Distinctive characteristics of upwelling along the Peninsular Malaysia's east coast during 2009/10 and 2015/16 El Niños

Abstract

We investigate the southwest monsoon average structure and interannual variability of upwelling along the Peninsular Malaysia's east coast (PMEC) based on satellite-derived sea surface temperature (SST), reanalysis wind data and cruise observations. The upwelling area prompted by southwest monsoon winds is represented by a patch of cooler water along the coast. This cooler water is also an outcome of the cooler water flooded from the Karimata Strait, nonetheless, localised upwelling conditions demonstrating their substantial impact to further cool down this already cooled water. Results from empirical orthogonal function (EOF) analysis revealed that variation in SST was dominated by the first EOF mode, which accountable of 80.99% of total variance and its loading map demonstrated a persistence of SST front, represented the signature of upwelling. The time series of the first EOF mode was highly correlated with the alongshore wind stress anomalies, indicating the Ekman transport driven nature of upwelling interannual variability. We demonstrate that a delayed El Niño Southern Oscillation (ENSO) effect as an important factor for the interannual variations of upwelling along the PMEC. Our analysis focusing on the two recent strongest El Niños, 2009/10 and 2015/16 revealed that the intense northwest Pacific anticyclone anomaly (NWPAA) and the occurrence of the northerly wind anomalies from the subtropical western Pacific (SWP) in 2010 weakened the upwelling along the PMEC. While in 2016, the occurrence of the ‘C-shape’ wind anomalies generated by the warming of the southeast tropical Indian Ocean (SETIO) weakened the upwelling along the PMEC.