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

背风波是水深上稳定分层流所产生的重力内波的一个例子。海洋内部背风波的水平波长在O（1-10）km之间，连接中尺度海流和小尺度湍流，并在海洋的能量级联中发挥核心作用。它们的产生对平衡流施加波阻，并提取中尺度能量，它们的传播通过波通量传输这种能量。当它们破裂时，它们将能量向下转换为湍流耗散和混合，维持海洋的分层，进而促进大尺度环流。该项目将研究为什么在水流与地形相互作用下游的深海中观察到的耗散比将背风波产生与耗散等同的常见假设所预测的要小。这项研究将确定背风波的作用，消散与重新分配能量更好的参数化的波阻力和海洋大气环流模式的混合。该项目将支持一名职业生涯早期的首席PI，一名研究生和两名本科生接受波浪动力学和海洋建模方面的培训。利用过程研究海洋模式（PSOM）进行区域数值模拟，可以模拟在平均切变作用下，背风波的产生、传播、相互作用和消散过程。PSOM是一个非静力海洋模式，已被广泛用于研究亚中尺度过程。PI将扩展先前的理想化模拟，以探索一系列地形变化，以检查可能抑制气流-地形相互作用背风面湍流的机制。这些机制是：（i）由于地形阻塞和分裂的非线性发电，（ii）背风波能量重新吸收回剪切平均流，（iii）远程耗散的形式，自由波逃脱本地生成电流，和（iv）下游平流的背风波能量从本地生成地形。在这些机制中，重吸收将发生在底部加强电流的被困背风波，而非线性发电和下游平流有很强的依赖性，而不是随机的，地形。主要的分析工具将是不同组件（平均射流、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。该奖项反映了NSF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。

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.