aerosol properties in partly cloudy regions...aerosol properties in partly cloudy regions tamás...

AerosolPropertiesinPartlyCloudyRegions

Tamás Várnai1,2,AlexanderMarshak1,Guoyong Wen1,3,RobertLevy1,ThomasEck1,4

1:NASAGSFC,2:UMBCJCET,3:MorganStateUniv.,4:USRA

Aerosolsaresometimesnearclouds

Saharandust&cloudsArctichaze

ViewfromDC-8;A.Wisthaler,NOAA ViewfromG-IV,J.Dunion,NOAA

DSCOVRspacecraft,EPICimager,February1,2018

Mostclearareasarenottoofarfromclouds

Aerosolsaredifferentnearclouds

“…aerosolmeasuredinthevicinityofcloudsissignificantlydifferentthanitwouldbewerethecloudfield,anditsproximatecause(highhumidity),notpresent”.

IPCCAR5,Chapter7

Aerosolsaredifferentnearcloudsdueto:

• Aerosolswelling• Cloudprocessingofaerosols• Newparticleformation

Remotesensingissuescanexaggeratethedifferences:

• Undetectedclouddroplets• 3Dcloudadjacencyeffect• Instrumentblurring

3Dadjacencyeffect

Projectgoals:

• Advanceourunderstandingontheeffectofcloudsandcloud-relatedprocessesonaerosolpropertiesandaerosolradiativeforcing.

• ImprovetheinterpretationofMODISandVIIRSaerosolobservationsnearcloudsthroughacorrectionmodelaccountingfortheadjacencyeffectofclouds.

eMAS dataoftenshownear-cloudaerosolenhancementsAODCloudmaskRGBimage

37km 37km

AODCloudmaskRGBimage

NASAER-2eMAS,SEAC4RS,Kentucky&Alabama,August30,2013

AquaMODIS,August5,2016

AODMODISimage

Satelliteimagesalsoshownear-cloudenhancement

CF-AODcorrelationispositivethroughouttheglobe

CF-AODcorrelation-0.500.5

MODIS MERRA-2

June-July-August,2012-2014 Similarbehaviorforothermodels(e.g.,Quaas etal.,ACP,2010)

AODincreaseswithbothCFandproximitytoclouds

Sept.14-29,2002-2011

Retrieved0.55µmAODis50%higherinthehalfofdatathatisclosertoclouds

CF: large-scale environment

D: effect of individual clouds

AEdecreasesnearcloudsevenifitincreaseswithCF

Sept.14-29,2002-2011

6km

3km

largerparticlessm

allerp

articles

Wavelength

AOD

Angstromexponent:“steepness”ofspectralslope

WhenCFincreases,inmanyareastheaerosolpopulationshiftstowardsmallersizes

MODISAqua,DJF2012-2014

ShifttosmallersizeShifttolargersize

AEcanincreasewithCFduetosmallmodeswelling

MODISAqua,JJA2012-2014

MODISobservation Simulationofsmallmodeswelling

Shiftto

ward

⇐largersizesm

allersize

⇒

• cloud contamination is not dominant (MAIAC, VIIRS 375 m TIR) • small mode swells more (MAIAC, MERRA-2, CALIOP)• cloud processing creates small aerosols (MERRA-2)• 3D adjacency effect

MODISAqua,JJA2012-2014

AODoftenincreaseswithCFmoreforsmallmode

3Dadjacencyeffect

AODincreasesmorewithCFforCoarsemodeSmallmode

MAIAC,MODISAqua,July31,2011,Baltimoreregion

400km

Globaloceans,60°N– 60°S,Nov.2006- Oct.2007

Distancetonearestcloud[km]

Relativeen

hancem

ent

inparticlesc

atterin

g[%

]MODISCALIOP

3Dcausessignificantpartofnear-cloudenhancements

CALIOPcanobserveenhancementsfrom:

• Aerosolswelling• Cloudcontamination• Cloudprocessing

Itisnotaffectedby:

