DOI: 10.57760/sciencedb.07724
title: Inﬂuence of Stationary Local Mean Field on the Scaling Anisotropy in MHD 1 Turbulence
title: Inﬂuence of Stationary Local Mean Field on the Scaling Anisotropy in MHD 1 Turbulence

description: Magnetohydrodynamic (MHD) turbulence is revealed to have scaling anisotropy based on a local mean magnetic ﬁeld, which is usually calculated through the average of the magnetic ﬁeld vectors at two points. However, the thus reconstructed parallel spectrum can be contaminated by intermittent events and nonparallel ﬂuctuations. In this work, we simulate the driven compressible MHD turbulence to investigate the inﬂuence of the stationary local mean ﬁeld on the scaling anisotropy. By examining whether the local parallel samplings are along the magnetic ﬁeld directions, we conﬁrm that the stationary local mean ﬁeld can be fulﬁlled by the criterion ϕ &lt; 10◦ with ϕ being the angle between the two local mean magnetic ﬁelds after cutting the sampled magnetic ﬁeld intervals into two halves. The three-dimensional (3D) numerical data also show that the samplings with the stationary local mean ﬁelds successfully prevent intermittency events and nonparallel ﬂuctuations from mixing into the measured parallel ﬂuctuations. With the true parallel samplings achieved, the local parallel spectra of the magnetic ﬁeld and the velocity are found to be closer to -5/3 scaling than -2 scaling. The requirement of the stationary local mean ﬁelds has nearly no eﬀects on the perpendicular scaling, which has a about -5/3 power-law index. Among the removed intermittent events from the local parallel samplings, one third of the events are identiﬁed as TDs, one third as RDs, and the rest as EDs. The samplings with the nonstationary local mean ﬁelds display large separations between the ﬁeld directions and the parallel directions, about two times of those with the stationary local mean ﬁelds according to statistical analyses. These results have important implications for interpreting the nonlinear interactions of MHD turbulence.
description: Magnetohydrodynamic (MHD) turbulence is revealed to have scaling anisotropy based on a local mean magnetic ﬁeld, which is usually calculated through the average of the magnetic ﬁeld vectors at two points. However, the thus reconstructed parallel spectrum can be contaminated by intermittent events and nonparallel ﬂuctuations. In this work, we simulate the driven compressible MHD turbulence to investigate the inﬂuence of the stationary local mean ﬁeld on the scaling anisotropy. By examining whether the local parallel samplings are along the magnetic ﬁeld directions, we conﬁrm that the stationary local mean ﬁeld can be fulﬁlled by the criterion ϕ &lt; 10◦ with ϕ being the angle between the two local mean magnetic ﬁelds after cutting the sampled magnetic ﬁeld intervals into two halves. The three-dimensional (3D) numerical data also show that the samplings with the stationary local mean ﬁelds successfully prevent intermittency events and nonparallel ﬂuctuations from mixing into the measured parallel ﬂuctuations. With the true parallel samplings achieved, the local parallel spectra of the magnetic ﬁeld and the velocity are found to be closer to -5/3 scaling than -2 scaling. The requirement of the stationary local mean ﬁelds has nearly no eﬀects on the perpendicular scaling, which has a about -5/3 power-law index. Among the removed intermittent events from the local parallel samplings, one third of the events are identiﬁed as TDs, one third as RDs, and the rest as EDs. The samplings with the nonstationary local mean ﬁelds display large separations between the ﬁeld directions and the parallel directions, about two times of those with the stationary local mean ﬁelds according to statistical analyses. These results have important implications for interpreting the nonlinear interactions of MHD turbulence.