The Quasi-Equilibrium Tropical Circulation Model (QTCM) is used to study the moist axisymmetric (Hadley) circulation. The model is solved for an aquaplanet domain with a zonally symmetric equatorial SST distribution and globally uniform insolation. The QTCM calculates moisture explicitly, has a Betts-Miller type convection scheme, and projects the vertical structure of atmospheric variables on a set of basis functions (one each for temperature and moisture, two for momentum) that are designed to optimize the model's representation of tropical convection. Using an intermediate complexity model like the QTCM is ideal for studying the moist Hadley cell as it incorporates explicit physical parameterizations of radiation and cloud physics in a set of semi-analytical equations that are simple compared to those of a GCM.

A goal of this study is to determine the nature of the feedback between the wind-dependent surface fluxes and the strength and width of the Hadley cell. This model has wind-dependent surface fluxes of latent and sensible heat, whereas previous studies of this kind have either used dry models, or moist models with wind-independent surface fluxes. For fixed SST, the circulation strength is found to be strongly dependent on the exchange coefficient in the bulk formula for the surface latent heat flux, indicating that surface flux feedbacks are important in determining the simulated circulation.