Understandinghowlarge-scalecirculationaffectslow-levelclouds:

HowbesttouseACE-ENAdata?

CatherineNaud,JimmyBooth,andFayçal Lamraoui Seealso:F.Lamraoui talk,Tuesday11.30amPoster,Tuesday,#69,A2

Contextforourresearchinterests:coldsectorofextratropicalcyclones• Whatarepost-coldfrontal(PCF) conditions?Coldsectorofacyclone,regioninthewakeofacoldfrontwithstrongsubsidenceandmostlylow-levelclouds• Whyareweinterested?GCMssufferfromunderestimateinlow-levelcloudamount,anditismostacuteinpost-coldfrontalregions.Thisissueisproblematicforsouthernhemisphereenergetics.• Whatdowedo?Moreobservationsneededofcloudpropertiesthemselves(notspecificallyexaminedyet),andimportanttohavethisinfoforconstraining/evaluatingshallowconvectionandPBLparameterizations• Howdowedoit?UseENAsiteobservationstogetabetterunderstandingofcloudsinPCFsandcontrastwithnon-PCFlow-levelclouds

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

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=>

Cloudbaseandtopheightdistributions:PCFvs.non-PCF

Solid=non-PCF

Dashed=PCF

CloudsarehigherinPCFconditions,becausePBLisdeeper

Environment:PCFvs.non-PCF

- PCFdynamicallymoreactive:strongersubsidence(a),strongersurfacewinds(b)

- EISandMindicatelowerstabilityinPCF(d,e)whilesurfacetemperaturecontrast/forcingslightlystrongerforPCF(f)

- InversionoccurslessofteninPCFthannon-PCF,butwhenitdoes,itishigher(g)

- RH&PWindicatedrierconditionsinPCF(h,i)

WhatmattersmostforcloudboundariesinPCF?

Stability surfaceforcing Dynamics Moisture

Vertica

lextent

CTH

CBH CBH:stability

(EIS/M)andmoisture(RH/PW)

CTH:stability(M)andsurfacewind

Cloudverticalextent:stability(M)andwind

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.