Gerd-Jan van Zadelhoff

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Comparing ice-cloud microphysical properties
using Cloudnet ARM data.
Gerd-Jan van Zadelhoff
Dave Donovan
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GOAL Compare and evaluate microphysical cloud
properties at 3 sites
2 sites coastal Europe, 1 site Southern great
plains USA

Site
Instrument
Period
1. Cabauw

• 35 GHz Radar

Oct 2001 June 2003

• 905 nm CT-75 Ceilometer

• ECMWF data (T P)

Oct 2001 March 2002
2. Chilbolton

• 94 GHz Radar (Galileo)

• 905 nm CT-75 Ceilometer

Due to problems with Galileo only Zgt -20 dB is
used

• ECMWF data (T P)

3. ARM

• 35 GHz Radar

Nov/Dec 1996 June 1997 Jan July 2000

• 532 nm Micro Pulse Lidar (MPL)

• Sonde data (T P)

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Selection of cloud typed

• T lt -2 oC
• Radar and Lidar top of
• cloud are roughly the same.
• Ice-clouds are optically thin.

1. Ice clouds
2. Visible in both Lidar and Radar

Both Radar and Lidar
Only Radar
24-05-2002
11-03-2002
Particle sizes (Reff)
Only Lidar
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Selection of cloud typed

• T lt -2 oC
• Radar and Lidar top of
• cloud are roughly the same.
• Ice-clouds are optically thin.

1. Ice clouds
2. Visible in both Lidar and Radar

INCLUDED
EXCLUDED
Particle sizes (Reff)
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High Cloud Statistics
Frequency of cumulated IR transmissive clouds
above 4 km.
(11 year mean of the month June, HIRS data NOAA)
Wylie Menzel (1998)
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Comparing vertical cloud statistics at the three
sites.
Observed low t clouds
ARM
Cabauw
Chilbolton
Shown is the normalized cloud height distribution
FOR EACH cloud pixel detected
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Example for an ice-cloud measured at Cabauw.
Radar Reflectivity (KNMI 35 GHz)
Effective radius of the particles (Reff)
Relative Backscatter (KNMI CT-75)
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How to deal with the observed clouds
Define the regions wherein 10, 30, 60, 90 and 99
of all observed values reside
Plot for every cloud pixel the appropriate values
(T vs Reff)
Calculate the mean in each x-bin (DT) and the
s of the distribution
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Reff vs. T
Doppler velocity vs. Reff
ARM vs CABAUW
a vs. Z
IWC vs Z
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Height vs. particle size
Reff vs T (complex poly-crystals)
Height vs. Size
ARM vs CABAUW
Depth from top of cloud vs. Size
IWC distribution
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Dependence of the retrieved particle sizes on Z.
Height dist. of the probed clouds (with lower
limit to used Z data)
Particle size versus Temperature (with lower
limit to used Z data)
Need to use data with Z gt -20 dBz for comparison
with The GALILEO radar in the 2001-2002 period.
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Reff vs. T
IWC vs. Z (complex poly-crystals)
-ARM
-Cabauw
-Chilbolton
Depth from top of cloud vs. Size
Height vs. particle size
Z gt -20 dB
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Seasonal influences on the low optical depth ice
clouds
Top row Cabauw
WINTER SPRING SUMMER AUTUMN
HEIGHT
Reff
Log10(IWC)
HEIGHT
Bottom row ARM
Reff
Log10(IWC)
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CONCLUSIONS

• Cabauw Chilbolton show very similar results
• (for Z gt -20 dBz)

• Derived parameter relations depend strongly on
  the lowest
• value of Z for Z gt -30 dBz

3. The ARM site has higher and thicker
ice-clouds the latter results in a larger
particle size distribution.
4. The cabauw site shows no seasonal dependence
for the low optical depth ice-clouds
studied here. The ARM site shows a small
dependence.
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THE END !
THANKS DAVE !!!
For questions or comments ask Dave or contact
me zadelhof_at_knmi.nl