The Akio Arakawa Symposium


Understanding the summertime large-scale circulation: implications for monsoon dynamics

Simona Bordoni, Univ. of California, Los Angeles, CA; and T. Schneider and B. Stevens

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.

Poster Session 1, Poster Session
Tuesday, 16 January 2007, 9:45 AM-11:00 AM, Exhibit Hall C

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