Transcript Cloud parameter retrieval from cloud Doppler radar

Stratus Cloud parameters
retrieval from Doppler radar
Virendra P. Ghate
Outline
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Introduction
Radar spectra and DSD
Model setup
Observations & Results
SHEBA data
Model Observation comparisons
Conclusion
Cloud Radar Spectra
Reflectivity dBZ=10*log10(Z)
Doppler Velocity
Doppler Spectrum Width
Lognormal DSD
 (x  x 0 )2 
N
n
exp  

2
2

2rx
x


x=loge(r)
x0=loge(r0)
Parameters
Known
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Reflectivity
Doppler Velocity
Doppler Spectrum
width
Unknown
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Total Number of
Droplets
Modal Radius
Lognormal Width
Moments are related
DSD Moment
r
k
Doppler Moment
2

k
k
2 
 r0 exp   x 
 2

Vk
 132x 
r0  a V D  b exp 

 2 

r  Vf  r  
6

Zexp(18 )
N
6 6
2 r0
2
x
D

r6
σx=0.35
???
k
Cloud Vs Drizzle
Cloud Vs Drizzle
Observations
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Atlantic Stratocumulus Transition
Experiment (ASTEX)
Porto Santo, Portugal; June 1992
Instrument
Product
35 GHz cloud Doppler Reflectivity, Doppler
radar
velocity, spectrum
width
3 channel Radiometer Liquid Water path,
Water vapor path
Observations on 6 June 1992
North
comp
East
comp
Retrievals
LWC Retrieval
Cooling Rate Retrieval
Conclusions
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Technique to derive cloud and drizzle
DSD, LWC from first three Doppler
moments.
Need to average long enough to
compensate for turbulent vertical
velocity, horizontal homogeneity etc.
Potential for surface based remote
sensors to do long-term monitoring.
Frisch Model Test
Get Known DSD
Calculate Bulk Parameters
Compute radar Moments
Apply Frisch Model
SHEBA/FACE
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Surface Heat Budget of the Arctic Ocean
• 1995-1996; 1997-1999; 2000-2002
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FIRE Arctic Cloud Experiment (FACE)
• April – July 1998
Instrumentation
Instrument
Forward Scattering
Spectrometer Probe
(FSSP)
1D Optical Array Probe
(OAP)
Characteristics
16 Channel,
2–47 µm,
~3 µm binwidth
64 Channel,
40-600 µm,
10 µm binwidth
Data
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18 July 1998 2230 UTC to 19 July 0300
UTC
Calculated dBZ and VD
Frisch derived D0 and N
DSD Comparison
Liquid Water Content
Conclusions
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Frisch technique can be applied to
retrieve cloud/drizzle characteristics
under Stratiform conditions.
The DSD obtained from the
technique might not fit the observed,
but the bulk parameter (LWC etc.)
are reasonably retrieved.