Variability of mean flow reversals in stably-stratified fluids with stochastic wave forcing
| When |
Sep 04, 2025
from 11:00 to 12:00 |
|---|---|
| Where | MGN1 105 |
| Attendees |
Jason Reneuve |
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The Quasi-Biennial Oscillation (QBO) of Earth's stratosphere is a slowly reversing, large-scale mean flow that is generated by fast, small-scale waves. The variability of QBO reversals in recent years has triggered significant interests in the intrinsic variability of wave-driven mean flows. In this study, we show a direct connection between the statistical properties of gravity waves randomly emitted at the bottom of a stably stratified fluid and the statistics of mean flow reversals. We perform wave-resolved, direct numerical simulations of the 2D Navier-Stokes equations under the Boussinesq approximation and generate waves at the bottom of the layer using three different types of forcing: a constant-amplitude monochromatic forcing, a finite band polychromatic forcing, and a stochastic forcing. We show that the stochastic forcing scheme consistently generates a mean flow with variable reversals and investigate the dependence of the reversal statistics on simple control parameters. In particular, we demonstrate that the mean flow reversals variability is highly sensitive to two wave parameters under stochastic forcing, whereas for similar parameter values the monochromatic and polychromatic forcing schemes trigger QBO-type flows that are highly regular. Thus, the mean flow variability under stochastic forcing is not linked to secondary mean-flow instabilities in our simulations, but rather evidence that small-amplitude waves can alter large-scale oscillations when their generation is chaotic.