Organized Convection Parameterization for Global Climate Models

Impressive advances have been made over 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 for global climate models (GCMs) has languished. Being neither resolved nor represented by convective parameterizations, organized convection is indeed a “missing process” in contemporary GCMs. This omission raises important issues that include but are not restricted to mesoscale extremes, severe convective weather, and the distribution, type, and intensity of precipitation. In a warmer-world scenario, it is unlikely that such issues can be fully addressed or successfully projected without serious attention to the treatment of organized convection in GCMs. A mesoscale dynamical system paradigm -- multiscale coherent structure parameterization (MCSP) -- treats organized moist convection as coherent structures embedded in a turbulent environment. The transport modules are observationally verified dynamical models based on nonlinear conservation principles. Cloud-system resolving numerical simulations of a MJO event during the Year of Tropical Convection (YOTC) reveal self-similar properties for squall lines, MCSs, and tropical superclusters. These properties are treated by the coherent structure concept in the form of lagrangian slantwise layer overturning models A computationally efficient prototype implemented in the NCAR Community Atmosphere Model (CAM) provides an encouraging proof-of-concept. Therein, the effects of organized convection are simply the difference between CAM simulations with and without MSCP. Consistent with TRMM precipitation measurements, the upscale effects of top-heavy convective heating and momentum transport by MCSP spontaneously generate large-scale patterns of precipitation in the tropical warm-pool/maritime continent region, improve the ITCZ, and also have positive effects on convectively coupled tropical waves and the Madden-Julian oscillation.