Large‐scale organization of moist convection in idealized aquaplanet simulations

Abstract

AbstractThis paper discusses results from idealized simulations using a non‐hydrostatic general circulation model with Cloud‐Resolving Convection Parameterization (CRCP, the ‘super parameterization’) pertinent to the large‐scale organization of tropical convection. The essence of tropical dynamics is the intricate balance between large‐scale processes—such as radiative transfer, large‐scale waves, monsoons, Hadley and Walker circulations—and the convective dynamics. Traditional approaches to this problem consider either large‐scale models using convection parameterization or cloud‐resolving models in which large‐scale effects are prescribed. The CRCP merges the two approaches. It uses a 2D cloud‐resolving model to represent the impact of cloud‐scale processes—such as convective motions, precipitation formation and fallout, interaction of clouds with radiative and surface processes—in every column of a large‐scale or global model. The global CRCP model is applied to the idealized problem of a rotating constant‐SST aquaplanet in convective–radiative equilibrium. The aquaplanet has the size and rate of rotation of the Earth. The global CRCP simulations feature pronounced large‐scale organization of convection within the equatorial waveguide. Prominent equatorial ‘super cloud clusters’ spontaneously develop in CRCP global simulations and bear a strong resemblance to the Madden–Julian Oscillation observed in the terrestrial tropics. Model results suggest that convective transport of zonal momentum, supposedly due to the impact of organized convection, plays a significant role in the large‐scale organization of tropical deep convection. Copyright © 2002 John Wiley & Sons, Ltd.