A study on cyclone induced productivity in South-Western Bay of Bengal during November-December 2000 using MODIS data products

The Bay of Bengal is a semi-enclosed tropical ocean basin that is highly influenced by monsoonal winds and receives large volumes of fresh water from both river discharges and rainfall. Tropical cyclones are a major hazard in coastal regions, both in terms of loss of life and economic damage. The extensive coastal belt of India is very vulnerable to these tropical cyclones. Such cyclones originate in the Bay of Bengal and the Arabian Sea during the spring (April-May) and fall (October-November). The surface circulation in the Bay of Bengal undergoes seasonal reversal and forced by remote effects from the equatorial Indian Ocean in addition to monsoon winds and fresh water inputs. These circulation features had a strong influence on the primary' productivity of the Bay of Bengal. Coastal upwelling along the southern part of the west coast of India turns the coastal waters into a region of high biological productivity. The open ocean upwelling, wind driven mixing and lateral advection makes the open ocean waters of the central Arabian Sea more productive (Prasanna Kumar et al. 2001). Kumar, P et al., (2002) reviewed the reasons for less production in the Bay of Bengal compared to Arabian Sea and attributed to the presence of strong stratified surface layer, warmer SST and weak winds. The weaker winds over the Bay are unable to erode the strong stratified surface layer, there by restricting the turbulent wind driven vertical mixing. This inhibits the injection of nutrients from below mixed layer to surface layer. The storm surge activity in the Bay of Bengal is one of the mechanism for the nutrient pulsing into the well-lit surface layer, when the observed patches of high chlorophyll and productivity in coastal regions of the Bay do not bear any obvious relation to the upwelling. Also the presence of gyres and physical processes leads to high chlorophyll in the western Bay of Bengal (Gomes et al. 2000)