Anisotropy of Solar-Wind Turbulence in the Inner Heliosphere at Kinetic Scales: PSP Observations. (arXiv:2102.13294v2 [physics.space-ph] UPDATED)

Anisotropy of Solar-Wind Turbulence in the Inner Heliosphere at Kinetic Scales: PSP Observations. (arXiv:2102.13294v2 [physics.space-ph] UPDATED)
<a href="http://arxiv.org/find/physics/1/au:+Duan_D/0/1/0/all/0/1">Die Duan</a>, <a href="http://arxiv.org/find/physics/1/au:+He_J/0/1/0/all/0/1">Jiansen He</a>, <a href="http://arxiv.org/find/physics/1/au:+Bowen_T/0/1/0/all/0/1">Trevor A. Bowen</a>, <a href="http://arxiv.org/find/physics/1/au:+Woodham_L/0/1/0/all/0/1">Lloyd D. Woodham</a>, <a href="http://arxiv.org/find/physics/1/au:+Wang_T/0/1/0/all/0/1">Tieyan Wang</a>, <a href="http://arxiv.org/find/physics/1/au:+Chen_C/0/1/0/all/0/1">Christopher H. K. Chen</a>, <a href="http://arxiv.org/find/physics/1/au:+Mallet_A/0/1/0/all/0/1">Alfred Mallet</a>, <a href="http://arxiv.org/find/physics/1/au:+Bale_S/0/1/0/all/0/1">Stuart D. Bale</a>

The anisotropy of solar wind turbulence is a critical issue in understanding
the physics of energy transfer between scales and energy conversion between
fields and particles in the heliosphere. Using the measurement of emph{Parker
Solar Probe} (emph{PSP}), we present an observation of the anisotropy at
kinetic scales in the slow, Alfv’enic, solar wind in the inner heliosphere.
textbf{The magnetic compressibility behaves as expected for kinetic Alfv’enic
turbulence below the ion scale.} A steepened transition range is found between
the inertial and kinetic ranges in all directions with respect to the local
background magnetic field direction. The anisotropy of $k_perp gg
k_parallel$ is found evident in both transition and kinetic ranges, with the
power anisotropy $P_perp/P_parallel > 10$ in the kinetic range leading over
that in the transition range and being stronger than that at 1 au. The spectral
index varies from $alpha_{tparallel}=-5.7pm 1.0$ to $alpha_{tperp}=-3.7pm
0.3$ in the transition range and $alpha_{kparallel}=-3.12pm 0.22$ to
$alpha_{kperp}=-2.57pm 0.09$ in the kinetic range. The corresponding
wavevector anisotropy has the scaling of $k_parallel sim k_perp^{0.71pm
0.17}$ in the transition range, and changes to $k_parallel sim
k_perp^{0.38pm 0.09}$ in the kinetic range, consistent with the kinetic
Alfv’enic turbulence at sub-ion scales.

The anisotropy of solar wind turbulence is a critical issue in understanding
the physics of energy transfer between scales and energy conversion between
fields and particles in the heliosphere. Using the measurement of emph{Parker
Solar Probe} (emph{PSP}), we present an observation of the anisotropy at
kinetic scales in the slow, Alfv’enic, solar wind in the inner heliosphere.
textbf{The magnetic compressibility behaves as expected for kinetic Alfv’enic
turbulence below the ion scale.} A steepened transition range is found between
the inertial and kinetic ranges in all directions with respect to the local
background magnetic field direction. The anisotropy of $k_perp gg
k_parallel$ is found evident in both transition and kinetic ranges, with the
power anisotropy $P_perp/P_parallel > 10$ in the kinetic range leading over
that in the transition range and being stronger than that at 1 au. The spectral
index varies from $alpha_{tparallel}=-5.7pm 1.0$ to $alpha_{tperp}=-3.7pm
0.3$ in the transition range and $alpha_{kparallel}=-3.12pm 0.22$ to
$alpha_{kperp}=-2.57pm 0.09$ in the kinetic range. The corresponding
wavevector anisotropy has the scaling of $k_parallel sim k_perp^{0.71pm
0.17}$ in the transition range, and changes to $k_parallel sim
k_perp^{0.38pm 0.09}$ in the kinetic range, consistent with the kinetic
Alfv’enic turbulence at sub-ion scales.

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