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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 2 | Copyright
Ann. Geophys., 36, 527-539, 2018
https://doi.org/10.5194/angeo-36-527-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 29 Mar 2018

Regular paper | 29 Mar 2018

Three-dimensional density and compressible magnetic structure in solar wind turbulence

Owen W. Roberts1, Yasuhito Narita2, and C.-Philippe Escoubet1 Owen W. Roberts et al.
  • 1ESA/ESTEC SCI-S, Keplerlaan 1, 2201 AZ, Noordwijk, the Netherlands
  • 2Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria

Abstract. The three-dimensional structure of both compressible and incompressible components of turbulence is investigated at proton characteristic scales in the solar wind. Measurements of the three-dimensional structure are typically difficult, since the majority of measurements are performed by a single spacecraft. However, the Cluster mission consisting of four spacecraft in a tetrahedral formation allows for a fully three-dimensional investigation of turbulence. Incompressible turbulence is investigated by using the three vector components of the magnetic field. Meanwhile compressible turbulence is investigated by considering the magnitude of the magnetic field as a proxy for the compressible fluctuations and electron density data deduced from spacecraft potential. Application of the multi-point signal resonator technique to intervals of fast and slow wind shows that both compressible and incompressible turbulence are anisotropic with respect to the mean magnetic field direction P ≫ P and are sensitive to the value of the plasma beta (β; ratio of thermal to magnetic pressure) and the wind type. Moreover, the incompressible fluctuations of the fast and slow solar wind are revealed to be different with enhancements along the background magnetic field direction present in the fast wind intervals. The differences in the fast and slow wind and the implications for the presence of different wave modes in the plasma are discussed.

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In this study we use multi-point spacecraft measurements of magnetic field and electron density derived from spacecraft potential to investigate the three-dimensional structure of solar wind plasma turbulence. We see that there is a dependence on the plasma beta (ratio of thermal to magnetic pressure) as well as a dependence on the type of wind i.e. fast or slow.
In this study we use multi-point spacecraft measurements of magnetic field and electron density...
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