WEST-AFRICAN MONSOON DYNAMICS AND EASTERN EQUATORIAL ATLANTIC AND PACIFIC SST ANOMALIES (1970-88)

The Laboratoire de Meteorologie Dynamique atmospheric GCM is used to i nvestigate relationships between West African monsoon dynamics and SST anomalies in the eastern equatorial Atlantic and Pacific for the peri od 1970-88. Positive SST anomalies in the eastern equatorial Pacific, mainly associated with a larger east-west divergent circulation over t he tropical Atlantic, are found to coincide with negative rainfall ano malies over West Africa. This is the case for the composite ENSO warm episodes of 1972, 1976, 1982, and 1983. By contrast, positive SST anom alies in the eastern equatorial Atlantic are accompanied by a southwar d shift of the intertropical convergence zone along with negative rain fall anomalies in the Sahel and positive rainfall anomalies in the Gui nean region. This was the case in 1987. The ENSO warm event during thi s year had apparently no significant impact on West African monsoon dy namics. A zonal atmospheric coupling associated with differences of SS T anomalies between the eastern equatorial Pacific and the Atlantic is evident in the period 1970-88. Positive (negative) phases of this cou pling could enhance the impact of ENSO warm (cold) events on West Afri can monsoon dynamics.