Discontinuity analysis of the leading switchback transition regions

M Akhavan-Tafti,J Huang,S Bale,J Kasper

doi:10.1051/0004-6361/202039508

Abstract

Context.Magnetic switchbacks are magnetic structures characterized as intervals of sudden reversal in the radial component of the pristine solar wind’s magnetic field. Switchbacks comprise of magnetic spikes that are preceded and succeeded by switchback transition regions within which the radial magnetic field reverses. Determining switchback generation and evolution mechanisms will further our understanding of the global circulation and transportation of the Sun’s open magnetic flux.Aims.The present study juxtaposes near-Sun switchback transition regions’ characteristics with similar magnetic discontinuities observed at greater radial distances with the goal of determining local mechanism(s) through which switchback transition regions may evolve.Methods.Measurements from fields and plasma suites aboard the Parker Solar Probe were utilized to characterize switchback transition regions. Minimum variance analysis (MVA) was applied on the magnetic signatures of the leading switchback transition regions. The leading switchback transition regions with robust MVA solutions were identified and categorized based on their magnetic discontinuity characteristics.Results.It is found that 78% of the leading switchback transition regions are rotational discontinuities (RD). Another 21% of the leading switchback transition regions are categorized as “either” discontinuity (ED), defined as small relative changes in both magnitude and the normal component of the magnetic field. The RD-to-ED event count ratio is found to reduce with increasing distance from the Sun. The proton radial temperature sharply increases (+ 29.31%) at the leading RD-type switchback transition regions, resulting in an enhanced thermal pressure gradient. Magnetic curvature at the leading RD-type switchback transition regions is often negligible. Magnetic curvature and the thermal pressure gradient are parallel (i.e., “bad” curvature) in 74% of the leading RD-type switchback transition regions.Conclusions.The leading switchback transition regions may evolve from RD-type into ED-type magnetic discontinuities while propagating away from the Sun. Local magnetic reconnection is likely not the main driver of this evolution. Other drivers, such as plasma instabilities, need to be investigated to explain the observed significant jump in proton temperature and the prevalence of bad curvature at the leading RD-type switchback transition regions.

Highlights

Magnetic switchbacks (Kahler et al 1996; McComas et al 1996; Yamauchi et al 2004; Suess 2007; Matteini et al 2014; Borovsky 2016) were identified in Ulysses’ observations of high-latitude solar coronal holes
The spike region corresponds to a region of enhanced VR and reversed BR
Spikes are separated into a core region with plasma conditions that are very different from those of the ambient solar wind, but they are relatively constant

Summary

Introduction

Magnetic switchbacks (Kahler et al 1996; McComas et al 1996; Yamauchi et al 2004; Suess 2007; Matteini et al 2014; Borovsky 2016) were identified in Ulysses’ observations of high-latitude solar coronal holes. They describe intervals of intermittent reversals in the radial component of the magnetic field. At 1 AU, solar wind magnetic discontinuities are observed on average once every hour. Their average duration is ∼2 s (Tsurutani & Smith 1979)

Results

Discussion

Conclusion