气象科技英语翻译

Likeafishintheocean,manisconfinedtoaveryshallowlayerofatmosphere.ThegaseousenvelopeoftheEarthisphysicallyinhomogeneousinboththeverticalandhorizontaldirections,althoughthehorizontalinhomogeneityismuchlessmarkedthantheverticalinhomogeneity.Variouscriteriahavebeendevisedfordividingtheatmosphereintolayers.Thisdivisioncanbebasedonthenatureoftheverticaltemperatureprofile,onthegaseouscompositionoftheairatdifferent altitudes, and the effect of theatmosphereonaircraftatdifferentaltitudes,etc.Thedivisionbasedonthevariationoftheairtemperature with altitude is used mostcommonlyinthemeteorologicalliterature.AccordingtoapublicationoftheagrologicalcommissionoftheWorldMeteorologicalOrganization(WMO)in1961,theEarth’satmosphere,isdividedintofivemainlayers:thetroposphere,thestratosphere,themesosphere,thethermosphereandtheexosphere.Theselayersareboundedbyfourthintransitionregions:thetropospause,thestratospause,themesospause,thethermospause.The troposphere is the lower layer of theatmospherebetweentheEarth’ssurfaceandthe tropopause.Thetemperaturedropswithincreasingheightinthetroposphere,atameanrateof6.5℃perkilometer(lapserate).Theupperboundaryofthetroposphereliesataheightofapproximately8to12kminthepolarandtropospherecontainsabout75%ofthetotalmassofatmosphericair,whileinthetropicsitcontains about 90%. The tropoause is anintermediatelayerinwhicheitheratemperaturein version or an isothermal temperaturedistributionisobserved.Thestratosphereistheatmosphericlayerabove

就像海洋中的鱼一样,人类被局限在大气中一个格外狭窄的层次之内。虽然地球的大气层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。但它确确实凿在水平和垂直两个方向上都是不均匀的。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，有的依据空气在不同高度上的大气成分，有的依据大气在不同高度上对飞机的影响来划分等等。依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。依据1961年世界气象组织大气学委会公布的5个主要层次：对流层，平流层，中层，热成层以及外逸层。这些层次之间邻接着4个浅薄的过渡区域：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6.5℃/km的递减率随高度的增加而降低，其上边界在极地和中纬度地区大约位于8—12Km的高16-18Km的高度。在极地和中纬度，对流层包含了大气层中空气质量的75%左右，然而在热带地区，包含了大约90%。对流层顶是一个中间层次，据观测，其温度是逆温或是等温分布。the troposphere. In the stratosphere thetemperature either increases with height orremainsnearlyconstant.Inthelowerpartofthestratosphere(uptoapproximately20kmabovethe Earth’s surface) the temperature ispracticallyconstant(about－56℃).Whilefurther up the temperature increases withaltitudeatarateofabout1 ℃/kmatheightsof20to30kmandabout2.8℃/kmataltitudesfrom32to47km.Underthestandardconditionsthetemperatureatthe47kmlevelisnormally-2.5℃.ThisincreaseintemperaturewithheightisduetotheabsorptionofUVsolarradiationbyozonemolecules.Itshouldbenotedthatabout99%ofthetotalmassofatmosphericairisconcentrated in the troposphere andstratosphere,whichextenduptoanlatitudeof30or35km.Thestratopauseisanintermediatelayer between the stratosphere and themesosphere(inthealtituderegionfrom47to52km),inwhichthetemperatureremainsconstantatabout0℃.The thermosphere is the atmospheric layerabovethemesopause.Thetemperatureinthislayer increases with increasing altitude,reachingabout2023℃atabout450km,themeanheightoftheupperboundaryof thethermosphere.ThetemperatureincreaseinthislayerismainlycausedbytheabsorptionofUVsolarradiationbyoxygenmolecules,whichdissociateasaresultofthis.Theexosphereisthefurthestoutandtheleaststudiedpartoftheupperatmosphere. Itislocatedabove450kmaltitude.Theairdensityintheexosphereissolowthatatomsandmoleculescanescapefromitintointerplanetaryspace.Finally,alongwiththeabovedivisionoftheatmosphere,wewillalsomakeuseofadivision

