南海西部夏季上升流锋面的次中尺度特征分析

利用卫星遥感资料和区域海洋数值模式ROMS(regional ocean modeling system)高分辨率数值模拟结果, 对南海西部夏季上升流锋面的次中尺度特征及其非地转过程进行了探讨。高分辨率卫星遥感观测和数值模拟结果显示, 南海西部夏季锋面海域存在活跃的次中尺度现象, 其水平尺度约为1~10km, 且具有O(1)罗斯贝数(Rossby number, Ro)的典型次中尺度动力学特征。进一步的诊断分析表明, 在夏季西南风的驱动下, 沿锋面射流方向的风应力(down-front wind stress)引起的跨锋面埃克曼输运有利于将海水由锋面冷水侧向暖水侧输运, 减小了锋面海域的垂向层结和Ertel位涡, 加剧了锋面的不稳定, 并形成跨锋面的垂向次级环流。高分辨率模拟结果显示, 锋面海域最大垂向流速可达100m?d ^-1, 显著增强了上层海洋的垂向物质交换。因此, 活跃在锋面海域的次中尺度过程可能是增强南海西部上升流海域垂向物质交换的重要贡献者。

Analysis of submesoscale characteristics of summer upwelling fronts in the western South China Sea

We investigate submesoscale characteristics of summer upwelling fronts in the western South China Sea (WSCS) and associated ageostrophic processes by using satellite measurements and high-resolution ROMS simulations. Active submesoscale filaments with a typical horizontal scale of O(1-10) km are detected to be characterized by O(1) Rossby number (Ro) from the fine-resolution satellite images and simulation results. The diagnostic analysis shows that down-front wind forcing drives a net cross-front Ekman transport and advects heavy water over light water. This process at submesoscale tends to reduce the stratification and potential vorticity (PV), exacerbates the frontal instabilities, and forms the cross-front secondary circulation. The high-resolution simulation results show that the maximum vertical velocity in the frontal zone can reach 100m?d ^-1, which significantly enhances vertical material exchange. In this context, active submesoscale processes may contribute to enhanced vertical exchanges of the upper ocean in the summer upwelling front of the western SCS.