氣象科技英語翻譯

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

就像海洋中的魚一樣,人類被局限在大氣中一個格外狹窄的層次之內(nèi)。雖然地球的大氣層在水平方向上的不均勻性比在垂直高度上的不均勻性要小得多。但它確確實鑿在水平和垂直兩個方向上都是不均勻的。人們設計了各種各樣的標準來劃分大氣的層次。有的基于垂直溫度廓線的性質(zhì)，有的依據(jù)空氣在不同高度上的大氣成分，有的依據(jù)大氣在不同高度上對飛機的影響來劃分等等。依據(jù)空氣溫度隨高度的變化來劃分〔大氣的層次〕是氣象文獻中用得最普遍的一種劃分方法。依據(jù)1961年世界氣象組織大氣學委會公布的5個主要層次：對流層，平流層，中層，熱成層以及外逸層。這些層次之間鄰接著4個淺薄的過渡區(qū)域：對流層是介于地球外表和對流層頂之間的大氣低層．在對流層中，溫度以平均6.5℃/km的遞減率隨高度的增加而降低，其上邊界在極地和中緯度地區(qū)大約位于8—12Km的高16-18Km的高度。在極地和中緯度，對流層包含了大氣層中空氣質(zhì)量的75%左右，然而在熱帶地區(qū)，包含了大約90%。對流層頂是一個中間層次，據(jù)觀測，其溫度是逆溫或是等溫分布。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

平流層是位于對流層之上的大氣層，在平流層中，溫度或是隨高度增加，或是幾乎保持定常。在平流層的低層〔直到地球外表之上大約20Km〕溫度實際是一個常數(shù)〔大約-56℃。然而再向上，大約20Km~30Km的高度，溫度隨高度以1℃/km的速度增30Km~47Km2.8℃/km47Km高度上正常的溫度是-2.5攝氏度。溫度隨高度的增加是由于太陽輻射的紫外線被臭氧分子吸取的原因。值得一提的是大氣層中空氣總質(zhì)量的99%都集中在對流層和平流層中，始終伸展到30-35Km的高度上。平〔大約從47-52Km的高度上0攝氏度。熱成層是位于中層頂上的大氣層，其溫度隨高度的增加而增加，到熱成層上邊界的平均高度，即大約在450Km高度上，到達大約2023攝氏度。該層中溫度的增加主要是由于外逸層是最遠的，也是爭論最少的大氣的上450Km的高度上。外逸層中空氣的密度格外小，以致原子和分子都能逃逸到星際空間。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.

最終，除了以上對大氣的劃分以外，我們也可以依據(jù)大氣和地面的相互作用得到另一種分法。依據(jù)此原則，大氣通常被劃分為所謂的邊界層〔有時也稱摩擦層〕和自由大氣。地球外表和渦度粘滯力對大氣邊界層〔知道1-1.5Km〕有相當大的影響；同時，作為一級近似，在自由大氣中我們可以無視渦度粘滯力的影響。以上這些大氣層中，只有對流層〔尤其是邊界層〕中氣象參數(shù)的垂直分布具有顯著的不穩(wěn)定性的特征。人們觀測到該層中存在逆穩(wěn)和溫度隨高度超絕熱變化。地球大氣是氣體和氣溶膠的混合物，所謂的氣溶膠指的是由分布在空氣中的微小的液體和固體顆粒組成的系統(tǒng)?？諝獠皇且环N特別的氣體，而是由很多氣體混合成的。其中一些氣體，如，氮，氧，氬，氖等，作為空氣的永久組成成分，總是以固水汽，二氧化碳和臭氧的含量是隨時間和地點的不同而轉(zhuǎn)變。氮在空氣中的含量最多，其中主要來源是腐爛的作物殘渣，動物尸體及火山爆發(fā)。另一方面，大氣中的氮又為包括植物和海洋生物在內(nèi)的生物過程的所消耗。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.

