understanding how large-scale circulation affects low ...sector of extratropical cyclones •what...
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Understandinghowlarge-scalecirculationaffectslow-levelclouds:
HowbesttouseACE-ENAdata?
CatherineNaud,JimmyBooth,andFayçal Lamraoui Seealso:F.Lamraoui talk,Tuesday11.30amPoster,Tuesday,#69,A2
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Contextforourresearchinterests:coldsectorofextratropicalcyclones• Whatarepost-coldfrontal(PCF) conditions?Coldsectorofacyclone,regioninthewakeofacoldfrontwithstrongsubsidenceandmostlylow-levelclouds• Whyareweinterested?GCMssufferfromunderestimateinlow-levelcloudamount,anditismostacuteinpost-coldfrontalregions.Thisissueisproblematicforsouthernhemisphereenergetics.• Whatdowedo?Moreobservationsneededofcloudpropertiesthemselves(notspecificallyexaminedyet),andimportanttohavethisinfoforconstraining/evaluatingshallowconvectionandPBLparameterizations• Howdowedoit?UseENAsiteobservationstogetabetterunderstandingofcloudsinPCFsandcontrastwithnon-PCFlow-levelclouds
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InteractionswithACE-ENA
• Whatitbringsthatisveryusefultous:cloudandaerosoldetailedobservations,atandnearthesite,esp.microphysics.• Whatwecancontribute:- WRFsimulationsofcasestudies(c.fLamraoui etalMWR2018underreview)- synopticclassification:basedonreanalysis/surfaceobservations• Notabledateforextensivestudy:Feb.15coldfrontpassage
WRFsimulation:coldfront(PW)on2015-12-25
Distributionofcloudsbelow5km
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CloudsinPCFsatENAIdentified77casesofPCFcondition(i.e.acoldfronthaspassedoverthesite,northwesterlywindsprevailandsubsidenceforatleast2hoursafterthat)fromCAP-MBLandpost2013:- 2/3rd ofthetimeduringPCFcloudsaredetectedby
micropulse lidar- 85%ofthesecloudshaveacloudbase<3kmand75%
CBHandCTH<3km- Precipitationisonlydetected~6%ofthetime
TocomparePCFcloudstootherlow-levelclouds,weidentifyperiodswith1)subsidenceand2)northeasterlywinds,thatarenotidentifiedasPCFs.è non-PCFperiods
SurfacePressure:PCF=>
PCF“end”=>
Non-PCF=>
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Cloudbaseandtopheightdistributions:PCFvs.non-PCF
Solid=non-PCF
Dashed=PCF
CloudsarehigherinPCFconditions,becausePBLisdeeper
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Environment:PCFvs.non-PCF
- PCFdynamicallymoreactive:strongersubsidence(a),strongersurfacewinds(b)
- EISandMindicatelowerstabilityinPCF(d,e)whilesurfacetemperaturecontrast/forcingslightlystrongerforPCF(f)
- InversionoccurslessofteninPCFthannon-PCF,butwhenitdoes,itishigher(g)
- RH&PWindicatedrierconditionsinPCF(h,i)
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WhatmattersmostforcloudboundariesinPCF?
Stability surfaceforcing Dynamics Moisture
Vertica
lextent
CTH
CBH CBH:stability
(EIS/M)andmoisture(RH/PW)
CTH:stability(M)andsurfacewind
Cloudverticalextent:stability(M)andwind
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Whatdidwelearn?HowcanACE-ENAhelp?
• CloudBoundariesdrivenbyinterplaybetweenlowertropospherestability(EIS)andsurfacefluxes(wind,temperaturecontrast)=>thismakesMagoodmetric• Innon-PCF,weakerwindsmeanweakersensibleheatflux,soMissmallerthanforPCF,butMstillmaindriverofcloudboundaries
• Theseresultsonlyinvolvecloudboundaries(baseandtopheights),butliquid/icecontentunknown,andradiativeimpacttoo=>ACE-ENAcouldhelp• February152018:coldfrontpassageatENAfollowedbyPCFforlongenoughperiodoftime• Multiplecasesofnon-PCFperiodsprior,withnortherlywindsandanticyclonenecessaryforcomparison.