EARLY PREDICTION OF ONSET OF SOUTH-WEST MONSOON FROM ERS-1 SCATTEROMETER WINDS

Detailed analysis of the surface winds over the Indian Ocean derived f rom ERS-1 scatterometer data during the years 1993 and 1994 has been u sed to understand and unambiguously identify the onset phase of south- west monsoon. Five day (pentad) averaged wind vectors for the period A pril to June during both years have been examined to study the exact r eversal of wind direction as well as the increase in wind speed over t he Arabian Sea in relation to the onset of monsoon over the Indian wes t coast (Kerala). The related upper level humidity available from othe r satellites has also been analysed. The results of our analysis clear ly shaw a consistent dramatic reversal in wind direction over the west ern Arabian Sea three weeks in advance of the onset of monsoon. The wi nd speed shows a large increase coinciding with the onset of monsoon. These findings together show the dominant role of sea surface winds in establishing the monsoon circulation. The study confirms that the cro ss equatorial current phenomenon becomes more important after the onse t of monsoon.