閃電及高溫燃燒過程將少量氮氣轉(zhuǎn)化為氮化物，再由雨雪帶出大氣。大氣中氮的損耗和產(chǎn)生是平衡的。地球生命必不行少的氣體——氧氣，在大氣中已有三千年左右的時間了。氧氣由植物釋放出來，即通過植物的光合作用吸取二氧化碳，釋放氧氣，被人類和動物所吸取，人和動物的呼吸系統(tǒng)同植物的呼吸系統(tǒng)恰恰相反。我們吸進氧氣呼出二氧化碳，氧氣溶進湖，河和海洋中，來維持海洋生物的生存。在同其他物質(zhì)發(fā)生化學反響或是有機物的腐爛過程也要消耗氧氣，比方說鋼鐵生銹就涉及到氧化過程。對人類來說，稀有的，多變的氣體是格外重要的。水汽，即水的氣態(tài)，在大氣的含量是比較稀有的，而且它的生成和消耗是比較快的。因此，水汽在大氣中存在的平均時間只11天，水汽是雨雪得源泉，沒有水汽我們就不能生存。眾所周知，水汽在大氣中的含量是多變的，在沙漠地帶，水汽含量格外低，只占空氣總量的很少的一局部，相反，在其他地區(qū)，特別是潮濕的熱的海面上，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

盡管大氣中的水汽的含量隨時間和地點的不同有很大的變化，但它在整個地球上的總量在過去的一百年里，這種稀有的但卻很重要的氣體的含量始終在上升腐爛的植物，土壤中的腐殖物以及燃燒煤，石油，自然氣，等化石燃料都能向大氣釋放植物需要二氧化碳進展光合作用，二十世紀八十年月中期，大氣化學家就森林的燃燒，砍伐對大氣中二氧化碳產(chǎn)生的影響進展了爭論。海洋吸取了大量的二氧化碳，大約占化石燃料燃燒釋放的二氧化碳總量的一半。人們推測，往后的幾十年，這局部吸取量將會逐步削減，而釋放的二氧化碳的總量則會增加，這種狀況至少會連續(xù)到下個世紀初。二十世紀八十年月，大氣中的二氧化碳，每年以空氣的百萬分之一的速度增加。但是，據(jù)推測，這種增加速度在將來的幾十年中還要更快一些。1983年，其含量平均為空氣的340。另一種重要多變的氣體 臭〔O3多存在于高層大氣中，但在交通擁擠，有很多工廠或是充分陽光照耀的地區(qū)也有臭氧存在。像洛杉磯這樣的城市，O3最多時可超過0.1ppm。大氣中臭氧的含量大多在1.0——10ppm之間。它們隨高度，季節(jié)，時間，天氣狀況的不同而不同。高層大氣中的O3層是由光化學反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.

應造成的。臭氧層之所以重要，是由于它通過吸取上層大氣紫外線輻射，從而削減紫外線到達地面的總量，承受紫外線照耀的時間越長，就越簡潔造成嚴峻的灼傷，從而增加皮膚癌的危急。生物學家指出，紫外線過度的增加還會影響生物圈中的其它組成成分。有些氣體，假設濃度過高，對人，動物及植物生命可能有害，比方，O3濃度過高會對生但洛杉磯這樣污染嚴峻的城市，有時接近地面的O3含量變得足以毀壞某些植物外表的葉片。人類活動將大量具有潛在危急的氣體帶入大氣。大型鍋爐，工廠，煉油廠和發(fā)動機，特別是汽油發(fā)動機排放出空氣污染物。全部這些場所以及其它特別類似場所：燃燒煤，石油，汽油，煤油等化石燃料，在燃燒這些顆粒經(jīng)過相當長的時間又和空氣中其他成分發(fā)生反響，形成有毒的化合物。分布最廣泛的，而且潛在危急最大的氣體污染物是一氧化碳，二氧化硫，氧化氮和碳氫化合物。這些化合物最終來源于蒸發(fā)的汽油和其他石油產(chǎn)物。第一課大氣的構造和組成UnitTwo:Frontogenesisandfrontalcharacteristics其次課鋒生和鋒的特征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.

