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PVThinkingandtheDynamicTropopause

JimSteenburghUniversityofUtah

Jim.Steenburgh@utah.edu

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