West African Monsoon Dynamics and Eastern Equatorial Atlantic and Pacific SST Anomalies (1970–88)

Serge Janicot,Vincent Moron,Bernard Fontaine,Ali Harzallah

doi:10.1175/1520-0442-11.8.1874

Abstract

Abstract The Laboratoire de Météorologie Dynamique atmospheric GCM is used to investigate relationships between West African monsoon dynamics and SST anomalies in the eastern equatorial Atlantic and Pacific for the period 1970–88. Positive SST anomalies in the eastern equatorial Pacific, mainly associated with a larger east–west divergent circulation over the tropical Atlantic, are found to coincide with negative rainfall anomalies over West Africa. This is the case for the composite ENSO warm episodes of 1972, 1976, 1982, and 1983. By contrast, positive SST anomalies in the eastern equatorial Atlantic are accompanied by a southward shift of the intertropical convergence zone along with negative rainfall anomalies in the Sahel and positive rainfall anomalies in the Guinean region. This was the case in 1987. The ENSO warm event during this year had apparently no significant impact on West African monsoon dynamics. A zonal atmospheric coupling associated with differences of SST anomalies between the eastern equatorial Pacific and the Atlantic is evident in the period 1970–88. Positive (negative) phases of this coupling could enhance the impact of ENSO warm (cold) events on West African monsoon dynamics.

Highlights

It is well known that connections between northern summer Sahel rainfall and sea surface temperature (SST) anomalies involve the global oceans (Folland et al 1986; Palmer 1986; Semazzi et al 1988, 1989; Ward 1992)
Statistical relationships are not unique (Rowell et al 1995): at the interdecadal timescale, the Sahel rainfall is correlated to an interhemispheric SST dipole pattern, whereas at the interannual timescale, correlations between Sahel rainfall and SST are stronger on the eastern equatorial Pacific
We investigate the role of the tropical divergent atmospheric circulation in connection with the relationship between the West African monsoon and SST anomalies in the eastern equatorial Atlantic and Pacific basins for the period 1970–88

Summary

Introduction

It is well known that connections between northern summer Sahel rainfall and sea surface temperature (SST) anomalies involve the global oceans (Folland et al 1986; Palmer 1986; Semazzi et al 1988, 1989; Ward 1992). We investigate the role of the tropical divergent atmospheric circulation in connection with the relationship between the West African monsoon and SST anomalies in the eastern equatorial Atlantic and Pacific basins for the period 1970–88.

Results

Conclusion