鋒生隨著很多與不同氣團之間的邊界(鋒面)形成與運動相聯(lián)系的逐日變化被揭露之后，我們對中緯度天氣變化的具體了解才取得了首次真正意義上的進步。在這些問題未解決之前，對溫度，風向，濕度和其他去理現(xiàn)象的觀測說明具有不同特征而又嚴密接觸的氣團之間常常存在不連續(xù)性。Theterm“front”,forthesesurfacess團之間交會的面——鋒面，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

一次世界大戰(zhàn)時期由在挪威工作的一批氣象學家提出的一個規(guī)律詞匯。他們的想法在大多數(shù)天氣分析和預報中，尤其是在中，高緯度仍是一個完整的局部。鋒波我們觀測到氣團的交界面即鋒面是一種典型的幾何狀，類似于一種波的形成。實際上，相像的波形也消滅在很多不同介質(zhì)的交界面，例如，海洋外表的波，沙灘上的漣漪和風吹成的沙丘等等。然而，并不象這些波形，大氣中的鋒面通常是不穩(wěn)定的，也就是說，它們突然生成，進展，然后漸漸消散。數(shù)值模式計算說明，在中緯度斜壓大氣中，假設鋒波波長超過幾千公里，那些鋒波是不穩(wěn)定的。鋒波的波長通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，最初引起興趣大氣波動系統(tǒng)和其他介質(zhì)交界面所形成的波類似的東西不適宜作為進一步解釋鋒面的根底。尤其是對流層上層的環(huán)流對鋒波的進展和壯大才是引起至關重〔就這一點論證中給出。鋒波低壓低壓〔又稱低壓區(qū)域氣旋，低壓〔又稱低壓區(qū)域氣旋的相對低壓區(qū)。他們直徑掩蓋100-3000Km，4-7天的生命史。具有這些特征的系統(tǒng)在每日的天氣圖上很突出，被稱為具有天氣尺度的特點。至少在中緯度地區(qū)，低壓通常是與相對的氣團之間的輻合聯(lián)系在一起的。這些氣團之間的交界面進展成波的形式，它的峰位于低壓區(qū)的中心。鋒波圍住了波前變性的冷空氣和波后穎冷空氣之間的一團暖空氣。鋒波的形成也造成了原始空氣團不連續(xù)的兩局部之間的差異。每一局部在冷暖空氣之間具有明顯的邊界，每一局部鄰近區(qū)域的天氣特征格外不同。鋒面的這兩局部由名為暖鋒波的前邊緣和冷鋒 波后冷空氣來區(qū)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

