The Evolution and Role of Solar Wind Turbulence in the Inner Heliosphere. (arXiv:1912.02348v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Chen_C/0/1/0/all/0/1">C. H. K. Chen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bale_S/0/1/0/all/0/1">S. D. Bale</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bonnell_J/0/1/0/all/0/1">J. W. Bonnell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Borovikov_D/0/1/0/all/0/1">D. Borovikov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bowen_T/0/1/0/all/0/1">T. A. Bowen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Burgess_D/0/1/0/all/0/1">D. Burgess</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Case_A/0/1/0/all/0/1">A. W. Case</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chandran_B/0/1/0/all/0/1">B. D. G. Chandran</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wit_T/0/1/0/all/0/1">T. Dudok de Wit</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Goetz_K/0/1/0/all/0/1">K. Goetz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Harvey_P/0/1/0/all/0/1">P. R. Harvey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kasper_J/0/1/0/all/0/1">J. C. Kasper</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Klein_K/0/1/0/all/0/1">K. G. Klein</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Korreck_K/0/1/0/all/0/1">K. E. Korreck</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Larson_D/0/1/0/all/0/1">D. Larson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Livi_R/0/1/0/all/0/1">R. Livi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+MacDowall_R/0/1/0/all/0/1">R. J. MacDowall</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Malaspina_D/0/1/0/all/0/1">D. M. Malaspina</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mallet_A/0/1/0/all/0/1">A. Mallet</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McManus_M/0/1/0/all/0/1">M. D. McManus</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Moncuquet_M/0/1/0/all/0/1">M. Moncuquet</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pulupa_M/0/1/0/all/0/1">M. Pulupa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stevens_M/0/1/0/all/0/1">M. Stevens</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Whittlesey_P/0/1/0/all/0/1">P. Whittlesey</a>

The first two orbits of the Parker Solar Probe (PSP) spacecraft have enabled
the first in situ measurements of the solar wind down to a heliocentric
distance of 0.17 au (or 36 Rs). 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 towards the Sun is consistent with turbulence-driven models in
which the solar wind is powered by this flux.

The first two orbits of the Parker Solar Probe (PSP) spacecraft have enabled
the first in situ measurements of the solar wind down to a heliocentric
distance of 0.17 au (or 36 Rs). 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 towards the Sun is consistent with turbulence-driven models in
which the solar wind is powered by this flux.

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