelowerlayerofthe的递减率随高度的增加而降低,其上边界在atmospherebetweentheEarth极地和中纬度地区大约位于812Km的高surfaceandthetropopause.The度,在热带地区大约位于16-18Km的高度.temperaturedropswithincreasing在极地和中纬度,对流层包含了大气层中空heightinthetroposphere,atamean气质

6、量的75%左右,然而在热带地区,包含rateof6.5Cperkilometer(lapserate).了大约90%.对流层顶是一个中间层次,据Theupperboundaryofthetroposphere观测,其温度是逆温或是等温分布.liesataheightofapproximately8to12kminthepolarandtropospherecontainsabout75%ofthetotalmassofatmosphericair,whileinthetropicsitcontainsabout90%.Thetropoauseisanintermediatelayerinwhi

7、cheitheratemperatureinversionoranisothermaltemperaturedistributionisobserved.Thestratosphereistheatmospheric平流层是位于对流层之上的大气层,在平流层中,温度或是随高度增加,或是几乎保持定常.在平流层的低层直到地球外表之上大约20Km温度实际是一个常数大约-56C.然而再向上,大约20Km30Km的高度,温度随高度以1C/km的速度增layerabovethetroposphere.Inthe力口,从30Km47Km高度上,以2.8C/kmstratospherethetemperatur

8、eeither的速率增加.在标准情况下,47Km高度上increaseswithheightorremainsnearly正常的温度是-2.5摄氏度.constant.Inthelowerpartofthestratosphere(uptoapproximately20kmabovetheEarth'ssurface)thetemperatureispracticallyconstant(about56C).Whilefurtherupthetemperatureincreaseswithaltitudeatarateofabout1C/kmatheightsof20to30kmand

9、about2.8C/kmataltitudesfrom32to47km.Underthestandardconditionsthetemperatureatthe47kmlevelisnormally-2.5.温度随高度的增加是由于太阳辐射的紫外线被臭氧分子吸收的缘故.值得一提的是大气层中空气总质量的99%都集中在对流层和平流层中,一直伸展到30-35Km的高度上.平流层顶位于平流层和中间层的中间层大约从47-52Km的高度上,平流层顶温度保持定常,约为0摄氏度.ThisincreaseintemperaturewithheightisduetotheabsorptionofUVsolarra

10、diationbyozonemolecules.Itshouldbenotedthatabout99%ofthetotalmassofatmosphericairisconcentratedinthetroposphereandstratosphere,热成层是位于中层顶上的大气层,其温度随whichextenduptoanlatitudeof30or高度的增加而增加,到热成层上边界的平均35km.Thestratopauseisan高度,即大约在450Km高度上,到达大约intermediatelayerbetweenthe2000摄氏度.该层中温度的增加主要是由于stratospherea

11、ndthemesosphere(inthe太阳辐射的紫外线被氧分子吸收,分解所致.altituderegionfrom47to52km),inwhichthetemperatureremainsconstantatabout0C.Thethermosphereistheatmosphericlayerabovethemesopause.The外逸层是最远的,也是研究最少的大气的上temperatureinthislayerincreaseswith层局部.它位于大约450Km的高度上.外increasingaltitude,reachingabout逸层中空气的密度非常小,以致原子和分子200

12、0Catabout450km,themean都能逃逸到星际空间.heightoftheupperboundaryofthethermosphere.ThetemperatureincreaseinthislayerismainlycausedbytheabsorptionofUVsolarradiationbyoxygenmolecules,whichdissociateasaresultofthis.Theexosphereisthefurthestoutandtheleaststudiedpartoftheupperatmosphere.Itislocatedabove450kmaltit

13、ude.Theairdensityintheexosphereissolowthatatomsandmoleculescanescapefromitintointerplanetaryspace.Finally,alongwiththeabovedivisionoftheatmosphere,wewillalsomakeuseofadivisionbasedontheextentofatmosphericinteractionwiththeEarth'ssurface.Accordingtothisprincipe,theatmosphereisusuallydividedintoas

