Maintenance of the Intertropical Convergence Zones and the Large-Scale Tropical Circulation on a Water-covered Earth

Abstract

How the surface boundary heating (sea surface temperature) and cumulus adjustment process affect the location, structure, energetics, and dynamics of the intertropical convergence zones (ITCZs) is investigated. A series of experiments is performed with a general circulation model where the lower boundary is specified to be water at a fixed sea surface temperature (SST), an aqua planet. All experiments are run using equinoctal insolation with no longitudinal variation in SST. Two different convective parameterization schemes (Kuo and moist convective adjustment) and several different zonally symmetric SST distributions are used in these experiments. The location of the ITCZ is found to be sensitive to the convective parameterization scheme and the SST distribution. The model with the moist convective adjustment scheme produces an ITCZ over the tropical SST maximum, even under conditions where the SST gradient is weak. By contrast, the model with the Kuo convective parameterization is not as sensitive to SST distribution: the model with the Kuo scheme yields two ITCZs straddling the equator at approximately 7° latitude for a wide variety of SST distributions, including when the warmest water is located on the equator. The location of the ITCZ affects the structure and strength of both the time-mean Hadley cells and the subtropical jets. Furthermore, the equatorial wave spectrum is strongly influenced by the type of cumulus parameterization scheme used. The ?convective characteristics? for each parameterization scheme are presented in detail to elucidate the influence of the large-scale environment on convection.