Aerosol Properties in Partly Cloudy Regions...Aerosol Properties in Partly Cloudy Regions Tamás...
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Aerosol Properties in Partly Cloudy Regions Tamás Várnai 1,2 , Alexander Marshak 1 , Guoyong Wen 1,3 , Robert Levy 1 , Thomas Eck 1,4 1: NASA GSFC, 2: UMBC JCET, 3: Morgan State Univ., 4: USRA
Transcript of 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)
AOD
Original:<AOD>=0.086Corrected:<AOD>=0.069
AirborneHSRL:aerosolopticaldepth(AOD)canbelargernearclouds,butnotalways
Suetal.(2008)
