RAS question
The phenomenon where cyclones in the Bay of Bengal undergo rapid intensification just before making landfall is primarily due to:
Correct answer: (A) Warm sea surface temperatures (>27°C) and low vertical wind shear near the coast.
Rapid intensification of Bay of Bengal cyclones near landfall is primarily driven by warm sea surface temperatures above about 27°C, high moisture and ocean heat, and low vertical wind shear near the coast.
Explanation
Bay of Bengal cyclones intensify rapidly when the ocean and atmosphere keep feeding the storm instead of disrupting it. Warm sea surface temperatures above 27°C, often 28-30°C in the Bay, high oceanic heat content, high humidity and low vertical wind shear are the key conditions. IMD's cyclone FAQ supports this mechanism: warm seas allow low pressure to deepen, moist air rises and condenses, latent heat is released, and the system can intensify into a cyclonic storm. IMD also notes that low vertical wind shear is favourable, while large shear can weaken or destroy a cyclone by disrupting deep convection around its centre. This is why option A captures the core cause.
Why the other options are wrong
- (B) Reduced humidity would cut off the moist-air supply and latent heat release that help a tropical cyclone intensify.
- (C) Mountainous terrain affects a cyclone after landfall and weakens its circulation, whereas the question asks about intensification just before landfall over warm coastal waters.
- (D) Cold ocean currents would lower sea surface temperatures and inhibit cyclone intensification rather than provide the warm-water energy source needed for it.
Concept
This tests the physical geography of tropical cyclones: sea surface temperature, moisture, latent heat and vertical wind shear. It recurs in RAS because Bay of Bengal cyclones directly connect Indian climatology with the geography of coastal cyclone risk.