1. 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

2. 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

3. 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

4. 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