Response of a Tropical Atmosphere and Ocean Model to Seasonally Variable Forcing1,,2

The atmospheric part of a pre-existing, interacting atmosphere and ocean model has been simplified considerably to provide a 3-yr prediction of intertropical convergence zone (ITCZ) behavior under the influence of seasonally variable solar heating of the sea. As before in shorter term experiments, a cold equatorial surface appears and a single ITCZ develops north or south of the Equator over the surface temperature maximum in the warmer hemisphere. The ITCZ migrates quickly between hemispheres, lagging only slightly behind the seasonal reversal of the hemispheric surface temperature asymmetry. Such behavior is qualitatively in accord with that of the updraft branch of the mean tropical Hadley circulation in the real atmosphere. The lag of maximum subequatorial sea-surface temperature behind the overhead sun of late summer is computed to be 9 weeks, a reasonable value.