Tidally generated island wakes and surface water cooling over Izu Ridge
Tidally generated island wakes and surface water cooling over Izu Ridge
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DOI：
10.1007/s10236-019-01302-1
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发表时间：
2019-11
期刊：
影响因子：
2.3
通讯作者：
T. Kodaira;T. Waseda
中科院分区：
文献类型：
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作者：
T. Kodaira;T. Waseda
黑潮在西北太平洋伊豆洋脊的岛屿后方产生冷尾流。2015-2017年地球同步卫星Himawari-8的观测数据显示，在黑潮流离开岛屿期间出现了冷水沃茨。以潮流为重点，本研究通过采用2017年7月发生的事件的高分辨率数值海洋模型，对导致低海面温度（SST）区域形成的动力学过程进行了调查。只有当潮流被包括在数值模型中时，冷水区才出现。模拟结果表明，由于上升流和垂直混合，在岛屿附近形成了冷的表层沃茨。每个岛屿冷水形成的定性特征取决于其大小，地形和环境电流。在小津岛附近，潮汐漂移足够大，足以引起涡流脱落。这些脱落的漩涡被潮汐流搅动，将表面冷却效果扩展到更广泛的地区。在八丈岛附近，一个持续的尾流是由周围的北向气流形成的。包含的潮流不稳定的尾流，并因此导致形成一个低SST区，虽然没有明显的涡流脱落检测。使用一个额外的无量纲参数，定义为潮汐漂移和岛屿直径之间的比率的岛屿周围的流型进行分类。
The Kuroshio current is well known for generating cold wakes behind islands over Izu Ridge in Northwestern Pacific. Observational data from the geostationary Himawari-8 satellite for 2015–2017 revealed the occurrence of cold waters during the period when the Kuroshio current flows away from the islands. With a focus on tidal currents, this study presents an investigation of dynamical processes responsible for the formation of areas with low sea surface temperature (SST) through the adoption of a high-resolution numerical ocean model for an event that happened in July 2017. Areas with cold water emerged only when tidal currents are included in the numerical model. The model results indicate the cold surface waters are formed in the vicinity of the islands because of upwelling and vertical mixing. Qualitative features of the cold water formation for each island are found to depend on its size, topography, and ambient currents. Near Kozu Island, the tidal excursion is large enough to cause eddy shedding. These shed eddies are stirred by tidal currents to extend the surface cooling effect to wider areas. Near Hachijo Island, a persistent wake is formed by the ambient northward current. Inclusion of tidal currents destabilizes the wake, and consequently leads to the formation of a low SST area, although no clear eddy shedding is detected. The flow patterns around the islands are classified using an additional non-dimensional parameter, defined as the ratio between tidal excursion and island diameter.