Formation of Large-Scale Eddies in the Bay of Bengal during Summer Monsoon

Air-sea Interaction in the Indian Ocean (ASIRI) is originally designed to study the Indian Oceanography and its inter-connection with the Indian Ocean monsoon.Circulation in the Indian Ocean and it's variability was one of the key objectives of the program.As part of this program, first drifter deployment was carried out in August 2013 off south of Sri Lanka to investigate the circulation patterns around Sri Lanka.The main target of this deployment was to investigate intensification of the circulation patterns with southwest monsoon wind.Past studies indicated that the Bay of Bengal region is substantially influencing for the Indian Ocean monsoon.The observations results indicated that the speed of surface current was ~1 m/s throughout the drifter trajectory in the Bay of Bengal.The inertial periods calculated based on different geographical locations (4.5°N, 6°N and 10°N) were recorded as 12.7 days, 9.5days and 5.8 days respectively.Also, the formation of large-scale eddies with 200 to 400kms diameters were observed in sea surface height anomaly maps which are consistent with the estimated diameters based on drifter trajectories.Further, it was noted that both drifters follow the parallel pathway at the beginning, until reaching 82°E and then separated and followed different paths.Apart from that the formation of mushroom like eddies were identified as characteristic features in the region.Sea surface height anomalies were observed in the years 2013 and 2014 and it is indicated the formation of 8 to 10 numbers of large-scale eddies during the southwest monsoon season.Further the formation, development and disappearing of Sri Lanka Dome was the dominant feature in the Bay of Bengal which could be observed in the satellite derived sea surface height anomaly maps.