南海北部陆架冬季锋面三维精细结构及其季节内演变机制

This project is carried out to study the three dimension structure and intra-seasonal variability mechanisms of coastal thermal fronts on the Northern South China Sea (NSCS) shelf. This front forms in the winter, covering the continent shelf area from the Lei Zhou Peninsula (Guangdong Province) to the eastern sea of Taiwan in the NSCS. The study for the dynamical mechanism of its intra-seasonal variations is limited, and need to be further studied. In this project, firstly, we carry out the in-situ observations using glider, MVP, underway CTD, high frequency surface wave radar and mooring buoys, and the regional non-hydrostatic ocean model, to investigate the 3-D structure of the coastal front in high spa-temporal resolution. Identify the front type according to the C-L type that explained by the bottom advection of buoyant water or the E-A type that induced by the combine effect of sea surface cooling the buoyancy flux. Using two－way nesting ROMS model with data assimilation that absorbs historical and new observation data to improve the simulation results of the costal fronts. According to the dynamical diagnose results of several sensitivities simulations, we clarify the dynamical response of multiple factors to the different intra-seasonal variations of front. These factors include the variation of topography such as widen shelf， the background coastal current and the offshore Edman transport induced the winter monsoon，as well as the spatial high-frequency perturbation of wind stress curl and air-sea interface heat flux induced by the front itself.

冬季形成于南海北部陆架区的热力锋面是一年之中在南海北部覆盖海区最广，海温梯度最显著的锋面。目前针对该锋面三维精细结构及季节内演变机制是国内沿岸海洋学研究中有待于继续深入细化的课题。本项目拟通过走航式温盐深剖面仪、水下滑翔机、高频地波雷达、锚定浮标以及PAM走航观测方法等综合观测手段，获取该海区冬季锋面温度、盐度、流场的三维精细结构。研究分析南海北部陆架锋面是属于底层浮力输送主导的C-L型锋面还是属于海面冷却和浮力通量共同主导的E-A型锋面。利用数据同化等方法，提高模式对研究海区热力锋面的模拟能力。通过敏感性试验和动力诊断分析，理清粤东陆架变宽等陆架地形变化在锋面发展及演变过程中的作用机理，揭示冬季风调制下的沿岸流及离岸Ekman输运的变化影响不同区域锋面结构和季节内演变的动力机制，为近岸热力锋面研究提供新的认识。

南海北部冬春季的近海锋面是一年之中在南海北部覆盖海区最广，海温梯度最显著的锋面过程，它与近岸物质循环以及距地天气气候都有着密切的联系。本项目针对该锋面三维精细结构和其伴随的局地海气耦合过程这一有待继续深入细化的课题开展了深入研究，取得了一些原创性成果。在项目执行过程中，深入探讨南海北部锋面结构的时空变化特征对海表及大气边界层的影响：揭示了温度引起的气压梯度力变化是引起跨越锋面的水平动量随高度变化的关键因子，进而影响大气边界层内湍流变化的动力机制。进一步挖掘南海北部上升流海洋锋面对局地气候的调制：提出了相比大尺度环流引起的湿度和对流不稳定性变化，由上升流系统调节的海陆风引起的局地海气相互作用对南海北部沿海降水日变化影响更为显著的论点，为近岸海洋现象调节局地天气气候的研究提供了新视角。本项目相关研究成果对近岸海洋环境的监测与预报、海洋生态环境修复以及提高极端天气事件预测预警能力等方面有一定的科学意义和应用价值。