On the emergence of helicity in rotating stratified turbulence

Abstract

We perform numerical simulations of decaying rotating stratified turbulence and show, in the Boussinesq framework, that helicity (velocity-vorticity correlation), as observed in super-cell storms and hurricanes, is spontaneously created due to an interplay between buoyancy and rotation common to large-scale atmospheric and oceanic flows. Helicity emerges from the joint action of eddies and of inertia-gravity waves (with inertia and gravity with respective associated frequencies $f$ and $N$), and it occurs when the waves are sufficiently strong. For $N/f<3$ the amount of helicity produced is correctly predicted by a quasi-linear balance equation. Outside this regime, and up to the highest Reynolds number obtained in this study, namely $Re\approx 10000$, helicity production is found to be persistent for $N/f$ as large as $\approx 17$, and for $ReF{r}^2$ and $ReR{o}^2$ respectively as large as $\approx 100$ and $\approx 24000$.

10 pages, 5 figures

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• Self-consistent Castaing distribution of solar wind turbulent fluctuations
• Interplay of waves and eddies in rotating stratified turbulence and the link with kinetic-potential energy partition
• Helicity dynamics in stratified turbulence in the absence of forcing
• Spontaneous decay of periodic magnetostatic equilibria
• Single-particle Lagrangian statistics from direct numerical simulations of rotating-stratified turbulence
• Helical Fluid and (Hall)-MHD Turbulence: a Brief Review
• Self-organisation and non-linear dynamics in driven magnetohydrodynamic turbulent flows
• Broken mirror symmetry of tracer's trajectories in turbulence