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1/3/18
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PVThinkingandtheDynamicTropopause
JimSteenburghUniversityofUtah
SupplementalReading:Lackmann (2011)Chapter4
WhatisPVThinking?Theuseofpotentialvorticity conservationand“invertability”forunderstandinglarge-scaleatmosphericdynamicsandtheevolutionofsynopticweathersystems
PotentialVorticity• Conservedfollowingfluidmotionforadiabatic,
frictionlessflow
• Components– Absolutevorticity
– StaticStability
! = −! !+ ! !"!" !!!!!!!!!!!!!!!"!" = !!
!+ !!
−!"!"!!
q+Dq
p
q
PotentialVorticity• UnitsofKkg-1 m2 s-1
• Define1PVU=10-6 Kkg-1 m2 s-1
• PVistypicallyhigherinthestratosphere(>2PVU)andlowerinthetroposphere(<2PVU)
• DynamicTropopause – Tropopause definedusingPV(Iuse2PVU,others1.5)
2 PVU
Stratosphere ( > 2 PVU)
Troposphere ( < 2 PVU)
DynamicTropopause
Example
Stratospheric Reservoir
Troposphere
DynamicTropopause
PV “Wall”Tropopause Undulation
Not quite a fold
KeyFeatures• Dynamictropopause – tropopause definedusing
potentialvorticity (i.e.,1.5or2.0PVsurface)
• Stratosphericreservoir– regionofhighPVinthestratosphere
• Tropopause undulation– wave-likeundulationinthetropopause
• Tropopause fold– areawherestratosphericairfoldsundertroposphericair
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MeanDistributionofPV• DTheightishighintropics,
lowinhighlatitudes
• DTpressureislowintropics,highinhighlatitudes
• DTpotentialtemperatureishighintropics,lowinhighlatitudes
• Onanisentropicsurface(e.g.,320K)PVincreasestowardthepoles
Bluestein(1993)
DynamicTropopause (DT)Analysis• Ananalysisofvariables(e.g.,wind,pressure)onthe
dynamictropopause
• Advantages– Jets(subtropicalandpolar)arefrequentlyatdifferingpressurelevels,butaretypicallynearthedynamictropopause
– Tropopause pressureorpotentialtemperaturecanbeusedtoidentifyPV“anomalies”&upper-leveltroughsandridges
– Containahugeamountofinformationabouttheupper-levelsonasinglemap
Note how jet cores all intersect same PV isosurface: Dynamic tropopause
The Dynamic Tropopause
GFS144-hforecastvalid12UTC10Feb2010
FromLackmann (2011)LectureNotes
500-mbheightandPV
DynamicTropopause Pressure
Conceptuallystraightforward,butnotconserved
Correspondencewith500mb DynamicTropopause Theta
Conservedforadiabatic,frictionlessflow(canuseadvectiontoexplain/anticipatechanges)
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PVonanIsentropicSurface(315K)
Conservedforadiabatic,frictionlessflow(canuseadvectiontoexplain/anticipatechanges)
PVThinking• Underadiabaticconditions,theevolutionofPViscontrolledbyadvection
– ChangesinDTpotentialtemperature(orPVonanisentropicsurface)canbeanticipatedbasedonadvection
• PVcanbe“inverted”todeducethethewindandthermodynamicfields– Changesinthelarge-scaleflowcanbeanticipatedbasedontheseadvective
changesinDTpotentialtemperature
• Non-conservationofPV(i.e.,changesinDTpotentialtemperaturenotexplainedbyadvection)canbeusedtounderstandhowdiabatic processesinfluencelarge-scalesystems
• Phenomenathatcanbediagnosedinthismannerincludecyclogenesis,troughandridgeamplification,troughfracture,troughmerger,downstreamdevelopment,etc.
PVInversion• PVcanbeinverted
assumingasuitablebalancecondition
• CyclonicPVanomalies(i.e.,locallyhighPV)induceacycloniccirculation
• Anticyclonic PVanomalies(i.e.,locallylowPV)induceananticyclonic circulation
+-
-+
Hoskinsetal.(1985)
PVInversion• Theinducedcyclonic
circulationandtemperatureanomaliesarestrongestnearthePVanomalyandspreadhorizontallyandvertically
• Verticalpenetrationisinverselyproportionaltostability– Highstability=weak
penetration– Lowstability=strong
penetration
+-
-+
Hoskinsetal.(1985)
SynopticApplication• RegionsoflowDTpotentialtemperature(highDTpressure)arecyclonicPV
anomaliesandaccompaniedbyupper-leveltroughs/cyclones
• RegionsofhighDTpotentialtemperature(lowDTpressure)areanticyclonic PVanomaliesandaccompaniedbyupper-levelridges/anticyclones
• Amplification(weakening)ofacyclonicPVanomalyisanindicationofadeveloping(decaying)trof
• Amplification(weakening)ofananticyclonic PVanomalyisanindicationofadeveloping(decaying)ridge
• Strongjetsareusuallyfoundinregionsoflargetropopause pressuregradients(a.k.a.thePVWall)
• Coveredinafuturelecture:CyclogenesisfromaPVperspective
ClassActivity:Real-TimeExamples
• weather.utah.edu graphics
• IDV
Bundles->Real-Time-WX->Diagnostics->PV-Thinking
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ClassActivity:Real-TimeExamples• IdentifythefollowingonaDTpressureandDTtheta
analysis/forecastlooporusingIDV3-Dvisualization– AcyclonicPVanomalyandupper-leveltrough– Ananticlonic PVanomalyandupper-levelridge– APVwall– Atropopausefold– Asubtropicaljet– Apolarjet– Anupper-levelcyclonicPVthatcontributestosurfacecyclogenesis
– AnexampleofPVfilamentformingduetodeformation– Anexampleofridgedevelopmentamplifiedbynon-conservativeprocesses