Upper ocean response to typhoon Kujira (2015) in the South China Sea by multiple means of observation

Abstract

The impact of typhoon Kujira (2015) on the ocean environment around Yongxing Island in the South China Sea was observed using multiple-satellite sensors and on-site data. A subsurface buoy and Agro float were located to the left and lower right of the track of the typhoon. Satellite observations revealed sea surface cooling of up to 2.5°C, a maximum decrease in sea surface salinity of 2 in the main study area because of heavy rain, and increases in the chlorophyll concentration induced by the slow-moving typhoon with a maximum observed instantaneous wind speed of 35.1 m/s. The sea surface temperature to the right of the typhoon track changed more than that on the left owing to a right bias of the typhoon associated with coupling of the typhoon with wind stress on the sea surface. In the ocean interior, there was obvious downwelling at 24.7 m and upwelling at a depth of 35.7 m with the vertical entrainment and agitation of the typhoon, and the effects extended to different depths of up to more than 1 000 m. When the typhoon passed through the main study area, the maximum flow velocity change at depths of 51 and 660 m was about 0.44 and 0.04 m/s, respectively. The typhoon affected the flow field to a depth of 660 m as it formed and decayed in 11 h, moved at an average speed of 60 m/h, and affected the sea surface over a range exceeding 700 km as it moved slowly and stayed at sea for 2 d. Vertical entrainment and agitation generated by the typhoon, as well as rainfall, cooled the sea surface. This inhibited the strengthening of the typhoon, but the energy transmitted to the ocean led to divergence-convergence flow from a shallow to deep layer.