台风事件对东中国海悬沙浓度时空演变的影响分析

东海大陆架常受台风侵扰, 强风浪在破坏水体结构的同时引起大量泥沙再悬浮。台风是影响东海表层悬沙浓度(suspended sediment concentration, SSC)的主要动力之一。本文将台风类型分为登陆和非登陆两大类共八种。基于GOCI (geostationary ocean color imager)遥感数据统计分析了2017~2020年9个不同类型台风事件对表层悬沙浓度时空分布的影响。结果表明, 近海活动型和远海活动型台风使SSC显著增高了150%~200%; 随着风速减小, SSC逐渐下降, 但需要3~4 d才能恢复至台风之前的SSC。风速变化与SSC变化率的相关性高达0.86。近海及远海活动型台风影响研究区域的风向为偏北风, 该类型台风使秋季SSC等值线向外海延伸, 出现舌状分布特点; 而登陆型台风影响研究区域的风向前期为偏北风, 后期为偏南风, 该类型台风使SSC等值线呈基本平行向外海移动较短距离, 但不出现向外海延伸的舌状分布。近海及远海活动型台风事件使SSC分布迅速向气候态平均天气下的冬季输运类型转变, 其中近海活动型台风对SSC分布的影响比远海活动型更显著。登陆型台风对研究区域SSC跨陆架方向分布的影响比远海活动型台风更小。

THE EFFECT OF TYPHOON EVENTS ON THE SPATIO-TEMPORAL EVOLUTION OF SUSPENDED SEDIMENT CONCENTRATION IN THE EAST CHINA SEA

The continental shelf of the East China Sea is often hit by typhoons in autumn. Strong winds and waves destroy the water structure and cause a large amount of sediment resuspension, which is one of the main driving forces affecting the suspended sediment concentration (SSC) in the surface layer of the East China Sea. Based on GOCI remote sensing data, the influence of 9 typhoon events during 2017~2020 on the spatio-temporal variation of SSC distribution in the East China Sea was analyzed statistically. The typhoons were classified into two categories (landed and non-landed) and eight types according to the trajectories. It was found that the non-landed typhoons could greatly increase SSC by 150% to 200%. With the decrease of wind speed, SSC decreased gradually, and it took at least 3~4 days to resume to the normal SSC after typhoon passage. Correlation coefficient between wind speed and the rate of SSC variation reached 0.86. The wind directions of the non-landed typhoons are mostly northward during passage through the study area, and this category of typhoon events could change obviously the SSC distribution pattern, presenting a tongue-shaped distribution towards the open sea, while those in the landed category were northward in the early stage and then bended towards southward in tendency. The landed category of typhoons could push the SSC contours moving in parallel seaward over a short distance with no tongue-shaped distribution. The non-landed typhoons passing offshore or nearshore could change quickly and obviously the SSC distribution into the winter transport pattern which means the SSC in the East China Sea spread gradually toward the open sea under the average weather conditions in winter, and the closer the typhoon passage to the coast zone, the more significant impact on the distribution of SSC. However, the landed category of typhoons had less impact on the cross-shelf distribution of SSC than non-landed typhoons when active at open sea.