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

海洋混合层是海洋与大气之间动量、热量和气体交换的通道和屏障。最近的模拟揭示了一系列相互竞争的亚中尺度混合层过程，这些过程既可以促进也可以抑制海气交换。这些过程是一个观测的挑战，因为需要无锯齿的时间和横向分辨率，以及足够的时间来建立持久的机制。这项研究计划通过在北太平洋副热带锋进行为期28天的实验，极大地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，该区域的大气强迫高于平均水平，典型的海洋中层中尺度平流和应变，以及典型的亚中尺度活动，最大限度地提高发现重要信号的可能性。这一观测方案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、气体转移和生物生产力。该项目将培养一名研究生，并为本科生提供研究经验。 一个巡航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（16-20个浮标测量温度、盐度、水平速度和微观结构）和一个漂移的海气通量平台将在混合-表征中央海洋环流的层锋。这些阵列将每30-40分钟同步一次，以消除时空混叠，在表面和100-150米深度（过渡层以下）之间循环。在部署期间和部署间隔期间，将利用（i）一个拖曳体和一个船载声学多普勒海流剖面仪对该区域进行反复勘测，以提供更大尺度的背景，以及（ii）一个多深度流通温度和盐度系统，以解决上部2-5米的较小水平尺度。 次中尺度地面混合层变率导致的动力过程不容易满足常用的准地转或一维近地层近似。虽然这些过程已在孤立或理想条件下进行了研究，但迄今为止的观测证据不足以澄清这些亚惯性过程是否能够在高频大气强迫和强内波切变的情况下运作。计划部署5-7个阵列，每个阵列部署3-5天，将有足够的时间将低频动力学的演变与主导短时间尺度的近惯性切变分开，从而可以通过混合层涡旋、风强迫和垂直过程来评估混合层抑制和去层速率。

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.