北部湾沿岸水位变化及对风场的响应

Variation of water level along the Beibu Gulf coast and its response to wind field

关键词:  潮汐特征  经向风  调和分析  水位变化  潮汐不对称  北部湾

Key words:  Tidal characteristics  Meridional wind  Harmonic analysis  Variation of water level  Tidal asymmetry  Beibu Gulf

摘要:

北部湾水位变化对北部湾沿岸生态环境、海洋工程建设等都有着重要影响。本文主要收集2022年布放于钦州茅尾海沙井港以及钦州港码头两处的临时潮位观测站的潮位数据，以及钦州、北海、涠洲岛三个验潮站2009全年的潮位数据，通过调和分析方法，并结合ERA5风场数据，对相关变化特征以及影响因素进行分析讨论。结果表明：（1）所收集的站点水位变化以正规全日潮为主，同时平均水位呈现为冬春低、夏秋高的季节变化特征；沙井港站冬季平均水位最低，为2.55m，秋季平均水位最高，达2.76m。（2）在北部湾河口以涨潮流占优，北部湾近岸及海域以落潮流占优，O1/K1/M2 对潮汐不对称性贡献最大。（3）风场也呈现显著的季节变化，冬季以东北风为主，平均风速最大可达3.7 m/s，夏季以西南风为主，秋季则为转换期；冬春两季经向风以北风为主，出现北风风速瞬时增大的现象频率较高，夏季经向风呈现南风变化为主；经向风季节性变化特征比纬向风更为显著。（4）在非台风期，经向风变化对低频水位的影响较为显著，当出现经向风以北风为主并且强度增大时，会促使海水离岸效应增强，进一步造成了水位的下降，同样导致异常减水现象的产生。通过经向风应力与增减水变化的线性关系式计算来回报水位，与实测水位相比存在不小的误差，表明在考虑水位变化影响因素时，不能够仅考虑风场这单一因素的影响。

Abstract:

Variations in the water level of the Beibu Gulf significantly influence the coastal ecological environment and marine engineering constructions along its shores. This paper mainly collected the tidal data of the temporary tide observation stations at Shajing Port in Maoweihai and Qinzhou Port in Qinzhou in 2022, and the tidal data of the three tidal stations in Qinzhou, Beihai and Weizhou Island in 2009. Through harmonic analysis method and combining with ERA5 wind field data, the variation of characteristics and influencing factors were analyzed and discussed. The results showed that: (1) the variation of water level at the collected stations was dominated by regular diurnal tide, with seasonal changes featuring lower levels during winter and spring, and higher levels during summer and autumn; the average winter water level at Shajing Harbor was the lowest, at 2.55 meters, while the average autumn water level reaches its highest, at 2.76 meters. (2) The flood tide was dominant within the gulf, while the ebb tide was dominant in the nearshore and offshore areas of the Beibu Gulf. O1/K1/M2 contributed the most to the tidal asymmetry. (3) Wind fields also displayed distinct seasonal variations, dominated by northeast winds in winter with an average maximum wind speed reaching 3.7 m/s, southwesterly wind in summer, and a transition period in autumn; zonal wind was mainly northerly in early and late season, with frequent instances of increased northerly wind speed, while summer zonal wind predominantly changed into southerly directions; the seasonal variation feature of zonal winds was more pronounced than that of meridional winds. (4) In the non-typhoon period, the variation of meridional wind had a more significant impact on the low-frequency water level, and when the meridional wind was dominated by the north wind and its intensity increased, the offshore effect of seawater will be enhanced, which further caused the decline of water level and also led to the abnormal water reduction phenomenon. The water level calculated through the linear relationship between the meridional wind stress and the increase and decrease of water volume showed considerable deviation from the measured water level, indicating that when considering the influencing factors of water level changes, the impact of the wind field alone could not be taken into account.