A numerical simulation of the generation and evolution of nonlinear internal waves across the Kara Strait
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摘要: 作为北冰洋的一个边缘海,喀拉海存在普遍的非线性内波活动。基于现场观测和卫星遥感的分析表明,其中的一个热点源区位于喀拉海峡。本文基于一个非静力近似的海洋模型分析了潮流与喀拉海峡典型地形断面相互作用激发非线性内波及其演化特征。模拟结果再现了卫星遥感所反映出的非线性内波基本特征。巴伦支海方向的内波波长在夏季大约25km,相速可达0.65m/s。卫星遥感显示巴伦支海一侧靠近源区附近,经常存在一个单波紧随内孤立波波列的双重结构,二者相距约5-8km。模拟结果显示这一结构源自于源区地形的特殊性,二者生成于同一潮周期,但尾随单波较弱,在一个周期后逐渐耗散消失。北向的背景流的加入能够强化(减弱)巴伦支海(喀拉海)方向的内波能量传输。尽管基本特征类似,背景流的加入使得喀拉海方向传播的内波呈现单波结构,这和卫星遥感捕捉到的特征一致。受冬季结冰的影响,喀拉海峡冬季层化特征主要由盐度决定,跃层深度相对于夏季明显增加,非线性条件减弱,内波呈现较为规则的线性波动。Abstract: Nonlinear internal waves (NIWs) are ubiquitous around the Kara Sea, a part of the Arctic Ocean that is north of Siberia. Three hot spot sources for internal waves, one of which is the Kara Strait, have been identified based on Envisat ASAR. The generation and evolution of the NIWs through the interactions of the tide and topography across the strait is studied based on a nonhydrostatic numerical model. The model captures most wave characteristics shown by satellite data. A typical inter-packets distance on the Barents Sea side is about 25 km in summer, with a phase speed about 0.65 m/s. A northward background current may intensify the accumulation of energy during generation, but it has little influence on the other properties of the generated waves. The single internal solitary wave (ISW) structure is a special phenomenon that follows major wave trains, with a distance about 5-8 km. This wave is generated with the leading wave packets during the same tidal period. When a steady current toward the Kara Sea is included, the basic generation process is similar, but the waves toward the Kara Sea weaken and display an internal bore-like structure with smaller amplitude than in the control experiment. In winter, due to the growth of sea ice, stratification across the Kara Strait is mainly determined by the salinity, with an almost uniform temperature close to freezing. A pycnocline deepens near the middle of the water depth (Barents Sea side), and the NIWs process is not as important as the NIWs process in summer. There is no fission process during the simulation.
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