Evolution of the temperature and moisture fields over Arabian Sea from pre-onset to onset phase the monsoon during 1979

Abstract

Prominent changes in the temperature and moisture fields over Arabian Sea from the pre-onset to onset phase of the monsoon during 1979 using aircraft and ship data have been discussed. The most revealing change was observed in the meridional cross sections of relative humidity. After the onset, dry air replaces moist air in the equatorial regions in the middle troposphere (above 750 mb) south of 10 deg. N over central and east Arabian Sea. Middle troposphere- over northwest Arabian Sea, which is mainly dry before the onset, becomes highly humid after the onset. Vertical circulations with rising motion over north Arabian Sea and compensatory descending motion southward over central Arabian Sea and over equatorial latitudes to the south of 10 deg. N are observed in the computed w field, which explain the above dryness.