荣成外海海流特征及影响因素

Characteristics and influencing factors of the currents in the Rongcheng offshore region

荣成是我国重要的海产养殖城市,为掌握荣成外海的海流特征,基于2016年1—10月于荣成外海楮岛岬角南侧布放的浮标观测数据,通过谱分析、调和分析等方法,分析了实测流速时间序列剖面及季节变化,分离出该观测点的潮流和余流并进行定性定量分析,探讨了该海域余流的影响因素。结果表明:1)荣成外海浮标观测点流速东西分量总体大于南北分量,实测流速均值为0.20 m/s,最大值为0.87 m/s,实测流速存在明显的季节差异,秋季流速最大,夏季次之,冬春季较小且冬春季节差异小。实测流存在涨落潮不对称现象。2)M_(2)分潮绝对占优,观测海域潮流性质为规则半日潮流,潮流以往复流形式运动,各层潮流均为顺时针旋转。浅水分潮十分显著,该点观测得到的最大潮流流速为0.38 m/s。3)余流相对较小,日平均余流速度均值为冬季<春季<夏季<秋季;流向上E和ENE向占优,余流总体向东。弱风条件下,余流流向主要集中于NNE—ESE,余流流速大于0.15 m/s的概率约为25%;强风条件下风速和余流流速的互相关系数可达0.95,夏秋季较强的风速可能是流速增快的原因。

Rongcheng is an important mariculture city in China.To determine the characteristics of ocean currents in the Rongcheng offshore region,we investigated the features of the measured currents using spectral and har-monic analysis methods based on the in situ observations obtained from a moored buoy south of the Chudao Island from January to October 2016.The tidal and residual currents are analyzed separately.The influencing factors of the residual currents are highlighted.The main conclusions are as follows.(1)The zonal component of the velocity generally has larger amplitudes than the meridional component.The average and maximum values of the measured velocity are 0.20 and 0.87 m/s,respectively.In addition,the velocity of the currents shows strong seasonal variation;the velocity is the strongest in autumn,followed by summer and weakest in winter and spring.Significant asymme-tries between flood and ebb flow are observed.(2)The observed currents are dominated by the M_(2) tidal component and the shallow water tide is significant.Further analysis shows that the dominant tide belongs to a type of regular semidiurnal tidal current that rotates clockwise in all layers.The observed tidal current velocity is 0.38 m/s.(3)The residual current is relatively small compared to the tidal component.The daily averaged residual flow is the largest and smallest in autumn and winter,respectively.E and ENE are dominant,and the residual current generally exhib-its the characteristics of eastward migration.Under the condition of weak wind,the residual current is primarily in the NNE–ESE direction.Approximately 25%of residual flow velocity is greater than 0.15 m/s.The correlation co-efficient between the wind speed and velocity under strong wind conditions can reach 0.95.The strong wind speeds in summer and autumn may account for the increase of the residual velocity during that time.