http://arxiv.org/abs/2204.09800
In this letter we report observations of magnetic switchback (SB) features near 1 au using data from the \emph{Wind} spacecraft. These features appear to be strikingly similar to the ones observed by the Parker Solar Probe mission (PSP) closer to the Sun: namely, one-sided spikes (or enhancements) in the solar-wind bulk speed $V$ that correlate/anti-correlate with the spikes seen in the radial-field component $B_R$. In the solar-wind streams that we analyzed, these specific SB features near 1 au are associated with large-amplitude Alfv\’enic oscillations that propagate outward from the sun along a local background (prevalent) magnetic field $\bf{B}_0$ that is nearly radial. We also show that, when $\bf{B}_0$ is nearly perpendicular to the radial direction, the large amplitude Alfv\’enic oscillations display variations in $V$ that are two-sided (i.e., $V$ alternately increases and decreases depending on the vector $\Delta\bf{B}=\bf{B} – \bf{B}_0$). As a consequence, SBs may not appear always as one-sided spikes in $V$, especially at larger heliocentric distances where the local background field statistically departs from the radial direction. We suggest that SBs can be well described by large-amplitude Alfv\’enic fluctuations if the field rotation is computed with respect to a well-determined local background field that, in some cases, may deviate from the large-scale Parker field.
S. Bourouaine, J. Perez, N. Raouafi, et. al.
Fri, 22 Apr 22
62/64
Comments: Accepted for publication in the Astrophysical Journal Letters
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