南海陆坡区第一模态内孤立波能量与能通量特征研究

Energy and Energy Flux Analysis of the Mode-1 Internal Solitary Wave in the Continental Slope of the South China Sea

  • 摘要: 对于南海北部内孤立波能量及通量特征的研究,受限于观测数据的缺乏,前人的工作主要针对南海东北部的深水区内孤立波,而对陆坡浅水区内孤立波能量特征研究较少,本文基于南海北部东沙群岛西侧陆坡区潜标观测资料,从结构特征和统计特征两方面对该海域第一模态内孤立波能量与能通量进行分析研究。结果表明:①研究区第一模态内孤立波能量主要分布于海洋上层,垂向空间分布上动能集中于0~100 m深度,在海表面达到最大,而势能更集中于水体50~150 m深度,在海表面为0;动势能比随振幅增大而增大,当振幅小于60 m时,动能与势能数值相似,统计拟合比值约为0.98,当振幅大于60 m时,大部分内孤立波动能大于势能,统计拟合比值约为1.60;观测期间内9月总能量最大,12月平均能量最大。②研究区第一模态内孤立波能通量主要分布于海洋上层且为负值,其中非线性平流项要远小于速度压强项,其统计拟合比值约为0.34;观测期间内8月总能通量最大,12月平均能通量最大。③与海盆区及东沙群岛东侧陆坡区的2套历史潜标观测结果对比可得,内孤立波从海盆区到陆坡区的传播过程中存在极大能量损耗,该海区内孤立波统计拟合动势能比大于东沙群岛东侧陆坡区,这可能由于东侧陆坡区地形更为陡峭使得波形易于陡化,导致动能向势能转化。观测区内孤立波非线性程度总体要小于东侧陆坡区,但比海盆区更强,且该海区存在较强的局地能量耗散。

     

    Abstract: Based on the ocean current data observed by mooring systems in the western continental slope region of the Dongsha Islands in northern South China Sea, the structural and statistical features of energy and energy flux of the mode-1 internal solitary waves (ISWs) are studied. The results indicate that the energy of the mode-1 ISWs is mainly confined in upper layers of the region. Kinetic energy ( E_\mathrmK ) is mainly in 0-100 m depth and reaches its maximum at sea surface, while available potential energy ( E_\mathrmA\mathrmP ) is mainly in 50-150 m depth and is 0 at sea surface. The ratio of E_\mathrmK to E_\mathrmA\mathrmP increases with amplitude, and is about 0.98 when amplitude is less than 60 m and about 1.60 when the amplitude is greater than 60 m. In observation period, total energy is highest in September, and average energy is highest in December. The energy flux of the mode-1 ISWs is negative and mainly confined in upper layers of theregion. The nonlinear advection term is significantly smaller than the velocity-pressure term, with a statistical ratio of about 0.34. In observation period, the total energy flux is highest in August, and the average flux is highest in December. By comparing the results of two sets of subsurface buoy observations in the basin area and the eastern continental slope region of the Dongsha Islands, significant energy loss is found during the propagation of ISWs from the basin region to the continental slope region, and E_\mathrmA\mathrmP/E_\mathrmK is greater than that in eastern continental slope region of the Dongsha Islands, which is possibly due to the steep topography in eastern continental slope region that leads to wave steepening and conversion of E_\mathrmK to E_\mathrmA\mathrmP . The overall nonlinearity of ISWs in the observation region is smaller than that in eastern continental slope region but stronger than that in the basin region, and local energy dissipation is strong in the region.

     

/

返回文章
返回