Original Research ARTICLE
Anisotropy of spectral index in ion scale compressible turbulence : MMS Observations in the magnetosheath
- 1Space Research Institute (OAW), Austria
- 2Goddard Space Flight Center, National Aeronautics and Space Administration, United States
Turbulence in the Earth’s magnetosheath at ion kinetic scales is investigated with the Magnetospheric MultiScale (MMS) spacecraft. The multi-point measurements allow the three dimensional power spectra in wave-vector space to be determined. Previously the three dimensional structure of fluctuations in the magnetic field and density (using spacecraft potential as a proxy) were possible with Cluster. However, using the excellent time resolution data set provided from both the Fluxgate Magnetometer (FGM) and the Fast Plasma Investigation (FPI) on MMS the spectra can be determined for a number of different parameters such as ion velocity, and ion temperatures parallel and perpencidular to the mean magnetic field directions. The spectra for different fluctuations show similar features to one another such as a strong power anisotropy with respect to the mean magnetic field direction, such that the energy decays faster in the direction parallel to the mean magnetic field than the perpendicular direction. A weak non-gyrotropy is also seen in the direction of the bulk velocity similar to what has been seen in magnetic field fluctuations with Cluster at ion kinetic scales in the solar wind. Velocity fluctuations are shown to be the most anisotropic. The density and temperature fluctuations exhibit similar anisotropies but are much weaker in comparison.
Keywords: Space Science, magnetosheath, Plasma, Turbulence, Plasma heating
Received: 31 May 2019;
Accepted: 29 Oct 2019.
Copyright: © 2019 Roberts, Narita, Nakamura, Voros and Gershman. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Owen W. Roberts, Space Research Institute (OAW), Graz, Austria, Owen.Roberts@oeaw.ac.at