對流層上層斜壓波

波包的結構、特征及傳播

TheStructure,Characteristicsand

PropagationofBaroclinicWavePackets

(Chang1993,1999,2000,&2001)

大氣動力學（第四講）管兆勇南京信息工程大學2008年5月本講要點

[參考文獻：

EDMUNDK.M.CHANG，

CharacteristicsofWavePacketsintheUpperTroposphere.PartII:SeasonalandHemisphericVariations，JAS,56,1729-1747,1999;

EDMUNDK.M.CHANG，

TheStructureofBaroclinicWavePackets,JAS,58,1694-1713,2001.]重點難點：波包；波作用量通量講授內(nèi)容：

斜壓波動

波包及其結構

波包的維持

波作用量通量

上下游效應第一部分：斜壓波包的結構1.1引言、問題1.2

波包能量學1.3波作用量和通量第二部分：波包的特征2.1北半球冬季2.2季節(jié)變化和半球內(nèi)變化

第三部分：波包的傳播斜壓波的下游發(fā)展對流層上層斜壓波與江淮流域降水內(nèi)容：第一部分：斜壓波包的結構

PartIThestructureofbaroclinicwavepackets1.1、引言●斜壓波動是影響中緯度地區(qū)的地面氣旋與反氣旋的承載系統(tǒng)●觀測研究表明，斜壓波動的下游發(fā)展發(fā)生于對流層中-上層（e.g.,NamiasandClapp1944；Cressman1948；Hovmoller1949）●數(shù)值模擬表明，斜壓不穩(wěn)定大氣中斜壓波的下游發(fā)展與起始的局地擾動有關(e.g.,SimmonsandHoskins1979；ChangandOrlanski1993)●研究表明，斜壓波傾向于組織成局地化的波包，其中一些可以持續(xù)相當長一段時間（Chang1993；LeeandHeld1993；BerberyandVera1996；ChangandYu1999；Chang1999）●線性理論中，波包向其上、下游雙向頻散能量（Inlineartheory,thewavepacketdispersesbothtowarditsupstreamanddownstreamdirections）●觀測研究波包能量頻散主要向下游方向（Observationalstudiesmentionedabovedonotsupportthelinearpicture,inthatpredominantlydownstreamdispersionisobserved,withlittleevidenceofupstreamdispersion

）●非線性理論提示：上游波動發(fā)展受到抑制可能與波動向下游傳播形成的正壓衰減有關（EslerandHaynes(1999)suggestedthatinaweaklydissipativesystemliketheatmosphere,wavepacketsareprobablymaintainedbynonlinearself-focusingratherthanenhancedupstreambarotropicdissipation）問題Aim:ToexaminethestructureofwavepacketsTotrytounderstandhowitismaintained目的：研究波包結構；理解波包維持1.2波包能量學Wavepacketenergetics(OrlanskiandKatzfey1991)a:

基本方程：

月或季節(jié)平均b:

動能方程的各項

(3.15)In(3.15)

Finally，foreddykineticenergy(EKE)(3.15)(1)(2)(3)(4)(5)(6)(7)(3.15)(1)---------convergenceoftotalenergyflux(advectivefluxplusageostrophicgeopotentialordispersiveflux)(2)---------baroclinicconversionfromeddyavailablepotentialenergy(3)---------barotropicconversion(4)---------conversionbetweenEKEand,whichisatransientkineticenergyequalto(5)---------convergenceofverticaladvectivefluxofEKE(6)---------verticalenergyflux(7)---------budgetresidue第4天長度：60經(jīng)度移速：30經(jīng)距第4天波幅先增后減Conclusion:Onaverage,boththelengthandwidthofwavepacketsremainaboutthesameastheyevolveintime.平均而言，波包演變過程中波包的長度（緯向）和寬度（經(jīng)向）基本不變。Next,wewillexaminethecompositesoftheenergeticstermsassociatedwiththesecoherentwavepackets.Perturbationheremeansthatthezonalaveragehasbeentakenouttohighlightthewavepacket.Conclusion:Typicalpackethasalengthofabout60oinlongitude,andawidthofnearly30oinlatitude（Fig5a）.（典型緯向尺度60經(jīng)向30）Thelargestbudgettermisconvergenceofthetotalenergyflux(5b),withthesecondlargesttermbeingbaroclinicconversion(5c).Barotropicconversionismuchsmaller(5d).（最大的收支項為總能量通量，其次為斜壓轉換項，正壓轉換項很小）

Theconvergenceoftotalenergyfluxisadipoleanditsmaineffectclearlyleadstothezonaltranslationofthewavepacket.（Fig5b-d）

（總能量通量散度具偶極結構，其導致波包的緯向局地增強與減弱）1.2WavepacketenergeticsNextwewillexaminethebudgetinaframemovingalongwiththewavepacket.When(3.15)isintegratedvertically,andtranslatedintoaframefollowingthewavepacket,theequationes(3.16)<>

representsverticalintegral,whilevaluesfollowedbythesubscriptT

representfluxesintooroutofthetoporthebottom(subscriptB)ofthecolumn.TheD/Dt

onthelhsrepresentrateofchangeintheframeofreferencefollowingthewavepacket.總能量通量散度斜壓轉換氣柱質(zhì)量變化Firstterm---------inflowofenergyduetototalhorizontalenergyfluxcomputedrelativetothespeedofthewavepacket.相對于波包移速而算出的總的能量通量Lastterm---------energychangeduetothechangeinmasswithinthecolumn

