Rapid directional alignment of velocity and magnetic field in magnetohydrodynamic turbulence

TL;DR

This paper demonstrates rapid local alignment of velocity and magnetic field in magnetohydrodynamic turbulence, observed in simulations and solar wind data, which weakens nonlinear interactions and influences turbulence dynamics.

Contribution

It reveals a fast, robust alignment process in MHD turbulence, linking simulation results with solar wind observations and identifying its role in turbulence relaxation.

Findings

Alignment occurs rapidly in MHD turbulence.

Observed in both simulations and solar wind data.

Weakens nonlinear interactions in small-scale structures.

Abstract

We show that local directional alignment of the velocity and magnetic field fluctuations occurs rapidly in magnetohydrodynamics for a variety of parameters. This is observed both in direct numerical simulations and in solar wind data. The phenomenon is due to an alignment between the magnetic field and either pressure gradients or shear-associated kinetic energy gradients. A similar alignment, of velocity and vorticity, occurs in the Navier Stokes fluid case. This may be the most rapid and robust relaxation process in turbulent flows, and leads to a local weakening of the nonlinear terms in the small scale vorticity and current structures where alignment takes place.