Large-scale intermittency and rare events boosted at dimensional crossover in anisotropic turbulence

TL;DR

This paper reveals that in anisotropic turbulence, a dimensional crossover from 2D to 3D enhances large-scale intermittency and rare events, driven by increased phase space and resulting in prominent non-Gaussian distributions and vortex structures.

Contribution

It uncovers a universal mechanism where anisotropic turbulence at large scales promotes intermittency and extreme events via a phase space increase at the dimensional crossover.

Findings

Large-scale fat-tailed distributions emerge in anisotropic turbulence.

Dimensional crossover leads to chain-like vortex structures.

Enhanced intermittency influences extreme weather unpredictability.

Abstract

Understanding rare events in turbulence provides a basis for the science of extreme weather, for which the atmosphere is modeled by Navier-Stokes equations (NSEs). In solutions of NSEs for isotropic fluids, various quantities, such as fluid velocities, roughly follow Gaussian distributions, where extreme events are prominent only in small-scale quantities associated with the dissipation-dominating length scale or anomalous scaling regime. Using numerical simulations, this study reveals another universal promotion mechanism at much larger scales if three-dimensional fluids accompany strong two-dimensional anisotropies, as is the case in the atmosphere. The dimensional crossover between two and three dimensions generates prominent fat-tailed non-Gaussian distributions with intermittency accompanied by colossal chain-like structures with densely populated self-organized vortices (serpentinely organized vortices (SOV)). The promotion is caused by a sudden increase of the available phase space at the crossover length scale. Since the discovered intermittency can involve much larger energies than those in the conventional intermittency in small spatial scales, it governs extreme events and chaotic unpredictability in the synoptic weather system.