Features of magnetic field switchbacks in relation to the local-field geometry of large-amplitude Alfv\'enic oscillations: \emph{Wind} and \emph{PSP} observations

Abstract

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.