Sea Level Interannual Variability Along the West Coast of India

Abstract

Interannual sea level anomalies (SLA), and the related thermocline variations, along the west coast of India (WCI) strongly impact the ecosystems, fisheries, and potentially the monsoon rainfall. Here we investigate the mechanisms driving the WCI interannual SLA using a linear continuously stratified ocean model, which realistically simulates the leading northern Indian Ocean SLA mode associated with the Indian Ocean Dipole (IOD). During, for example, positive IOD events, easterly wind anomalies near Sri Lanka in late summer and fall force downwelling coastal Kelvin waves, which induce positive WCI SLA within days. Meanwhile, equatorial easterlies force upwelling Kelvin waves that travel to WCI through the Bay of Bengal coastal waveguide. Part of this opposite signal also transits slowly through the Bay of Bengal interior as Rossby waves, eventually yielding negative SLA along the WCI in winter. The WCI SLA thus shifts from positive in fall to negative in winter during positive IOD events.