High primary productivity along the central east coast of India is usually related to coastal upwelling activity that injects
nutrients into the euphotic zone in response to prevailing longshore winds. The upwelling process has maximum
intensity during March and August-September, with the coastal upwelling index varying from 10 to 150 m3/s per 100 m
of coastline. Along the entire coast of the peninsula, the upwelling intensity changes in accordance with local wind
conditions. I have identified the seasonal and synoptic variability of upwelling signatures on the central east coast of
India, using averaged monthly and weekly sea surface temperature (SST) distributions obtained from remote sensing
imagery from the Advanced Very High Resolution Radiometer in the period from 2000 to 2003. Analyse the seasonal
mean variability of the upwelling-forced conditions, the average monthly PFEL coastal upwelling index (CUI) for 1990
through 2003 have been calculated for the entire central east coast with latitude resolution of 0.5°, attending to the local
coastline orientation for each point. The index also shows a near-perfect confirmation of both the upwelling
intensification during March, and the decrease of upwelling-favorable conditions towards the south. Spectra calculated
using entire time series of from 2000 to 2003 wind data show that the frequency ranges from 0.1 to 0.2 cycles/day
(corresponding to periods of 5 to 10 days) and has a number of significant energy peaks. The presence of energy
frequency ranges from 0.1 to 0.2 cycles/day became evident, especially for the Visakhapatnam and Chennai stations.
Seasonal and interannual variability in satellite-derived estimates of near-surface chlorophyll-a concentrations were examined in the four regions off the southwest coast of India from 1998-2003. Wind-induced upwelling predominates in late spring and summer, coinciding with the maximum in solar radiation, leading to increased accumulations of phytoplankton biomass. Chlorophyll concentrations varied from 2 to 10 mg/m3 and were generally lower in January-April and maximal in May-September. Chlorophyll concentrations along the coast followed a similar seasonal pattern (ranging from 0.5 to 4 mg/m3); however, concentrations were always greater on the Trivendrum and Cochin coast compared to the Calicut and Mangalore coast. The southwest coast is often cloud covered; data density maps provide an index of confidence in the 'regional' applicability of the summary statistics. One consequence of the 1997-1998 El Nino appears to be a reduction in chlorophyll concentration off Trivendrum and Cochin in 1998. An increased frequency of El Nino events may lead to a reduction in offshore carbon in this dynamic upwelling region. Six-month median chlorophyll concentrations were maximal in 2002 off Trivendrum and Cochin.
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/m3 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.