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Spectral anisotropy of Elsässer variables in two-dimensional wave-vector space as observed in the fast solar wind turbulence

Yan, L; He, J; Zhang, L; Tu, C; Marsch, E; Chen, CHK; Wang, X; ... Wicks, RT; + view all (2016) Spectral anisotropy of Elsässer variables in two-dimensional wave-vector space as observed in the fast solar wind turbulence. The Astrophysics Journal Letters , 816 (2) , Article L24. 10.3847/2041-8205/816/2/L24. Green open access

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Abstract

Intensive studies have been conducted to understand the anisotropy of solar wind turbulence. However, the anisotropy of Elsässer variables Z± in 2D wave-vector space has yet to be investigated. Here we first verify the transformation based on the projection-slice theorem between the power spectral density PSD2D(k∥,k⊥) and the spatial correlation function CF2D(r∥,r⊥) Based on the application of the transformation to the magnetic field and the particle measurements from the WIND spacecraft, we investigate the spectral anisotropy of Elsässer variables (Z±), and the distribution of residual energy ER, Alfvén ratio R∧, and Elsässer ratio RE in the (k∥,k⊥) space. The spectra PSD2D(k∥,k⊥) of B, V, and Zmajor (the larger of Z±) show a similar pattern that PSD2D(k∥,k⊥) is mainly distributed along a ridge inclined toward the k⊥ axis. This is probably the signature of the oblique Alfvénic fluctuations propagating outwardly. Unlike those of B, V, and Zmajorm the spectrum PSD2D(k∥,k⊥) of Zminor is distributed mainly along the k⊥ axis. Close to the k⊥ axis, |ER| becomes larger while R∧ becomes smaller, suggesting that the dominance of magnetic energy over kinetic energy becomes more significant at small k∥. RE is larger at small k∥, implying that PSD2D(k∥,k⊥) of Zminor is more concentrated along the k⊥ direction as compared to that of Z major. The residual energy condensate at small k∥ is consistent with simulation results in which ER is spontaneously generated by Alfvén wave interaction.

Type: Article
Title: Spectral anisotropy of Elsässer variables in two-dimensional wave-vector space as observed in the fast solar wind turbulence
Open access status: An open access version is available from UCL Discovery
DOI: 10.3847/2041-8205/816/2/L24
Publisher version: http://dx.doi.org/10.3847/2041-8205/816/2/L24
Language: English
Additional information: Copyright © 2016. The American Astronomical Society. All rights reserved.
Keywords: solar wind, turbulence, waves
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics > Advanced Instrumentation Systems
URI: https://discovery.ucl.ac.uk/id/eprint/1482212
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