Characteristics and dynamics of mesoscale eddies in the eastern Arabian sea

Abstract

Present study investigates the characteristics and dynamics of mesoscale eddies in the eastern Arabian Sea (EAS), which is relatively less explored and quantified compared to the western Arabian Sea (WAS), using 26-year long altimeter data and numerical simulations. Our study shows that the continental slopes of the northern and southern parts of the EAS are the hotspots of the eddy generation. The EAS eddies propagate westward with speeds in the range of 10–30 cm/s and most of them dissipate before crossing central Arabian Sea (AS). In EAS, more number of eddies are formed in the winter season (44.2%) followed by spring (40.9%) and summer (10.5%) whereas in the WAS, summer season accounts for about 36.4% of eddies, followed by winter (30%) and spring (24%). While the eddy generation in the WAS is mainly associated with the instability caused by strong monsoon winds, our analysis shows that large positive baroclinic instability during winter associated with the propagation of intraseasonal, coastally-trapped Kelvin Waves from the equatorial Indian Ocean and subsequent Rossby wave radiation play an important role in the generation of eddies in the EAS. Our results confirm that remote forcing in the EAS plays a significant role in setting up instabilities compared to the local wind forcing. Estimation of eddy-induced transport shows that mesoscale eddies account for around 22% (8%) of the westward transport of heat (salt) in the upper 100 m in the EAS, especially in the southern part during winter when the low-saline water from the Bay of Bengal (BoB) intrudes into the AS.