• 3Denhancement• Instrumentblurring

Analyticalmodelistestedforremoving3Denhancements

0.55µmreflectance

3Dre

flectanceenh

ancemen

t,△R

Cloudalbedo

Truevalue(MonteCarlo)Analyticalmodelestimate

3DcorrectionoverlandreducesretrievedAOD-sandincreasesAngstromexponents

15eMAS flightsegmentsoverSouth-CentralUSduringSEAC4RS(2013)

0 5 10 15Flight Track #

0.5

0.6

0.7

0.8

Aver

age

AE

Orig Corr ∆AE = 8.8%

0 5 10 15

0.0

0.2

0.4

0.6

0.8

1.0

Aver

age

AOT

Orig Corr

0.47µm∆τ = 9.8%

0 5 10 15

0.0

0.2

0.4

0.6

0.8

1.0

Orig Corr

0.55µm∆τ = 10.5%

0 5 10 15Flight Track #

0.0

0.2

0.4

0.6

0.8

1.0

Aver

age

AOT

Orig Corr

0.66µm∆τ = 11.2%

0 5 10 15Flight Track #

0.0

0.2

0.4

0.6

0.8

1.0

Orig Corr

2.13µm∆τ = 13.8%

AverageAO

D

Flighttrack#

34km

Distancetonearestcloud[km]

Relativeen

hancem

ent[%]

OriginalCorrected

OriginalCorrected

AverageAE

(0.47–0.65

µm)

Online3Dradiativetransfersimulatorisavailable• Quick1D&3DMonteCarlosimulationsthroughwebinterface(15sec- 4min)• Reflectanceat5MODISwavelengths:0.47,0.55,0.65,0.86,2.13µm• Goal:helpinitialexplorationofideas,classprojects• PartoftheIntercomparison of3DRadiationCodes(I3RC)project:i3rcsimulator.umbc.edu

SampleinputLESfields

Summary• CloudfractionandAODarepositivelycorrelatedthroughmosttheglobeandforall

aerosoltypes.CorrelationisstrongerforMODISthanMERRA-2.

• Inmanyareas,aerosolsizedistributionsshifttowardsmallersizesasCFincreases,butitalwaysshiftstowardlargersizenearclouds.

• 3Dradiativeeffectshaveasignificantimpactonsatelliteradiancesnearclouds,wherealargeportionofclear-skycolumnsoccur.

• Ananalyticalmodelisbeingdevelopedtohelpaerosolretrievalsbyestimating3Dreflectanceenhancements.

MODISAqua,JJA2012-2014

MODISCF&AODwell-correlatedforallMERRA-2aerosoltypes

Aeronet:AODjumpswhencloudsappear,butaerosolsizedistributiondoesnotchange

Ecketal.(2014),DISCOVER-AQ

Wavelength

AOD

Angstromexponent:“steepness”ofspectralslope

Impactof3Deffectvarieswithretrievalalgorithm

3Deffectsvarywith• Wavelength(deepbluevs.darktarget)• Polarization(POLDERvs.MODIS)• Viewdirections(MISRvs.MODIS)

POLDER:3Deffectsdonotcauseproblemsif

CF<5%ortcloud <5

ForCF=25%andtcloud =10:

DAOD=0.12(≈25%),DSSA=0.09

Stap etal.(JQSRT,2016):

Aeronet:smallmodeincreasesnearclouds

Ecketal.(2014)

Analyticalmodelistestedforremoving3Denhancements

80LES-basedscenes(FrankEvans)

･ R3D – R1D･ R3Dcorr – R1D

0.55µmreflectance

3DcorrectionoveroceanreducesretrievedAOD-sandcanchangeAngstromexponentseitherway

31MODISgranulesofftheWestcoastofNorth&SouthAmerica,August1-8,2013

Original:<AE>=0.62Corrected:<AE>=0.66

Angstromexponent

Aerosolopticaldepth(0.55µm)

PDF

AOD

Original:<AOD>=0.086Corrected:<AOD>=0.069

AirborneHSRL:aerosolopticaldepth(AOD)canbelargernearclouds,butnotalways

Suetal.(2008)