ZONAL AND MERIDIONAL CIRCULATIONS IN THE EQUA-TORIALZONE AS DEDUCED FROM THE DIVERGENCE FIELD OF THE SURFACE WIND

The zonal and meridional circulations and their variability arc examined on the basis of the surface wind data for 1950-1979. The climatological mean zonal wind and its divergence arc examined in reference to the Walker Circulation. The role played by the meridional circulation in contributing to convergence of the surface wind field within the equatorial zone is emphasized. Regression coefficients are used to infer seasonal mean anomalies of divergence of the surface wind in years when the sea level pressure is 1 hPa above normal at Darwin, a condition representative of El Nino events. It is shown that anomalies in the divergence associated with the meridional wind component are primarily responsible for the heavy precipitation in the Central Pacific, while the anomalous divergence associated with the zonal wind component may cause the drought in the Western Pacific near Indonesia. A similar pattern of divergence anomalies is evident during three consecutive seasons beginning in northern summer and end