Anisotropic Magnetic Turbulence in the Inner HeliosphereRadial Evolution of Distributions Observed by Parker Solar Probe
Abstract
Observations from Parker Solar Probe's first five orbits are used to investigate the helioradial evolution of probability density functions (pdfs) of fluctuations of magneticfield components between ~28 and 200 R _{⊙}. Transformation of the magneticfield vector to a local meanfield coordinate system permits examination of anisotropy relative to the mean magneticfield direction. Attention is given to effects of averaginginterval size. It is found that pdfs of the perpendicular fluctuations are well approximated by a Gaussian function, with the parallel fluctuations less so: kurtoses of the latter are generally larger than 10, and their pdfs indicate increasing skewness with decreasing distance r from the Sun, with the latter observation possibly explained by the increasing Alfvénicity of the fluctuations. The ratio of perpendicular to parallel variances is greater than unity; this variance anisotropy becomes stronger with decreasing r. The ratio of the total rms fluctuation strength to the meanfield magnitude decreases with decreasing r, with a value ~0.8 near 1 au and ~0.5 at 0.14 au; the ratio is well approximated by an r ^{1/4} power law. These findings improve our understanding of the radial evolution of turbulence in the solar wind, and have implications for related phenomena such as energeticparticle transport in the inner heliosphere.
 Publication:

The Astrophysical Journal
 Pub Date:
 November 2022
 DOI:
 10.3847/15384357/ac9386
 arXiv:
 arXiv:2205.14096
 Bibcode:
 2022ApJ...939...33C
 Keywords:

 Solar wind;
 Interplanetary magnetic fields;
 Interplanetary turbulence;
 1534;
 824;
 830;
 Astrophysics  Solar and Stellar Astrophysics;
 Physics  Plasma Physics;
 Physics  Space Physics
 EPrint:
 doi:10.3847/15384357/ac9386