On the effects of Cyclone Ashobaa on sub-inertial oscillations over the Arabian Sea

Abstract

Coastally Trapped Waves (CTWs) are studied along the east and north shelves of the Arabian Sea (AS) through field measurements and numerical modeling. A nondispersive barotropic wave, induced by Cyclone Ashobaa, with periods of 10–14 days propagated in wider parts of the shelf. The phase velocities and CTW amplitudes significantly decreased in narrower parts, where a stronger stratification also exists. The long waves are represented by first barotropic and lower bottom trapped modes in deeper and shallower parts of these narrow shelves, respectively. Although the low frequency oscillations, with peak periods of 10–14 days, can be detected in shallow water level data, the wavelet transforms of alongshore currents reveal these long waves exist only in deep waters. This can be attributed to the effect of bottom friction, which causes the effective coastal boundary to move offshore. The Ras al Hadd jet was deflected by the interaction of Cyclone Ashobaa with preexisting eddies and an intensified current was observed where the Ras al Hadd jet crossed the northern shelf.