14、ocalledboundarylayer(sometimesalsocalledthefrictionlayer)andthefreeatmosphere.Theatmosphericboundarylayer(upto1or1.5km)isinfluencedconsiderablybytheEarthssurfaceand最后,除了以上对大气的划分以外,我们也可以根据大气和地面的相互作用得到另一种分法.根据此原那么,大气通常被划分为所谓的边界层有时也称摩擦层和自由大气.地球外表和涡度粘滞力对大气边界层知道1-1.5Km有相当大的影响；同时,作为一级近似,在自由大气中我们可以忽略涡度粘滞力的

15、影响.以上这些大气层中,只有对流层尤其是边界层中气象参数的垂直分布具有显著的不稳定性的特征.人们观测到该层中存在逆稳和温度随高度超绝热变化.byeddy-viscosityforces.Atthesame地球大气是气体和气溶胶的混合物,所谓的time,wecanneglect,asafirst气溶胶指的是由分布在空气中的微小的液体approximation,theinfluenceof和固体颗粒组成的系统.eddy-viscosityforcesinthefreeatmosphere.Ofalltheaboveatmosphericlayers,only空气不是一种特殊的气体,而是由许多气体t

16、hetroposphere(especiallyitsboundary混合成的.其中一些气体,如,氮,氧,僦,layer)ischaracterizedbyamarked窟等,作为空气的永久组成成分,总是以固instabilityoftheverticaldistributionof定的比例存在于大气中.其中一些成分,如,themeteorologicalparameters.Itisin水汽,二氧化碳和臭氧的含量是随时间和地thislayerthatbothtemperature点的不同而改变.inversionsandsuperadiabatictemperaturevariationsw

17、ithheightareobserved.TheEarth'satmosphereisamixtureof氮在空气中的含量最多,其中主要来源是腐gasesandaerosols,thelatterbeingthe烂的作物残渣,动物尸体及火山爆发.另namegiventoasystemcomprisedof方面,大气中的氮又为包括植物和海洋生物smallliquidandsolidparticles在内的生物过程的所消耗.distributedintheair.Airisnotaspecificgas:rather,itisamixtureofmanygases.Someofthem,s

18、uchasnitrogen,oxygen,argon,neon,andsoon,mayberegardedaspermanentatmosphericcomponentsthatremaininfixedproportionstothetotalgasvolume.Otherconstituentssuchaswatervapor,carbondioxide,andozonevaryinquantityfromplacetoplaceandformtimetotime.Theprincipalsourcesofnitrogen,themostabundantconstituentofair,a

19、redecayingfromagriculturaldebris,animalmatter,andvolcaniceruption.Ontheothersideoftheledger,nitrogenisremovedfromtheatmospherebybiologicalprocessesinvolvingplantsandsealife.Toalesserextent,lightningandhightemperaturecombustionprocesses闪电及高温燃烧过程将少量氮气转化为氮化物,再由雨雪带出大气.大气中氮的损耗和产生是平衡的.地球生命必不可少的气体一一氧气,在大气中

20、已有三千年左右的时间了.氧气由植物释放出来,即通过植物的光合作用吸收二氧化碳,释放氧气,被人类和动物所吸收,人和动物的呼吸系统同植物的呼吸系统恰恰相反.我们吸进氧气呼出二氧化碳,氧气溶进湖,河和海洋中,来维持海洋生物的生存.在同其他物质发生化学反响或是有机物的腐烂过程也要消耗氧气,比方说钢铁生锈就涉及到氧化过程.convertnitrogengastonitrogencompoundsthatarewashedoutoftheatmospherebyrainorsnow.Thedestructionofnitrogenisintheatmospheresinbalancewithproduct

21、ion.对人类来说,稀少的,多变的气体是非常重要的.水汽,即水的气态,在大气的含量是Oxygen,agascrucialtolifeonEarth,比拟稀少的,而且它的生成和消耗是比拟快hasanaverageresidencetimeinthe的.因此,水汽在大气中存在的平均时间只atmosphereofabout3000years.Itis有11天,水汽是雨雪得源泉,没有水汽我们producedbyvegetationthat,inthe就不能生存.photosyntheticgrowthprocess,takesupcarbondioxideandreleasesoxygen.Itisb

