Abstract
Vertical motion fields at 850 mbar over the tropical Pacific region are calculated from the 1963–1973 mean wind fields for 4 months of the year and for October 1972, the peak month in the 1972–1973 El Niño event. These vertical motion fields are derived using the projective separation technique, which has the unique property of separating vertical motion into components due to meridional wind convergence and zonal wind convergence. This separation permits investigation of the response of the Hadley and Walker circulations to annual and interannual variation of the sea surface temperature in the tropical Pacific. The large‐scale features of the computed vertical motion fields are in agreement with those of highly reflective clouds, which indicate the locations of deep convection. Examination of the annual cycle of the vertical motion and its components shows no strong variation of the Walker circulation with the east‐west gradient of sea surface temperature. On the other hand, a strong correlation is found between meridional overturning in the eastern Pacific and the local equatorial sea surface temperature: during El Niño events, the eastern and central Pacific contribution to the Hadley circulation tends to increase.
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