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

合作研究：黑潮海山的开尔文-亥姆霍兹不稳定性 (KHIKS)

• 批准号: 2048764
• 负责人: Anda Vladoiu
• 金额: $ 150.41万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-08-01 至 2025-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2048764&HistoricalAwards=false
• 关键词: Collaborative; Research; Kelvin; Helmholtz; Instabilities

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.

风力驱动的西部边界流，如西太平洋的黑潮，向北输送大量的热、盐和动量，有助于海洋颠覆环流和气候系统热平衡。西方边界流在时间和空间上如何变化，以及它们如何向周围环境失去能量，是长期存在的问题。与地貌稀少的大西洋湾流不同，黑潮经常与海脊、岛屿和海山相互作用。因此，能量通过湍流混合从大尺度流动中提取，特别是在水平速度具有大剪切的环境中。它们支持各种剪切不稳定性，如开尔文-亥姆霍兹(KH)或Holmboe，由此流动中的微小扰动放大，成为湍流产生的重要机制。尽管KH剪切不稳定性在理想化的实验室实验和数值模拟中得到了广泛的研究，但在海洋中直接观测的情况很少，而且大多局限于河口和岩床。因此，高雷诺数海洋流动中类KH波的产生、演变和衰减，以及它们被背景流调制并衰变为湍流，在开阔的海洋中没有得到足够的观测。该项目是与台湾科学家的合作，利用他们现有的航行时间，测量高分辨率的温度、盐度和速度精细结构，包括初级类似KH的巨浪的结构和黑潮路径上海山的背风处的演变。还将部署几个系泊设施，以便对海山附近的可变性进行较长期的空间评估。将对观测到的KH类巨浪内的湍流耗散和混合进行评估，以确定它们在与环流有关的热量、盐度、质量和营养物质的湍流通量、黑潮和局部水团的修改以及黑潮能量耗散中的作用。该项目支持两名职业生涯早期的科学家向观测性海洋学家过渡。国际合作将提供船运时间和进入具有全球科学重要性的黑潮水域。其中包括为威斯康星州大学本科生举办的暑期活动，以及对K-12教室的教育访问，以及在威斯康星州大学和当地科学中心的推广活动。具有Kelvin-Helmholtz(KH)特征的切变不稳定性将在台湾以东黑潮路径的海山背风处测量。FineScale 3-D(垂直、顺流和横流)密度结构将使用拖曳CTD链测量，并配以船载ADCP和回声探测仪，水平分辨率为10米，垂直密度结构为1米。在这样的高雷诺数海洋流动中进行如此详细的测量是史无前例的，将阐明它们的运动结构、动态演变和相关的湍流，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以下额外的时间序列剖面：(1)海山上游的剪切和层化；(2)海山顶端三维速度和回声探测仪图像的高时间和垂直分辨率；以及(3)海山背风处速度场沿河流和横流的三维时间序列剖面。来自多种估算方法和直接微结构测量的湍流耗散和混合将有助于确定这些流动/地形相互作用在水-质转换和西部边界流耗散中的作用。从科学上讲，理解海洋中平衡环流的消散和昼夜混合的来源仍然是物理海洋学中最紧迫的挑战之一。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。