Impact of tropical and extra tropical climate variability on Indian Ocean surface waves

Abstract

Understanding the impact of various climate features on wave climate is important for effective coastal climate adaptation and mitigation strategy planning. In the present study, the effect of tropical and extra-tropical climate modes such as Indian Ocean Dipole (IOD), El Nino Southern Oscillation (ENSO) and Southern Annular Mode (SAM) on wind-wave climate of the Indian Ocean (IO) is studied using multiple linear regression of individual climate indices on relevant wind-wave parameters. There are two regions of importance for swell generation in the Indian Ocean - a region between 40° and 60° S in the Southern Ocean (SO) and another region in the Eastern Tropical Indian Ocean (ETIO; 10°–30° S, 60°–100 °E). SAM, the strongest inter-annual mode of the SO, generates swells in the 40°–60°S band throughout the year that eventually propagates to the entire North IO. Both the positive and negative phases of SAM generate swells from SO, but it’s genesis region vary meridionally depending on the phase of SAM. The positive phase of ENSO (LaNina) generally reduce the westerly wind anomalies in the SO caused by a positive phase of SAM and hence reduce the swell generation from SO, but causes stronger south-easterlies in the ETIO, generating more swells from there. IOD that peaks in September–October–November period has its effect on swell generation limited to eastern equatorial IO. Our analysis suggests that interannual climate features are important in modulating wind-wave climate of IO and a basin-wide model set-up with an accurate representation of various interannual climate features is a prerequisite for accurate wave forecast.