风场在渤海表层悬浮体多年变化中的作用

The role of wind in the multi-year variations of surface suspended sediment in the Bohai Sea

  • 摘要: 渤海悬浮体浓度(Suspended Sediment Concentration, SSC)的长期变化,对海域水质环境及生态系统等有重要影响。近年来黄河输沙量锐减,风作为重要的驱动要素,已成为影响渤海SSC长期变化的主要原因。本文基于2003—2021年中等分辨率成像光谱仪(Moderate Resolution Imaging Spectrometer, MODIS) 的Level-1B(L1B)卫星遥感数据,结合渤海多个航次的实测SSC建立反演模型,进一步获得渤海表层SSC的多年数据,采用经验正交函数(Empirical Orthogonal Function, EOF)分析的方法获得SSC的时空变化特征,结合CFSR(Climate Forecast System Reanalysis)风场资料,探明风场在渤海表层悬浮体多年变化中的作用。渤海表层SSC的EOF分析结果显示:前三个模态累积方差贡献率为73.4%,其中第一模态对总体方差贡献率为53.15%,表现为全海域同步变化,主要受冬季风速变化控制,尤其表现为2009年以前,SSC随冬季风速的升高而增大,2009年以后随冬季风速的下降而减小;第二模态对总体方差贡献率为14.14%,显示的是渤海湾和莱州湾SSC反相位的变化特征,与风向控制下的平流输沙作用有关。研究渤海SSC的长期变化特征及不同海湾间的物质输运与交换,对于保护渤海生态环境、预测河口海岸地貌变化及防灾减灾等具有重要意义。

     

    Abstract: The multi-year variations of suspended sediment concentration (SSC) in the Bohai Sea have important impacts on the water quality and ecosystem. In recent years, the river-delivered sediments, especially from the Yellow River, have decreased significantly. As one of the influencing factors, wind has become the main factor affecting the long-term changes of SSC in Bohai Sea. Based on the moderate resolution imaging spectrometer (MODIS) L1B data from 2003 to 2021, this paper established an inversion model combined with the measured SSC from several voyages in the Bohai Sea to obtain the multi-year data of the surface SSC in the Bohai Sea. And the empirical orthogonal function (EOF) method was used to analysis the spatial and temporal patterns of the surface SSC in the Bohai Sea. Furthermore, the climate forecast system reanalysis(CFSR) wind data were collected to explore the role of wind field in the multi-year variations of the surface SSC in the Bohai Sea. The results of EOF analysis of the SSC showed that the cumulative variance contributed by the first three modes was 73.4%. The first mode contributed 53.15% to the overall variance and was dominated by the synchronous variation of the whole sea area. This mode was mainly controlled by the wind speed change in winter, which indicated that the SSC increased with the enhanced winter wind speed before 2009 and decreased with the weakened winter wind speed after 2009. The second mode contributed 14.14% to the overall variance and showed the variation characteristics of the inverse phase of SSC in Bohai Bay and Laizhou Bay, which was related to the advective transport of sediment controlled by the wind direction. The study of long-term changes of the SSC in the Bohai Sea and the exchange of sediment between different bays are important scientific supports to the ecological environment protection in the Bohai Sea. And the results can also be used to predict the change of coastal geomorphology and seabed disaster.

     

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