Signature of La Niña in interannual variations of the East India Coastal Current during spring

Abstract

We have investigated interannual variations of the spring (February–April average) East India Coastal Current (EICC) magnitude between 2000 and 2018 using OSCAR (Ocean Surface Current Analysis Real-time) current and a linear, continuously stratified (LCS) model. Interannual variability of the EICC shows significant decrease in magnitude during spring of 2000, 2008 and 2011, the years when high negative ONI (Oceanic Nino Index for sea surface temperature) value has been observed due to dominance of strong La Nina events. Our LCS model also successfully simulates these interannual variability of the spring average EICC between 2000 and 2018. We carried out numerical experiments using LCS model related to local and remote forcing response on EICC. Dynamics of the EICC during spring are dominated by four different forcing processes; local wind along east coast of India, remote forcing response from the eastern and northern boundary of the BoB including islands, interior BoB and the Equatorial Indian Ocean (EIO). During El Nino and normal spring years, strong poleward interannual EICC are due to very weak negligible (order of 0–5 cm s $$^{-1}$$ ) EICC from EIO remote response and in-phase poleward EICC formation using other three forcings. However, during La Nina spring years, weak (order of 0–10 cm s $$^{-1}$$ ) poleward interannual EICC are formed due to destructive interference between equatorward current (order of 10–25 cm s $$^{-1}$$ ) from EIO forcing and in-phase poleward current from other three forcings. We have also found propagation of interannual upwelling (downwelling) favorable Kelvin wave from EIO via eastern and western boundary of the BoB during spring in the El Nino (La Nina) years. The interannual variations in the propagation of EIO Kelvin wave are associated with the changes in the EIO zonal wind direction by climate mode like ENSO (El Nino–Southern Oscillation).