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Published byClaire Byrd Modified over 9 years ago
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Cloudnet Workshop April 2003 A.Tompkins 1 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
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Cloudnet Workshop April 2003 A.Tompkins 2 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
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Cloudnet Workshop April 2003 A.Tompkins 3 Total Water q t = vapour + liquid + ice q sat G(q t ) Cloudy Region qvqv q l +q i 1. The PDF form G(q t ) 2. The moments of the distribution 3. The mean saturation mixing ratio q sat Cloud cover can be derived Horizontal GCM grid points Statistical Schemes for Cloud Parameterization
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Cloudnet Workshop April 2003 A.Tompkins 4 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
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