因氣柱質(zhì)量變化而產(chǎn)生的能量變化Theothertermsareasdiscussedaboveunder(3.15).Fig6a-------TheEKEtendencyduetotransformingintoaframemovingalongwiththewavepacketFig6b--------Thesumofthistermandtheconvergenceoftotalenergyflux,whichmakesupthefirsttermontherhsof(3.16)Fig6c--------DK/DtFig6d--------convergenceofrelativeenergyflux(REF)-6h，0，+6h粗實線虛線點線EKEREFConclusion1:Wecanconcludethatthetotalenergyfluxhasthreemaineffectsonthewavepacket（FromFigs6and7）:

1)Actstomovethepacketatitsgroupvelocity（起使波包按群速度移動的作用）

2)Changestheshapeofthepacketnearitspeak（改變波包峰部形狀）

3)Redistributesenergyfromtheupstreampartofthewavepackettowarditsdownstreamend,maintainingthedownstreampartofthewavepacket（將波包上游的能量重新分布至下游，維持波包的下游部分）Conclusion2:Intheframemovingwiththewavepacket,themainbalanceisbetweenconvergenceofrelativeenergyflux(Fig6d),baroclinicconversion(Fig5c),barotropicconversion(Fig5d),anddissipation.移動坐標系中，四項之間平衡REF斜壓轉換Overthedownstreamendofthewavepacketwherewavesaregrowing,themaintermcontributingtopositivetendencyisrelativeenergyfluxconvergence,anditisclearthatoverthatregionthistermbalancesfrictionalandbarotropicdissipation,withsomesmallpositivecontributionsfrombaroclinicgeneration.Towardtheupstreamendofthewavepacket,baroclinicgenerationbalancesenergyfluxdivergenceanddissipation.在波包的下游尾部，波動增強，其趨勢性增強的主要貢獻來自于相對的能量通量散度，此項平衡了摩擦和正壓耗散。斜壓轉換的貢獻很小。Conclusion(Fig8)1.3WaveactivityandfluxesNextwewillshowwavepacketcompositesbasedontheframeworkofanapproximatelyconservededdyactivityanditsfluxesasderivedbyPlumb(1986).波包活動與波作用量守恒位渦守恒Whenthemeanflowiszonal,Itcanbeshownthatinthealmost-planewavelimitsuggestthatMalongwithitsfluxesshouldbeagooddiagnosticofeddyactivity.Wetransformedallbudgettermsintoaframemovingalongwiththewavepacketatitsgroupvelocity.Inthisframe,therelativefluxofwaveactivityis波包由其尾部向上的通量所維持，這個通量轉向位于對流層上層的波包下游并再次環(huán)繞波包。這樣，波包下游區(qū)域的波作用量全部由來自波包上游的波作用量通量維持，即使跟隨了波包移動。

Figure11suggeststhatthewavepacketismaintainedbyupwardfluxatitsrear,whichturnstowardthedownstreamsideintheuppertroposphereandrecirculatesaroundthewavepacket.Thuswaveactivityinthedownstreamportionofthewavepacketisentirelymaintainedbywaveactivityfluxesfromtheupstreampartofthewavepacket,eveninaframemovingwiththewavepacket.Conclusion(Fig11)PartIICharacteristicsofwavepacketsintheuppertroposphere對流層上層的波包特征2Characteristicsofwavepacketsintheuppertroposphere1°用一點相關發(fā)現(xiàn)波包

經(jīng)向風v’的一點相關基點：(180，40N）NorthernhemispherewinterEnvelopeofwaves,WavePacket?Ve為包絡函數(shù)Ve的一點相關可估算波包結構及群速度Basicpropertiesofwavesandwavepackets2°由相關估計波長和周期周期波長/相速度波數(shù)波長由相關分布估計相速群速群速Similarly,wecandefineaphasedecorrelationtimebasedonsamephasecoherence(Fig.7c).WCI2indexisdefinedastheaveragemagnitudeofapairofthestrongest(eitherpositiveornegative)correlationvalues3°波動的凝聚特征波動凝聚:WAVECOHERENCECharacteristicsofwavepropagationoverselectedregions(Entrance

tothePacificstormtrack)4°波導與波包傳播經(jīng)向風v’的一點相關基點：(65E，25N）波導特征波數(shù)，由相關獲得相速度：由-1至+1天最大相關的移動特征周期：波長/相速度緯向群速度：由-1至+1天最大相關的移動經(jīng)向群速度：由-1至+1天最大相關的移動下游/上游不對稱指數(shù)：＞1表示下游發(fā)展Downstream/upstreamasymmetryindexcomparestherelativemagnitudeoftheupstreamanddownstreamnegativecorrelationcentersflankingthereferencepositivecenteratdays+1and-1.

Itisequaltothesumofthemaximumnegativecorrelationupstreamatday-1andthatdownstreamatday+1,dividedbythesumofthemaximumdownstreamnegativecorrelationatday-1andthatupstreamatday+1.TheWCIindexbasicallyindicateshowwellthewavesateachlocationcorrelatewithupstreamwaves2daysearlieranddownstreamwaves2dayslater,thusshowingthetendencyofthedownstreamdevelopmentofwaves.Thewavecoherenceindexateachbasepointrepresentstheaverageofthemaximum(positiveornegative)correlationupstreamonday22anddownstreamonday12.3

PropagationofbaroclinicwavesintheuppertropospherePartIIIPropagationofwavepacketsintheuppertroposphereSchematicdiagramofdownstreamdevelopment1°

下游發(fā)展Downstreamdevelopmentofbaroclinicwavesasinferredfromregressionanalysis2°斜壓波發(fā)展

3.2RelationshipbetweenbaroclinicwavepacketsandMeiyuRelationshipbetweenbaroclinicwavepacketsinupper-troposphereandMeiyuinReachesofYangtzeandHuaiheValley(2003、19