Stratus Cloud parameters retrieval from Doppler radar
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Stratus Cloud parameters Stratus Cloud parameters retrieval from Doppler radarretrieval from Doppler radar
Virendra P. GhateVirendra P. Ghate
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OutlineOutline IntroductionIntroduction Radar spectra and DSDRadar spectra and DSD Model setupModel setup Observations & ResultsObservations & Results SHEBA dataSHEBA data Model Observation comparisonsModel Observation comparisons ConclusionConclusion
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Cloud Radar Spectra Cloud Radar Spectra
Reflectivity dBZ=10*log10(Z)Doppler VelocityDoppler Spectrum Width
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Lognormal DSDLognormal DSD
202xx
(x x )Nn exp22 r
x=loge(r)x0=loge(r0)
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ParametersParameters
KnownKnown ReflectivityReflectivity Doppler VelocityDoppler Velocity Doppler Spectrum Doppler Spectrum
widthwidth
UnknownUnknown Total Number of Total Number of
DropletsDroplets Modal RadiusModal Radius Lognormal WidthLognormal Width
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Moments are relatedMoments are related
2k k 2
0 xkr r exp2
k6f
k6D
r V rV
r
2x
0 D
13r a V b exp2
DSD Moment Doppler Moment
2x
6 60
Zexp( 18 )N2 r
σx=0.35???
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Cloud Vs DrizzleCloud Vs Drizzle
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Cloud Vs DrizzleCloud Vs Drizzle
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ObservationsObservations
Atlantic Stratocumulus Transition Atlantic Stratocumulus Transition Experiment (ASTEX)Experiment (ASTEX)
Porto Santo, Portugal; June 1992Porto Santo, Portugal; June 1992
InstrumentInstrument ProductProduct
35 GHz cloud Doppler 35 GHz cloud Doppler radarradar
Reflectivity, Doppler Reflectivity, Doppler velocity, spectrum velocity, spectrum widthwidth
3 channel Radiometer3 channel Radiometer Liquid Water path, Liquid Water path, Water vapor pathWater vapor path
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Observations on 6 June 1992Observations on 6 June 1992
Northcomp
Eastcomp
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RetrievalsRetrievals
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LWC RetrievalLWC Retrieval
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Cooling Rate RetrievalCooling Rate Retrieval
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ConclusionsConclusions Technique to derive cloud and drizzle Technique to derive cloud and drizzle
DSD, LWC from first three Doppler DSD, LWC from first three Doppler moments.moments.
Need to average long enough to Need to average long enough to compensate for turbulent vertical compensate for turbulent vertical velocity, horizontal homogeneity etc.velocity, horizontal homogeneity etc.
Potential for surface based remote Potential for surface based remote sensors to do long-term monitoring.sensors to do long-term monitoring.
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Frisch Model TestFrisch Model Test
Get Known DSD
Compute radar Moments Apply Frisch Model
Calculate Bulk Parameters
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SHEBA/FACESHEBA/FACE Surface Heat Budget of the Arctic OceanSurface Heat Budget of the Arctic Ocean
• 1995-1996; 1997-1999; 2000-20021995-1996; 1997-1999; 2000-2002 FIRE Arctic Cloud Experiment (FACE) FIRE Arctic Cloud Experiment (FACE)
• April – July 1998April – July 1998
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InstrumentationInstrumentation
InstrumentInstrument CharacteristicsCharacteristics
Forward Scattering Forward Scattering Spectrometer Probe Spectrometer Probe (FSSP)(FSSP)
16 Channel, 16 Channel, 2–47 µm,2–47 µm,~3 µm binwidth~3 µm binwidth
1D Optical Array Probe 1D Optical Array Probe (OAP)(OAP)
64 Channel, 64 Channel, 40-600 µm,40-600 µm,10 µm binwidth10 µm binwidth
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DataData 18 July 1998 2230 UTC to 19 July 0300 18 July 1998 2230 UTC to 19 July 0300
UTCUTC
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Calculated dBZ and VCalculated dBZ and VDD
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Frisch derived DFrisch derived D00 and N and N
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DSD ComparisonDSD Comparison
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Liquid Water ContentLiquid Water Content
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ConclusionsConclusions
Frisch technique can be applied to Frisch technique can be applied to retrieve cloud/drizzle characteristics retrieve cloud/drizzle characteristics under Stratiform conditions.under Stratiform conditions.
The DSD obtained from the The DSD obtained from the technique might not fit the observed, technique might not fit the observed, but the bulk parameter (LWC etc.) but the bulk parameter (LWC etc.) are reasonably retrieved.are reasonably retrieved.
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