Collaborative Research: A Study of Submesoscale Mixed-Layer Dynamics at a Mid-Latitude Oceanic Front: Isolating the Sub- and Super-Inertial Response to Atmospheric Forcing

海洋混合层既是大气与海洋之间动量、热量和气体交换的管道又是屏障。最近的模型揭示了许多相互竞争的亚尺度混合层过程，这些过程可以促进或抑制海气交换。这些过程是观察上的挑战，因为需要无混叠的时间和横向分辨率，以及足够的持续时间来建立持久机制。本研究计划通过在北太平洋副热带锋区进行为期 28 天的实验，显着提高对三维混合层动力学中 1-10 公里尺度横向过程的理解。北太平洋副热带锋区具有高于平均水平的大气强迫、典型的海洋中部中尺度平流和应变以及典型的亚中尺度活动，从而最大限度地提高发现重要信号的可能性。该观测计划的结果将改善混合层参数化的物理基础，从而更好地预测海气通量、气体传输和生物生产力的模型。该项目将培养一名研究生，并为本科生提供研究经验。 邮轮博客和实验网站将向更广泛的科学界和公众提供该项目的结果。多艘船舶调查、分析浮子阵列部署（16-20个浮子测量温度、盐度、水平速度和微观结构）和一个漂流海气通量平台将在存在中央海洋环流特征的混合层锋面的情况下，对上层海洋对冬季风暴强迫的响应进行采样。这些阵列将每 30-40 分钟同步进行一次剖面分析，以消除时空混叠，在地表和 100-150 m 深度（过渡层下方）之间循环。在部署期间和部署之间，将使用 (i) 拖曳体和船载声学多普勒海流剖面仪对该区域进行反复勘测，以提供更大范围的环境；(ii) 多深度流过温度和盐度系统，以解析上部 2-5 m 的较小水平尺度。 表面混合层的亚介尺度变化导致动力学过程不容易满足常用的准地转或一维表面层近似。尽管这些过程已经在孤立或理想化条件下进行了研究，但迄今为止的观测证据不足以阐明这些亚惯性过程是否能够在存在高频大气强迫和强内波切变的情况下运行。计划部署 5-7 个阵列，每次部署 3-5 天，将有足够的持续时间来将低频动力学的演变与在短时间尺度上占主导地位的近惯性切变分开，从而可以通过混合层涡流、风力和垂直过程来评估混合层再分层和去层化速率。

The ocean mixed-layer is both conduit and barrier for exchange of momentum, heat and gases between the atmosphere and ocean. Recent modeling has revealed a host of competing submesoscale mixed-layer processes which can either promote or inhibit air-sea exchange. These processes are an observational challenge because of the need for unaliased temporal and lateral resolution, as well as sufficient duration to establish persistent mechanisms. This study plans to dramatically improve understanding of 1-10 km scale lateral processes in three-dimensional mixed-layer dynamics with a 28-day experiment in the North Pacific Subtropical Front, a region of above-average atmospheric forcing, typical mid-ocean mesoscale advection and straining, and typical submesoscale activity, maximizing the likelihood of finding significant signals. The results of this observational program will improve the physical basis of mixed-layer parameterizations, leading to better model predictions for air-sea fluxes, gas transfer and biological productivity. The project will train one graduate student and provide research experiences to undergraduate students. A cruise blog and experiment website will make the results of the project available to the wider scientific community and general publicMultiple ship surveys, profiling float array deployments (16-20 floats measuring temperature, salinity, horizontal velocity and microstructure) and a drifting air-sea flux platform will sample the upper-ocean's response to winter storm forcing in the presence of the mixed-layer fronts that characterize the central ocean gyres. The arrays will profile in sync every 30-40 minutes to eliminate space-time aliasing, cycling between the surface and 100-150 m depth (below the transition layer). During and between deployments, the region will be surveyed repeatedly with (i) a tow-yo body and a shipboard Acoustic Doppler Current Profiler to provide larger-scale context and (ii) a multi-depth flow-through temperature and salinity system to resolve smaller horizontal scales in the upper 2-5 m. Submesoscale variability in the surface mixed-layer leads to dynamical processes which do not readily satisfy the quasigeostrophic or 1-D surface layer approximations in common use. Although these processes have been examined in isolation or idealized conditions, observational evidence to date is insufficient to clarify whether these subinertial processes are able to operate in the presence of high-frequency atmospheric forcing and strong internal-wave shears. The planned 5-7 array deployments of 3-5 days each will be of sufficient duration to separate the evolution of low-frequency dynamics from near-inertial shear that dominates short timescales, allowing evaluation of mixed-layer restratification and destratification rates by mixed-layer eddies, wind-forcing and vertical processes.