热带海洋学报 ›› 2016, Vol. 35 ›› Issue (5): 10-19.doi: 10.11978/2015150CSTR: 32234.14.2015150

• 海洋水文学 • 上一篇    下一篇

南海北部次中尺度过程数值研究*

罗士浩1, 2, 经志友1, 齐义泉1, 谢强1   

  1. 1. 热带海洋环境国家重点实验室(中国科学院南海海洋研究所), 广东 广州 510301; 2. 中国科学院大学, 北京 100049;
  • 收稿日期:2015-12-07 出版日期:2016-08-29 发布日期:2016-09-22
  • 通讯作者: 经志友。E-mail: jingzhiyou@scsio.ac.cn
  • 作者简介:罗士浩(1990—), 男, 广东省湛江市人, 硕士研究生, 主要从事南海北部次中尺度过程的数值模拟研究。E-mail: shluo@scsio.ac.cn
  • 基金资助:
    基金项目:海洋公益性行业科研专项(201305031-7); 国家自然科学基金项目(41276022、41230962); 广东省近海海洋变化与灾害预警重点实验室开放课题(GLOD1401)

Numerical study on sub-mesoscale processes in the northern South China Sea

LUO Shihao1, 2, JING Zhiyou1, QI Yiquan1, XIE Qiang1   

  1. 1. State Key Laboratory of Tropical Oceanography (South China Sea Institute of Oceanology, Chinese Academy of Sciences),Guangzhou 510301, China; 2. University of Chinese Academy of Sciences, Beijing 100049, China;
  • Received:2015-12-07 Online:2016-08-29 Published:2016-09-22
  • Contact: Corresponding author: JING Zhiyou. E-mail: jingzhiyou@scsio.ac.cn
  • Supported by:
    Foundation item: Public Science and Technology Research Funds Projects of Ocean (201305031-7); National Natural Science Foundation of China (41276022、41230962); Guangdong Province Key Laboratory for Coastal Ocean Variation and Disaster Prediction (GLOD1401)

摘要: 近年来的观测与理论研究发现, 海洋上混合层存在一类水平尺度为0.1~10km、时间尺度为~O(1天)的重要物理过程, 称之为次中尺度过程。该过程具有较大的罗斯贝数(Ro)和较小的理查森数(Ri), 它能有效地通过次级不稳定从中尺度地转过程中汲取能量, 并向小尺度湍流混合串级, 从而对上层海洋物质能量输运、中尺度过程变异、海气相互作用, 以及混合层再分层等产生重要影响。利用区域海洋模式系统ROMS(Regional Ocean Modeling System)进行水平分辨率约为1km的高分辨率数值实验, 对南海北部的次中尺度过程进行了初步探讨。分析结果表明, 南海北部海域有着丰富的中尺度涡旋与海洋锋面活动, 且涡旋与锋区边缘存在显著的次中尺度现象。通过对次中尺度涡旋个例的稳定性和能量分析发现, 锋面海域强烈的水平浮力梯度导致了涡丝边缘的Ertel位涡小于0, 并引起对称不稳定, 锋生作用是该次中尺涡旋南侧发生对称不稳定的主要动力机制。同时, 对称不稳定能有效地从地转剪切中汲取能量并向小尺度湍流混合串级, 其能量汲取的最大值出现在20m深度, 约为4×10-7W•kg-1

关键词: 南海北部, 次中尺度过程, 数值模拟, 锋生作用

Abstract: Recent field observations and theoretical analysis revealed the processes with the lateral scale of 0.1-10 km and time scale of O(1 day) in the mixed layer, which are termed sub-mesoscale processes. Physics at these scales are distinguished by big Rossby number (Ro) and small Richardson number (Ri). They are able to effectively extract energy from geostrophic shear through sub-mesoscale instabilities, and then forward cascade the energy to dissipation at smaller scales. Moreover, sub-mesoscale processes can play a crucial role in the transport of upper-ocean mass and energy, mesoscale variability, air-sea interaction, and upper-ocean restratification, among others. Base on the Regional Ocean Modeling System (ROMS) high-resolution (1-km) numerical experiment, we preliminarily discuss sub-mesoscale processes in the northern South China Sea (NSCS) in this paper. The results suggest that mesoscale eddies and fronts were ubiquitous in the NSCS with significant sub-mesoscale process at their edges. Analytical investigation of stability and energy in one sub-mesoscale eddy as a case study indicates that the generation of negative potential vorticity (q) resulting in symmetric instability (SI) was primarily attributable to the strong lateral buoyancy gradients adjacent to frontal vortex filament. This instability is mainly produced by the frontogenesis at the southern edge of the sub-mesoscale eddy. Moreover, the extracted energy by the SI from geostrophic shear tends to forward cascade to the turbulence at small scale, with a maximum energy extraction of 4×10-7W•kg-1 at about 20-m depth.

Key words: northern South China Sea, sub-mesoscale physics, numerical modelling, frontogenesis