Response of Temperature to Successive Typhoons in the South China Sea

Abstract

Typhoons are serious natural disasters in coastal areas. During the summer of 2011, successive typhoons Nesat and Nalgae appeared in the South China Sea, providing a unique opportunity for us to study the response of the upper ocean to successive typhoons. We comprehensively use satellite data and COAWST model data to explore the effects of successive typhoons on the temperature structure of the South China Sea. Nesat caused the sea surface temperature to decrease by up to 4.4 °C on the right side of the typhoon path, and the ensuing Nalgae caused the temperature to decrease by up to 2.2 °C. Because Nesat had already cooled the ocean, the response to Nalgae was more to the left of the track than one would normally expect. The upwelling dominates the change in subsurface temperature. Based on the increase caused by Nesat, the isotherm was further raised by Nalgae. The isotherm rising amplitude is larger in the upper and deeper layer and is smaller in the middle layer in the depth range of 0–200 m. Heat budget analysis indicates that in the area close to the typhoon path, vertical diffusion is the main reason for the decrease in ocean surface temperature, while total advection suppresses the decrease in temperature. In the area with a larger distance from the typhoon path, vertical diffusion and total advection lead to the decrease in ocean surface temperature, and total advection will gradually contribute more to temperature change and become the dominant factor. On the right side of the typhoon track, the reduction of the contribution rate of vertical diffusion with distance from typhoon track is slower than that on the left side of the typhoon track. Whether Nesat or Nalgae, the intensity and depth of effects of vertical diffusion on the right side of typhoon path are greater than those on the left side of typhoon path, and the near-inertial periodic oscillation of local temperature change rate is more obvious. When the vertical diffusion is weak, the influence of vertical advection and horizontal advection is deeper. Moreover, the near-inertial periodic oscillation of the local temperature change occurs in lower depth after Nalgae passed through than that after Nesat. The typhoon intensity of the two typhoons shows the opposite change: the first typhoon increases, and the second typhoon weakens. Therefore, the special case of successive typhoons should be fully considered in typhoon prediction to improve accuracy.