22、yremovedfromtheatmospherehumansandanimals,whoserespiratorysystemsarejustthereverseofthoseoftheplantcommunities.Weinhale众所周知,水汽在大气中的含量是多变的,oxygenandexhalecarbondioxide.在沙漠地带,水汽含量非常低,只占空气总量的很少的一局部,相反,在其他地区,特Oxygendissolvesinthelakes,riversand别是潮湿的热的海面上,或者赤道洋面上,oceans,whereitservestomaintain水汽可以占到大气总量的

23、5%左右.marineorganisms.Itisalsoconsumedintheprocessofdecayoforganicmatterandinchemicalreactionswithmanyothersubstances.Forexample,therustingofsteelinvolvesitsoxidation.Fromthehumanpointofview,thescarce,highlyvariablegasesareofgreat尽管大气中的水汽的含量随时间和地点的不同有很大的变化,但它在整个地球上的总量实际上是不变的.而二氧化碳却不是这样的.在过去的一百年里,这种稀少

24、的但却很重要的气体的含量一直在上升importance.Themassofwatervapor,thatis,H2Oinagaseousstate,intheatmosphereisrelativelysmallandisaddedtoandremovedfromtheatmosphererelativelyfast.As腐烂的植物,土壤中的腐殖物以及燃烧煤,result,theaverageresidencetimeof石油,天然气,等化石燃料都能向大气释放watervaporisonly11days.Watervapor.氧化碳.二氧化碳主要的汇是海洋和植物,isthesourceofra

25、inandsnow,without植物需要二氧化碳进行光合作用,whichwecouldnotsurvive.Fromcommonexperiencesitiswellknownthatthewatervaporcontentofairvariesagreatdeal.Inadesertregiontheconcentrationofwatervaporcanbesolowastorepresentonlyatinyfractionoftheairvolume.Attheother二十世纪八十年代中期,大气化学家就森林的燃烧,砍伐对大气中二氧化碳产生的影响进行了争论.海洋吸收了大量的二氧化碳,

26、大约占化石燃料燃烧释放的二氧化碳总量的一半.人们预测,往后的几十年,这局部吸收量将会逐步减少,而释放的二氧化碳的总extreme,inhot,moistairnearsealevel,sayoveranequatorialocean,watervapormayaccountforasmuchasperhaps5percentoftheairvolume.Therearelargevariationsofatmosphericwatervaporfromplacetoplaceandfromtimetotime,butthetotalquantityovertheentireEarthisvir

27、tuallyconstant.Thesamecannotbesaidaboutcarbondioxide(co2).Theconcentrationofthissparsebutimportantgashasbeenincreasingforthelasthundredyearsorso.Carbondioxideisaddedtotheatmospherebythedecayofplantmaterialandhumusinthesoil,andby量那么会增加,这种情况至少会延续到下个世纪初.二十世纪八十年代,大气中的二氧化碳,每年以空气的百万分之一的速度增加.但是,据预测,这种增加速度在

28、未来的几十年中还要更快一些.1983年,其含量平均为空气的百万分之340.另一种重要多变的气体臭氧O3,多存在于高层大气中,但在交通拥挤,有许多工厂或是充足阳光照射的地区也有臭氧存在.像洛杉矶这样的城市,O3最多时可超过0.1ppm.大气中臭氧的含量大多在1.010Ppm之间.theburningoffossilfuels:coal,oil,andgas.Theprincipalsinksofco2aretheoceansandplantlifethatusesco2in它们随高度,季节,时间,天气状况的不同photosynthesis.而不同.高层大气中的O3层是由光化学反应造成的.臭氧层之

29、所以重要,是由于它通Inthemiddle1980s,atmospheric过吸收上层大气紫外线辐射,从而减少紫外chemistswerestilldebatingaboutthe线到达地面的总量,接受紫外线照射的时间effectsonatmosphericco2ofburning,越长,就越容易造成严重的灼伤,从而增加harvestingandclearingofforests.The皮肤癌的危险.oceanstakeuplargeamountsofco2,abouthalftheamountreleasedbyfossilfuelcombustion.Itisexpectedthatthi

30、sfractionwilldiminishwiththepassingdecadeswhereasthetotalmass生物学家指出,紫外线过度的增加还会影响ofco2releasedwillincrease,atleast生物圈中的其它组成成分.throughtheearlypartofthenextcentury.Duringthe1980satmosphericco2was有些气体,如果浓度过高,对人,动物及植accumulatingatarateofabout1part物生命可能有害,比方,O3浓度过高会对生permillion(ppm)ofairperyear,butitis物有机

