Storm-Driven Near-Inertial Waves and Mixing in the Western North Pacific

海洋混合的量化和理解仍然是物理海洋学和海洋气候中最具挑战性的问题之一。海洋环流模式中混合的准确表示(参数化)和分布对于正确再现从赤道西太平洋降水到经向翻转单元强度和生物地球化学循环的广泛过程至关重要。近惯性波是深海混合的三个主要来源之一。除了风力发电外，人们对它们的能量路径知之甚少，而且只有15%-25%的风力驱动的近惯性波能以低模波的形式向赤道辐射。这些波包含了海洋中一半的动能和大部分的垂直切变。大约一太瓦的惯性风能是由几十个中纬度的秋季和冬季风暴注入的。虽然数值和观测证据表明，大部分惯性风能损失在风暴强迫、消散和混合的近场中，但几乎没有观测工作来详细研究这一主要的惯性能量收支。除了确定风强迫的近惯性波的命运外，拟议的工作还将量化在跃层中湍流混合的气候学上重要的深度依赖关系。项目研究人员将根据他们的观测结果，就如何改进内波驱动的湍流混合的参数化问题与数值模型师进行磋商。一名研究生将接受数据分析和解释方面的培训，项目科学家将继续他们在当地的公共宣传工作。提出了一种创新的观测策略，以确定惯性风能的零级近场命运和风暴后上层混合的垂直分布。一个由12个配置电磁海流计和温度微结构传感器的剖面浮标组成的阵列将部署在西北太平洋秋冬季节惯性风电增益最大附近。使用双向Iridium通信，动态采样将专注于风暴响应。这些仪器将每三个小时重复一次在约3米的表面到500米深之间的剖面，收集大约5000条温度、盐度、水平速度和湍流温度变化耗散率的剖面。这些测量将提供大约50个独立的表层混合层和上层跃层风暴响应的深度-时间序列，在5到10个秋季和冬季风暴之后，随机变化的海洋涡旋状态。谐波匹配将分离近惯性、亚惯性和高频信号。这些测量将量化近惯性切变在哪里以及如何对湍流混合做出贡献，并估计辐射损失。

Quantification and understanding of ocean mixing remains one of the most challenging problems in physical oceanography and ocean climate. The accurate representation (parameterization) and distribution of mixing in ocean circulation models is critical to correctly reproduce a wide range of processes from precipitation in the western equatorial Pacific to the strength of the meridional overturning cell and biogeochemical cycles. Near-inertial waves are one of three major sources of deep-ocean mixing. Little is known about their energy pathways beyond their wind generation and that only 15-25% of the wind-forced near-inertial wave energy radiates equatorward as low mode waves. These waves contain half the kinetic energy and most of the vertical shear in the ocean. About a terawatt of inertial wind power is injected by a few dozen mid-latitude fall and winter storms. While numerical and observational evidence points to the bulk of the inertial wind power being lost in the near-field of storm forcing, dissipating and mixing immediately below the surface layer, there has been little observational work to investigate this major piece of the inertial energy budget in detail. As well as determining the fate of wind-forced near-inertial waves, the proposed work will quantify the climatologically-important depth dependence of turbulent mixing in the pycnocline. The project investigators will consult with numerical modelers to how to improve parameterizations for internal-wave-driven turbulent mixing based on their observational findings. A graduate student will be trained in data analysis and interpretation and the project scientists will continue their local public outreach efforts.An innovative observational strategy is proposed to determine the zero-order near-field fate of inertial wind power and the vertical distribution of upper-ocean mixing following storms. An array of twelve profiling floats with electro-magnetic current meters and temperature microstructure sensors will be deployed in the western North Pacific near the inertial wind power gain maximum for a fall-winter season. Using bi-directional Iridium communications, dynamic sampling will focus on storm responses. The instruments will repeatedly profile every three hours between ~ 3 m of the surface and 500-m depth, collecting roughly five thousand profiles of temperature, salinity, horizontal velocity and turbulent temperature-variance dissipation rate. These measurements will provide about fifty independent depth-time series of the surface mixed-layer and upper pycnocline storm responses following five to ten fall and winter storms for a random variety of ocean eddy states. Harmonic fits will separate near-inertial, sub-inertial and higher-frequency signals. The measurements will quantify where and how near-inertial shear contributes to turbulence mixing, as well as estimate radiative losses.