| description abstract | The interannual variability of surface meteorological fields over the Indian Ocean during the period 1954?76 is studied using 2 million ship reports obtained from different sources. Monthly mean fields of wind, pressure, air temperature, mixing ratio, cloud cover and sea surface temperature (SST) on a grid mesh of 2° have been determined by computing the monthly mean values of the data around each grid point. Because data coverage is poor over certain areas, an objective analysis based on the successive correction method was performed. Seasonal anomaly fields are presented for the Northern Hemisphere summers of 1956 and 1972, with the two summers having opposite extreme features. During 1956 (1972), the intensity of the trade winds in the Southern Hemisphere and the summer cross-equatorial flow were above (below) normal. Sea surface temperature was below (above) normal over the entire Indian Ocean in 1956 (1972). Time series of the anomalies over different key areas show that weaker than normal trade winds persisted during a period extending from 1968?74. As a consequence, the summer cross-equatorial flow was reduced, mainly along the African coast, by about 20%. During the same period, SST and air temperatures were above normal (up to 2°C during the 1972 summer) presumably due to the decrease of evaporation and turbulent mixing of the surface layer by weaker winds. The fluctuations of the different surface parameter anomalies seem to be related to a similar variation of the activity of the summer monsoon: the end of the sixties and the beginning of the seventies correspond to dry monsoons. This is supported by fields of correlation coefficients between summer rainfall over India and different parameters over the Indian Ocean. | |
