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Title: IMPRINTS OF EXPANSION ON THE LOCAL ANISOTROPY OF SOLAR WIND TURBULENCE

Abstract

We study the anisotropy of II-order structure functions (SFs) defined in a frame attached to the local mean field in three-dimensional (3D) direct numerical simulations of magnetohydrodynamic turbulence, with the solar wind expansion both included and not included. We simulate spacecraft flybys through the numerical domain by taking increments along the radial (wind) direction that form an angle of 45° with the ambient magnetic field. We find that only when expansion is taken into account do the synthetic observations match the 3D anisotropy observed in the solar wind, including the change of anisotropy with scale. Our simulations also show that the anisotropy changes dramatically when considering increments oblique to the radial directions. Both results can be understood by noting that expansion reduces the radial component of the magnetic field at all scales, thus confining fluctuations in the plane perpendicular to the radial. Expansion is thus shown to affect not only the (global) spectral anisotropy, but also the local anisotropy of second-order SF by influencing the distribution of the local mean field, which enters this higher-order statistics.

Authors:
 [1];  [2]
  1. Dipartimento di fisica e astronomia, Università di Firenze, Firenze (Italy)
  2. LPP, Ecole Polytechnique, Palaiseau (France)
Publication Date:
OSTI Identifier:
22518915
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal Letters
Additional Journal Information:
Journal Volume: 808; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 2041-8205
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANISOTROPY; COMPUTERIZED SIMULATION; FLUCTUATIONS; HELIOSPHERE; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; MEAN-FIELD THEORY; PLASMA; SOLAR WIND; SPACE VEHICLES; STRUCTURE FUNCTIONS; SUN; TURBULENCE

Citation Formats

Verdini, Andrea, and Grappin, Roland. IMPRINTS OF EXPANSION ON THE LOCAL ANISOTROPY OF SOLAR WIND TURBULENCE. United States: N. p., 2015. Web. doi:10.1088/2041-8205/808/2/L34.
Verdini, Andrea, & Grappin, Roland. IMPRINTS OF EXPANSION ON THE LOCAL ANISOTROPY OF SOLAR WIND TURBULENCE. United States. https://doi.org/10.1088/2041-8205/808/2/L34
Verdini, Andrea, and Grappin, Roland. 2015. "IMPRINTS OF EXPANSION ON THE LOCAL ANISOTROPY OF SOLAR WIND TURBULENCE". United States. https://doi.org/10.1088/2041-8205/808/2/L34.
@article{osti_22518915,
title = {IMPRINTS OF EXPANSION ON THE LOCAL ANISOTROPY OF SOLAR WIND TURBULENCE},
author = {Verdini, Andrea and Grappin, Roland},
abstractNote = {We study the anisotropy of II-order structure functions (SFs) defined in a frame attached to the local mean field in three-dimensional (3D) direct numerical simulations of magnetohydrodynamic turbulence, with the solar wind expansion both included and not included. We simulate spacecraft flybys through the numerical domain by taking increments along the radial (wind) direction that form an angle of 45° with the ambient magnetic field. We find that only when expansion is taken into account do the synthetic observations match the 3D anisotropy observed in the solar wind, including the change of anisotropy with scale. Our simulations also show that the anisotropy changes dramatically when considering increments oblique to the radial directions. Both results can be understood by noting that expansion reduces the radial component of the magnetic field at all scales, thus confining fluctuations in the plane perpendicular to the radial. Expansion is thus shown to affect not only the (global) spectral anisotropy, but also the local anisotropy of second-order SF by influencing the distribution of the local mean field, which enters this higher-order statistics.},
doi = {10.1088/2041-8205/808/2/L34},
url = {https://www.osti.gov/biblio/22518915}, journal = {Astrophysical Journal Letters},
issn = {2041-8205},
number = 2,
volume = 808,
place = {United States},
year = {Sat Aug 01 00:00:00 EDT 2015},
month = {Sat Aug 01 00:00:00 EDT 2015}
}