Organized Convection Parameterization for Global Climate Models

Impressive advances have been made during recent decades in our understanding of the physics and dynamics of organized moist convection, notably the mesoscale convective system (MCS). But the parameterization of organized convection in GCMs has languished severely. A new dynamical systems paradigm, referred to as multiscale coherent structure parameterization (MCSP), treats organized convection (e.g., MCS) as coherent structures embedded in a turbulent environment. Specifically, the heat and momentum transport tendencies by organized convection are derived from observation-verified Lagrangian models based on nonlinear conservation principles. Numerical simulations of a MJO event during the Year of Tropical Convection (YOTC) identifies self-similar properties for squall lines, MCSs, and tropical superclusters approximated by the dynamical models. A computationally efficient prototype MCSP implemented in the NCAR Community Atmosphere Model (CAM 5.5) provides proof-of-concept. Differences between simulations with and without MSCP directly measure the effects of organized convection on the global atmosphere. Consistent with TRMM measurements, the upscale effects of MCSP generates large-scale precipitation patterns in the tropical warm-pool/maritime continent region, improves the ITCZ, and positively affects the MJO and convectively-coupled tropical waves. Organized convective momentum transport and top-heavy convective heating are found to have distinct effects.