冲淡水影响下南海北部近岸环流的天气尺度变化和动力机制

Circulations over the continental shelf and in the estuaries, especially the cross-shelf transport and water exchange between the estuary and shelf, are of vital importance to the redistribution of the terrestrial and oceanic materials. Through enhanced coastal observations (Phase Averaging Methods (PAM) cruise, High-Frequency Radar (HF-Radar) ) and numerical model with data assimilation (ROMS and 3DVAR), circulations and related water transport over the inner northern South China Sea (NSCS) shelf and around the Pearl River Estuary (PRE) will be studied. Two main focuses are the influence of the synoptic variability of monsoon and Pearl River plume to the along-shore and cross-shore transport, and the influence of the wind-driven shelf circulation to the estuarine-shelf water exchange rate. The contributions of the stratification, secondary circulation associated with plume front, and the spatial variation of the wind stress and fresh water buoyancy flux to the estuarine and shelf circulations will be studied by numerical experiments and diagnostic analysis. The project will adopt novel and comprehensive observations with numerical simulations to study the circulations in the inner shelf of the NSCS, the results will help to reveal the dynamic processes that are critical to the variations of the circulations in the PRE and NSCS, but are not well understood. It will also provide a valuable scientific basis for the study of the biogeochemical processes and marine environmental protections in this region.

河口、陆架海区环流，尤其是跨陆架输运与河口-陆架水交换，对陆源和大洋物质的再分布起着至关重要的作用。本项目拟通过近岸强化观测（相位平均方法（PAM）走航观测、高频地波雷达（HF-Radar））和数值同化模拟（ROMS模式和三维变分同化（3DVAR））相结合，研究南海北部内陆架以及珠江口附近的环流，重点关注天气尺度过程中，珠江冲淡水影响下的沿陆架、跨陆架水体输运，以及季风驱动的近岸环流对河口陆架水交换的影响。通过数值实验、动量、能量和涡度等诊断分析方法，探讨冲淡水层结以及锋面导致的次级环流以及风场与冲淡水浮力通量的空间不均性对河口、陆架环流的贡献。项目采用较新颖的综合观测、数值模拟研究方式对南海北部内陆架一些关键但尚不清楚的环流动力开展研究，研究成果将有助于进一步揭示珠江口与南海北部内陆架环流变化的动力特征和驱动机制，对于该海区生物地球化学循环的研究以及海洋环境保护有重要科学价值。

南海北部近海陆架环流受季风、潮汐和珠江冲淡水的影响，表现出复杂的时空变化特征，影响着跨陆架水体输运，对陆源和大洋物质的再分布有重要作用。项目通过对现场观测、卫星遥感的水文资料的收集与分析，开展数值模拟和动力诊断，揭示了南海北部近海环流在冲淡水影响下的天气尺度变化特征的区域差异，量化了风、潮、冲淡水的空间分布差异对粤西、珠江口、粤东海区跨陆架水体输运的影响。结果显示近海跨陆架净水体输运天气尺度变化在珠江口和粤东主要受季风影响，季风的空间差异使得非局地风可以通过改变陆架背景流场及其底Ekman层影响跨陆架输运；而在粤西，由于南海北部近岸潮汐强度的空间分布不均引起的沿陆架方向压强变化导致其跨陆架净输运主要受大-小潮周期变化影响。冲淡水锋面不稳定性增强了向岸/离岸水体输运，但对净水体输运影响较小。项目研究成果拓展了对南海北部近海环流和跨陆架水体输运的动力过程的认识，丰富了南海北部近海水文观测、模拟数据。