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-56℃。然而再向上，大约20Km~30Km的高度，温度随高度以1℃/km的速度增30Km~47Km2.8℃/km47Km高度上正常的温度是-2.5摄氏度。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取的原因。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，始终伸展到30-35Km的高度上。平〔大约从47-52Km的高度上0摄氏度。热成层是位于中层顶上的大气层，其温度随高度的增加而增加，到热成层上边界的平均高度，即大约在450Km高度上，到达大约2023摄氏度。该层中温度的增加主要是由于外逸层是最远的，也是争论最少的大气的上450Km的高度上。外逸层中空气的密度格外小，以致原子和分子都能逃逸到星际空间。basedontheextentofatmosphericinteractionwith the Earth’ssurface.Accordingtothisprincipe,theatmosphereisusuallydividedintoasocalledboundarylayer(sometimesalsocalled the friction layer) and the freeatmosphere. The atmospheric boundarylayer(up to 1 or 1.5 km) is influencedconsiderablybytheEarth’ssurfaceandbyeddy-viscosityforces.Atthesametime,wecanneglect,asafirstapproximation,theinfluenceofeddy-viscosityforcesinthefreeatmosphere.Ofalltheaboveatmosphericlayers,onlythetroposphere(especiallyitsboundarylayer)ischaracterizedbyamarkedinstabilityoftheverticaldistributionofthemeteorologicalparameters.Itisinthislayerthatbothtemperatureinversionsandsuperadiabatictemperaturevariationswithheightareobserved.TheEarth’satmosphereisamixtureofgasesandaerosols,thelatterbeingthenamegiventoasystemcomprisedofsmallliquidandsolidparticlesdistributedintheair.Airisnotaspecificgas:rather,itisamixtureofmanygases.Someofthem,suchasnitrogen,oxygen, argon, neon, and so on, may beregarded as permanent atmosphericcomponentsthatremaininfixedproportionstothetotalgasvolume.Otherconstituentssuchaswatervapor,carbondioxide,andozonevaryinquantityfromplacetoplaceandformtimetotime.Theprincipalsourcesofnitrogen,themostabundantconstituentofair,aredecayingfromagriculturaldebris,animalmatter,andvolcaniceruption.Ontheothersideoftheledger,nitrogenisremovedfromtheatmospherebybiologicalprocessesinvolvingplantsandsealife.

最终，除了以上对大气的划分以外，我们也可以依据大气和地面的相互作用得到另一种分法。依据此原则，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无视涡度粘滞力的影响。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。地球大气是气体和气溶胶的混合物，所谓的气溶胶指的是由分布在空气中的微小的液体和固体颗粒组成的系统。空气不是一种特别的气体，而是由很多气体混合成的。其中一些气体，如，氮，氧，氩，氖等，作为空气的永久组成成分，总是以固水汽，二氧化碳和臭氧的含量是随时间和地点的不同而转变。氮在空气中的含量最多，其中主要来源是腐烂的作物残渣，动物尸体及火山爆发。另一方面，大气中的氮又为包括植物和海洋生物在内的生物过程的所消耗。To a lesser extent, lightning and hightemperature combustion processes convertnitrogengastonitrogencompoundsthatarewashedoutoftheatmospherebyrainorsnow.The destruction of nitrogen is in theatmospheresinbalancewithproduction.Oxygen,agascrucialtolifeonEarth,hasanaverageresidencetimeintheatmosphereofabout3000years.Itisproducedbyvegetationthat, in the photosynthetic growth process,takesupcarbondioxideandreleasesoxygen.Itisremovedfromtheatmospherebyhumansandanimals,whoserespiratorysystemsarejustthereverseofthoseoftheplantcommunities.Weinhaleoxygenandexhalecarbondioxide.Oxygendissolvesinthelakes,riversandoceans,whereitservestomaintainmarineorganisms.Itisalsoconsumedintheprocessofdecayoforganicmatterandinchemicalreactionswithmanyothersubstances.Forexample,therustingofsteelinvolvesitsoxidation.Fromthehumanpointofview,thescarce,highlyvariablegasesareofgreatimportance.Themassofwatervapor,thatis,H2Oinagaseousstate,intheatmosphereisrelativelysmallandisaddedtoandremovedfromtheatmosphererelativelyfast. As a result ,theaverageresidencetimeofwatervaporisonly11days.Watervaporisthesourceofrainandsnow,withoutwhichwecouldnotsurvive.Fromcommonexperiencesitiswellknownthatthewatervaporcontentofairvariesagreatdeal.Inadesertregiontheconcentrationofwatervaporcanbesolowastorepresentonlyatinyfractionoftheairvolume.Attheotherextreme,inhot,moistairnearsealevel,sayoveranequatorialocean,watervapormayaccountforasmuchasperhaps5percentoftheairvolume.

