Wind and topography influence on an upwelling system at the eastern Hainan coast

Abstract

During the summer monsoon, an upwelling dominates east of Hainan Island, which can be observed by means of field studies and satellite sea surface temperature images. The centers of cold water at the surface always show a strong patchiness. A 3-D high-resolution model is applied to study the impact of the topography on the wind-driven upwelling system. The experiments show that the upwelling-favoring wind is the main driving force, and we concluded that the formation of the centers of cold water at the surface significantly depends on the strength of southwesterly and southerly winds. Moreover, the internal waves are generated at the shelf break representing the most prominent interaction between inner shelf and open ocean. The alongshore topographic variations play an important role in the distribution of the upwelling centers. This combined effect of wind and topography leads to the following processes: (1) When the southwesterly or southerly wind is strong enough, topographic variations cause upwelling centers at the downstream side of topographic high and a downwelling center at the upstream side which in turn lead to density variations. (2) These density variations cause additional pressure gradients which advect the upwelling centers toward the northeast. (3) A longer period of upwelling favorable winds support the advection processes which cause an enlargement of the cold water centers. All these processes together can explain the observed uneven distribution of upwelling centers.