Three-dimensional local anisotropy of velocity fluctuations in the solar wind - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Monthly Notices of the Royal Astronomical Society Année : 2019

Three-dimensional local anisotropy of velocity fluctuations in the solar wind

Résumé

We analyse velocity fluctuations in the solar wind at magneto-fluid scales in two data sets, extracted from Wind data in the period 2005-2015, that are characterized by strong or weak expansion. Expansion affects measurements of anisotropy because it breaks axisymmetry around the mean magnetic field. Indeed, the small-scale three-dimensional local anisotropy of magnetic fluctuations (deltaB) as measured by structure functions (SFB) is consistent with tube-like structures for strong expansion. When passing to weak expansion, structures become ribbon-like because of the flattening of SFB along one of the two perpendicular directions. The power-law index that is consistent with a spectral slope -5/3 for strong expansion now becomes closer to -3/2. This index is also characteristic of velocity fluctuations in the solar wind. We study velocity fluctuations (deltaV) to understand if the anisotropy of their structure functions (SFV) also changes with the strength of expansion and if the difference with the magnetic spectral index is washed out once anisotropy is accounted for. We find that SFV is generally flatter than SFB. When expansion passes from strong to weak, a further flattening of the perpendicular SFV occurs and the small-scale anisotropy switches from tube-like to ribbon-like structures. These two types of anisotropy, common to SFV and SFB, are associated with distinct large-scale variance anisotropies of deltaB in the strong- and weak-expansion data sets. We conclude that SFV show anisotropic three-dimensional scaling similar to SFB, with however systematic flatter scalings, reflecting the difference between global spectral slopes.

Mots clés

Fichier principal
Vignette du fichier
stz1041.pdf (2.69 Mo) Télécharger le fichier
Origine : Fichiers éditeurs autorisés sur une archive ouverte

Dates et versions

hal-02272436 , version 1 (26-06-2023)

Identifiants

Citer

Andrea Verdini, Roland Grappin, Olga Alexandrova, L. Franci, S. Landi, et al.. Three-dimensional local anisotropy of velocity fluctuations in the solar wind. Monthly Notices of the Royal Astronomical Society, 2019, 486, pp.3006-3018. ⟨10.1093/mnras/stz1041⟩. ⟨hal-02272436⟩
20 Consultations
5 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More