Collaborative Research: Kelvin-Helmholtz Instabilities at a Kuroshio Seamount (KHIKS)

风驱动的西边界流，如西太平洋的黑潮，向北输送大量的热量，盐和动量，有助于海洋翻转环流和气候系统热平衡。西部边界流如何在时间和空间上变化，以及它们如何将能量损失到周围环境中，这是一个长期存在的问题。与大西洋的墨西哥湾流不同，黑潮经常与山脊，岛屿和海山相互作用。因此，通过湍流混合从大规模流动中提取能量，特别是在水平速度具有大剪切的设置中。这些已知支持各种剪切不稳定性，例如Kelvin-Helmholtz（KH）或Holmboe，由此流动中的小扰动放大，成为湍流产生的重要机制。尽管人们已经在理想化的实验室实验和数值模拟中广泛研究了KH剪切不稳定性，但在海洋中的直接观察却很少，而且大多局限于河口和海床。因此，在高雷诺数的海洋流动，其调制的背景流和衰减成湍流的KH样波涛的产生，演变和衰减是在开放的海洋观察不足。该项目是与台湾科学家合作，利用他们现有的船时，测量高分辨率的温度、盐度和速度，以及黑潮路径上一座海山背风面的原始KH样巨浪的精细结构和演变。还将部署几个系泊设备，以便对海山附近的变化进行较长期的空间评估。湍流耗散和混合内观察到的KH样的波涛将进行评估，以确定其在湍流通量的热量，盐度，质量和营养物质，修改黑潮和当地的水团，能量耗散在黑潮，相关的涡旋尺度环流的作用。该项目支持两名早期职业科学家过渡到观察海洋学家。国际合作将提供船期和进入具有全球科学重要性的黑潮沃茨的机会。包括UW本科生暑期课程中的活动，沿着对K-12教室的教育访问，以及在UW和当地科学中心的推广活动。本文将在台湾以东黑潮路径上的海山背风面测量具有类似开尔文-亥姆霍兹（KH）特征的剪切不稳定性。使用拖曳式CTD链测量，加上船载ADCP和回声测深仪，将精细尺度三维（垂直、沿着和跨流）密度结构解析为水平10米和垂直1米。在这种高雷诺数的海洋流动中进行如此详细的测量是前所未有的，将阐明其运动学结构，动力学演变和相关湍流，为现实的数值模型模拟和实验室实验提供指导。系泊的ADCP和温度传感器阵列将提供更多的时间序列剖面图：㈠海山上游的剪切和分层，㈡海山山顶三维速度和回声测深仪图像的高时间和垂直分辨率，㈢海山背风面速度场的三维沿着和跨流时间序列剖面图。从多种估计方法和直接微观结构测量的湍流耗散和混合将有助于确定这些流量/地形相互作用的作用，对水质量的转换和耗散的西部边界电流。科学家，理解海洋中平衡环流的消散和底辟混合的来源仍然是物理海洋学中最紧迫的挑战之一。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Wind-driven western boundary currents, such as the Kuroshio in the western Pacific, transport large amounts of heat, salt and momentum northward, contributing to the ocean overturning circulation and the climate system heat balance. How western boundary currents vary in time and space, and how they lose energy to their surroundings, are long-standing questions. Unlike the Gulf Stream in the Atlantic where topographic features are rare, the Kuroshio frequently interacts with ridges, islands and seamounts. Energy is thus extracted from the large-scale flow through turbulent mixing, particularly in settings with large shear in horizontal velocities. These are known to support a variety of shear instabilities, such as Kelvin-Helmholtz (KH) or Holmboe, whereby small perturbations in the flow amplify, to become important mechanisms for turbulence generation. Although KH shear instability has been widely studied in idealized laboratory experiments and numerical simulations, direct observations in the ocean are rare and mostly confined to estuaries and sills. Consequently, the generation, evolution and decay of KH-like billows in high-Reynolds-number oceanic flows, their modulation by background flow and decay into turbulence are under-observed in the open ocean. The project is a collaboration with Taiwanese scientists, using their available ship-time, to measure high-resolution temperature, salinity and velocity finestructure of primary KH-like billows and evolution in the lee of a seamount in the path of the Kuroshio. Several moorings will also be deployed to gain longer-term spatial assessment of variability in the seamount vicinity. Turbulent dissipation and mixing within the observed KH-like billows will be assessed, to determine their roles in turbulent fluxes of heat, salinity, mass, and nutrients, modification of Kuroshio and local water-masses, and energy dissipation in the Kuroshio, of relevance to the gyre-scale circulation. This project supports two early-career scientists in their transition to observational oceanographers. International collaborations will provide shiptime and access to Kuroshio waters of global scientific importance. Activities within the summer program for UW undergraduate students are included, along with educational visits to K-12 classrooms, and outreach at UW and local science centers. Shear instabilities with Kelvin-Helmholtz (KH)-like characteristics will be measured in the lee of a seamount in the path of the Kuroshio east of Taiwan. The finescale 3-D (vertical, along- and across-stream) density structure will be resolved to 10-m horizontally and 1-m vertically using towed CTD chain surveys, augmented with shipboard ADCP and echosounder. Such detailed measurements in such high-Reynolds-number oceanic flows are unprecedented, and will elucidate their kinematic structure, dynamic evolution and associated turbulence, to offer guidance for realistic numerical model simulations and laboratory experiments. A moored array of ADCPs and temperature sensors will provide additional time-series profiles of (i) shear and stratification upstream of the seamount, (ii) high temporal and vertical resolution of 3-D velocity and echosounder images on the seamount summit, and (iii) 3-D along- and across-stream time- series profiles of velocity fields in the lee of the seamount. Turbulent dissipation and mixing from multiple estimation methods and direct microstructure measurements will help determine the role of these flow/topography interactions on water-mass transformation and dissipation of a western boundary current. Scientifically, understanding the dissipation of the balanced circulation and the sources of diapycnal mixing in the ocean remain among the most pressing challenges in physical oceanography.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.