Abstract. High-resolution ocean color observation offers an opportunity to investigate the oceanic small-scale processes. In this study, The Medium Resolution Imaging Spectrometer (MERIS) daily 300 m data are used to study small-scale processes in the western South China Sea. It is indicated that the cyclonic eddies with horizontal scales of the order of 10 km are frequently observed during upwelling season of each year over 2004–2009. These small-scale eddies are generated in the vicinity of the southern front of the cold tongue, and then propagate eastward with a speed of approximately 12 cm s−1. This propagation speed is consistent with the velocity of the western boundary current. As a result, the small-scale eddies keep rotating high levels of the phytoplankton away from the coastal areas, resulting in the accumulation of phytoplankton in the interior of the eddies. The generation of the small-scale eddies may be associated with strengthening of the relative movement between the rotation speed of the anticylconic mesoscale eddies and the offshore transport. With the increases of the normalized rotation speed of the anticyclonic mesoscale eddies relative to the offshore transport, the offshore current become meander under the impacts of the anticyclonic mesoscale eddies. The meandered cold tongue and instability front may stimulate the generation of the small-scale eddies. Unidirectional uniform wind along cold tongue may also contribute to the formation of the small-scale eddies.
Satellite observations of the small-scale cyclonic eddies in the western South China Sea