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。地球生命必不行少的气体——氧气，在大气中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取二氧化碳，释放氧气，被人类和动物所吸取，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。对人类来说，稀有的，多变的气体是格外重要的。水汽，即水的气态，在大气的含量是比较稀有的，而且它的生成和消耗是比较快的。因此，水汽在大气中存在的平均时间只11天，水汽是雨雪得源泉，没有水汽我们就不能生存。众所周知，水汽在大气中的含量是多变的，在沙漠地带，水汽含量格外低，只占空气总量的很少的一局部，相反，在其他地区，特别是潮湿的热的海面上，或者赤道洋面上，5%左右。Therearelargevariationsofatmosphericwatervaporfromplacetoplaceandfromtimetotime,butthetotalquantityovertheentireEarthisvirtuallyconstant.Thesamecannotbesaidaboutcarbondioxide(co2).Theconcentrationof this sparse but important gas has beenincreasingforthelasthundredyearsorso.Carbondioxideisaddedtotheatmospherebythedecayofplantmaterialandhumusinthesoil,andbytheburningoffossilfuels:coal,oil,andgas.Theprincipalsinksofco2aretheoceansandplantlifethatusesco2inphotosynthesis.Inthemiddle1980s,atmosphericchemistswerestilldebatingabouttheeffectsonatmosphericco2 of burning,harvestingand clearing offorests.Theoceanstakeuplargeamountsofco2,abouthalftheamountreleasedbyfossilfuelcombustion.Itisexpectedthatthisfractionwilldiminishwiththepassingdecadeswhereasthetotalmassofco2releasedwillincrease,atleastthroughtheearlypartofthenextcentury.During the 1980s atmospheric co2 wasaccumulatingatarateofabout1partpermillion(ppm)ofairperyear,butitisexpectedto increase more rapidly in decades tocome.In1983itaveragedabout340ppmofair.Ozone(o3),anotherimportant,highlyvariablegas,occursmostlyatupperaltitudes,butitisalsofoundinurbanlocalitieshavingagreatdealofindustryandautomotivetrafficandageneroussupplyofsunshine.IncitiessuchasLosAngeles,ozoneconcentrationmaybemorethan0.1ppminextremecases.Mostatmosphericozoneconcentrationsoftenexceed1.0ppmandmaybelargeas10ppm.Theyvarygreatlywithlatitude,season,timeofday,andweatherpatterns.Thehigh-altitude

