[1] Using long-term (1871-2005) summer monsoon rainfall data over 30 meteorological subdivisions of India, overall tendencies of the rainfall have been studied. Further, the subseasonal (monthly) trends have been evaluated. For this purpose, simple linear regression technique is applied. To examine the trends in different segments for summer monsoon rainfall, 11-year running averages are calculated. Most of the subdivisions reveal systematic increasing and decreasing trends in different segments of the time series. India experienced wet monsoon conditions during the late 1950s and dry monsoon conditions around the early 1900s. In the global warming era , 19 out of 30 meteorological subdivisions showed negative tendencies in summer monsoon rainfall. This decrease in summer monsoon rainfall is associated with a weakening of the Southern Oscillation and relaxation of the meridional temperature gradient over the Indian Ocean. The gamma distribution is used to study the distribution of the rainfall by calculating scale and shape parameters. In general, larger values of scale parameter are found over west coast during summer monsoon and individual months. The shape parameter is high over northeast India.

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The seasonal and interannual variation of upwelling along the east coast of India between 68N and 228N was studied for the period 1985Á2003 using NOAAÁAVHRR sea surface temperature data. The seasonal migration of pronounced upwelling, which follows the seasonal shift of the winds in transition period and northeast monsoon, was confined. The temporal mean sea surface temperature images clearly show the upwelling season, as does the seasonal sea surface temperature anomaly. These dominant features of the upwelling system are also the most variable, with most of the variance being explained by the seasonal cycle. Quasi-cyclic behaviour of sea surface temperature on interannual scales has also been observed.

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An index of El Niño Southern Oscillation (ENSO) in the Pacific during pre monsoon season is shown to account for a significant part of the variability of coastal Sea Surface Temperature (SST) anomalies measured a few months later within the wind driven southwest coast of India coastal upwelling region 7 • N-14 • N. This teleconnection is thought to result from an atmospheric bridge between the Pacific and north Indian Oceans, leading to warm (cold) ENSO events being associated with relaxation (intensification) of the Indian trade winds and of the wind-induced coastal upwelling. This ENSO related modulation of the wind-driven coastal upwelling appears to contribute to the connection observed at the basin-scale between ENSO and SST in the Arabian Sea. The ability to use this teleconnection to give warning of large changes in the southwest coast of India coastal upwelling few months in advance is successfully tested using data from 1998 and 1999 ENSO events.

Seasonal and interannual variability of chlorophyll a concentration along the West Coast of India (WCI) was detected spatially by ocean colour satellite remote sensing during 1998 -2003. Start timing of the summer bloom was different spatially. The summer bloom started Trivendrum in May, along Cochin coast in June, northward of it in July and also showed interannual variability that corresponding with the wind speed in the area. Summer bloom in 1998 and 2002 appeared about two weeks earlier than in 1999, 2000, 2001 and 2003, and it corresponded with weak winds that can lead to an early development of the thermocline. The bloom was late in 1999 and 2001 at Trivendrum and along the Cochin coast, and in the northern are in 2000. It corresponded with stronger wind stress that delayed seasonal thermocline formation. The winter bloom appeared from early October to last week of January, and it did not have a clear temporal transition. The area where chlorophyll a concentration exceeds 5 mg/m 3 was wider in northern area than in the southern area of the WCI every year. The magnitude of winter bloom was different between years, but it did not show a relation with average wind speed in winter. Those results indicated that the timing of the seasonal bloom along the WCI is largely affected by the variability of global climate such as El Nino Southern Oscillation (ENSO) events.

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