Mechanisms Controlling Variability of the Interhemispheric Sea Surface Temperature Gradient in the Tropical Atlantic

Abstract The seasonal evolution of sea surface temperature (SST) fields in the tropical Atlantic is explored for composites of extremely STRONG and WEAK northward SST gradients, because these are known to control the basinwide pressure gradient, latitude position of the intertopical convergence zone (ITCZ), and regional rainfall. Aimed at the origin and maintenance of anomalies in the interhemispheric SST gradient, and using surface and subsurface marine observations, differences in forcing of SST patterns from surface heat fluxes and entrainment are scaled by calendar-monthly mixed layer depth, and compared to the observed evolution of SST. For years with a STRONG as compared to WEAK gradient in boreal winter, a substantial portion of anomalous SST evolution from September to February can be attributed to departures in SST forcing by latent heat transfer: in the North Atlantic, strengthened northeast trades associated with a stronger North Atlantic high promote enhanced evaporative cooling, while weakene...