天氣學(xué)分析診斷-T-lnp-圖-詳解

TheSKEW-TDiagramSKEWTDiagramThemostcommondiagramusedtoplotrawinsondesoundingsandtoanalyzestabilityiscalledtheSKEWT-logPdiagrambecauseitisconstructedwithT+klnPontheverticalaxis(SkewT)and-RdlnPonthehorizontalaxis(logP).Theoperationalversionofthediagramisrotatedsothatpressuredecreasestowardthetoplikeitdoesintheatmosphere.VariablesontheSKEWTFivedifferentvariablesareplottedonthebasicSKEWT.IsobarsIsothermsDryadiabatsPseudoadiabatsMixingratiosIsobarsIsobarsareroughlyhorizontallinesthatrepresentthepressuresontheSKEWT.Theyareplottedevery10mbandarelabeledevery50mb1000mb950mbIsothermsIsothermsarenearlystraightlinesrunningfromthelowerlefttotheupperrightthatrepresentthetemperatures.Bothtemperaturesanddewpointtemperaturesareplottedusingtheisotherms.Isothermsareplottedevery1°Candarelabeledevery5°C.1000mb950mb1520DryAdiabatsDryadiabatsarenearlystraightcurvesrunningfromthelowerrighttotheupperleftthatrepresenttheDryAdiabaticLapseRate.Unsaturatedairparcelsmoveverticalalongtheadiabatsastheyareliftedorsink.Thetemperatureofanunsaturatedairparcelmovingverticallyduringandadiabaticprocesscanbedeterminedbyfollowingtheadiabat1000mb950mb1520AdiabatsPseudoadiabatsPseudoadiabatsarecurvesrunningfromthebottomofthediagramandgraduallycurvingtowardtheupperleftthatultimatelybecomenearlyparalleltothedryadiabats.TheyrepresenttheSaturatedAdiabaticLapseRate.Thechangeintemperatureofsaturatedairparcelsmovingverticallyoccursalongthepseudoadiabats.1000mb950mb1520AdiabatsPseudoadiabatsMixingratiosThemixingratiosarealsoplottedasstraightdashedlinesrunningfromthelowerlefttoupperrightmoresteeplythantheisotherms.Themixingratioscanbeusedtofindtheheightatwhichcondensationwouldoccurundervariousconditionsifunsaturatedparcelsrise.1000mb950mb1520AdiabatsPseudoadiabatsMixingratiosSoundingsontheSKEWTOneofthemostbasicusesofaSKEWTdiagramistoplottemperaturesanddewpointtemperaturesobservedbyradiosondesinordertodisplayandanalyzetheverticalstructureoftheatmosphere.SampleSoundingpressure(mb) T(°C) Td(°C)1000 26 20950 23 19900 20 17850 14 11800 11 8750 7 4700 5 1650 3 0600 0 -6550 -4 -10500 -8 -15450 -10 -18400 -14 -22(LiftingCondensationLevel,簡稱:LCL)