低壓通常在開頭錮囚后12-24小時強度到達最大。鋒的特征從天氣方面來說，鋒的活潑程度依靠空氣團的垂直運動。假設暖區(qū)中的空氣相對鋒區(qū)是上升的，那么，鋒通常是格外活潑的，被稱為上滑鋒。相反，暖空氣相對于冷空氣團下沉的，則會產(chǎn)生不活潑的下滑鋒。暖鋒暖鋒是指鋒波中暖區(qū)的前邊緣。這兒所提的鋒區(qū)是一個格外稍微的坡度，量級在1/2°----1°之間，所以，與鋒的上部相聯(lián)系的云系在地面鋒到來之前的12小時甚至更早就預示了鋒的接近。隨著暖空氣上升的上滑暖鋒有多層云系，這最開頭的云石薄而縹緲的卷云，緊接著是成片的卷層云和高層云。當高層云加厚開頭下毛毛雨或者開頭下大雨時，太陽就開頭昏暗了。常常會伸展到對流層大局部地區(qū)而且伴隨著連續(xù)性降水發(fā)生的云系通常叫做雨層云。當下降的雨水穿過冷空氣時經(jīng)過蒸發(fā)，快速的到達飽和，也可能形成一片片的層云。下滑鋒中的下沉暖空氣極大限制了中高層云的進展。鋒面云系主要是層積云，由于在冷暖空氣團中下沉逆溫的作用，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，由于凍結(jié)高度比較多地傾向于在逆溫層之上，尤其是在夏季。暖鋒過境時，風向發(fā)生轉(zhuǎn)變，溫度上升，氣壓下降。暖空氣中，降水是間歇性的或者無雨，薄的片狀層積云也可能斷裂開來。由于大多數(shù)鋒在對流層的全部層次上或者說貫穿鋒的整個長度并不都是上滑鋒或者下滑鋒，所以要預報與暖鋒相聯(lián)系的雨帶的范圍是很簡單的。由于這個緣由，雷達波越來越多的用來直接測定雨帶的準確范圍和雨量強度的差異。這些爭論說明，大多數(shù)降水的產(chǎn)生和分布是由寬達幾百公里，厚達幾公里的寬闊氣流所掌握，這股氣流平行于地面冷鋒，位于地面冷鋒之前1Km之上隨著風速增大到25-35m/s，這股氣流形成了低空急流。暖濕空氣在暖鋒上上升，在暖鋒前轉(zhuǎn)〔由于在中緯度傳輸大尺度的熱量和動量潛在不穩(wěn)定是由與對流層中部潛在的干冷空氣在低層氣流上爬越作用而造成的。Instabilityisreleasedmainlyinsmall-scale不穩(wěn)定主要在形成的對流群---即中尺度降convectioncellsthatareorganizedintoclusters,水區(qū)的小尺度對流單體中釋放。這些中尺度knownasmeso-scaleprecipitation50---100Kmareas(MPAs).TheseMPAsarefurtherarranged寬。inbands,50-100kmwide.Aheadofthewarmfront,thebandsarebroadly在暖鋒前，這條帶狀區(qū)域橫向平行于傳送帶paralleltotheairflowintherisingsectionof上升區(qū)中的氣流，然而，在暖區(qū)中，則平行theconveyorbelt,whereasinthewarnsector于冷鋒和低空急流。在某些狀況下，對流單theyparallelthecoldfrontandthelow-level體和對流群在暖區(qū)中和暖鋒前進一步排列成jet.Insomecases,cellsandclustersarefurther帶狀。arrangedinbandswithinthewarmsectorandaheadofthewarmfront.Precipitationfromwarmfrontrainbandsofteninvolves“seeding”byiceparticlesfallingfrom 暖鋒雨帶的降水常常隨著來自上層云層“散theuppercloudslayers.Ithasbeenestimated 布的冰粒據(jù)估量大約20--35%的降水來that20%-35%oftheprecipitationoriginatesin 源于“催化劑”區(qū)，其余的來源于低層云系。the“seeder”zoneandtheremainderinthelowerclouds.Someofthecellsandclustersareundoubtedly一些對流單體和對流群天氣會通過地形影響setupthroughorographiceffectsandthese而成，而且但大氣不穩(wěn)定時，這些影響會延influencesmayextendwelldown-windwhen伸到下風方向。theatmosphereisunstable.冷鋒Thecoldfront 冷鋒的天氣狀況同樣是多變的，它依靠于暖Theweatherconditionsobservedatcold區(qū)氣團的穩(wěn)定性和相對于鋒區(qū)的垂直運動。frontsareequallyvariable,dependinguponthestabilityofthewarmsectorairandtheverticalmotionrelativetothefrontalzone.Theclassicalcold-frontmodelisofthe經(jīng)典的冷鋒模式是上滑型的，云系通常是積ana-type,andthecloudisusually雨云.在大不列顛島上空暖區(qū)中的空氣很少是cumulonimbus.OvertheBritishIslesairinthe不穩(wěn)定的，導致在冷鋒上消滅雨層云的概率warmsectorisrarelyunstable,sothat更多。nimbostratusoccursmorefrequentlyatthecoldfront.Withthekata-coldfrontthecloudisgenerally伴隨下滑型鋒面的云系一般是層積云，降水stratocumulusandprecipitationislight.With較少。伴隨著上滑型冷鋒，通常會短暫的傾ana-coldfrontsthereareusuallybrief,heavy盆大雨，有時還會伴隨打雷。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)