31、体造成危害.虽然这种情况不常发生.expectedtoincreasemorerapidlyin但洛杉矶这样污染严重的城市,有时接近地decadestocome.In1983itaveraged面的O3含量变得足以毁坏某些植物外表的about340ppmofair.叶片.Ozone(o3),anotherimportant,highlyvariablegas,occursmostlyatupperaltitudes,butitisalsofoundinurbanlocalitieshavingagreatdealofindustry人类活动将大量具有潜在危险的气体带入大andautomotiv

32、etrafficandagenerous气.大型锅炉,工厂,炼油厂和发动机,特supplyofsunshine.IncitiessuchasLos别是汽油发动机排放出空气污染物.Angeles,ozoneconcentrationmaybemorethan0.1ppminextremecases.Mostatmosphericozoneconcentrationsoftenexceed1.0ppmandmaybelargeas10ppm.Theyvarygreatlywithlatitude,season,timeofday,andweatherpatterns.Thehigh-altitud

33、eozonelayer所有这些场所以及其它特别类似场所：燃烧煤,石油,汽油,煤油等化石燃料,在燃烧过程中,它们向空气中排放气体或烟尘颗粒,这些颗粒经过相当长的时间又和空气中其他成分发生反响,形成有毒的化合物.ismaintainedbyphotochemicalreactions.Theozonelayerisimportant分布最广泛的,而且潜在危险最大的气体污because,byabsorbingUVradiationin染物是一氧化碳,二氧化硫,氧化氮和碳氢theupperatmosphere,itreducesthe化合物.这些化合物最终来源于蒸发的汽油amountreachingt

34、hesurfaceofthe和其他石油产物.Earth,exposuretoincreaseddosesofultravioletrayswouldcausemoreseveresunburnsandincreasetheriskofskincancers.BiologistsindicatethatasubstantialincreaseinUVradiationcouldalsoaffectothercomponentsofthebiosphere.Certaingages,iftheyexistinsufficientlyhighconcentrations,canbetoxictope

35、ople,animalandplantlife.Forexample,whenozoneoccursinhighconcentrations,itistoxictobiologicalorganisms.Thisdoesnothappenoften,butinheavilypollutedlocalitiessuchasLosAngeles,ozonenearthegroundsometimesissufficientlyabundanttocauseleafdamagetocertainplantspecies.Verylargequantitiesofpotentiallyhazardou

36、sgasesareintroducedintotheatmosphereasaresultofhumanactivities.Airpollutantsareemittedfromfurnaces,factories,refineries,andengines,particularlyautomobileengines.Allthesethingsandotherslikethemburnfossilfuels:coal,oil,gasoline,andkerosene.Intheprocesstheyemitgasesandsmokeparticlesthatmayspendagreatde

37、aloftimeintheatmospherereactingwithothersubstancesandcausingtheformationoftoxiccompounds.Themostwidespreadandpotentiallyhazardousgaseouspollutantsarecarbonmonoxide,sulfurdioxide,nitrogenoxide,andhydrocarbons.Thelastofthesecompoundscomesfromvaporizedgasolineandotherpetroleumproducts.第一课大气的结构和组成UnitTw

38、o:Frontogenesisandfrontalcharacteristics第二课锋生和锋的特征Thefirstrealadvanceinourdetailedunderstandingofmid-latitudeweathervariationswasmadewiththediscoverthatmanyoftheday-to-daychangesareassociatedwiththeformationandmovementofboundaries,orfronts,betweendifferentairmasses.Observationsofthetemperature,windd

39、irections,humidityandotherphysicalphenomenaduringunsettledperiodsshowedthatdiscontinuitiesoftenpersistbetweenimpingingairmassesofdifferingcharacteristics.Theterm“front,forthesesurfacesofairmassconflict,wasalogicaloneproposedduringtheFirstWorldWarbyagroupofmeteorologistsworkingin锋生随着许多与不同气团之间的边界锋面形成与

