The Fluid-like and Kinetic Behavior of Kinetic Alfv\ en Turbulence in Space Plasma

Author
Keywords
Abstract
<p>Kinetic Alfv\ en waves (KAWs) are the short-wavelength extension of the magnetohydrodynamics Alfv\ en-wave branch in the case of highly oblique propagation with respect to the background magnetic field. Observations of space plasma show that small-scale turbulence is mainly KAW-like. We apply two theoretical approaches, a collisional two-fluid theory and a collisionless linear kinetic theory, to obtain predictions for the KAW polarizations depending on\&nbsp;<em>β</em>\&nbsp;<sub>p</sub>\&nbsp;(the ratio of the proton thermal pressure to the magnetic pressure) at the ion gyroscale in terms of fluctuations in density, bulk velocity, and pressure. We perform a wavelet analysis of\&nbsp;<em>Magnetospheric Multiscale\&nbsp;</em>magnetosheath measurements and compare the observations with both theories. We find that the two-fluid theory predicts the observations better than the kinetic theory, suggesting that the small-scale KAW-like fluctuations exhibit a fluid-like behavior in the magnetosheath although the plasma is weakly collisional. We also present predictions for the KAW polarizations in the inner heliosphere that are testable with\&nbsp;<em>Parker Solar Probe</em>\&nbsp;and\&nbsp;<em>Solar Orbiter</em>.</p>
Year of Publication
2019
Journal
The Astrophysical Journal
Volume
870
Number
Number of Pages
106
Date Published
01/2019
URL
http://stacks.iop.org/0004-637X/870/i=2/a=106?key=crossref.82a2db48f1fad21f326ef5e3fb4b795
DOI
10.3847/1538-4357/aaef77