Can continental rainfall influence climate variability over tropical Atlantic Ocean

Variability of the tropical Atlantic sea surface temperature (SST) and Intertropical Convergence Zone (ITCZ) peaks in boreal spring (March-April-May), when the cross-equatorial SST gradient is annually weakest and rainfall over South America is strongest. What causes such strong variability and whether large-scale convection over South America could contribute to such variability are open questions key to the understanding of climate variability over the tropical Atlantic Ocean and Pan American regions. Using QuikSCAT ocean surface winds, TRMM daily rainrate and other observations, we have detected systematic changes in direction and magnitude of the surface winds over the tropical western Atlantic induced by rainfall variations over the western Amazon during boreal spring. Such change also has a clear diurnal variation, as expected from strong diurnal variation of the continental rainfall. Systematic changes of ocean surface fluxes associated with large-scale increase of Amazon rainfall are also detected. Using an ocean mixing layer model (Alexander 1992) forced by observed changes of wind stress and surface fluxes, our sensitivity tests suggest that, collectively, the 20% strongest rainy events over Amazon during boreal spring could induce SST anomalies over the western tropical Atlantic comparable to those influenced by El Ni�os. The pattern of the SST anomalies tends to weaken the cross-equatorial SST gradient. We will also discuss possible influence of continental rainfall on the migration and variation of the Atlantic ITCZ during boreal spring season.