北部湾海浪季节变化和驱动因素的数值模拟研究

Numerical investigations on seasonal variations and forcing factors to waves in the Beibu Gulf

基于NCEP CFSV2再分析风场驱动SWAN模型,对南海至北部湾为期1年的海浪逐时过程进行了数值模拟,利用Jason-2卫星和近岸浮标整年观测数据检验了模拟效果。在此基础上,评估了模型空间网格尺度对北部湾内波浪模拟的影响,分析了波浪的季节变化特征,辨析了局地风和南海传入浪对海湾波浪的驱动贡献。研究显示:(1)较Jason-2卫星观测值,有效波高模拟值的均方根误差和分散系数分别约为0.4 m和0.2;较北部湾湾顶近岸浮标逐时观测值,有效波高的均方根误差和分散系数分别约为0.2 m和0.4,平均波周期的均方根误差和分散系数分别约为0.6 s和0.2,平均波向的均方根误差约为30°;(2)空间网格分辨率为12'×12'的模型对北部湾20 m以深开敞海域波浪的模拟效果良好,模拟值较2'×2'模型的平均相对偏差在10%以下;(3)北部湾冬季盛行东北向波,夏季盛行偏南向浪,季风转换期盛行东南向浪,全年波浪在季风期强于季风转换期,冬季最强、冬夏转换期最弱;(4)局地风对北部湾波浪的驱动贡献自湾口向湾内增强,季风期强于季风转换期;南海传入浪的驱动贡献自湾口向湾内减弱,季风转换期强于季风期;海湾中部和北部的波浪以局地风为主控因素,海南岛南部和东部水域以传入浪的影响为主,海南岛西南水域受局地风和传入浪的共同控制。

Driven by the reanalysis wind data NCEP CFSV2,the third-generation wave model SWAN is utilized in a self-nested grid system to simulate waves in the Beibu Gulf(BG),South China Sea(SCS)for a period of one year.The model accuracy is examined by comparing the numerical results with the Jason-2 satellite altimetry data and the near-shore buoy measurements.Based on the numerical simulations,the influence of spatial resolutions on model predication is evaluated,the seasonal characteristics of waves in the BG are analyzed,and the forcing contributions of local wind in BG and sea waves from SCS are discussed.The results show that:(1)Compared with the Jason-2 satellite data,the root-mean square bias(RMSB)and scatter index(SI)for significant wave height are approximately 0.4 m and 0.2,respectively.Compared with the near-shore buoy observations,the RMSB and SI for significant wave height are about 0.2 m and 0.4,respectively;the RMSB and SI for mean wave period are roughly 0.6 s and 0.2,respectively;and the RMSB for mean wave direction is around 30°.(2)The numerical model with the spatial resolution 12'×12'can predict reasonable results for the open sea area of BG,and the mean relative bias compared to the model results of 2'×2'is not exceeding 10%.(3)In the BG,the northeasterly waves prevail in winter monsoon,the southerly waves reign in summer monsoon,and the southeast waves predominate during the periods of monsoon transition(MT).Waves are stronger in monsoons than MTs,up to the strongest in winter monsoon and down to the weakest when winter goes to summer.(4)The driving contribution of local wind to waves in the BG increases gradually from the bay mouth to the inner bay,and the contribution is stronger in monsoons than MTs.The driving contribution of sea waves from SCS gradually weakens from the bay mouth to the inner bay,and the contribution is weaker during monsoons than MTs.In the middle and northern parts of BG,waves are mainly controlled by local wind.In the water areas to the south and east of Hainan Island,waves are mainly dominated by sea waves from SCS.While in the areas to the southwest of Hainan Island,waves are jointly affected by the both factors.