Abstract
The link between El Nino/Southern Oscillation (ENSO) and the equatorial Atlantic precipitation during boreal spring (March–April–May) is explored using a coupled general circulation model (CGCM). Interannual variability of the equatorial Atlantic sea surface temperature (SST) in the CGCM is excluded by nudging the modeled SST toward the climatological monthly mean of observed SST in the equatorial Atlantic, but full air–sea coupling is allowed elsewhere. It is found that the equatorial Atlantic precipitation is reduced (increased) during El Nino (La Nina) in the case where the interannual variability of the equatorial Atlantic SST is disabled. The precipitation anomalies in the equatorial Atlantic during ENSO are not strongly associated with the meridional migration of the Atlantic inter-tropical convergence zone. We find the reduced precipitation in the equatorial Atlantic during El Nino is associated with an enhanced Atlantic Walker circulation characterized by strengthened low-level easterlies and anomalous dry, downward winds over the equatorial Atlantic, while the Pacific Walker circulation is weakened. The upper-level anomalous westerlies over the equatorial Atlantic are consistent with a Matsuno–Gill-type response to heating in the eastern equatorial Pacific. Our results of the CGCM experiments suggest that changes to the Walker circulation induced by ENSO contribute significantly to changes in precipitation over the equatorial Atlantic.
Published Version
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