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在过去的一百年里，这种稀有的但却很重要的气体的含量始终在上升腐烂的植物，土壤中的腐殖物以及燃烧煤，石油，自然气，等化石燃料都能向大气释放植物需要二氧化碳进展光合作用，二十世纪八十年月中期，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展了争论。海洋吸取了大量的二氧化碳，大约占化石燃料燃烧释放的二氧化碳总量的一半。人们推测，往后的几十年，这局部吸取量将会逐步削减，而释放的二氧化碳的总量则会增加，这种状况至少会连续到下个世纪初。二十世纪八十年月，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，据推测，这种增加速度在将来的几十年中还要更快一些。1983年，其含量平均为空气的340。另一种重要多变的气体 臭〔O3多存在于高层大气中，但在交通拥挤，有很多工厂或是充分阳光照耀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1.0——10ppm之间。它们随高度，季节，时间，天气状况的不同而不同。高层大气中的O3层是由光化学反ozonelayerismaintainedbyphotochemicalreactions.Theozonelayerisimportantbecause,by absorbing UV radiation in the upperatmosphere,itreducestheamountreachingthesurfaceoftheEarth,exposuretoincreaseddosesofultravioletrayswouldcausemoreseveresunburnsandincreasetheriskofskincancers.BiologistsindicatethatasubstantialincreaseinUVradiationcouldalsoaffectothercomponentsofthebiosphere.Certaingages,iftheyexistinsufficientlyhighconcentrations,canbetoxictopeople,animalandplantlife.Forexample,whenozoneoccursinhighconcentrations,itistoxictobiologicalorganisms.Thisdoesnothappenoften,butinheavilypollutedlocalitiessuchasLosAngeles,ozonenearthegroundsometimesissufficientlyabundanttocauseleafdamagetocertainplantspecies.Verylargequantitiesofpotentiallyhazardousgasesareintroducedintotheatmosphereasaresultofhumanactivities.Airpollutantsareemittedfromfurnaces,factories,refineries,andengines,particularlyautomobileengines.Allthesethingsandotherslikethemburnfossilfuels:coal,oil,gasoline,andkerosene.Intheprocesstheyemitgasesandsmokeparticlesthatmayspendagreatdealoftimeintheatmospherereactingwithothersubstancesandcausingtheformationoftoxiccompounds.Themostwidespreadandpotentiallyhazardousgaseouspollutantsarecarbonmonoxide,sulfurdioxide,nitrogenoxide,andhydrocarbons.Thelastofthesecompoundscomesfromvaporizedgasolineandotherpetroleumproducts.

应造成的。臭氧层之所以重要，是由于它通过吸取上层大气紫外线辐射，从而削减紫外线到达地面的总量，承受紫外线照耀的时间越长，就越简洁造成严峻的灼伤，从而增加皮肤癌的危急。生物学家指出，紫外线过度的增加还会影响生物圈中的其它组成成分。有些气体，假设浓度过高，对人，动物及植物生命可能有害，比方，O3浓度过高会对生但洛杉矶这样污染严峻的城市，有时接近地面的O3含量变得足以毁坏某些植物外表的叶片。人类活动将大量具有潜在危急的气体带入大气。大型锅炉，工厂，炼油厂和发动机，特别是汽油发动机排放出空气污染物。全部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。分布最广泛的，而且潜在危急最大的气体污染物是一氧化碳，二氧化硫，氧化氮和碳氢化合物。这些化合物最终来源于蒸发的汽油和其他石油产物。第一课大气的构造和组成UnitTwo:Frontogenesisandfrontalcharacteristics其次课锋生和锋的特征The first real advance in our detailedunderstanding of mid-latitude weathervariationswasmadewiththediscoverthatmanyoftheday-to-daychangesareassociatedwith the formation and movement ofboundaries, or fronts, between different airmasses.Observationsofthetemperature,winddirections,humidityandotherphysicalphenomenaduringunsettledperiodsshowedthatdiscontinuitiesoftenpersistbetweenimpingingairmassesofdifferingcharacteristics.

锋生随着很多与不同气团之间的边界(锋面)形成与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具体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有不同特征而又严密接触的气团之间常常存在不连续性。Theterm“front”,forthesesurfacess团之间交会的面——锋面，是第conflict,wasalogicaloneproposedduringtheFirstWorldWarbyagroupofmeteorologistsworkinginNorway,andtheirideasarestillanintegral part of most weather analysis andforecasting particularly in middle and highlatitudes.1. FrontalwavesItwasobservedthatthetypicalgeometryoftheairmassinterface,orfront,resemblesawavefrom.Similarwavepatternsare,infact,foundto occur on the interface between manydifferentmedia,forexample,wavesonseasurface,ripplesonbeachsand,aeoliansanddunes,etc.Unlikethesewaveforms,however,thefrontalwavesintheatmospherearecommonlyunstable:thatis,theysuddenlyoriginate,increaseinsize,andthengraduallydissipate.Numericalmodelcalculationsshowthat,inmiddlelatitudeswavesinabaroclinicatmosphereareunstableiftheirwavelengthexceedsafewthousandkilometers.Frontalwavecyclonesaretypically1500-3000kmin

