Impact of Indian Ocean Dipole on the mesoscale eddies and their energy in the Bay of Bengal

Oceanic mesoscale eddies and their physical and dynamical characteristics are studied using a high-resolution numerical model in the Bay of Bengal (BoB), a semi-enclosed based in the northeast Indian Ocean (IO). The formation, duration,and kinetic energy of these eddies are primarily influenced by the intensity of surface currents, upper-ocean stratification, and regional bathymetry. The Indian Ocean Dipole (IOD) is a dominant mode of interannual variability in the IO, which influences ocean currents in the BoB apart from the well-known dipole observed in sea surface temperature between eastern and western IO. The high-resolution numerical experiments with positive and negative phases of IOD atmospheric forcing reveal the influence of anomalous circulation prevailing in the negative IOD (nIOD) and positive IOD (pIOD) on mesoscale eddies and their kinetic energy in the BoB. A notable disparity in the eddies’ characteristics was observed in both nIOD and pIOD and compared to normal years. In pIOD or nIOD, the number of eddies enhanced but their average lifespan reduced in the BoB. The increase in eddies was higher (38%) in nIOD than pIOD (11.2%) when compared to normal (non-IOD) years. The contribution of eddies to the total eddy kinetic energy (EKE) of the BoB increased from about 10% in normal years to about 25% in either of the IOD phases. The largest influence of IOD is seen at the thermocline depth. Within the BoB, the Andaman Sea region experienced the largest variations in eddies during IOD years.