Observed Variability of Thermohaline Fields, Currents and Eddies in the Western Bay of Bengal During BOBMEX-99

Abstract

Field measurements during the Bay of Bengal Monsoon Experiment (BOBMEX-99), data from a deep sea moored buoy, and satellite altimeter were used to describe variability in the hydrographic and meso-scale features in the Bay of Bengal (BoB) during the summer monsoon of 1999. The thermohaline fields showed two regions of upsloping of isopleths centered at 82°E and 84.75°E, ∼110 km and 450 km away from the coast, respectively, followed by downsloping. The upsloping/downsloping of isopleths and the alternating currents was part of cyclonic and anti-cyclonic circulation patterns in the western BoB. In this region, both wind and current were important in the dynamics of coastal upwelling. The observations showed a relationship between the propagating waves and eddy on variability of thermohaline fields. On an annual cycle, four Kelvin waves were observed in the BoB, but only the downwelling Kelvin wave formed during October entered the Arabian Sea. During the monsoon season, four eddies were formed in the western BoB, of which the anticyclonic eddy centered at 15°N, 84°E and the cyclonic eddy centered at 17.5°N, 84.5°E were prominent. The baroclinic instability caused by the opposing currents along the east coast and the wind stress curl favored the formation of eddies. Okhubo-Weiss and Isern-Fontanet parameter confirmed the presence of eddies in the BoB.

Keywords:

• Bay of Bengal
• BOBMEX-99
• circulation
• thermo-haline variability
• eddy evolution
• planetary waves

Acknowledgements

The authors are thankful to participants of BOBMEX and the ship's company for their effort in data collection. Authors gratefully acknowledge NIOT, Chennai and the WOCE team for providing the moored buoy data and the processed TOPEX/POSEIDON data, respectively. One of the authors, T. N. Shyni, acknowledges the Space Application Centre, Ahmedabad, for providing the fellowship.