Impact of Oceanic Processes on the Life Cycle of Severe Cyclonic Storm “Jal”

The cyclonic system “Jal” initiated as a depression in the South China Sea on 31st of October, 2010, and propagated westward into the Bay of Bengal (BoB). In line with the forecast, it developed into a “severe cyclonic storm” by 5th November. It was predicted to intensify further to a “very severe cyclonic storm” and hit the east coast of India; however, it dramatically diminished to a “cyclonic storm” prior to the landfall. The best possible physical parameterizations in a numerical atmospheric model fail to simulate the intensity of Jal sytem. The analysis of satellite derived ocean surface properties revealed that the propagating Jal system encountered distinct oceanic environments in the eastern and western BoB and these have great impact on the intensity changes undergone by the system. The intense precipitation (from July to October, 2010) and the convergence associated with a downwelling coastal Kelvin wave preconditioned the eastern BoB with thick barrier layer and high cyclone heat potential (CHP) that enabled the Jal system to gradually reach a stage of severe-cyclonic-storm. However, the system encountered a region of shallow thermocline with low CHP associated with an upwelling eddy in the western BoB, which influenced the movement of the system and alleviated its intensity to cyclonic-storm. In the western BoB, even though the precipitation freshened the surface layer, the divergence associated with upwelling eddy weakened the barrier layer formation and stratification.