MICROSTRUCTURE MEASUREMENT AND PARAMETERIZATION FOR THE ASSESSMENT OF TURBULENT MIXING IN THE NORTH PACIFIC LOW-LATITUDE WESTERN BOUNDARY CURRENT SYSTEM
MICROSTRUCTURE MEASUREMENT AND PARAMETERIZATION FOR THE ASSESSMENT OF TURBULENT MIXING IN THE NORTH PACIFIC LOW-LATITUDE WESTERN BOUNDARY CURRENT SYSTEM
Turbulent mixing plays an important role in regulating the oceanic vertical material and energy exchanges as well as climate change,especially in the North Pacific low-latitude Western Boundary Current System,where turbulent mixing plays a key role in the structure and evolution of the Western Pacific Warm Pool as well as in the onset and development of the El Nino and the Southern Oscillation,through the regulation of the thermocline and the air-sea interactions.However,direct turbulence observations are scarce due to the high-risk and high ship-time characteristics of turbulence observations,and thus most of the knowledge of turbulent mixing in this region derives from fine-scale parameterized estimates.In view of the high time-varying turbulence,complex ocean circulation structure,and unique dynamical environment in the western boundary current zone,validating the applicability of various fine-scale parameterization methods for turbulence estimation is crucial for understanding vertical mixing characteristics and improving numerical simulation accuracy.In this study,we applied the direct microstructure observation profiler and the fine-scale thermohaline flow measurements in September 2020 along 130°E at 10°～18°N in the North Pacific low-latitude Western Boundary Current System,to investigate the characteristics of turbulent mixing and the applicability of the two commonly used parameterization methods:the GHP(Gregg-Henyey-Polzin)parameterization and MG(MacKinnon-Gregg)parameterization.Results indicate that the turbulent mixing in the upper 200 m was strong in total,with an average turbulent kinetic energy dissipation rate of about 10-8 W/kg.In the thermocline,the observed turbulent energy dissipation rate reached 10-7 W/kg at some stations,especially near 14°N,and a strong turbulent energy dissipation region was found between 24.5 σθ and 25.5 σθ.Preliminary analysis suggested that the mechanism was related to the parametric subharmonic instability of the diurnal internal tide.The results of the parameterization evaluation show that the proportion of difference by 0.5 orders of magnitude between the MG method and the observations was 95％,while those between the strain-based GHP method and the shear-based GHP method,and the observations were 55％and 58％,respectively,which suggests that the MG method is able to better estimate the turbulent mixing characteristics of the low-latitude Western Boundary Current System and exhibits consistent features in the horizontal and vertical distributions.The results of this study provided a useful reference for researchers to select a fine-scale parameterization to explore the intensity and spatial distribution of turbulent mixing in the low-latitude western boundary current system in the North Pacific Ocean.
关键词
北太平洋低纬度西边界流系/微结构观测/GHP参数化方法/MG参数化方法
Key words
North Pacific low-latitude western boundary current system/microstructure observations/GHP parameterization/MG parameterization
维普
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