A Prototype Organized Convection Parameterization for GCMs

A new approach for treating organized convection in global climate models (GCMs) referred to as multiscale coherent structure parameterization (MCSP) introduces physical and dynamical effects of organized convection that are missing from contemporary parameterizations. The effects of vertical shear on convective structure are approximated by a nonlinear slantwise overturning model based on Lagrangian conservation principles. Simulation of the April 2009 Madden-Julian Oscillation event during the Year of Tropical Convection (YOTC) by the Weather Forecasting and Research (WRF) model at 1.3 grid-spacing identifies self-similar properties for squall lines, MCSs, and superclusters embedded in equatorial waves. The slantwise overturning model approximates this observed self-similarity. The large-scale effects of MCSP are examined in two categories of GCM. Firstly, large-scale convective systems simulated in an aquaplanet model are approximated by slantwise overturning with attention to convective momentum transport. Secondly, MCSP is utilized in the Community Atmosphere Model, Version 5.5 (CAM 5.5) as tendency equations for second-baroclinic heating and convective momentum transport. The difference between MCSP and CAM 5.5 is a direct measure of the global effects of organized convection. Consistent with TRMM measurements, the MCSP generates large-scale precipitation patterns in the tropical warm-pool and the adjoining locale and improves precipitation in the Intertropical Convergence Zone (ITCZ), South Pacific Convergence Zone (SPCZ), and Maritime Continent regions and also positively affects tropical wave modes. In conclusion, the treatment of organized convection by MCSP is salient for the next-generation of GCMs.