CLIMATIC ZONAL PRESSURE-GRADIENT IN THE EQUATORIAL ZONE OF THE INDIAN-OCEAN

On the basis of observations at 51 equatorial sections (1962 - 1988) the climatic annual cycle of zonal pressure gradient (ZPG) is studied in the upper 200 m layer with monthly resolution in time. At least in the layer 0-100 m there evidently prevails westward ZPG that is connected with prevailing westerlies. Only in February - March, at the end of winter monsoon season, it becomes eastward. In the annual cycle of ZPG semiannual harmonic with minima in February - March and August and maxima in May and October - December is clearly expressed. Mean annual value of surface ZPG is estimated as 3.63 x 10(-7) N kg-1 and its semiannual amplitude as 2.5 x 10(-7) N kg-1. Zonal wind stress tau(x) and ZPG in the upper 100 m layer change practically in phase. The quantitative relation between tau(x) and ZPG shows the non-linearity of equatorial dynamics in the Indian Ocean. Correlation of annual evolution of ZPG with variability of equatorial currents could be well interpreted by non-linear model of Cane (1980).