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Oceanography
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Connective activity over the tropical Indian Ocean
M.R. Ramesh Kumar and L.V. Gangadhara Rao
Physical Oceanography Division
National Institute of Oceanography
Dona Paula, Goa - 03004
Abstract
The convective activity over the tropical Indian Ocean is studied in relation to monsoon activity over India for the years 1986, 1987 and 1988 using the outgoing long wave radiation (OLR) values from the satellite data (INSAT-1B) and the seas surface temperature data from satellite and institute observations (blend analysis).
The premonsoon OLR values were higher during a poor monsoon (1987) year as compared to the other two years. A high OLR value of 240 W/m2 was observed between 65° E and 85° E along the equatorial belt which was absent during 1986 and 1988. Further, it was observed that the OLR values were higher over the Indian subcontinent during the poor monsoon year (1987) as compared to the normal monsoon years (1986 and 1988). An analysis of the as surface temperature (SST) anomalies has shown that the positive SST anomalies have prevailed throughout the monsoon season in Arabian Sea in a poor monsoon year (1987), which may be probably due to weak cross equatorial flow off the Somali coast and weak winds over the Arabian Sea compared to the normal monsoon years (1986 and 1988). Thus higher OLR values over the Indian subcontinent and positive SST anomalies over the Arabian Sea appear to be responsible for poor monsoon rainfall lover Indian subcontinent in 1987.
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