Switchback-like structures observed by Solar Orbiter

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, and α-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 and α-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.