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

合作研究：中纬度海洋锋的亚尺度混合层动力学研究：分离对大气强迫的亚惯性和超惯性响应

• 批准号: 1536359
• 负责人: John Farrar
• 金额: $ 35.47万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-10-01 至 2020-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1536359&HistoricalAwards=false
• 关键词: Collaborative; Research; Study; Submesoscale; Mixed

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.

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气海交换。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。这项研究计划通过在北太平洋副热带锋（一个高于平均大气强迫的区域，典型的海洋中中尺度）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平流和应变，以及典型的亚尺度活动，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）以及漂流海空通量平台将在存在代表中央海洋环流特征的混合层锋的情况下，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）拖曳体和舰载声学多普勒海流剖面仪对该区域进行反复勘测，以提供更大规模的背景信息，以及（ii）多深度流通温度和盐度系统来解决上部 2-5 m 的水平尺度较小。 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。计划的 5-7 个阵列部署，每次部署 3-5 天，将有足够的持续时间，以将低频动力学的演变与主导短时间尺度的近惯性剪切分开，从而允许通过混合层评估混合层再分层和去层化率。层涡流、风力作用和垂直过程。