40、运动相联系的逐日变化被揭露之后,我们对中纬度天气变化的详细了解才取得了首次真正意义上的进步.在这些问题未解决之前,对温度,风向,湿度和其他去理现象的观测说明具启不同特征而乂紧密接触的气团之间经常存在不连续性.这些/、同气团之间交会的面一一锋面,是第一次世界大战时期由在挪威工作的一批气象学家提出的一个逻辑词汇.他们的想法在大多数天气分析和预报中,尤其是在中,高纬Norway,andtheirideasarestillanintegralpartofmostweatheranalysisandforecastingparticularlyinmiddleandhighlatitudes.1.Fro

41、ntalwavesItwasobservedthatthetypicalgeometryoftheairmassinterface,orfront,resemblesawavefrom.Similarwavepatternsare,infact,foundtooccurontheinterfacebetweenmanydifferentmedia,forexample,wavesonseasurface,ripplesonbeachsand,aeoliansanddunes,etc.Unlikethesewaveforms,however,thefrontalwavesintheatmosph

42、erearecommonlyunstable:thatis,theysuddenlyoriginate,increaseinsize,andthengraduallydissipate.Numericalmodelcalculationsshowthat,inmiddlelatitudeswavesinabaroclinic度仍是一个完整的局部.1.锋波我们观测到气团的交界面即锋面是一种典型的几何状,类似一种波的形成.实际上,相似的波形也出现在许多不同介质的交界面,例如,海洋外表的波,沙滩上的涟漪和风吹成的沙丘等等.然而,并不象这些波形,大气中的锋面通常是不稳定的,也就是说,它们忽然生成,发展

43、,然后逐渐消散.数值模式计算说明,在中纬度斜压大气中,如果锋波波长超过几千公里,那些锋波是不稳定的.锋波的波长通常是1500-3000km.atmosphereareunstableiftheirwavelengthexceedsafewthousand因此,最初引起兴趣大气波动系统和其他介kilometers.Frontalwavecyclonesaretypically1500-3000kminwavelength.质交界面所形成的波类似的东西不适宜作为Theinitiallyattractiveanalogybetween进一步解释锋面的根底.尤其是对流层上层的环流对锋波的开展和壮大才是

44、引起至关重atmosphericwavesystemsandwaves要的适当条件就这一点,我们将在以下的formedoninterfaceofothermediais,论证中给出.therefore,aninsufficient-basisonwhichtodevelopexplanationsoffrontalwaves.Inparticular,thecirculationoftheuppertroposphereplaysakeyroleinprovidingappropriateconditionsfortheirdevelopmentandgrowth,aswill锋波低压besh

45、ownbelow.低压又称低压区域气旋,低压又称低压2.Thefrontalwavedepression区域气旋,是一个有着或多或少闭合等压线的相对低压区.他们直彳5覆盖100-3000Km,通常用4-7天的生命史.Adepression(alsotermedaloworcyclone)isanareaofrelativelylow具有这些特征的系统在每日的天气图上很突pressure,withamoreorlesscircular出,被称为具有天气尺度的特点.至少在中isobaricpattern.Itcoversanarea纬度地区,低压通常是与相对的气团之间的100-3000kmindi

46、ameterandusuallyhasalife-spanof4-7days.辐合联系在一起的.Systemswiththesecharacteristics,whichareprominentondailyweathermapsarereferredtoassynopticscalefeatures.Thedepression,inmid-latitudesatleast,isusuallyassociatedwithacontrastingairmasses.convergenceof这些气团之间的交界面开展成波的形式,它的峰位于低压区的中央.锋波围住了波前变性的冷空气和波后新鲜冷空气之间

47、的一团暖空气.锋波的形成也造成了原始空气团不连续的两局部之间的差异.Theinterfacebetweentheseairmassdevelopsintoawaveformwithitsapexlocatedatthecentreofthelow-pressurearea.Thewaveenclosesamassofwarmairbetweenmodifiedcoldairinfrontandfreshcoldairintherear.Theformationofthewavealsocreatesa每一局部在冷暖空气之间具有明显的边界,每一局部邻近区域的天气特征十分不同.锋面的这两局部由名为

48、暖锋-波的前边缘和冷锋-波后冷空气来区分.distinctionbetweenthetwosectionsoftheoriginalairmassdiscontinuityfor,althougheachsectionstillmarkstheboundarybetweencoldandwarmair,theweathercharacteristicsfoundintheneighborhoodofeachsectionareverydifferent.Thetwosectionsofthefrontalsurfacearedistinguishedbythenameswarmfrontfor

