An assessment of the impact of oceanic initial conditions on the interaction of upper ocean with the tropical cyclones in the Arabian Sea

Abstract

ABSTRACT The Regional Ocean Modelling System (ROMS) is utilised to estimate the cyclone-induced mixing and cooling associated with two tropical cyclones, namely Phet and Nilofar over the Arabian Sea (AS). Numerical experiments were carried out with realistic and idealistic oceanic conditions to assess the impact of oceanic initial condition and stratification on the interaction of upper ocean with the tropical cyclones in the AS. The model simulated profiles of temperature and baroclinic kinetic energy are analysed to examine the post-cyclonic cooling and vertical distribution of inertial kinetic energy which interacts with the upper-ocean stratification. Following the cyclone-induced upwelling, the inertial mixing acts to deepen the mixed layer depth (MLD) up to 50 and 100 m from its initial values of 15 and 22 m for the Phet and Nilofar, respectively. The analysis suggests that the combined effect of higher maximum sustained winds and slower translational speed of Nilofar cyclone leads to the excessive cooling (by 1.5°C) of the sea surface as compared to Phet. A decrement in the magnitude of cooling is observed when oceanic initial stratification was altered. The available baroclinic velocity shear at different depths found to modulate the magnitude of upper-ocean cooling in different model experiments.