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Changes to the ECMWF cloud scheme

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

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Changes to the ECMWF cloud scheme

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  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. 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. qv ql+qi Cloudy Region G(qt) Total Water qt= vapour + liquid + ice qsat Statistical Schemes for Cloud Parameterization Horizontal GCM grid points 1. The PDF form G(qt) 2. The moments of the distribution 3. The mean saturation mixing ratio qsat Cloud cover can be derived

  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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