Discrete and mesoscopic regimes of finite-size wave turbulence

TL;DR

This paper identifies and describes three regimes of wave turbulence in finite systems—discrete, mesoscopic, and kinetic—highlighting the unique behaviors and transitions among them based on wave excitation levels.

Contribution

It introduces the mesoscopic wave turbulence regime, bridging discrete and kinetic theories, and characterizes its broad amplitude range and sandpile spectrum behavior.

Findings

Discrete WT involves chaotic interactions of finite wave clusters.

Mesoscopic WT exhibits sandpile behavior and spans multiple amplitude orders.

Kinetic WT is described by classical wave-kinetic equations.

Abstract

Bounding volume results in discreteness of eigenmodes in wave systems. This leads to a depletion or complete loss of wave resonances (three-wave, four-wave, etc.), which has a strong effect on Wave Turbulence, (WT) i.e. on the statistical behavior of broadband sets of weakly nonlinear waves. This paper describes three different regimes of WT realizable for different levels of the wave excitations: Discrete, mesoscopic and kinetic WT. Discrete WT comprises chaotic dynamics of interacting wave "clusters" consisting of discrete (often finite) number of connected resonant wave triads (or quarters). Kinetic WT refers to the infinite-box theory, described by well-known wave-kinetic equations. Mesoscopic WT is a regime in which either the discrete and the kinetic evolutions alternate, or when none of these two types is purely realized. We argue that in mesoscopic systems the wave spectrum experiences a sandpile behavior. Importantly, the mesoscopic regime is realized for a broad range of wave amplitudes which typically spans over several orders on magnitude, and not just for a particular intermediate level.