Dynamical Response of Changjiang River Plume to a Severe Typhoon With the Surface Wave-Induced Mixing

Typhoons (or hurricanes) are the most energetic atmospheric forcing acting on coastal waters. Here in this study, we investigated the response of the summertime Changjiang River plume to a typical typhoon, Chan-hom (1509), with a combination of field observation and numerical simulation. Surface wave-induced mixing was considered in the model configuration. The results showed that the typical offshore-extending summer Changjiang River plume completely disappeared under the influence of typhoon wind. Instead, it extended southward along the Zhejiang and Fujian (Zhe-Min) coast as a typical wintertime Changjiang River plume. The along-shelf plume extension lasted for extra ~10 days after the typhoon passage, until another strong weather event came. The competition between wind-driven current and buoyancy-driven current dominated the recovery of the Changjiang River plume. Through calculation, we found that the freshwater transported to the Zhe-Min Coastal Water reached ~4.7 × 10 ¹⁰  m ³ as influenced by typhoon Chan-hom, which was ~5% of the total Changjiang River discharge in 2015 or ~12% of the total dry season Changjiang River discharge (October-April) when the majority of Changjiang River plume extended to Zhe-Min Coastal Water. The remote sensing data of chlorophyll-α from Geostationary Ocean Color Imager also showed that significant algal bloom occurred when the southward extending Changjiang River plume retreated. Surface wave-induced mixing caused by typhoon wind was found to be important in destroying the vertical plume stratification and elongating the recovery processes from the typhoon influence.