49、theleadingedgeofthewaveandcoldfrontforthatofthecoldairtotherear.Thedepressionusuallyachievesitsmaximumintensity12-24hoursafterthebeginningofocclusion.FrontalcharacteristicsTheactivityofafrontintermsofweatherdependsupontheverticalmotionintheairmasses.Iftheairinthewarmsectorisrisingrelativetothefronta

50、lzonethefrontsareusuallyveryactiveandaretermedana-fronts.Whereassinkingofthewarmairrelative低压通常在开始锢囚后12-24小时强度到达最大.锋的特征从天气方面来说,锋的活泼程度依靠空气团的垂直运动.如果暖区中的空气相对锋区是上升的,那么,锋通常是十分活泼的,被称为上滑锋.相反,暖空气相对于冷空气团卜沉的,那么会产生不活泼的下滑锋.暖锋暖锋是指锋波中暖区的前边缘.这儿所提的锋区是一个十分稍微的坡度,量级在1/2°-1之间,所以,与锋的上部相联系的云系在地面锋到来之前的12小时甚至更早就预示了锋的临

51、近.tothecoldairmassesgivesrisetolessinactivekata-fronts.1.ThewarmfrontThewarmfrontrepresentstheleadingedgeofthewarmsectorinthewave.Thefrontalzoneherehasaverygentleslope,oftheorder1/2-1°,sothatthecloudsystemsassociatedwiththeupperportionofthefrontheralditsapproachsome12hoursormorebeforethearrival

52、ofthesurfacefront.Theana-warmfront,withrisingwarmair,hasmulti-layeredcloudwhichsteadilythickensandlowerstowardsthesurfacepositionofthefront.Thefirstcloudsarethin,wispycirrus,followedbysheetsofcirrusandcirrostratusandaltostratus.随着暖空气上升的上滑暖锋有多层云系,这些云系稳定的增厚,并向锋的地面位置下降.最开始的云石薄而缥缈的卷云,紧接着是成片的卷层云和高层云.当高层云

53、加厚开始下毛毛雨或者开始下大雨时,太阳就开始昏暗了.经常会伸展到对流层大局部地区而且伴随着连续性降水发生的云系通常叫做雨层云.当下降的雨水穿过冷空气时经过蒸发,迅速的到达饱和,也可能形成一片片的层云.下滑锋中的下沉暖空气极大限制了中高层云的开展.锋面云系主要是层积云,由于在冷暖空气团中下沉逆温的作用,云系的厚度受Thesunisobscuredasthealtostratuslayerthickens,anddrizzleorrainbeginstofall.Thecloudoftenextendsthroughmostofthetroposphereandwithcontinuousprec

54、ipitationoccurringisgenerallydesignatedasnimbostratus.Patchesofstratusmayalsoforminthecoldairasrainfallingthroughthisairundergoesevaporationandquicklysaturatesit.Thedescendingwarmairofthekata-warmfrontgreatlyrestrictsthedevelopmentofmedium-andhigh-levelclouds.Thefrontalcloudismainlystratocumulus,wit

55、halimiteddepthasaresultofthesubsidenceinversionsinbothairmasses.Precipitationisusuallylightrainordrizzleformedbycoalescencesincethefreezingleveltendstobeabovetheinversionlayer,particularlyinsummer.到了限制.降水通常是由雨滴的合并作用引起的小雨或毛毛雨,由于冻结高度比拟多地倾向于在逆温层之上,尤其是在夏季.暖锋过境时,风向发生转变,温度升高,气压卜.降.暖空气中,降水是间歇性的或者无雨,薄的片状层积云也可能断裂开来.由于大多数锋在对流层的所有层次上或者说贯穿锋的整个长度并不都是上滑锋或者下滑锋,所以要预报与暖锋相联系的雨带的范围是很复杂的.由于这个原因,雷达波越来越多的用来直接测定雨带的精确范围和雨量强度的差异.Inthepassageofthewarmfrontthewindveers,thetemperaturerisesandthefallofpressureischecked.Therainbecomesinter