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规律词汇。他们的想法在大多数天气分析和预报中，尤其是在中，高纬度仍是一个完整的局部。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，类似于一种波的形成。实际上，相像的波形也消灭在很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，它们突然生成，进展，然后渐渐消散。数值模式计算说明，在中纬度斜压大气中，假设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1500-3000km。wavelength.Theinitiallyattractiveanalogybetweenatmosphericwavesystemsandwavesformedoninterfaceofothermediais,therefore,aninsufficient-basisonwhichtodevelopexplanationsoffrontalwaves.Inparticular,thecirculationoftheuppertroposphereplaysakeyroleinprovidingappropriateconditionsfortheirdevelopmentandgrowth,aswillbeshownbelow.ThefrontalwavedepressionAdepression(alsotermedaloworcyclone)isanareaofrelativelylowpressure,withamoreorlesscircularisobaricpattern.Itcoversanarea100-3000kmindiameterandusuallyhasalife-spanof4-7days.Systemswiththesecharacteristics,whichareprominentondailyweathermapsarereferredtoassynopticscalefeatures.Thedepression,inmid-latitudesatleast,isusuallyassociatedwithaconvergenceofcontrastingairmasses.Theinterfacebetweentheseair massdevelopsintoawaveformwithitsapexlocatedatthecentre of the low-pressure area. The waveenclosesamassofwarmairbetweenmodifiedcoldairinfrontandfreshcoldairintherear.The formation of the wave also creates adistinctionbetweenthetwosectionsoftheoriginalairmassdiscontinuityfor,althougheachsectionstillmarkstheboundarybetween cold and warm air, the weathercharacteristicsfoundintheneighborhoodofeach section are very different. The twosectionsofthefrontalsurfacearedistinguishedbythenameswarmfrontfortheleadingedgeofthewaveandcoldfrontforthatofthecoldairtotherear.

因此，最初引起兴趣大气波动系统和其他介质交界面所形成的波类似的东西不适宜作为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进展和壮大才是引起至关重〔就这一点论证中给出。锋波低压低压〔又称低压区域气旋，低压〔又称低压区域气旋的相对低压区。他们直径掩盖100-3000Km，4-7天的生命史。具有这些特征的系统在每日的天气图上很突出，被称为具有天气尺度的特点。至少在中纬度地区，低压通常是与相对的气团之间的辐合联系在一起的。这些气团之间的交界面进展成波的形式，它的峰位于低压区的中心。锋波围住了波前变性的冷空气和波后颖冷空气之间的一团暖空气。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。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格外不同。锋面的这两局部由名为暖锋波的前边缘和冷锋 波后冷空气来区分。Thedepressionusuallyachievesitsmaximumintensity12-24hoursafterthebeginningofocclusion.FrontalcharacteristicsTheactivityofafrontintermsofweatherdependsupontheverticalmotionintheairmasses.Iftheairinthewarmsectorisrisingrelativetothefrontalzonethefrontsareusuallyveryactiveandaretermedana-fronts.Whereassinkingofthewarmairrelativetothecoldairmassesgivesrisetolessinactivekata-fronts.ThewarmfrontThewarmfrontrepresentstheleadingedgeofthewarmsectorinthewave.Thefrontalzoneherehasaverygentleslope,oftheorder1/2°-1°,sothatthecloudsystemsassociatedwiththeupperportionofthefrontheralditsapproachsome12hoursormorebeforethearrivalofthesurfacefront.Theana-warmfront,withrisingwarmair,hasmulti-layeredcloudwhichsteadilythickensandlowerstowardsthesurfacepositionofthefront.Thefirstcloudsarethin,wispycirrus,followedby sheets of cirrus and cirrostratus andaltostratus.Thesunisobscuredasthealtostratuslayerthickens,anddrizzleorrainbeginstofall.Thecloud often extends through most of thetroposphereandwithcontinuousprecipitationoccurring is generally designated asnimbostratus.Patchesofstratusmayalsoforminthecoldairasrainfallingthroughthisairundergoesevaporationandquicklysaturatesit.Thedescendingwarmairofthekata-warmfrontgreatlyrestrictsthedevelopmentofmedium-andhigh-levelclouds.Thefrontalcloudismainlystratocumulus,withalimiteddepthasaresultofthesubsidenceinversionsin

