High Frequency Radar Observations of East India Coastal Current Eddies

Abstract

The East India Coastal Current (EICC) flows poleward along the east coast of India during spring and equatorward during winter. In the summer, it flows equatorward in the northern bay and poleward in the south, converging in the central part of the coast. Data from three pairs of HF radars located at three stations, Odisha (ORCO), Andhra Pradesh (APCO), and Tamil Nadu (TNCO), along the east coast of India are used in this study to present the characteristics and dynamics of eddies for a decade, from 2010 to 2020. The seasonal reversal of the EICC occurs through a gentle transition in the north, marked by strong offshore flows in the middle part of the coast, and eddies of different signs in the south. Eddy formation peaks in winter and most frequent off TNCO, followed by APCO and ORCO. Cyclonic eddies have longer lifespans and larger sizes in winter, while anticyclonic eddies show similar characteristics in spring. Most eddies have a radius between 10–30 km and life of 5 days. Seasonal mean Eddy Kinetic Energy (EKE) is higher in spring and winter, when EICC is well organized. Barotropic (BT) energy conversion takes place for all three stations for all seasons. Baroclinic (BC) energy transfer occurs in winter for all three stations and additionally off ORCO during summer. Spatial patterns of energy conversion occur in both mean-to-eddy and eddy-to-mean directions; they are spatially non-uniform and show marked differences between coastal and offshore regions.