Large-scale organization of moist convection in idealized aquaplanet simulations

This 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.