NOAA technical report NWS/NCEP ; 99-01

Abstract -- Introduction -- Basic relations -- The updraft cloud model -- The Cheng and Arakawa downdrift -- Modificatioin of the environment -- Vertically discrete formulation -- Semi-prognostic evaluation -- Application strategy -- Summary -- Acknowledgements -- Appendix A. Derivation of the quadratic equation for the entrainment parameter -- Appendix B. Evaporation of falling precipitation in the environment -- References.

"In this report we have provided a detailed documentation of an advanced version of the Relaxed Arakawa-Schubert convection parameterization. This version of RAS includes several important improvements over the original RAS. The cloud model now includes the virtual effects of moisture on buoyancy. It also includes condensate loading and takes into account the production of precipitation as the updraft ascends. Quadratic entrainment is an option that is included with minimal additional complexity. A crude representation of ice phase for the condensate is also included. Detrainment at the cloud top provides a source of cloud condensate for models having cloud condensate as a prognostic variable"--Page 37.

National Weather Service (NWS)