冷鋒的坡度大約是續(xù)時間比暖鋒要短。冷鋒過境，風向急劇變化，氣壓開頭上升，溫度下降。天空會突然放晴，有些狀況下，甚至在地面冷鋒過境前就放晴了，雖然下滑鋒的變化總的來說要緩和得多。1.錮囚鋒錮囚鋒分為冷式和暖式。區(qū)分在于暖區(qū)前和暖區(qū)后的冷氣團的相對狀態(tài)。假設氣團比其后更冷，則為暖式錮囚鋒，相反，則成為冷式錮囚鋒。當冬季歐洲上空的低壓錮囚以及很冷的空氣影響大陸時，低壓前的空氣很可能是最冷的。暖空氣楔形隆起的外形是與層云區(qū)相聯(lián)系的，常常會有降水。因此，在一些天氣圖上，它的位置會單獨標識，加拿大氣象學家稱之為高空暖舌。這一段的錮囚鋒和高空暖舌帶來與極地空氣團天氣相反的變化。當極地槽和主要的極鋒相互作用，會產(chǎn)生不同的過程，會引起短暫的錮囚。極鋒的暖傳送帶上升到對流層上部的急流區(qū)形成層狀云帶，然而在低空極地槽傳送帶與90鋒向極的對流云帶和降水區(qū)。盡管鋒消代表鋒面存在的最終階段，但鋒消isnotnecessarilylinkedwithocclusion,althoughitrepresentsthefinalphaseofafront’sexistence.Decayoccurswhendifferencesnolongerexistbetweenadjacentairmasses.Thismayariseinfourways:throughtheirmutualstagnationoverasimilarsurface,asaresultofbothairmassesmovingonparalleltracksatthesamespeed,asaresultoftheirmovementinsuccessionalongthesametrackatthesamespeed,orbythesystemincorporatingintoitselfairofthesametemperature.

并不肯定與錮囚聯(lián)系在一起。當接近的氣團之間的差異不再存在時，消亡就發(fā)生了。這4個方面引起的：一是由于它們在同一平面共同停滯；二是由于兩氣團的一樣的速度平行的軌跡行動；三是由于它們緊接著以一樣的速度沿著一樣的軌跡運動；四是由于系統(tǒng)并入到與它本身具有同樣溫度的空氣中。留意表“緣由”的幾種用法since由于 緣由狀語從句例sincetheoperatorhadmoreexperiencewithmountingtapethanaprogrammer,setupwasreduced鑒于操作員比程序員有更多的安裝磁盤的閱歷，所以〔由操作員進展的〕安裝時間削減了。for 由于theoutputpowercanneverequaltheinputpower,fortherearealwayslosses輸出功率決不行能等于輸入功率，由于存在耗損。bythefactthat：though介詞，由于，由于asaresultof……作為……結(jié)果,由于例theroughly365-dayyearistheresultoftheearthtravelingaroundthesuninoneperiod365天左右約一年里地球圍繞太陽轉(zhuǎn)動一個周期的結(jié)果。其他表緣由的用法becauseof ,dueto(由于),bethecauseof(是……的緣由), onaccountof(緣由) 等等例inthecloudlessnightgroundtemperaturedecreasesonaccountoftheheatlosttothespace在無云夜間地面溫度由于其熱量散失到空間而下降。as…… 引導緣由狀語從句Asnomachineeverrunswithoutsomefriction,overcomingthewasteswork由于沒有一臺機器可以無摩擦的運轉(zhuǎn)，所以抑制摩擦力只是白費工夫。itthat 由于〔接從句〕Insummerpeoplefeelstockinginthatrelativehumidityisquitehigh.inviewof介詞后接名詞或代詞做賓語〔后不能接that從句〕必需加詞Inviewoftheimportanceoftheplatentotheweatherandclimateoverbroadareas,ascientificinvestigationwascarriedoutafewyearsago.UnitThree:MeteorologicalForecasts第三課：氣象預報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

國家氣象局從事各種活動供給天氣預報。它們主要是收集資料，為各地方臺供給大氣狀況的根本分析及預報圖作預備，不但為短，農(nóng)業(yè)及其他一些商業(yè)，工業(yè)用戶供給特別服務，此外