| 摘要: |
| 湍流混合在调控海洋垂向物质、能量交换以及气候变化中都起着重要作用，尤其是在北太平洋低纬度西边界流系，湍流混合通过调节温跃层及海气相互作用，在西太平洋暖池结构及演化和厄尔尼诺与南方涛动的发生、发展中都起着关键作用。然而，由于湍流观测的高风险性和高费船时特征，直接的湍流观测资料非常稀缺，因此，对该海域的湍流混合认知大多数来自细尺度参数化估计。但鉴于湍流的高时变特征及该海域海洋环流结构的复杂性及西边界流区动力环境的特殊性，验证不同细尺度参数化方法对该海域湍流估算的适用性对于我们准确了解该海域的垂向混合特征、提升其在数值模拟的精度具有重要作用。本研究利用2020年9月在北太平洋低纬度西边界流系沿130°E，10°N-18°N进行的直接的微结构观测剖面仪和同期获取的细尺度温盐流测量，研究该海域湍流混合的特征及两种常用的参数化方法—GHP (Gregg-Henyey-Polzin)参数化方法、MG (MacKinnon-Gregg)参数化方法在该海域的适用性。观测结果表明，该海域上800 m湍流混合总体较强，直接观测得到的湍动能耗散率在10-8 W/kg。在温跃层中，某些站点观测的湍动能耗散率可达10-7 W/kg，特别是在14°N附近, 24.5 与25.5 之间发现一块强湍动能耗散区，初步分析表明其机制与全日内潮的参数化亚谐不稳定有关。参数化评估结果显示，MG方法与观测值相差0.5个数量级的比例为90%，而基于应变的GHP方法和基于剪切的GHP方法与观测值相差0.5个数量级的比例分别为54%和55%，表明MG方法能较好地估算低纬度西边界流系的湍流混合特征并在水平分布和垂直分布表现出一致的分布特征。本研究对提升模式对该海域垂向混合的估算，改进模拟精度等具有重要的参考价值。 |
| 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 |
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| 基金项目:国家自然科学基金项目（面上项目，重点项目，重大项目），崂山实验室科技创新项目，中国科学院战略性优先发展研究计划，“一带一路”国际科学组织联盟联合研究合作专项资助 |
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| Microstructure measurements and parameterization for assessment of turbulent mixing in the North Pacific low-latitude Western Boundary Current System |
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Sun Bin1, Zhou Hui2, Wang Jia-Ning2, Yang Wen-Long3, Liu Heng-Chang4, Yu Xiao-Tong2, Dong Huan-He2
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1.Shandong University of Science and Technology;2.Institute of Oceanology, Chinese Academy of Sciences;3.Naval Research Institute;4.Beijing institute of Applied Meteorology
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| Abstract: |
| 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 Ni?o 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. However, given the high time-varying characteristics of turbulence, the complexity of the ocean circulation structure in this area, and the special characteristics of the dynamical environment in the western boundary current zone, validating the applicability of different fine-scale parameterization methods for turbulence estimation in this area plays an important role in understanding the vertical mixing characteristics in this region and improving the accuracy of numerical simulations. In this study, we utilize the direct microstructure observation profiler and the fine-scale thermohaline flow measurements obtained in September 2020 along 130°E, 10°N-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 parameterizations—the GHP (Gregg-Henyey-Polzin) parameterization and MG (MacKinnon-Gregg) parameterization in this region. The results indicate that the turbulent mixing in the upper 800 m is strong in total, and the directly observed turbulent energy dissipation rate is in the range of 10-8 W/kg. In the thermocline, the observed turbulent energy dissipation rate can reach 10-7 W/kg at some stations, especially near 14°N, and a strong turbulent energy dissipation region is found between 24.5and 25.5, and the preliminary analysis suggests that the mechanism is related to the parametric subharmonic instability of the diurnal internal tide. The results of the parameterization evaluation show that the proportion of the MG method differing from observations by 0.5 orders of magnitude is 90%, while the proportion of the strain-based GHP method and the shear-based GHP method differing from observations by 0.5 orders of magnitude are 54% and 55%, respectively, which suggests that the MG method is able to estimate the turbulent mixing characteristics of the low-latitude Western Boundary Current System better and exhibits consistent features in the horizontal and vertical distributions. This study has important reference value for upgrading the model to estimate the vertical mixing in this sea area and improving the simulation accuracy. |
| Key words: North Pacific low-latitude Western Boundary Current System ? microstructure observations ? GHP? parameterization ? MG parameterization |