為當(dāng)空氣塊自地面受外舉升并沿乾絕熱線上升而開始產(chǎn)生凝結(jié)的高,因此可知其為動作用所導(dǎo)致之凝結(jié)面.一般而言,此凝結(jié)面為層云之云底高所在位置.【求法】(1)由氣壓(P)與點(diǎn)(Td)之交點(diǎn)沿飽和混合比線上升.(2)由氣壓(P)與溫(T)之交點(diǎn)沿乾絕熱線上升.者之交點(diǎn)即為舉升凝結(jié)面.LiftingCondensationLevelTheLiftingCondensationLevel(LCL)representstheleveltowhichanunsaturatedairparcelmustbeliftedinorderforittobecomesaturatedandforcondensationtobegin.TheLCLwouldbethecloudbaseondayswhereliftingofairisthemechanismproducingtheclouds.DeterminingtheLCLontheSKEWTPlotapointwheretheisothermfortheairtemperatureintersectstheisobarfortheairpressure.FindingtheLCL(Cont.)Plotapointwheretheisothermforthedewpointtemperatureintersectstheisobarfortheairpressure.FindingtheLCL(Cont.)Drawalinealongthedryadiabatfromthepointplottedwheretheairtemperatureintersectedtheairpressure.FindingtheLCL(Cont.)Drawalinealongthemixingratiofromthepointplottedwherethedewpointtemperatureintersectedtheairpressure.FindingtheLCLTheLiftingCondensationLevelisthepointatwhichthetwolinesdrawninsteps3and4intersect.LCLSampleSoundingpressure(mb) T(°C) Td(°C)1000 26 20950 23 19900 20 17850 14 11800 11 8750 7 4700 5 1650 3 0600 0 -6550 -4 -10500 -8 -15450 -10 -18400 -14 -22LCL=918mbAbovetheLCLIftheparcelisliftedabovetheLiftingCondensationLevelitwillbesaturatedanditwillcoolattheSaturatedAdiabaticLapseRate.AbovetheLCL,theparcelshouldbeliftedalongthecurvedpseudoadiabats.對流凝結(jié)面(ConvectiveCondensationLevel,簡稱CCL)

當(dāng)?shù)厍虮砻媸芴柹浼訜嶙饔?而使空氣塊產(chǎn)生上升運(yùn)動,并造成凝結(jié)之高即稱之為『對凝結(jié)面』,因此可知其為熱作用所導(dǎo)致之凝結(jié)面.一般而言,此凝結(jié)面為積云之云底所在高.【求法】由Td與1000hPa之交點(diǎn)沿飽和混合比線上升或下至與探空溫曲線相交所在之高即稱為CCL.對流溫度(Tc):

當(dāng)?shù)厍虮砻媸芴栞椛浼訜嶙饔煤箝_始形成對流時之地面溫度。求法：由CCL沿干絕熱線向下至地面氣壓時所具有之溫度。自由對流面(LevelofFreeConvection,簡稱:LFC)

當(dāng)空氣塊經(jīng)干絕熱舉升達(dá)飽和,而在隨后的飽和絕熱過程中當(dāng)空氣塊變得比周圍環(huán)境空氣暖時之高即稱為『自由對高』.此時由于空氣塊本身所具有之浮較環(huán)境場大,因此空氣塊可自由上升，直到溫較周圍環(huán)境溫低時才停止.【求法】由LCL/CCL沿濕絕熱線上升至與探空溫曲線相交所的高度.混合凝結(jié)層(MixingCondensationLevel,簡稱:MCL)近地層有風(fēng)擾動而使氣層完全混合,則當(dāng)其發(fā)生飽和時之最低高即稱為混合凝結(jié)層.求法：經(jīng)過平均之后的飽和混合比線與平均干絕熱線之交點(diǎn)即為混和凝結(jié)面.可用面積法加以判斷.平衡面(簡稱:EL)：當(dāng)一原本溫度較周圍環(huán)境高的浮升空氣塊，上升過程中降溫，其溫度再與周圍環(huán)境溫相等時之高即稱為『平衡面』,此時空氣塊繼續(xù)上升,則空氣塊之溫會低於環(huán)境大氣.求法：探空溫曲線與對凝結(jié)面后或抬升凝結(jié)高度后的濕絕熱線再相交點(diǎn)之位置即為平衡面之所在高.正面積(正能區(qū))(PositiveArea,簡稱:PA)【定義】由于空氣塊于氣層內(nèi)所沿升之絕熱線溫度均大于四周環(huán)境之溫,因此空氣塊能自由上升,此時濕絕熱線與探空溫度曲線所夾之面積與空氣塊所釋放出的動總合成正比,此面積即稱之為『正能區(qū)』.正面積的大小代表著空氣塊在上升過程中所釋放出的能大小,也就表示大氣的對流有效位能【求法】1.因加熱作用所形成:(如:太陽射)由對凝結(jié)高(C.C.L.)沿濕絕熱線上升至與溫探空曲線相交為止,此探空曲線與濕絕熱線所圍之區(qū)域即為因加熱作用所導(dǎo)致之正能區(qū).2.因舉升作用所形成:(如:地形,鋒面)由自由舉升凝結(jié)面(L.F.C.)沿濕絕熱線上升至與溫探空曲線相交,此溫探空曲線與濕絕熱線所圍成的區(qū)域即為因舉升作用導(dǎo)致之正能區(qū)負(fù)面積(負(fù)能區(qū))(NegativeArea,簡稱:NA)【定義】當(dāng)空氣塊于某氣層內(nèi)上升的絕熱線溫度均小於其四周環(huán)境之溫度時,此空氣塊于該氣層內(nèi)

