Collaborative Research: Lee Waves and Sheared Mean Flow: Interactions and Impacts of Topography

背风波是由稳定分层流在水深测量上强迫的内重力波的一个例子。海洋内背风波的水平波长在O(1-10)公里之间，连接了中尺度流和小尺度湍流，并在海洋的能量级联中发挥了中心作用。它们的产生对平衡流施加波浪阻力，提取中尺度能量，它们的传播通过波通量输送这些能量。当它们破裂时，它们将能量向下转化为湍流耗散和混合，保持海洋的层化，进而促进大范围的环流。这个项目将研究为什么在流动-地形相互作用的下游深海中观测到的耗散比通常将背风波产生等同于耗散的假设所预测的要小。这项研究将确定背风波在能量耗散和再分配中的作用，以便更好地对海洋环流模式的波浪阻力和混合进行参数化。该项目将支持一名早期职业生涯带头人PI、一名毕业生和两名本科生接受海浪动力学和海洋建模方面的培训。过程研究海洋模式(PSOM)的区域数值模拟将模拟平均切变中背风波的产生、传播、相互作用和消散。PSOM是一种非静力海洋模式，被广泛应用于亚中尺度过程的研究。PI将扩展先前的理想化模拟，以探索一系列地形变化，以检查可能抑制流-地形相互作用背风中的湍流的机制。这些机制是：(I)地形阻塞和分裂导致的非线性产生，(Ii)背风波能量重新吸收回到切变平均流，(Iii)以自由波形式逃离局地发电流的远程耗散，以及(Iv)来自局地发电地形的背风波能量的下游平流。在这些机制中，底部强化流中捕获的背风波将发生重吸收，而非线性产生和下游平流强烈依赖于特定的地形，而不是随机的地形。主要的分析工具将是不同组成部分(平均急流、背风波和自由波)的节能预算，以量化背风波的耗散和非耗散命运。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。

Lee waves are an example of internal gravity waves forced by stably stratified flow over bathymetry. Oceanic internal lee waves have horizontal wavelengths between O(1–10) km that bridge mesoscale currents and smallscale turbulence and play a central role in the ocean’s energy cascade. Their generation exerts wave drag on balanced flow and extracts mesoscale energy, and their propagation transports this energy through wave-fluxes. When they break, they convert energy downscale to turbulent dissipation and mixing, maintaining ocean’s stratification and in turn contributing to the largescale circulation. This project will examine why observed dissipation in the deep ocean downstream from flow-topography interactions is smaller than predicted by the common assumption of equating lee-wave generation with dissipation. This research will determine the role of lee waves in dissipating versus redistributing energy for better parameterizations of wave drag and mixing for oceanic general circulation models. This project will support an early-career lead PI, a graduate and two undergraduate students to be trained on wave dynamics and ocean modeling. Regional numerical modeling with Process Study Ocean Model (PSOM) will simulate the generation, propagation, interaction and dissipation of lee waves in mean shear. PSOM is a non-hydrostatic ocean model that has been widely used to study submesoscale processes. The PIs will extend prior idealized simulations to explore a range of topographic variations to examine mechanisms that may suppress turbulence in the lee of flow-topography interactions. These mechanisms are: (i) nonlinear generation due to topographic blocking and splitting, (ii) reabsorption of lee-wave energy back to the sheared mean flow, (iii) remote dissipation in the form of free waves that escape the localized generating current, and (iv) downstream advection of lee-wave energy from localized generating topography. Among these mechanisms, reabsorption will occur for trapped lee waves in bottom-intensified currents, while nonlinear generation and downstream advection have a strong dependence on specific, as opposed to random, topographies. The primary analysis tool will be energy conservation budgets for different components (mean jet, lee waves, and free waves) to quantify the dissipative and non-dissipative fates of lee waves.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.