Detection of materially coherent eddies in the Bay of Bengal

Eddies are prominent features in the ocean and these energetic circulatory motions influence lateral and vertical transport of heat, mass and momentum. Ability of these eddies to coherently transport various scalar species is an important consideration in understanding freshwater transport, locating regions of harmful algal blooms, oxygen deficient zones and potential fishing zones. In this study, we present an implementation of Lagrangian Averaged Vorticity Deviation (LAVD) technique to detect materially coherent eddies from satellite derived sea surface currents in the Bay of Bengal (BoB). We also evaluate the efficacy of a Eulerian method based on sea surface height (SSH) in capturing materially coherent eddies in the BoB. Parameter values for robust detection of eddies are determined by performing a systematic sensitivity analysis in both the methods. Finite time material behaviour of eddies detected using both the methods are evaluated by numerical particle advection experiments. We then focus on material coherence of Sri Lanka Dome (SLD), an annually occurring cyclonic eddy of dynamical relevance in the BoB. SLD characteristics including its spatio-temporal evolution is discussed by analysing ocean surface currents data spanning 27 years from 1993 to 2019.