West African and Brazilian seasonal rainfall in CFS -- a diagnostic investigation

James A. Carton

University of Maryland


In the tropical Atlantic sector the climate of continental regions is determined by modest shifts of convective zones around their climatological seasonal position. Any misplacement of the modelled position of convection will have consequences for precipitation forecasts. In this talk we focus on the seasonal representation of precipitation and those factors that seem to be responsible for precipitation differences from observations. In boreal winter in the west we find that the ITCZ shifts too far south, while sea surface temperatures in the neighboring ocean are reasonably represented. In boreal summer in the east the ITCZ has differences of both position and intensity, while SSTs in the southeast are 2C too high and the thermocline is too warm.

We next examine the surface heat flux balance in the ocean mixed layer in comparison with data from the PIRATA moorings as well as in comparison with satellite climatologies. We find substantial differences in surface fluxes, such as excess solar radiation, which is partly compensated for by other flux terms. We examine the consequences of these flux differences for the Hadley circulation and the corresponding thermohaline circulation. We conclude with a discussion of amip-type experiment(s) that would help to test our ideas.