Journal of Tropical Oceanography >
Observations of fine-scale structure and study of turbulent mixing in the deep northeastern South China Sea*
Received date: 2024-10-23
Revised date: 2025-02-10
Online published: 2025-03-03
Supported by
National Natural Science Foundation of China(61871354)
National Natural Science Foundation of China(6172780176)
Based on direct turbulence measurements at 4000 m depth from Station H2 (17°N, 116°E) in the South China Sea in 2022, this study comprehensively investigates the vertical distribution and correlation of turbulent mixing parameters — including turbulent kinetic energy dissipation rate, mixing rate, Thorpe scale — in the northeastern South China Sea. The mixing rate and Thorpe scale characterize the turbulent mixing intensity from the perspectives of turbulent dissipation and water mass overturning, respectively. Both parameters exhibit consistent average fluctuations every 500 m in the 1500~4000 m depth range, diaplaying a four-layer “big-small-big-small” distribution (inverse z-shaped) with high correlation. The MacKinnon-Gregg parameterization model was applied to this station, yielding reliable estimates, with an overall correlation coefficient exceeding 0.7 between the estimated mixing rate and Thorpe scale. Based on their correlation coefficient distribution, we select depths with strong (1755 m) and weak (3785 m) correlations between the mixing rate and Thorpe scale for wavelet analysis. The results reveal more intense multi-scale energy cascade in regions of strong correlation, demonstrating that the correlation coefficient between parameters can effectively identify genuine turbulent mixing and filter out false errors caused by instrument noise or environmental factors. By combining fine-structure direct observations with parameterization methods, this study provides valuable insights into turbulence observation, the vertical distribution of mixing parameters and the evolution mechanisms of turbulent mixing in the middle and deep layers of the South China Sea.
ZHU Xiaoyu , YANG Hua , MAO Beibei , ZHENG Yuxuan . Observations of fine-scale structure and study of turbulent mixing in the deep northeastern South China Sea*[J]. Journal of Tropical Oceanography, 2025 , 44(5) : 22 -30 . DOI: 10.11978/2024201
图1 站点位置图基于自然资源部标准地图服务网站下载的审图号为GS(2023)2762号的标准地图制作。图中“▲”为2022年秋季H2测站位置 Fig. 1 Location map of the station. The “▲” marks the location of the H2 station in autumn 2022 |
表1 湍流传感器参数Tab. 1 Parameters of turbulence sensor |
| 名称 | 性能参数 |
|---|---|
| 采样频率/Hz | 1000 |
| 响应时间/ms | 1 |
| 空间分辨率/mm | 0.35 |
| 剪切流灵敏度/(V·m·s2·kg-1) | 2.68×10-2 |
| 耗散率测量范围/(W·kg-1) | 1×10-11~1×10-4 |
图3 H2站位的直接观测的参数面积图a. 浮力频率; b. 耗散率; c. 混合率; d. Thorpe尺度的计算结果(均平滑后)。图中的橘色虚线对应的深度分别为1755m和3785m Fig. 3 Area plots of parameters from direct observations at station H2. (a) Buoyancy frequency |
图5 直接观测的平均参数分布a. 浮力频率; b. 耗散率; c. 混合率; d. Thorpe尺度。图中“●”表示7个深度段的平均参数值, 纵坐标为每个500m的深度区间上限; 粉色虚线框对应1500~4000m的参数分布 Fig. 5 Distribution of average parameters from direct observation. (a) Buoyancy frequency; (b) dissipation rate; (c) mixing rate; (d) Thorpe scale. The “●” marks represent average parameter values from seven depth segments, with the ordinate showing the upper limit of each 500 m depth interval. The rectangular box highlights parameter distributions between 1500~4000 m |
图8 两个深度段的小波谱a. 1755~1760m; b. 3785~3790m。此处采用的是Haar小波进行的连续小波变换(continuous wavelet transform, CWT) Fig. 8 Wavelet spectra of two depth segments. (a) 1755~1760 m; (b) 3785~3790 m. Continuous wavelet transform (CWT) using Haar wavelet is applied here. The x, y, and z axes represent time, frequency, and wavelet coefficient values respectively |
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