Issue |
A&A
Volume 656, December 2021
Solar Orbiter First Results (Cruise Phase)
|
|
---|---|---|
Article Number | A6 | |
Number of page(s) | 14 | |
Section | The Sun and the Heliosphere | |
DOI | https://doi.org/10.1051/0004-6361/202140672 | |
Published online | 14 December 2021 |
Evolution of anisotropic turbulence in the fast and slow solar wind: Theory and Solar Orbiter measurements
1
Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899, USA
e-mail: la0004@uah.edu
2
Department of Space Science, University of Alabama in Huntsville, Huntsville, AL 35899, USA
3
National Institute for Astrophysics–Astrophysical Observatory of Torino Via Osservatorio 20, 10025 Pino Torinese, Italy
4
Department of Physics, The Blackett Laboratory, Imperial College London, London, UK
5
Mullard Space Science Laboratory, University College London, Holmbury St. Mary, UK
6
Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse Université de Toulouse, CNRS 5 UMR5277, Toulouse, France
Received:
26
February
2021
Accepted:
19
April
2021
Aims. Solar Orbiter (SolO) was launched on February 9, 2020, allowing us to study the nature of turbulence in the inner heliopshere. We investigate the evolution of anisotropic turbulence in the fast and slow solar wind in the inner heliosphere using the nearly incompressible magnetohydrodynamic (NI MHD) turbulence model and SolO measurements.
Methods. We calculated the two dimensional (2D) and the slab variances of the energy in forward and backward propagating modes, the fluctuating magnetic energy, the fluctuating kinetic energy, the normalized residual energy, and the normalized cross-helicity as a function of the angle between the mean solar wind speed and the mean magnetic field (θUB), and as a function of the heliocentric distance using SolO measurements. We compared the observed results and the theoretical results of the NI MHD turbulence model as a function of the heliocentric distance.
Results. The results show that the ratio of 2D energy and slab energy of forward and backward propagating modes, magnetic field fluctuations, and kinetic energy fluctuations increases as the angle between the mean solar wind flow and the mean magnetic field increases from θUB = 0° to approximately θUB = 90° and then decreases as θUB → 180°. We find that solar wind turbulence is a superposition of the dominant 2D component and a minority slab component as a function of the heliocentric distance. We find excellent agreement between the theoretical results and observed results as a function of the heliocentric distance.
Key words: solar wind / turbulence
© ESO 2021
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