The Dependence of the Low-Level Equatorial Easterly Jet on Hadley and Walker Circulations

How the time-mean Hadley and Walker circulations affect the formation of a low-level equatorial easterly jet is investigated. Experiments are conducted for equinoctial conditions using a general circulation model, the Community Climate Model (CCM1), that includes a Kuo convective scheme and a lower boundary that is specified to be water at a fixed sea surface temperature (SST). Several zonally symmetric SST forcings are used to determine how various Hadley circulations affect the tropical zonal wind field. A zonal wavenumber one equatorial SST anomaly superimposed on a zonally symmetric SST distribution forces a wind field that includes both Hadley and Walker circulations. The Hadley circulation experiments produce equatorial easterlies and low-level jets on the poleward sides of the intertropical convergence zone (ITCZ) 10° to 15° from the equator. In an experiment with a single, dominant off-equatorial ITCZ in the Northern Hemisphere, the Southern Hemisphere jet moves to within 7.5° of the equa...