Arakawa helped pioneer the development of general circulation models to understand moist circulations. In this study, we use idealized numerical experiments with both a dry and a moist GCM to investigate the response of the Hadley circulation to seasonally varying radiative forcing.

The dry simulations show that, as the latitude of the maximum radiative-equilibrium temperature is progressively displaced off the equator, the cross-equatorial Hadley cell undergoes a regime transition from a regime in which eddy momentum fluxes strongly influence the Hadley cell strength, to a regime in which the influence of eddy momentum fluxes is weak. In this latter regime, the cross-equatorial Hadley circulation closely resembles the large-scale monsoon, featuring surface westerlies, strong ascending motion in the subtropics and a close-to-angular momentum conserving upper branch.

Simulations with a moist model are performed to investigate how moist processes, such as WISHE feedback, affect the transition of the cross-equatorial Hadley cell to a large scale monsoon-like circulation. The question as to what determines the location and northward extent of the large-scale monsoon is also addressed.