在孟加拉湾使用区域海洋模拟系统的涡旋-淡水相互作用
Eddy-freshwater Interaction using Regional Ocean Modeling System in the Bay of Bengal
摘要：
利用区域海洋模拟系统对孟加拉湾北部的涡旋-淡水相互作用进行了高分辨率模拟研究。根据观测结果，该模式模拟了2015年11月至11月的次月时间尺度上气旋性中尺度涡对河水的截留和均匀化。由于新鲜的河水被困在涡流中，其特征在于盐度的强烈垂直和横向梯度。在几周内，这些梯度随着涡流内淡水的逐渐均匀化而放松。一个混合层的盐度收支表明，在涡旋内的盐度演变过程中，除了横向平流外，非地转垂直平流也很重要。通过对海洋上层涡动动能收支的分析，揭示了正压和斜压不稳定斜压不穩定的发展。EKE转换项的垂直廓线表明，地面淡水参与了混合层内斜压不穩定的演变。此外，涡可用位能（EPE）预算表明，夹带的河水提高EPE，这是由于横向盐度梯度的增加，在整个漩涡的捕获事件。随后，盐度均匀化导致EPE的减少，其衰减率由表面浮力通量和密度异常之间的相关性调制。最后，再分析数据显示，多年来类似的捕获和均质化事件，突出了这种机制的重要性，在BoB的亚季节性淡水演变。
英文摘要：
Eddy-freshwater interaction is studied in the north Bay of Bengal (BoB) with a high-resolution simulation using the Regional Ocean Modeling System. Following observations, the model simulates the trapping and homogenization of river water by a cyclonic mesoscale eddy on a sub-monthly time scale from October-November of 2015. As fresh river water is trapped in the eddy, it is characterized by strong vertical and lateral gradients in salinity. Within a few weeks, these gradients relax along with the progressive homogenization of freshwater within the eddy. A mixed layer salinity budget shows the importance of ageostrophic vertical advection in addition to lateral advection during the evolution of salinity within the eddy. An analysis of the eddy kinetic energy (EKE) budget in the upper ocean indicates the development of barotropic and baroclinic instabilities. The vertical profiles of EKE conversion terms reveal that the surface freshwater was involved in the evolution of baroclinic instability within the mixed layer. In addition, an eddy available potential energy (EPE) budget shows that the entrainment of the river water raises the EPE, which is due to an increase in lateral salinity gradients across the eddy during the trapping event. Subsequently, the salinity homogenization leads to a decrease in the EPE, and its rate of decay is modulated by a correlation between surface buoyancy fluxes and density anomalies. Finally, reanalysis data show similar trapping and homogenization events across multiple years, highlighting the importance of this mechanism of subseasonal freshwater evolution in the BoB.
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