低压通常在开头锢囚后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。假设暖区中的空气相对锋区是上升的，那么，锋通常是格外活泼的，被称为上滑锋。相反，暖空气相对于冷空气团下沉的，则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格外稍微的坡度，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接近。随着暖空气上升的上滑暖锋有多层云系，这最开头的云石薄而缥缈的卷云，紧接着是成片的卷层云和高层云。当高层云加厚开头下毛毛雨或者开头下大雨时，太阳就开头昏暗了。常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，快速的到达饱和，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进展。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bothairmasses.Precipitationisusuallylightrainordrizzleformedbycoalescencesincethefreezingleveltends to be above the inversion layer ,particularlyinsummer.Inthepassageofthewarmfrontthewindveers,thetemperaturerisesandthefallofpressureischecked.Therainbecomesintermittentorceasesinthewarmairandthethinstratocumuluscloudsheetmaybreakup.Forecastingtheextentofrainbeltsassociatedwiththewarmfrontiscomplicatedbythefactthat most fronts are not ana-or kata-frontsthroughouttheirlengthorevenatalllevelsinthetroposphere.Forthisreason,radarisbeingusedincreasinglytodeterminebydirectmeansthepreciseextentofrainbeltsandtodetectdifferencesinrainfallintensity.Suchstudieshaveshownthatmostoftheproductionanddistributionofprecipitationiscontrolledbyabroadairflowafewhundredkilometresacrossandseveralkilometresdeep,whichflowsparalleltoandaheadofthesurfacecoldfront.Justaheadofthecoldfronttheflowoccursasalow-leveljetwithwindsupto25-30m/satabout1kmabovethesurface.Theair,whichiswarmandmoist,risesoverthewarmfrontandturnssoutheastwardaheadofitasitmergeswiththemidtroposphericflow.Thisflowhasbeentermeda“conveyorbelt”(forlarge-scaleheatandmomentumtransferinmid-latitudes). Broad-scaleconvective(potential)instabilityisgeneratedbythe over-runningof this low-levelflow bypotential colder, drier air in the middletroposphere.

