Upwelling in the northwest Sabah during the northeast monsoon and its relation with El–Niño

This study analyzes the characteristics of upwelling events during the northeast monsoon, as well as El-Niño impacts towards upwelling in the northwest Sabah, which is located in southern part of the South China Sea by combining remote sensing, reanalysis, and modeling data. The data used in this study obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite for the sea surface temperature (SST) and chlorophyll a concentration data, Hybrid Coordinate Ocean Model (HYCOM) for the vertical cross section of temperature and salinity data, and European Centre for Medium-range Weather Forecast (ECMWF) Interim Reanalysis (ERA-Interim) for the wind data, as well as Ekman transport and Ekman pumping analysis during December to April 2003-2016. The monthly mean of the climatological data were analyzed and the results showed that the MODIS-Aqua satellite indicates the presence of cooler sea surface temperature (SST) and higher chlorophyll-a concentration along the inshore region of northwest Sabah during the northeast monsoon, indicating the existence of upwelling. Cross-sectional temperature profles obtained from the HYCOM further confrmed the existence of upwelling as the thermohaline was uplifted from the deeper layer and reached the surface during the northeast monsoon. Ekman transport and Ekman pumping derived from the ECMWF showed an upwelling favorable condition during the northeast monsoon. Comparison between climatological data and El-Niño year in 2016 represented that El-Niño events somehow increase the upwelling intensity due to the intensifcation of Ekman transport and Ekman pumping.