Mechanism analysis of alongshore shock current phenomenon in Yangjiang sea area along the coast of western Guangdong in spring and summer
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摘要: 通过分析2018–2019年粤西阳江沿岸流海域多站点周年观测水文气象实测资料，发现2019年春季和夏季阳江沿岸流海域存在激流现象。研究结果表明：（1）2019年5月5日凌晨6时，观测站点2 m水深处流速达到164.7 cm/s，9 m水深处流速达到127.6 cm/s。2019年8月1日凌晨4时至5时，阳江沙扒海域2 m水深处流速达到161.8 cm/s，9 m水深处流速达到156.6 cm/s。（2）粤西沿岸流阳江20～30 m水深海域春夏季突发性强流具有典型的激流特征。激流在涨急时刻发生在海洋表层，持续2～4 h。（3）在西南风与东北风转换期间，粤西沿岸海域容易形成海水幅聚带，近岸海域海平面上升，外海海域海平面下降，强劲的自岸向外水平压强梯度力导致近岸海水加强向西运动，从而产生激流。Abstract: We can discover that there exist storm currents along Yangjiang sea area of western Guangdong waters in spring and summer of 2019 by analyzing materials which measure hydrologic and hydrometeorological along west coast of Guangdong flow Yangjiang sea area from 2018 to 2019. The result of research shows: Firstly, the velocity of 2 m water depth at the observation site reached 164.7 cm/s and 9 m water depth at the observation site reached 127.6 cm/s at 6:00 a.m. on May 5, 2019. The velocity of Yangjiang Shapa sea area 2 m water depth at the observation site reached 161.8 cm/s and 9 m water depth at the observation site reached 156.6 cm/s at 4:00 to 5:00 a.m. on August 1, 2019. Secondly, the suddenly strong currents in spring and summer have typically shock current trait in the Yangjiang 20 m to 30 m sea area along the shore current area of western Guangdong. The strong current happens at the surface of the ocean during the time of rising tide for 2 h to 4 h. Thirdly, during the transition period of southwest wind and northeast wind, the coastal sea area of western Guangdong is prone to form a water convergence zone. The sea level of the coastal sea area rises, and the sea level of the offshore sea area drops. The strong horizontal pressure gradient force from the shore to the outside causes the coastal water to strengthen the westward movement, resulting in shock current.
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图 1 阳江海域长周期观测站位置
图中S1站为风观测站，观测时间为2018年10月至2020年2月；T1站为海流、潮汐和波浪观测站，观测时间为2018年10月至2019年9月；T2站为海流观测站，观测时间为2019年3月至2020年2月；图中虚线为水深（单位：m）
Fig. 1 Location map of long-term observation stations in Yangjiang sea area
S1 Station is a wind observation station, and the observation time is from October 2018 to February 2020; T1 Station is a current, tide and wave observation station, and the observation time is from October 2018 to September 2019; T2 Station is a current observation station, and the observation time is from March 2019 to February 2020. The dotted line in the figure is the water depth (unit: m)
图 2 T1站2018年10月至2019年9月观测期间每月最大流速
Fig. 2 Maximum monthly current velocity of T1 Station during observation period from October 2018 to September 2019
图 3 2019年5月S1站风矢量图（a）和T1站（b）、T2站（c）不同水深海流矢量变化过程
Fig. 3 Wind vector diagram of Station S1 (a) and current vector change process of different water depth at Station T1 (b) and Station T2 (c) in May, 2019
图 4 2019年8月S1站（a）风矢量和T1站（b）、T2站（c）不同水深海流矢量变化过程
Fig. 4 Variation process of wind vector at Station S1 (a) and current vector at different water depths at Station T1 (b) and Station T2 (c) in August 2019
图 5 T1站 2019年5月4日17:00至5月5日18:00海流矢量图
Fig. 5 Current vector diagram of T1 Station from 17:00 on May 4 to 18:00 on May 5, 2019
图 6 T1站 2019年7月31日17:00至8月1日18:00海流矢量图
Fig. 6 Current vector diagram of T1 Station from 17:00 on July 31 to 18:00 on August 1, 2019
图 7 2019年5月1日至10日激流期间S1站风速和T1站流速、潮高、平均波高变化过程
Fig. 7 Variation process of wind speed at Station S1 and flow velocity, tide height and average wave height at Station T1 during shock current period from May 1 to 10, 2019
图 8 2019年8月1日至10日激流期间S1站风速和T1站流速、潮高、平均波高变化过程
Fig. 8 Variation process of wind speed at Station S1 and flow velocity, tide height and average wave height at Station T1 during shock current period from August 1 to 10, 2019
图 9 2019年春季南海北部海表面温度和T1、T2站余流分布
左图为GHRSST遥感海表面温度，右图为左图同日T1、T2站表层余流和底层余流（右图区域为左图红框内区域）
Fig. 9 Distribution of sea surface temperature and residual current at stations T1 and T2 in the northern South China Sea in the spring of 2019
The left figures show the GHRSST remote sensing sea surface temperature, and the right figures show the surface residual current and bottom residual current at stations T1 and T2 on the same day (the area in the right figure is the area in the red box in the left figure)
图 10 2019年春季南海北部激流期间AVISO表面高度异常和海表地转流
Fig. 10 AVISO surface level anomaly and surface geostrophic current during the torrent in the northern South China Sea in spring 2019
图 11 2019年夏季南海北部海表面温度和T1、T2站余流分布
左图为GHRSST遥感海表面温度，右图为左图同日T1、T2站表层余流和底层余流（右图区域为左图红框内区域）
Fig. 11 Distribution of sea surface temperature and residual current at stations T1 and T2 in the northern South China Sea in the summer of 2019
The left figures show the GHRSST remote sensing sea surface temperature, and the right figures show the surface residual current and bottom residual current at stations T1 and T2 on the same day (the area in the right figure is the area in the red box in the left figure)
图 12 2019年夏季南海北部激流期间AVISO表面高度异常和海表地转流
Fig. 12 AVISO surface level anomaly and surface geostrophic current during the torrent in the northern South China Sea in summer 2019
表 1 观测站位经纬度、水深及观测要素
Tab. 1 Longitude and latitude water depth and observation elements of observation stations
站号 纬度 经度 站位水深/m 观测要素 T1 21°19'36.02''N 111°28'59.17''E 25.4 潮汐、海流、波浪 T2 21°05'21.36''N 112°13'34.68''E 47.1 海流 
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表 2 2019年5月和8月典型激流流况
Tab. 2 Typical shock current conditions in May and August, 2019
日期 发生时间 站位 最大流速/（cm·s–1） 最大流速方向/（°） 激流发生前流速/（cm·s–1） 激流与发生前流速之比 持续时间/h 2019年5月5日 6时 T1 164.7 234 40.7 4.0 2 4时 T2 74.2 275 18.4 4.0 2 2019年5月8日 0时 T1 161.4 239 33.8 4.8 3 0时 T2 65.9 267 48.2 1.4 2 2019年8月1日 5时 T1 161.8 250 45.5 3.6 4 6时 T2 107.7 309 21.1 5.1 3
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