Features of Magnetic Field Switchbacks in Relation to the Local-field Geometry of Large-amplitude Alfvénic Oscillations: Wind and PSP Observations

In this Letter, we report observations of magnetic switchback (SB) features near 1 au using data from the Wind spacecraft. These features appear to be strikingly similar to the ones observed by the Parker Solar Probe mission closer to the Sun: namely, one-sided spikes (or enhancements) in the solar-wind bulk speed V that correlate/anticorrelate with the spikes seen in the radial-field component BR. In the solar-wind streams that we analyzed, these specific SB features near 1 au are associated with large-amplitude Alfvénic oscillations that propagate outward from the Sun along a local background (prevalent) magnetic field B0 that is nearly radial. We also show that, when B0 is nearly perpendicular to the radial direction, the large-amplitude Alfvénic oscillations display variations in V that are two sided (i.e., V alternately increases and decreases depending on the vector ΔB = B − B0). As a consequence, SBs may not always appear 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 Alfvénic 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.