The retrieval of the LWC in water clouds
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The retrieval of the LWC in water clouds
O. A. Krasnov and H. W. J. Russchenberg
International Research Centre for Telecommunications-transmission and Radar,
Faculty of Information Technology and Systems, Delft University of Technology,
Mekelweg 4, 2628 CD Delft, The Netherlands.
Ph. +31 15 2787544, Fax: +31 15 2784046
E-mail: [email protected], : [email protected]
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Are power laws useful?
bLWCaZ
Radar reflectivity Liquid water content
Dropsize distributionVery sensitive to tail of dsd
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A million droplets of 10 microngive the same radar reflection as one droplet of 100 micron!
A million droplets of 10 micron containa thousand times as much water as one one droplet of 100 micron...
And so: one drizzle droplet changes the reflectivity significantly without changing the liquid water content
drizzle “transition” drizzle
non-drizzling
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Common opinion: No, there is too much scatter due to drizzle
unless
we can identify the drizzle droplets somehow...
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Techniques for identification
• Radar reflectionSeparation based on differences in reflectivity of drizzleand non-drizzling clouds
• High resolution Doppler radarSeparation based on differences in fall speeds
• Radar – lidar combinationSeparation based on differences in sensitivity of reflection on droplet size
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Radar reflection
Non-drizzling
Drizzling
Coarse classification
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Radar and lidar observables in relation to microphysical water cloud.
Radar and lidar observables in relation to microphysical water cloud.
Radar reflectivity vs liquid water content Radar-lidar ratio vs effective radius
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The Radar, Lidar, and Radiometer datasetfrom the Baltex Bridge Cloud (BBC) campaign
August 1- September 30, 2001, Cabauw, NL
• Radar Reflectivity from the 95 GHz Radar MIRACLE (GKSS)
• Lidar Backscattering Coefficient from the CT75K Lidar Ceilometer (KNMI)
• Liquid Water Path from the 22 channel MICCY (UBonn)
All data were presented in equal time-height grid with time interval 30 sec and height interval 30 m.
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Case study: August 28, 2001, Cabauw, NL, 10.12-11.20 The profiles of measured variables
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Case study: August 28, 2001, Cabauw, NL, 10.12-11.20 The profiles of Optical Extinction and Radar-Lidar Ratio
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Z1 = -20 dBZ, Z2 = -10 dBZ; thresholds for radar only
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+ 0 dB
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+ 5 dB
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+ 10 dB
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+ 5 dB
+ 10 dB
0 dB
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Frisch’s algorithmFrisch’s algorithm
2
log0, LWCNaZ
effr
• log-normal drop size distribution
• concentration and distribution width are equal to constant values
max
0
2/1
2/1
)(
)()(
h
h
RMMW
hZ
hZ
h
LWPhLWC
From radiometer’s LWP and radar reflectivity profile:
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Case study: August 28, 2001, Cabauw, NL, 10.12-11.20 Retrieval Results for Frisch’s algorithm
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Case study: August 28, 2001, Cabauw, NL, 10.12-11.20 Histogram of Differences in Retrieval Results for
the Frisch’s and the Radar-Lidar algorithm
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Difference between LWC that retrieved using Frisch method and retrieved from radar-to-lidar ratio
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Frisch’s fittings
Log-Normal DSDN=1000 - 2000 cm-3, = 0.8N=1000 - 2000 cm-3, = 0.1
Case study: August 28, 2001, Cabauw, NL, 10.12-11.20 Representation results on the Z-LWC plane
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Case: cloud without drizzle
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Case study: September 23, 2001, Cabauw, NL, 8.00-10.00 The profiles of measured variables
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Case study: September 23, 2001, Cabauw, NL, 8.00-10.00 The Resulting Classification Map (radar and lidar data)
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Atlas Z-LWC relationshipAtlas Z-LWC relationship
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Frisch’s fittings
Case study: September 23, 2001, Cabauw, NL, 8.00-10.00 The results of Frisch’s algorithm application
Log-Normal DSDN=1000 - 2000 cm-3, = 0.8N=1000 - 2000 cm-3, = 0.1
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Z-LWC relationship based on aircraft data
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Comparison aircraft – radar data
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September 23, 2001, Z+13 dBZ
Merlin flight
Frisch Z-LWC relations after adding 13 dB to Z
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September 23, 2001, Z+13 dBZ
Atlas equation
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September 23, 2001, Z+13 dBZ
Frisch retrievals
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September 23, 2001, Z+13 dBZ
Atlas - Baedi - Drizzle equations
Frisch retrievals –
Z/ retrieval
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Radar intercomparison; Miracle - KNMI
In ice cloudsalso agreement with Tara
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Possible explanations for radar – aircraft difference
Cloud inhomogeneity: temporal and spatial sampling?Clipping of Doppler spectrum?
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Conclusions
Given a proper calibration of the instruments,
• Radar-lidar
• Radar-microwave radiometer
• Radar alone
produce similar LWC profiles of non-drizzling clouds.
What’s going on with the radar data?