Tropical cyclones over NIO during La-Niña Modoki years

Abstract

Tropical cyclones over NIO (North Indian Ocean) are highly influenced by the El-Niño and La-Niña activities over the Pacific Ocean. Influences of air-sea interaction processes like El-Niño Modoki and La-Niña Modoki on tropical cyclones are less studied. During La-Niña Modoki years the splitting of Walker circulation results in two ascending limbs over the west and east Pacific Ocean, and one descending limb over the Central Pacific, this makes large magnitude for Low Level Convergence over the West Pacific and Bay of Bengal region, which is favorable for the formation of tropical cyclones over Bay of Bengal. Other air-sea interaction parameters such as Low Level Relative Vorticity, Vertical Wind Shear are also found favorable for the cyclones over Bay of Bengal. This study states that the magnitude of Low Level Convergence over Bay of Bengal during La-Niña Modoki years is low compared to that of canonical La-Niña years hence the intensification of cyclones is decreased over this basin during this period. It also results that there are no cyclones over Arabian Sea during La-Niña Modoki years.