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，由于冻结高度比较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，温度上升，气压下降。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全部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简单的。由于这个缘由，雷达波越来越多的用来直接测定雨带的准确范围和雨量强度的差异。这些争论说明，大多数降水的产生和分布是由宽达几百公里，厚达几公里的宽阔气流所掌握，这股气流平行于地面冷锋，位于地面冷锋之前1Km之上随着风速增大到25-35m/s，这股气流形成了低空急流。暖湿空气在暖锋上上升，在暖锋前转〔由于在中纬度传输大尺度的热量和动量潜在不稳定是由与对流层中部潜在的干冷空气在低层气流上爬越作用而造成的。Instabilityisreleasedmainlyinsmall-scale不稳定主要在形成的对流群---即中尺度降convectioncellsthatareorganizedintoclusters,水区的小尺度对流单体中释放。这些中尺度knownasmeso-scaleprecipitation50---100Kmareas(MPAs).TheseMPAsarefurtherarranged宽。inbands,50-100kmwide.Aheadofthewarmfront,thebandsarebroadly在暖锋前，这条带状区域横向平行于传送带paralleltotheairflowintherisingsectionof上升区中的气流，然而，在暖区中，则平行theconveyorbelt,whereasinthewarnsector于冷锋和低空急流。在某些状况下，对流单theyparallelthecoldfrontandthelow-level体和对流群在暖区中和暖锋前进一步排列成jet.Insomecases,cellsandclustersarefurther带状。arrangedinbandswithinthewarmsectorandaheadofthewarmfront.Precipitationfromwarmfrontrainbandsofteninvolves“seeding”byiceparticlesfallingfrom 暖锋雨带的降水常常随着来自上层云层“散theuppercloudslayers.Ithasbeenestimated 布的冰粒据估量大约20--35%的降水来that20%-35%oftheprecipitationoriginatesin 源于“催化剂”区，其余的来源于低层云系。the“seeder”zoneandtheremainderinthelowerclouds.Someofthecellsandclustersareundoubtedly一些对流单体和对流群天气会通过地形影响setupthroughorographiceffectsandthese而成，而且但大气不稳定时，这些影响会延influencesmayextendwelldown-windwhen伸到下风方向。theatmosphereisunstable.冷锋Thecoldfront 冷锋的天气状况同样是多变的，它依靠于暖Theweatherconditionsobservedatcold区气团的稳定性和相对于锋区的垂直运动。frontsareequallyvariable,dependinguponthestabilityofthewarmsectorairandtheverticalmotionrelativetothefrontalzone.Theclassicalcold-frontmodelisofthe经典的冷锋模式是上滑型的，云系通常是积ana-type,andthecloudisusually雨云.在大不列颠岛上空暖区中的空气很少是cumulonimbus.OvertheBritishIslesairinthe不稳定的，导致在冷锋上消灭雨层云的概率warmsectorisrarelyunstable,sothat更多。nimbostratusoccursmorefrequentlyatthecoldfront.Withthekata-coldfrontthecloudisgenerally伴随下滑型锋面的云系一般是层积云，降水stratocumulusandprecipitationislight.With较少。伴随着上滑型冷锋，通常会短暂的倾ana-coldfrontsthereareusuallybrief,heavy盆大雨，有时还会伴随打雷。downpourssometimesaccompaniedbythunder.Thesteepslopeofthecoldfront,roughly2°,meansthatthebadweatherisofshorterdurationpressurebeginstoriseandtemperaturefalls.Theskymayclearveryabruptly,evenbeforethepassageofthesurfacecoldfrontinsomecases,althoughwithkata-coldfrontsthechangesarealtogethermoregradual.TheocclusionOcclusionsareclassifiedaseithercoldorwarm,thedifferencedependingontherelativestatesofthecoldairmasseslyinginfrontandtotherearofthewarmsector.Iftheairiscolderthantheairfollowingitthentheocclusioniswarm,butifthereverseisso,itistermedacoldocclusion.TheairinadvanceofthedepressionismostlikelytobecoldestwhendepressionoccludeoverEuropeinwinterandverycoldofairisaffectingthecontinent..Thelineofthewarmairwedgealoftisassociatedwithazoneoflayeredcloudandoftenofprecipitation.HenceitspositionisindicatedseparatelyonsomeweathermapsanditisreferredtobyCanadianmeteorologistsasatrowal.Thepassageisanoccludedfrontandtrowalbringsachangebacktopolarair-massweather.Adifferentprocessoccurswhenthereisinteractionbetweenapolartroughandthemainpolarfront,givingrisetoaninstantocclusion.Awarmconveyorbeltonthepolarfrontascendsanuppertroposphericjetformingastratiformcloudband,whilealow-levelpolartroughconveyorbeltatrightanglestoitproducesaconvectivecloudbandandprecipitationareapolewardofthemainpolarfrontontheleadingedgeofthecoldpool.Theoccurrenceofthefrontolysis(frontaldecay)

