ESSO - Indian National Centre for Ocean Information Services

Surface and sub-surface ocean response to Tropical Cyclone Phailin: Role of Pre-existing oceanic features

Jyothi Lingala, Sudheer Joseph, Suneetha P

Abstract : The upper oceanic thermal response induced by Tropical Cyclone Phailin (9th -14 th October 2013) under the influence of East India Coastal Current (EICC) and a cyclonic eddy are investigated and contrasted with the response from open ocean region using a high-resolution HYbrid Coordinate Ocean Model (HYCOM) simulation. There is significant cooling (7 °C) inside the cold core eddy and negligible cooling (0.5°C) within the EICC a region characterized by the shallow and deeper thermocline, respectively. Our analysis of mixed layer heat budget terms showed that the horizontal advection plays a significant role in determining the temperature tendency for the location within the EICC, in contrary to the general dominance of vertical processes as reported in the previous studies during the cyclone period. The analysis for the locations Inside Eddy (IE) and Open Ocean (OO) concur with the previous studies showing the dominance of vertical processes towards the temperature tendency. Further, near the coast, the surface cooling is minimal compared to the subsurface cooling, dominantly seen between 50m to 100m depth. This disparity indicates that the factors responsible for the surface temperature anomalies are different from those of subsurface. Our analysis of thermal signatures after the passage of cyclone showed that the EICC and cyclonic eddy contributes to the faster advection of cold wake and recovery of SST to the pre-storm state.

• 1.Runoff from monsoon-fed rivers creates a shallow pool of low-salinity water in the 10 open north Bay of Bengal in late summer.
• 2.The vertical gradient of salinity creates extremely stable stratification underneath 12 the layer of river water.
• 3.Ship-borne measurements show that salinity stratification gives rise to a "squeezed" 14 Ekman spiral, trapping wind momentum in the upper 10 m.

Please contact Dr. Sudheer Joseph (sjo@incois.gov.in) for further detail if any.