Collaborative Research: Submesoscale Dynamics over the Continental Shelf: Drivers and Implications for Across-Shelf Exchange

本项目研究了小型（2-10公里）沿海海洋流在大陆架上搅动水团的机制，并有助于海岸和公海之间的物质运输。将部署独特的高频雷达系统阵列，以高空间分辨率测量表面电流。这些测量将能够分辨大小从2 ？在新英格兰大陆架（NES）上的20公里。要覆盖的陆架区域延伸至离岸30至80公里，水深30至70米。这些表面电流测量将通过使用水下仪器同时进行水下测量来增强，而自主水面车辆和漂浮器将用于测量大陆架中部速度结构、精细水平梯度和漂浮器轨迹。对收集到的数据的分析将增加我们对海岸和广阔大陆架上公海之间物质交换的理解。这种交换对生物地球化学、大陆架生产力、渔业、污染物的运输以及确定热量和淡水预算都有影响；这是诊断大陆架生态系统变异性、提高其可预测性、从而有助于更好地区分人为和自然生态系统变化的关键步骤。提议的高频雷达测量数据将输入NOAA运营的国家高频雷达（HFR）网络，数据将用于沿海海洋模型的数据同化，以及支持搜索、救援和污染响应的轨迹参数化。该项目将通过为伍兹霍尔海洋研究所的暑期学生研究员提供研究机会，并使美国海岸加尔学院（一个以本科教学为重点的机构）的本科生参与实地工作，并将研究活动纳入他们的高级项目，从而为教育做出贡献。通过在1200平方公里的新英格兰陆架（NES）上以大约2公里的分辨率测量整个年周期的表面速度场，该项目将表征涡旋场的动态变化和季节性。这项工作将确定导致亚中尺度洋流变化和跨大陆架水团和性质交换的过程和参数。该研究假设涡变率是由斜压不稳定性驱动的，但与风和底部应力有内在联系，它们产生空间和时间变化的埃克曼流和剪切引起的混合，可以反对或加强锋面环流。观测结果将用于确定NES内横向和垂直浮力梯度的季节性循环如何调节涡旋动力学。将利用示踪剂和粒子来计算观测到的表面速度内的色散和涡流通量，评估亚中尺度动力学在跨大陆架交换中的作用，而漂浮物将用于获得实地的直接测量。所有的估计都将与我们对涡旋的动力学特征相结合，以了解不同季节导致跨大陆架运输的过程及其相对于更大规模交换机制的重要性。

This project studies the mechanisms by which small scale (2-10km) coastal oceanic flows, over the continental shelf can stir the water masses and contribute to the transport material between the coast and the open ocean. A unique array of high frequency (HF) radar systems will be deployed to measure surface currents at high spatial resolution. These measurements will be able to resolve eddies with sizes ranging from 2 ? 20 km that are present over the New England Shelf (NES). The shelf area to be covered extends 30 to 80 km offshore, with water depths of 30 to 70 m. These surface current measurements will be augmented by simultaneous underwater measurement using a submerged instrumentation, while autonomous surface vehicles and drifters will be used to measure mid-shelf velocity structure, fine-scale horizontal gradients, and drifter trajectories. The analysis of the data collected will increase our understanding of exchange of material between the coast and the open ocean over a broad continental shelf. This exchange has implications for biogeochemistry, shelf productivity, fisheries, transport of pollutants, as well as for determining heat and freshwater budgets; this is a crucial step in diagnosing shelf-wide ecosystem variability, improving its predictability and thus contributing to better discriminating between anthropogenic and natural ecosystem changes. The proposed HF radar measurements will feed into the National High Frequency Radar (HFR) Network operated by NOAA and the data will be available for data assimilation into coastal ocean models as well as trajectory parameterizations that support search and rescue, and pollution responses. The project will contribute to education by providing the research opportunities for summer student fellows at the Woods Hole Oceanographic Institution and enable undergraduate students from the US Coast Gard Academy, an undergraduate teaching-focused institution, to participate in the field work and incorporate research activities into their senior projects. By measuring the surface velocity fields at about 2 km resolution over 1,200 square kilometers of the New England Shelf (NES) through an entire annual cycle the project will characterize the dynamical variability and seasonality of the eddy field. This work would identify processes and parameters that lead to submesoscale current variability and the across-shelf exchange of water masses and properties. The study hypothesizes that eddy variability is driven by baroclinic instability, but is intrinsically linked with wind and bottom stress, which generate spatially and temporally varying Ekman currents and shear-induced mixing that can oppose or reinforce frontal circulations. The observational results will be used to identify how eddy dynamics are modulated by the seasonal cycle of lateral and vertical buoyancy gradients within the NES. The role of submesoscale dynamics in across-shelf exchange will be assessed using tracers and particles to calculate dispersion and eddy fluxes both within the observed surface velocities, while drifters will be used to gain a direct measure in the field. All estimates will be synthesized with our dynamical characterization of the eddies to gain an understanding of the processes leading to across-shelf transport in different seasons and their importance relative to larger-scale exchange mechanisms.