Lee-Wave Energy Sinks in Bottom-Intensified Flow: Reabsorption, Dissipation, and PSI

README: Lee-Wave Energy Sinks in Bottom-Intensified Flow This repository contains the numerical configurations required to reproduce the results presented in Wu et al. (JPO, under revision). The study investigates the partition of lee-wave energy sinks in bottom-intensified flows, with particular emphasis on reabsorption into the mean flow versus explicit and indirect dissipation. Scientific Overview This research identifies Parametric Subharmonic Instability (PSI) as a significant but previously overlooked nonlinear energy cascade that enhances lee-wave dissipation at the expense of reabsorption. Key Findings PSI as a Major Sink: Nonlinear energy transfer via PSI cascades energy from twice the Coriolis frequency toward the inertial frequency and high vertical wavenumbers, leading to indirect dissipation. Energy Partition: For typical broadband topographic height spectra at mid- and high latitudes, the net dissipative fraction is 90–95%, while reabsorption accounts for only 5–10%. New Parameterization: A new dissipative fraction parameterization, $y$, is proposed as a function of the normalized lee-wave generation frequency $\alpha\equiv|kU_0/f|$: $$y(\alpha) = \begin{cases} -0.1\alpha + 1.2, & \text{if } \alpha > 2 \\ 1, & \text{if } \alpha \le 2 \end{cases}$$ Negligible Radiation: Free-wave radiation is found to be a negligible energy sink (~1%) and cannot explain the observed turbulence shortfall. Model Configurations The study utilizes two independent numerical models to ensure that the findings are insensitive to vertical discretization, forcing, and dissipation schemes. 1. Process Study Ocean Model (PSOM) Setup: Configured with a bottom-intensified, laterally confined jet over 1-D, sinusoidal topography. Zonally periodic simulations. Grid: Terrain-following vertical discretization with 4 m resolution to align bottom cells with topography. Mixing: Explores two extreme scenarios: High viscosity: $4 \times 10^{-3} \ \mathrm{m}^2\mathrm{s}^{-1}$ to ensure stationarity. Low viscosity: $10^{-4} \ \mathrm{m}^2\mathrm{s}^{-1}$ to permit wave–wave interactions. 2. MIT General Circulation Model (MITgcm) Setup: Same as PSOM except being forced at the zonal open boundaries. Non-periodic simulations. Grid: Employs a partially filled-cell representation to handle steeper topography. Mixing: Utilizes the turbulence parameterization of Klymak et al. (2010). Repository Structure PSOM 48x176x256 output.zip — PSOM output for monochromatic lee waves over 1-D linear topography. PSOM 48x176x256 results.zip — PSOM results for monochromatic lee waves over 1-D linear topography. MITgcm test9 mono.zip — MITgcm sensitivity tests for steeper topography extending from linear to weakly nonlinear topography. Contact Yue Cynthia Wu, Ph.D. Department of Naval Architecture and Marine Engineering University of Michigan, Ann Arbor Email: [e-mail]