Abstract
Context.Rapid polarity reversals of the radial heliospheric magnetic field were discovered by Ulysses and they are now frequently observed as a common near-Sun phenomenon by NASA’s Parker Solar Probe (PSP). Other solar wind missions, including ESA-NASA Solar Orbiter (SolO), also observe similar phenomena. The nature of these fluctuations is unclear, and the relation between the “switchbacks” observed near the Sun and similar events observed at 1 AU is unknown.Aims.We make a detailed case study of the SolO plasma and magnetic field data obtained in a region that is magnetically connected to a coronal hole. We aim to check whether such fluctuations might have the same origin as the “switchbacks” observed by PSP.Methods.We used PSP magnetic field and plasma data to support our analysis of SolO data. We used the magnetic field data, electron pitch angle distributions, proton velocity distribution functions, andα-particle parameters measured by SolO to perform a detailed analysis of the observed solar wind perturbations.Results.On 27 September 2020, PSP and SolO were located around the same Carrington longitude and their latitudinal separation was very small. Solar wind plasma and magnetic field data during this time interval confirms that (at least at certain times) the solar wind observed by both spacecraft does originate from the same coronal hole region and that during these time intervals, SolO experiences several short variations similar to the “switchbacks” regularly observed by PSP.Conclusions.The suprathermal electron pitch angle distributions andα-particle speed variations indicate that the magnetic field line was bent by 180° by solar wind velocity shear. Variations in electron and proton velocity distribution functions suggest that bent field lines reconnect with each other, producing flux ropes. The observed flux ropes might be the surviving and modified remains of the switchbacks created near Sun and observed by PSP.
Highlights
In 1995-1996, during the solar minimum, the Ulysses spacecraft, orbiting at high heliolatitudes, observed numerous radial magnetic field polarity inversions in the fast solar wind that is magnetically mapped to the polar coronal hole
The low energy part of ion velocity distribution functions (VDF) belonging to the antisunward field line is mirroring relative to the de Hoffman-Teller frame origin while it passes from sunward line to antisunward one via the reconnection kink
On 27 September 2020, Solar Orbiter sampled a solar wind stream magnetically connected to a southern hemisphere coronal hole
Summary
In 1995-1996, during the solar minimum, the Ulysses spacecraft, orbiting at high heliolatitudes, observed numerous radial magnetic field polarity inversions (see Balogh et al 1999) in the fast solar wind that is magnetically mapped to the polar coronal hole. The first orbit of NASA’s Parker Solar Probe (PSP) (Fox et al 2016), in November 2018, led to the discovery of a similar, but unexpected feature of the near-Sun solar wind: the presence of frequent and rapid polarity reversals of the radial magnetic field (Bale et al 2019). In the lightly red shaded intervals, PSP observed a rather high speed solar wind similar to that observed by SolO when connected to the same coronal hole. Since PSP measures solar wind that would not reach SolO for several days, the similar velocity profiles on both spacecrafts tell us that we see a quasi steadystate spacial structure of the coronal hole. Since we are extensively using the first data from the Solar Orbiter SWAPAS (Solar Wind Analyzer - Proton Alpha Sensor) instrument, our additional goal is to present the advantages of such modern measurements
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