TROPICAL ATLANTIC SEA-SURFACE TEMPERATURE VARIABILITY AND ITS RELATION TO EL-NINO SOUTHERN-OSCILLATION

Past analyses of tropical Atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tr opics, across the Intertropical Convergence Zone (ITCZ). By analyzing an improved 43-year (1950-1992) record of SST [Smith er al., 1996] and other data derived from the Comprehensive Ocean-Atmosphere Data Set ( GOADS), it is shown that the regions north and south of the ITCZ are s tatistically independent of each other at the seasonal to interannual timescales dominating the data, confirming the conclusions of Houghton and Tourre [1992]. Some dipole behavior does develop weakly during th e boreal spring season, when there is a tendency for SST anomaly west of Angola to be opposite of that in the tropical North Atlantic. It is further shown that tropical Atlantic SST variability is correlated wi th Pacific El Nino-Southern Oscillation (ENSO) variability in several regions. The major region affected is the North Atlantic area of NE tr ades west of 40 degrees W along 10 degrees N - 20 degrees N and extend ing into the Caribbean. There, about 50-80% of the anomalous SST varia bility is associated with the Pacific ENSO, with Atlantic warmings occ urring 4-5 months after the mature phases of Pacific warm events. An a nalysis of local surface flux fields derived from GOADS data shows tha t the ENSO-related Atlantic warmings occur as a result of reductions i n the surface NE trade wind speeds, which in turn reduce latent and se nsible heat losses over the region in question, as well as cooling due to entrainment. This ENSO connection is best developed during the bor eal spring following the most frequent season of maximum ENSO anomalie s in the Pacific. A region of secondary covariability with ENSO occurs along the northern edge of the mean ITCZ position and appears to be a ssociated with northward migrations of the ITCZ when the North Atlanti c warmings occur. Although easterly winds are intensified in the weste rn equatorial Atlantic in response to Pacific warm events, they do not produce strong local changes in SST. Contrary to expectations from st udies based on equatorial dynamics, these teleconnected wind anomalies do not give rise to significant correlations of SST in the Gulf of Gu inea with the Pacific ENSO. As the teleconnection sequence matures, st rong SE trades at low southern latitudes follow the development of the North Atlantic SST anomaly and precede by several months the appearan ce of weak negative SST anomalies off Angola and stronger positive ano malies extending eastward from southern Brazil along 15 degrees-30 deg rees S.