Eddy Characteristics and Vertical Structure in the Bay of Bengal during Different Monsoon Regimes

Abstract

The evolution of mesoscale eddies in the Bay of Bengal (BoB) and their characteristics (number of eddies, radius, amplitude, and eddy kinetic energy) are addressed during all strong, normal, and weak monsoon regimes from 1993 to 2019. Their impacts on the 3–7-day synoptic oscillations of atmospheric precipitation and upper ocean heat content are also assessed. In the western Bay, eddies are located in the meandering East India Coastal Current (EICC). The propagation of coastally trapped Kelvin waves into the Andaman Sea varies with monsoon intensity. Eddies with smaller radii, weaker amplitudes, increased vertical mixing, and deeper vertical extents were found during weak monsoons. Eddy kinetic energy (EKE) of EICC anticyclonic eddies is high (1200–2000 cm2 s−2) in May and November-December during weak and normal monsoon regimes, and EKE attains a maximum off the Sri Lanka coast during the strong monsoon regime. Throughout the Bay, density anomalies at ~100 m depth are influenced by subsurface temperature anomalies, while those at the surface more closely follow salinity anomalies. Wavelet coherence analysis for all three monsoon regimes reveals stronger coherence between eddy amplitude, atmospheric precipitation, and ocean heat content than the number of eddies for both anticyclonic and cyclonic eddies.