Turbulence in stratified rotating topographic wakes

TL;DR

This study uses large-eddy simulations to analyze how stratification and rotation influence turbulence mechanisms in topographic wakes, revealing distinct instability regimes and their dependence on environmental parameters.

Contribution

It systematically identifies and quantifies the dominant turbulence instabilities in stratified, rotating wakes, providing new predictive relationships for different flow regimes.

Findings

Vertical shear-driven Kelvin-Helmholtz instability dominates under strong stratification.

Centrifugal/inertial instability peaks at intermediate rotation rates.

Rotation suppresses vertical shear and Kelvin-Helmholtz turbulence.

Abstract

Turbulence generation mechanisms in stratified, rotating flows past three-dimensional (3D) topography remain underexplored, particularly in submesoscale (SMS) regimes critical to geophysical applications. Using turbulence-resolving large-eddy simulations, we systematically dissect the interplay of stratification and rotation in governing the dynamics of wake turbulence. Our parametric study reveals that turbulent dissipation in the near wake is dominated by two distinct instabilities: (1) vertical shear-driven Kelvin-Helmholtz instability (KHI), amplified by oblique dislocation of K\'arm\'an vortices under strong stratification, and (2) centrifugal/inertial instability (CI), which peaks at intermediate rotation rates (Rossby number order unity, SMS regime) and relatively weaker stratification. Notably, strong rotation dampens vertical shear and weakens KHI-driven turbulence, while strong stratification imposes smaller vertical length scales that restrict CI-driven turbulence. By quantifying dissipation across a broad parameter space of stratification and rotation, predictive relationships between the environmental parameters and instability dominance is established. These findings highlight the regime dependence of instability mechanisms and may inform targeted observational campaigns and numerical models of oceanic and atmospheric wakes.