冷锋的坡度大约是续时间比暖锋要短。冷锋过境，风向急剧变化，气压开头上升，温度下降。天空会突然放晴，有些状况下，甚至在地面冷锋过境前就放晴了，虽然下滑锋的变化总的来说要缓和得多。1.锢囚锋锢囚锋分为冷式和暖式。区分在于暖区前和暖区后的冷气团的相对状态。假设气团比其后更冷，则为暖式锢囚锋，相反，则成为冷式锢囚锋。当冬季欧洲上空的低压锢囚以及很冷的空气影响大陆时，低压前的空气很可能是最冷的。暖空气楔形隆起的外形是与层云区相联系的，常常会有降水。因此，在一些天气图上，它的位置会单独标识，加拿大气象学家称之为高空暖舌。这一段的锢囚锋和高空暖舌带来与极地空气团天气相反的变化。当极地槽和主要的极锋相互作用，会产生不同的过程，会引起短暂的锢囚。极锋的暖传送带上升到对流层上部的急流区形成层状云带，然而在低空极地槽传送带与90锋向极的对流云带和降水区。尽管锋消代表锋面存在的最终阶段，但锋消isnotnecessarilylinkedwithocclusion,althoughitrepresentsthefinalphaseofafront’sexistence.Decayoccurswhendifferencesnolongerexistbetweenadjacentairmasses.Thismayariseinfourways:throughtheirmutualstagnationoverasimilarsurface,asaresultofbothairmassesmovingonparalleltracksatthesamespeed,asaresultoftheirmovementinsuccessionalongthesametrackatthesamespeed,orbythesystemincorporatingintoitselfairofthesametemperature.

并不肯定与锢囚联系在一起。当接近的气团之间的差异不再存在时，消亡就发生了。这4个方面引起的：一是由于它们在同一平面共同停滞；二是由于两气团的一样的速度平行的轨迹行动；三是由于它们紧接着以一样的速度沿着一样的轨迹运动；四是由于系统并入到与它本身具有同样温度的空气中。留意表“缘由”的几种用法since由于 缘由状语从句例sincetheoperatorhadmoreexperiencewithmountingtapethanaprogrammer,setupwasreduced鉴于操作员比程序员有更多的安装磁盘的阅历，所以〔由操作员进展的〕安装时间削减了。for 由于theoutputpowercanneverequaltheinputpower,fortherearealwayslosses输出功率决不行能等于输入功率，由于存在耗损。bythefactthat：though介词，由于，由于asaresultof……作为……结果,由于例theroughly365-dayyearistheresultoftheearthtravelingaroundthesuninoneperiod365天左右约一年里地球围绕太阳转动一个周期的结果。其他表缘由的用法becauseof ,dueto(由于),bethecauseof(是……的缘由), onaccountof(缘由) 等等例inthecloudlessnightgroundtemperaturedecreasesonaccountoftheheatlosttothespace在无云夜间地面温度由于其热量散失到空间而下降。as…… 引导缘由状语从句Asnomachineeverrunswithoutsomefriction,overcomingthewasteswork由于没有一台机器可以无摩擦的运转，所以抑制摩擦力只是白费工夫。itthat 由于〔接从句〕Insummerpeoplefeelstockinginthatrelativehumidityisquitehigh.inviewof介词后接名词或代词做宾语〔后不能接that从句〕必需加词Inviewoftheimportanceoftheplatentotheweatherandclimateoverbroadareas,ascientificinvestigationwascarriedoutafewyearsago.UnitThree:MeteorologicalForecasts第三课：气象预报National MeteorologicalServicesperform avarietyofactivitiesinordertoprovideweatherforecasts. The principal ones are datacollection,thepreparationofbasicanalysesandprognosticchartsatmosphereconditionsforuseby local weather offices,the preparation ofshort-andlong-termforecastsforthepublicaswellasspecialservicesforaviation,shipping,agricultural and other commercial andindustrialusers,andtheissuanceofsevereweatherwarnings.1.DatasourcesThedatarequiredforforecastingandotherservicesareprovidedbyworldwidestandardsynopticreportsat00,06,12,and18GMT,similarobservationsmadehourly,particularlyinsupportofnationalaviationrequirements,upper-airsoundings(at00and12GMT),satellitedataandotherspecializednetworkssuchasradarstationsforsevereweather.Under the World WeatherWatch (WWW)program,synopticreportsaremadeatsome4,000landstationsandby7,000ships.Thereare about 700 stations making upper-airsoundings (temperature, pressure, humidity,and,wind).Thesedataaretransmittedincodeviateletypeandradiolinksinregionalornationalcenters

国家气象局从事各种活动供给天气预报。它们主要是收集资料，为各地方台供给大气状况的根本分析及预报图作预备，不但为短，农业及其他一些商业，工业用户供给特别服务，此外