Collaborative Research: Study of Convectively-Breaking Internal Solitary Waves of Depression: High Accuracy/Resolution Modeling and Observational Data Analysis

内孤立波是一种普遍存在于陆坡和陆架、海底峡谷和海洋地形地貌上的海洋现象。它们可以在保持形状的同时长距离输送能量，是上层海洋营养物质的有效供应者，并可以通过公海和沿海水域之间的热量、盐分、营养物质和水团交换影响初级生产和海洋生态。例如，最近对新泽西州大陆架浅海的内孤立波的测量表明，与其内部的切变不稳定有关的波动占穿越跃层的总热通量的50%，并驱动水平粒子输送超过几公里，从而对大陆架的能量学和生态学发挥至关重要的作用。由于其内部的巨大翻转，对流破碎的ISW中的湍流扩散系数和颗粒传输预计将比切变不稳定的ISW中的大100倍。由于对流不稳定的瞬变性质和仪器的限制，现有对流不稳定的现场观测在其对相关湍流的分辨率方面是有限的。这一项目将能够有力地确定浅水区对流(和切变)不稳定的机制和优先位置。对流破裂的影响将通过量化相关的湍流通量和粒子传输作为参数空间的函数来解决。对对流破裂的ISW是否是大多数富含高振幅波的环境的关键重要特征进行更可靠的评估将是可能的。在优先发生地点、基本物理、湍流通量和陆上颗粒输送方面，对浅海中的对流破裂过程有更好的理解和量化，将有助于在更大尺度的模式中对这类过程进行可靠的参数化。ISW破裂和由此产生的湍流现象集中在大陆坡和大陆架上，其参数化可能与通常用于内潮、内背风波和公海分层湍流的参数化有根本不同。一名波多黎各土生土长的博士生将接受分层海洋物理和高性能计算方面的培训。这项研究的结果将被整合到康奈尔大学环境流体力学的相关课程中，并被整合到伊萨卡高中和华盛顿大学空间助学金夏季本科生研究计划的应用物理实验室正在进行的推广工作中。分析代码、后处理结果和选定的原始数据将通过一个专门的在线数据库提供给更广泛的社区。该项目将调查主要由于对流(但也包括切变)不稳定造成的内孤立波(ISW)在缓坡现实(和理想)水深上空的破裂。高精度/分辨率大涡模拟(LES)将与南中国海陆坡对流破裂大涡模拟(LES)的大量数据集的分析相结合。之前对这些观测结果的分析揭示了对流不稳定的大范围ISW，其内部有再循环的湍流核心，与100米量级的翻转和增强的耗散和混合有关，大约是开阔海洋中的1000倍。导致对流不稳定和与之相关的湍流混合的机制尚不清楚。二维模拟将首先研究对流不稳定引起的ISW破裂的机制和优选位置，它是底坡、初始波陡度和背景斜压潮流的函数。以对流破裂为中心，配备拉格朗日粒子跟踪的一系列计算/数据密集的并行三维大涡模拟将提高破裂过程的时空分辨率，并将量化由此产生的湍流通量和波浪尺度水平能量通量对上述参数的依赖关系。除了向LES提供水深测量和层结/海流强迫外，现有的南海观测及其进一步分析将作为检查和探索LES与现场数据之间参数空间的共同趋势的基础。通过对实际和模型数据的分析，拉格朗日浮子将检查和量化对流破裂的ISW(即具有再循环核心的波)对颗粒的夹带、输送和脱离。对湍流通量和耗散率的另一种拉格朗日估计将使计算相关的涡旋扩散系数成为可能。这些结果将决定ISW驱动的湍流与弱波-波相互作用和层状湍流以及它们之间的转换之间的关系。

Internal solitary waves (ISWs) are ubiquitous oceanic phenomena found on continental slopes and shelves, in submarine canyons, and over oceanic topographic features. They can carry energy over long distances while maintaining their shapes, are efficient suppliers of nutrients into the upper ocean, and can impact primary production and marine ecology through the exchange of heat, salt, nutrient, and water masses between the open ocean and coastal waters. For example, recent measurements of internal solitary waves shoaling on the continental shelf of New Jersey indicate that waves linked to shear instability in their interior are responsible for 50% of the total heat flux across the pycnocline and drive horizontal particle transport over a few kilometers, thereby exerting a critically important role for the shelf energetics and ecology. On account of the massive overturns in their interior, the turbulent diffusivities and particulate transport in convectively-breaking ISWs are expected to be as much as a hundred times larger than those in shear-unstable ISWs. Existing in-situ observations of convectively unstable ISWs are limited in their resolution of the associated turbulence due to the transient nature of these instabilities and instrument limitations. This project will enable the robust determination of the mechanisms and preferred locations of convective (and shear) instability of shoaling ISWs. The implications of convective breaking will be addressed through quantifying the associated turbulent fluxes and particle transport as a function of parameter space. A more reliable assessment of whether convectively-breaking ISWs are a critically important feature of most environments rich in high-amplitude waves will be possible. The improved understanding and quantification of the convective breaking process in shoaling ISWs, in terms of preferred locations of occurrence, underlying physics, turbulent fluxes and onshore particulate transport, will facilitate the reliable parameterization of such processes in larger-scale models. The parameterizations of ISW breaking and resulting turbulence, phenomena focused on the continental slope and shelf, might be fundamentally different from those typically used for internal tides, internal lee waves and stratified turbulence in the open ocean. One Ph.D. student, a native of Puerto Rico and member of a under-represented minority, will be trained in stratified ocean physics and high performance computing. The findings of this study will be integrated in relevant coursework in Environmental Fluid Mechanics at Cornell and in on-going outreach efforts at Ithaca High School and the Applied Physics Laboratory at the University of Washington's Space Grant Summer Undergraduate Research Program. Analysis codes, post-processed results and select raw data will be made available to the broader community through a dedicated online database.This project will investigate the breaking, due to primarily convective (but also shear) instability, of internal solitary waves (ISWs) shoaling over gently sloping realistic (and idealized) bathymetries. High-accuracy/resolution Large Eddy Simulations (LES) will be integrated with analysis of an extensive dataset of convectively breaking ISWs over the continental slope in the South China Sea. Previous analysis of these observations has revealed convectively unstable, large-amplitude ISWs with recirculating turbulent cores in their interior associated with order 100 meter overturns and intensified dissipation and mixing, roughly a thousand times greater than in the open ocean. The mechanisms leading to the convective instability and the associated turbulence mixing remain unknown. Two-dimensional simulations will first investigate the mechanisms and preferred locations of ISW breaking due to convective instability as a function of bottom slope, initial wave steepness and background baroclinic tidal current. Focusing on convective breaking, a range of computation/data intensive parallel three-dimensional LES, equipped with Lagrangian particle tracking, will then provide enhanced spatiotemporal resolution of the breaking process and will quantify the dependence of the resulting turbulent fluxes and wave-scale horizontal energy fluxes on the above parameters. Beyond providing bathymetric and stratification/current forcing to the LES, the existing SCS observations, and further analysis thereof, will serve as a basis for consistency checks and exploration of common trends in parameter space between LES and field data. Analysis of data from, actual and model, Lagrangian floats will examine and quantify particle entrainment, transport and detrainment by convectively-breaking ISWs, namely waves with recirculating cores. Alternative Lagrangian estimates of turbulent fluxes and dissipation rates will enable the computation of associated eddy diffusivities. These results will determine how ISW-driven turbulence relates to the regimes of weak wave-wave interaction and stratified turbulence and the transition between them.