East Hainan upwelling fronts detected by remote sensing and modelled in summer

Using the Belkin and O’Reilly algorithm and high-resolution (1 km) satellite sea surface temperature (SST) and chlorophyll-a (chl-a) data from 2002 to 2011, fronts were detected off the east/northeast coast of Hainan Island, South China Sea. These fronts were mainly produced by upwelling off eastern Hainan Island, through which cold, high-salinity, high-density, and nutrient-rich bottom water was brought to the surface and subsurface and then transported to the northeast of Hainan Island by the along-shore currents. The fronts are anisotropic, with a dominant orientation SSW–NNE. A three-dimensional ocean model forced by the Quick Scatterometer (QuikSCAT) winds was employed to study the three-dimensional structure of these fronts as well as the relationship between the fronts and upwelling or summer monsoon. The results show that the front intensity (cross-frontal gradient) is strongly correlated with the along-shore local winds, and has a strong seasonal and a weak inter-annual variation with a maximum of about 0.5°C km^–1 at the subsurface (about 15 m) rather than the surface.