Abstract
Impressive advances have been made during recent decades in our knowledge of organized convection processes, notably the mesoscale convective system (MCS), but the parameterization of those processes in global climate models (GCMs) has languished. Being neither resolved nor parameterized, organized convection is omitted and thus missing from contemporary GCMs, so its effects on the large-scale environment remain to be quantified. This omission is identified with the questionable general validity of the assumption of a scale-gap between the cumulus and the GCM grid which underpins cumulus parameterization -- MCSs occupy the gap. Cloud-system resolving models show that organized convection in the Madden Julian Oscillation (MJO) is remarkably scale-invariant, i.e., squall lines, MCSs, and tropical superclusters tend to have similar dynamical structure and transport properties. In other words, the MCS-based parameterization can be generalized, albeit with due attention to the mean-state vertical wind-shear. The Multiscale Coherent Structure Parameterization (MCSP) is a new paradigm that treats organized moist convection as coherent dynamical structures in the form of slantwise circulations that overturn entire tropospheric layers (slantwise layer overturning), and is thereby distinguished from mixing-based cumulus parameterization in the turbulent environment of the coherent structures. The large-scale effects of convective organization are simply the difference between GCM runs with and without MSCP. Via the slantwise layer overturning transport module, MCSP generates large-scale coherent structures in a state-of-the-art GCM. Specifically, a prototype MCSP implemented in the Community Atmosphere Model (CAM 5.5) provides an elementary proof-of-concept (Moncrieff et al. 2017). Consistent with the NASA TRMM 3B42 global precipitation database, the upscale effects of organized convective heating and momentum transport (in different ways) generate large-scale patterns of precipitation in the tropical warm-pool and maritime-continent regions. Precipitation distribution in the ITCZ, and the multiscale character of the MJO and convectively coupled tropical waves are improved. The MCSP paradigm, and its advancements, will be implemented in E3SM with emphasis on convective momentum transport and tropical convection-wave interaction.
Moncrieff, M.W., C. Liu, and P. Bogenschutz, 2017: Simulation, modeling and dynamically based parameterization of organized tropical convection for global climate models. J. Atmos. Sci., 74, 1363-1380, doi:10.1175/JAS-D-16-0166.1.