Bistability of the large-scale dynamics in quasi-two-dimensional turbulence

TL;DR

This study investigates the persistence and characteristics of bistability in large-scale quasi-two-dimensional turbulence, revealing that bistability grows with system size and turbulence intensity, and predicting a transition to pure hysteresis at high parameters.

Contribution

It demonstrates that bistability in quasi-2D turbulence persists and expands with increasing domain size and Reynolds number, and predicts a crossover to pure hysteresis at high parameters.

Findings

Bistability range increases with domain size and Reynolds number.

Bistability is not limited by finite size or turbulence intensity.

A crossover from bimodal to hysteretic regime is predicted at high parameters.

Abstract

In many geophysical and astrophysical flows, suppression of fluctuations along one direction of the flow drives a quasi-2D upscale flux of kinetic energy, leading to the formation of strong vortex condensates at the largest scales. Recent studies have shown that the transition towards this condensate state is hysteretic, giving rise to a limited bistable range in which both the condensate state as well as the regular 3D state can exist at the same parameter values. In this work, we use direct numerical simulations of thin-layer flow to investigate whether this bistable range survives as the domain size and turbulence intensity are increased. By studying the time scales at which rare transitions occur from one state into the other, we find that the bistable range grows as the box size and/or Reynolds number Re are increased, showing that the bistability is neither a finite-size nor a finite-Re effect. We furthermore predict a crossover from a bimodal regime at low box size, low Re to a regime of pure hysteresis at high box size, high Re, in which any transition from one state to the other is prohibited at any finite time scale.