On the properties of Alfv’enic switchbacks in the expanding solar wind: three-dimensional numerical simulations. (arXiv:2205.09446v2 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Johnston_Z/0/1/0/all/0/1">Zade Johnston</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Squire_J/0/1/0/all/0/1">Jonathan Squire</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mallet_A/0/1/0/all/0/1">Alfred Mallet</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Meyrand_R/0/1/0/all/0/1">Romain Meyrand</a>
Switchbacks — abrupt reversals of the magnetic field within the solar wind
— have been ubiquitously observed by Parker Solar Probe (PSP). Their origin,
whether from processes near the solar surface or within the solar wind itself,
remains under debate, and likely has key implications for solar wind heating
and acceleration. Here, using three-dimensional expanding box simulations, we
examine the properties of switchbacks arising from the evolution of
outwards-propagating Alfv’en waves in the expanding solar wind in detail. Our
goal is to provide testable predictions that can be used to differentiate
between properties arising from solar surface processes and those from the
in-situ evolution of Alfv’en waves in switchback observations by PSP. We show
how the inclusion of the Parker spiral causes magnetic field deflections within
switchbacks to become asymmetric, preferentially deflecting in the plane of the
Parker spiral and rotating in one direction towards the radial component of the
mean field. The direction of the peak of the magnetic field distribution is
also shown to be different from the mean field direction due to its highly
skewed nature. Compressible properties of switchbacks are also explored, with
magnetic-field-strength and density fluctuations being either correlated or
anticorrelated depending on the value of $beta$, agreeing with predictions
from theory. We also measure dropouts in magnetic-field strength and density
spikes at the boundaries of these synthetic switchbacks, both of which have
been observed by PSP. The agreement of these properties with observations
provide further support for the Alfv’en wave model of switchbacks.
Switchbacks — abrupt reversals of the magnetic field within the solar wind
— have been ubiquitously observed by Parker Solar Probe (PSP). Their origin,
whether from processes near the solar surface or within the solar wind itself,
remains under debate, and likely has key implications for solar wind heating
and acceleration. Here, using three-dimensional expanding box simulations, we
examine the properties of switchbacks arising from the evolution of
outwards-propagating Alfv’en waves in the expanding solar wind in detail. Our
goal is to provide testable predictions that can be used to differentiate
between properties arising from solar surface processes and those from the
in-situ evolution of Alfv’en waves in switchback observations by PSP. We show
how the inclusion of the Parker spiral causes magnetic field deflections within
switchbacks to become asymmetric, preferentially deflecting in the plane of the
Parker spiral and rotating in one direction towards the radial component of the
mean field. The direction of the peak of the magnetic field distribution is
also shown to be different from the mean field direction due to its highly
skewed nature. Compressible properties of switchbacks are also explored, with
magnetic-field-strength and density fluctuations being either correlated or
anticorrelated depending on the value of $beta$, agreeing with predictions
from theory. We also measure dropouts in magnetic-field strength and density
spikes at the boundaries of these synthetic switchbacks, both of which have
been observed by PSP. The agreement of these properties with observations
provide further support for the Alfv’en wave model of switchbacks.
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