A Weakened Cascade Model for Turbulence in Astrophysical Plasmas

TL;DR

This paper introduces a refined cascade model for kinetic turbulence in astrophysical plasmas, accounting for the transition between weak and strong turbulence and the influence of nonlocal interactions, to better explain observed energy spectra.

Contribution

It presents a new model that incorporates nonlocal effects and transitions between turbulence regimes, advancing understanding of plasma turbulence in astrophysical contexts.

Findings

The model describes the transition from weak to strong MHD turbulence.

It explains the nearly power-law energy spectra in the dissipation range.

Nonlocal shearing effects are crucial in energy transfer processes.

Abstract

A refined cascade model for kinetic turbulence in weakly collisional astrophysical plasmas is presented that includes both the transition between weak and strong turbulence and the effect of nonlocal interactions on the nonlinear transfer of energy. The model describes the transition between weak and strong MHD turbulence and the complementary transition from strong kinetic Alfven wave (KAW) turbulence to weak dissipating KAW turbulence, a new regime of weak turbulence in which the effects of shearing by large scale motions and kinetic dissipation play an important role. The inclusion of the effect of nonlocal motions on the nonlinear energy cascade rate in the dissipation range, specifically the shearing by large-scale motions, is proposed to explain the nearly power-law energy spectra observed in the dissipation range of both kinetic numerical simulations and solar wind observations.