The Evolution and Role of Solar Wind Turbulence in the Inner Heliosphere

Author
Keywords
Abstract
<p>The first two orbits of the Parker Solar Probe spacecraft have enabled the first in situ measurements of the solar wind down to a heliocentric distance of 0.17 au (or 36 <em>R</em>\&nbsp;⊙\&nbsp;\&nbsp;R⊙ ). Here, we present an analysis of this data to study solar wind turbulence at 0.17 au and its evolution out to 1 au. While many features remain similar, key differences at 0.17 au include increased turbulence energy levels by more than an order of magnitude, a magnetic field spectral index of -3/2 matching that of the velocity and both Elsasser fields, a lower magnetic compressibility consistent with a smaller slow-mode kinetic energy fraction, and a much smaller outer scale that has had time for substantial nonlinear processing. There is also an overall increase in the dominance of outward-propagating Alfv\ enic fluctuations compared to inward-propagating ones, and the radial variation of the inward component is consistent with its generation by reflection from the large-scale gradient in Alfv\ en speed. The energy flux in this turbulence at 0.17 au was found to be ̃10\% of that in the bulk solar wind kinetic energy, becoming ̃40\% when extrapolated to the Alfv\ en point, and both the fraction and rate of increase of this flux toward the Sun are consistent with turbulence-driven models in which the solar wind is powered by this flux.</p>
Year of Publication
2020
Journal
The Astrophysical Journal Supplement Series
Volume
246
Number
Number of Pages
53
Date Published
02/2020
URL
https://iopscience.iop.org/article/10.3847/1538-4365/ab60a3
DOI
10.3847/1538-4365/ab60a3