需要依賴外界環(huán)境能量的輸入才可運(yùn)動,此時濕絕熱線與探空溫曲線所圍之面積與空氣塊獲自四周環(huán)境之動能成正比,此面積即稱為『負(fù)能區(qū)』.所以負(fù)面積的大小代表著外屆對上升空氣塊作功使其達(dá)到自由上升之作功.

【求法】1.因加熱作用所形成:由對凝結(jié)高(LCL)沿干絕熱線下至地面為止,此溫度探空曲線與干絕熱線所圍成之區(qū)域即為因加熱作用所導(dǎo)致的負(fù)能區(qū).2.因舉升作用所形成:由地面沿干絕熱線上升至L.C.L.,再從L.C.L.沿濕絕熱線至與探空溫曲線相交為止(此點(diǎn)即為舉升凝結(jié)面(L.F.C.)),此所圍成的區(qū)域即為因舉升作用所導(dǎo)致的負(fù)能區(qū)StabilityIndicesTherearemanyindicesofthestabilityorpotentialinstabilityofairthatarebasedontheradiosondesoundingsandthatcanbeplottedonSKEWTdiagrams.StabilityIndices(Cont.)Therearemanywaystocomputestabilityindices.Astabilityindexmaybecomputedforagivenpressurelevel(e.g.thesurface).

StabilityIndices(Cont.)Insomeapplicationstheparcel’sairtemperatureiscomputedastheaverageofthetemperatureswithin50mboftheEarth’ssurface,andthedewpointtemperatureistakenfromthelevelwherethepressureis25mblowerthanthepressurefromtheEarth’ssurface.LiftedIndexTheLiftedIndex(LI)

iscomputedasthetemperatureoftheairintheenvironmentoutsidearisingairparcelat500mb(usuallymeasuredbyaradiosonde)minusthetemperatureaparcelwouldhaveifitwereliftedtothe500mblevel.LI=Tobservedat500mb–Tparcelliftedto500mb

LiftedIndex(Cont.)TheLiftedIndexindicatesthestabilityofanairparcelifitweretobeliftedtothe500mblevel.WhenLI<0,thentheparcelwouldbeunstable.LI>0,thentheparcelwouldbestable.

LiftedIndex(Cont.)WhentheLiftedIndexisnegativeorisslightlypositive(i.e.LI<4),itindicatesagreaterchanceofthunderstorms.LiftedIndex(Cont.)WhatwastheLIofoursamplesounding?LI(Cont.)LI=-8°C-(-6.5°C)=-1.5°CKIndexTheKIndex(K)combinestheeffectsofatmosphericstabilityandmoistureintoasingleindex.Kisbasedentirelyondatafromanatmosphericsoundinganditdoesnotconsidertheparcel.KIndex(Cont.)K=T850mb–T500mb+Td850mb–(T–Td)700mbwhereT850mb–T500mbincorporatestheeffectsoftheenvironmentallapserate,andTd850mb-(T–Td)700mbincoporatestheeffectsofthemoistureinthelowertroposphere.KIndex(Cont.)TheKIndexwillbelargestwhenthelowertroposphereisunstableandmoist.WhenK>24,thenthepotentialforconvectionexists;K>30,thenthepotentialforstrongthunderstormsexists.KIndex(Cont.)WhatistheKIndexofoursamplesounding?SampleSoundingpressure