WAARSCHUWINGEN GEVAARLIJK WEER

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Testing a new ice parameterization scheme based
on CloudNET ARM observations.
Gerd-Jan van Zadelhoff

CloudNet Final meeting October 2005
Co-authors Dave Donovan, Erik van Meijgaard
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April 18, 1996, CLARA
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Comparing microphysical ice cloud properties
Comparison of results obtained over coastal
Europe and Central U.S.
Particle size vs. Temperature
Cabauw
ARM
ARM
Cabauw
Size-vs-Fall speed similar between ARM-SGP and
Cabauw
Doppler Velocity vs. Particle size
Size-vs-temperature relationship different for
ARM-SGP and Cabauw ! (Chilbolton and Cabauw
similar)
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Particle size to cloud depth from cloud-top
Reff vs-distance from cloud-top Reff(Dz)
ARM
H lt 1.5 km
1.5 lt H lt 3.0 km
ARM
Cabauw
3.0 lt H lt 4.5 km
Hgt 4.5 km
- Reff(T) ? ARM-SGP Cabauw
results are different - Reff(DZ) ?
ARM-SGP Cabauw results are similar (DZ lt 3 km)
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Comparing mean profiles to normalized cloud
thickness
ARM
Cabauw
- Reff(DZ, complex polycrystals) ? ARM-SGP
Cabauw results are the same within the errors.
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Parameterization of Reff versus cloud thickness
ReffAB(DZ/H)C(DZ/H)2
ARM
AA0A1.H BB0B1.H CC0C1.H
- Reff(DZ, complex polycrystals) Use parabolic
fits to the observed values
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Current Reff(T) relationship in Racmo vs. Obs
Mean Reff-T relationship observed, using Complex
polycrystals as habit.
Current Racmo parameterization
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Reff parameterization distribution.
Resulting distribution (left) of the new Reff
parameterizations based on cloud-thickness.
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Differences due to changes in parameterization
Climate run (1995)
Hindcast run (1995)
Differences in the mean net short wave flux at
the surface and cloud cover. Comparing the new
parameterization with the current operational one.
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Differences due to changes in parameterization
Climate run (1995)
Hindcast run (1995)
Differences in the mean net short wave flux at
the surface and cloud cover. Comparing the new
parameterization with the current operational one.
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Conclusions

• New parameterization gives back both the mean
  Reff-T relationship and its distribution.
• There is no temperature dependent input needed.
• Current vertical resolution RACMO too large for
  thinnest clouds.
• Monthly mean (day night) planetary albedo
  changes by up to 4 in the hindcast case due to
  smaller ice particles.
• Combination of both IWC and Reff has to change
  in RACMO to give observed SW fluxes.
• Comparison of Reff(DH) has to be confirmed using
  all three CloudNET, the ARM SGP, TWP and NSA
  sites.