ESSO - Indian National Centre for Ocean Information Services

Momentum input from monsoon winds trapped in a thin fresh layer in the Bay of Bengal

Dipanjan Chaudhuri, Debasis Sengupta, S Shivaprasad

Abstract : Surface wind stress is a primary driver of global ocean circulation. However, the effect of salinity on momentum transfer from wind to the turbulent upper ocean has not yet been explored using observations. Here we study wind-forced ocean currents from ship-based measurements within and outside a shallow pool of river water in the open north Bay of Bengal during the summer monsoon. The observations reveal Ekman spirals that are "squeezed" by salinity-dominated density stratification, effectively trapping momentum input from wind in the upper 10 m. Our findings are consistent with Ekman depth scaling as 1/√(Nf), where is maximum stratification and f is Coriolis frequency. Estimates based on this scaling indicate that salinity stratification leads to seven-fold enhancement of wind energy input W to the Bay of Bengal, making it comparable to the regions of highest W in the world ocean.

• 1.Tropical Cyclone Phailin induced ocean thermal responses near to the coast are dominated by horizontal advection in contrary to the open ocean.
• 2.Weak Sea Surface Temperature cooling is observed near the coast despite the passage of an intense cyclone.
• 3.Post-storm thermal recovery of the ocean is modulated by coastal boundary current and associated cyclonic eddy.

Please contact Mr. S Shivaprasad (shivaprasad.s@incois.gov.in) for further detail if any.