Collaborative Research: Characterization of Langmuir Supercells in the Coastal Ocean

朗缪尔环流（Langmuir circulation， LC）产生于风强迫和波浪动力学的相互作用，由一对平行的反旋转涡旋（或单体）组成，其方向大致与风的方向一致。在大陆架上空，海水较浅，混合相对较好，强风暴的通过可以诱发大型朗缪尔微泡，其中最大的可以跨越整个水柱，对沉积物的再悬浮有很强的影响。这些所谓的Langmuir超级细胞（LS）作为沉积物和生物活性物质在浅大陆架上运输的载体发挥着重要作用：它们的准组织性质使它们比底部边界层剪切湍流更有效地将物质从靠近底部的低速层移出并进入大块流进行横向运输。本研究将分析三个不同地点在15、26和40米深度的现有观测资料，以及高分辨率数值模拟，以确定大尺度流量、潮流、较低密度的表层和风向与波浪方向不一致等因素对LS的影响。大陆架在生物学上具有很高的生产力，LS对影响这种生产力或分销其产品的过程有直接影响。因此，架子模型必须包含这些主要过程的熟练参数化。这项研究将改进用于解释Langmuir环流的许多沿海和区域模式的参数化，因为区域的大小阻碍了以足够高的分辨率运行模式来直接捕获Langmuir环流。每年夏季将对一名博士后研究员、两名研究生和一名本科生进行物理海洋学、湍流动力学、闭包和数值技术方面的培训。其中一名学生来自未被充分代表的少数群体。在沿海海域，通过底部安装的垂直波束声学多普勒电流剖面仪（VADCPs）测量，在潮汐和地转流分量、地表热通量和影响LS强度和相干性的失调风和波的作用下观测到了LS。观测点包括罗格斯大学低轨道天文台，位于新泽西州南部海岸内大陆架15米深的水中，海军R2塔位于佐治亚州海岸中部大陆架26米深的水中，以及哈特拉斯角以北40米深的另一个观测点。在近地轨道和近地轨道上的测量分析表明了LS特征的差异，在近地轨道上发生了更连贯和强烈的LS。对哈特拉斯角数据的新分析，以及紧跟VADCP在三个地点测量的LS流大涡模拟（LES），将阐明潮汐和地转流、地表浮力和不对准的风和波共同影响LS和相关垂直输送的动力学。LES将有助于提供现场数据集中缺少的关键信息，例如地表和底部边界层的详细速度结构，这些信息是对影响不同地点LS的各种强迫机制的作用作出明确结论所必需的。在影响其强度和相干性的各种过程下，将使用LES获得代表LS引起的非局部垂直混合强度的垂直速度波动的标度。垂直速度波动的标度将用于为PI开发的KPP （k廓线参数化）提供信息，该参数化考虑了整体Langmuir湍流的局部传输和LS引起的非局部传输。更新后的LS KPP将在一维垂直水柱一般海洋湍流模式（GOTM）中实施，通过与LES和实地测量结果的比较进行验证。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Langmuir circulation (LC) arises from the interplay of wind forcing and wave dynamics, and consists of pairs of parallel counter-rotating vortices (or cells) oriented approximately in the direction of the wind. Over the continental shelf , where the water is shallow and relatively well-mixed, the passage of strong storms can induce large Langmuir cells, the largest of which can span the entire water column and have a strong influence on sediment re-suspension. These so-called Langmuir supercells (LS) play an important role as vectors for the transport of sediment and bioactive material on shallow shelves: their quasi-organized nature makes them more effective than bottom boundary layer shear turbulence at moving material out of the low-speed layer near bottom and into the bulk flow for lateral transport. This study will analyze existing observations from three different sites at 15, 26 and 40m depths as well as high resolution numerical simulations to determine the influence on LS of a number of factors such as large scale flows, tidal currents, less dense surface layers and misalignment between wind and wave direction. Continental shelves are biologically highly productive and LS have direct impact on processes affecting this productivity or distributing its products. Thus, it is essential that shelf models incorporate skillful parameterization of such dominant processes. This study will improve parameterizations used to account for Langmuir circulation in many coastal and regional models where the size of the domain precludes running the model at a high enough resolution to capture Langmuir circulations directly. One post-doctoral researcher, two graduate students and one undergraduate student in each summer will be trained in physical oceanography, turbulence dynamics and closures and numerical techniques. One of the students is from an underrepresented minority group.In the coastal ocean, LS has been observed under tidal and geostrophic flow components, surface heat fluxes and misaligned winds and waves serving to influence LS strength and coherency, as measured through bottom-mounted vertical-beam acoustic Doppler current profilers (VADCPs). Observation sites consist of the Rutgers LEO observatory in 15m of water at the inner shelf off the coast of southern New Jersey, the Navy's R2 tower in 26m of water at mid-shelf off the coast of Georgia, and an additional site north of Cape Hatteras in 40m of water. Analyses of the measurements at LEO and R2 have demonstrated differences in LS characteristics, with more coherent and intense LS occurring at LEO. New analysis of the Cape Hatteras data as well as large eddy simulations (LES) of LS flows closely following the VADCP measurements at the three sites will elucidate the dynamics by which tidal and geostrophic flows, surface buoyancy and misaligned wind and waves combine to affect LS and associated vertical transport. The LES will help provide key information missing from the field data sets, such as detailed velocity structure in the surface and bottom boundary layers, required to make definite conclusions regarding the roles of the various forcing mechanisms influencing the LS at the different sites. LES will be used to obtain a scaling of vertical velocity fluctuations representative of the strength of non-local vertical mixing induced by LS under the various processes affecting its strength and coherency. The scaling of vertical velocity fluctuations will be used to inform a KPP (K-profile parameterization) developed by the PI accounting for the local transport of the overall Langmuir turbulence and the non-local transport induced by the LS. The updated LS KPP will be implemented in the one-dimensional vertical water column General Ocean Turbulence Model (GOTM) for validation via comparisons with the LES and the field measurements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.