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

Abstract

AbstractTyphoons (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 × 1010 m3 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.