Interannual variability of upwelling indices in the Southeastern Arabian Sea: A satellite based study

Increase in sea surface temperature with global warminghas an impact on coastal upwelling. Past two decades (1988 to 2007) of satellite observed sea surface temperatures and space borne scatterometermeasured winds have provided an insight into the dynamics of coastal upwellingin the southeastern Arabian Sea, in the global warmingscenario. These high resolution data products have shown inconsistent variability with a rapid rise in sea surface temperature between 1992 and 1998 and again from 2004 to 2007. The upwellingindices derived from both sea surface temperature and wind have shown that there is an increase in the intensity of upwellingduring the period 1998 to 2004 than the previous decade. These indices have been modulated by the extreme climatic events like El-Nino and Indian Ocean Dipolethat happened during 1991–92 and 1997–98. A considerable drop in the intensity of upwellingwas observed concurrent with these events. Apart from the impact of global warmingon the upwelling, the present study also provides an insight into spatial variability of upwellingalong the coast. Noticeable fact is that the intensity of offshore Ekman transportoff 8°N during the winter monsoon is as high as that during the usual upwellingseason in summer monsoon. A drop in the meridional wind speed during the years 2005, 2006 and 2007 has resulted in extreme decrease in upwellingthough the zonal wind and the total wind magnitude are a notch higher than the previous years. This decrease in upwellingstrength has resulted in reduced productivity too.