Transcript Document

Changes to the ECMWF cloud scheme
 Recent package of changes for 25r3:
 COMPLETE REWRITE OF NUMERICS FOR CLOUD
SCHEME – ALL CLOUD PROCESSES TREATED ON
SAME TIME LEVEL
 Showed that method of solution of equations was
equally important as parameterization methodology
 ICE FALL SPEEDS CHANGED
 Large ice proportion diagnosed as before
 Large ice fall speed as HD90 (function of mass)
 Small ice fall speed 0.15 m/s
 Considerable changes to cloud top entrainment process
 OVERALL EFFECT: More ice, less liquid
Cloudnet Workshop April 2003
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Near Future Upgrades
 New PBL scheme under development
 This has been combined with a diagnostic statistical cloud
scheme
 Symmetrical beta distribution used to diagnose cloud cover
 Beta distribution moments fixed from cloud mass and
vapour mixing ratio
 Cloud cover is no longer a prognostic variable under this
new scheme
Cloudnet Workshop April 2003
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Statistical Schemes for Cloud
Horizontal GCM grid points
Parameterization
qv
ql+qi
Cloudy Region
G(qt)
qsat
Total Water qt=
vapour + liquid + ice
1. The PDF form G(qt)
2. The moments of the distribution
3. The mean saturation mixing ratio qsat
Cloudnet Workshop April 2003
Cloud cover
can be derived
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Far Future developments
 A prognostic variance equation will be added to give the
statistical scheme more flexibility
 Separate ice microphysics will be included:
 Homogeneous nucleation of ice phase
 Autoconversion etc etc…
 Supersaturation wrt ice will be allowed
 Treatment of ice fall out still to be determined (timestep
problems)
 Consistent use of subgrid information in microphysics and
radiation
Cloudnet Workshop April 2003
A.Tompkins
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