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

TL;DR

This study analyzes magnetic switchback features near 1 au using Wind data, revealing their association with large-amplitude Alfvénic oscillations and the influence of local magnetic field geometry on their appearance.

Contribution

It demonstrates that magnetic switchbacks are linked to Alfvénic fluctuations and highlights the importance of local magnetic field orientation in their observational characteristics.

Findings

Switchbacks are associated with large-amplitude Alfvénic oscillations.

The appearance of switchbacks depends on the local magnetic field orientation.

Switchbacks may not always be one-sided spikes at larger heliocentric distances.

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.