Impact of global warming on cyclonic storms over north Indian Ocean

The impact of global warming on the cyclonic storms over the north Indian Ocean have been studied using a suite of multiple datasets that includes the NCEP/NCAR Reanalysis, the extended reconstruction sea surface temperature (ERSST) and tracks of storms over the north Indian Ocean for the period 1951 to 2007. Results suggest that the frequency of storms and severe storms do not show a dramatic rise in-spite of substantial increase in the sea surface temperature in the Bay of Bengal from 1951-2007 compared to the 1901-1951. This prompted us to conclude that, the frequency of storms is related to the changes in a couple of atmospheric parameters over the north Indian Ocean during the global warming period. It is identified that there is a large decrease in the mid-tropospheric humidity over the Bay of Bengal during the latter period (1951-2007). The relationship between the SST over the Bay of Bengal and the maximum wind speed of the cyclonic systems is complex and there is no preferred range for the formation of cyclonic or severe cyclonic storms over the north Indian Ocean. Examination of various aspects related to storms in the present study revealed that warm SST's alone are not sufficient for the initiation of convective systems over the Bay of Bengal. The present study thus suggests that atmospheric parameters, such as low-level vorticity, mid-tropospheric humidity and vertical wind shear, play an influential role on the genesis and intensification of storms over the north Indian Ocean. The present study assumes significance due to the large contribution of rainfall over India from storms that form over the north Indian Ocean during the summer and the winter monsoons.