Direct evidence for magnetic reconnection at the boundaries of magnetic switchbacks with Parker Solar Probe

¹ LPC2E, CNRS/University of Orléans/CNES, 3A avenue de la Recherche Scientifique, Orléans, France
e-mail: clara.froment@cnrs-orleans.fr
² Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450, USA
³ Institut de Recherche en Astrophysique et Planétologie, CNRS, UPS, CNES, Toulouse, France
⁴ Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁵ National Institute for Astrophysics-Institute for Space Astrophysics and Planetology, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
⁶ Department of Earth, Planetary, and Space Sciences, UCLA, Los Angeles, CA 90095, USA
⁷ Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA
⁸ Astrophysical and Planetary Sciences Department, University of Colorado, Boulder, CO 80303, USA
⁹ Physics Department, University of California, Berkeley, CA 94720-7300, USA
¹⁰ The Blackett Laboratory, Imperial College London, London, SW7 2AZ, UK
¹¹ School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK
¹² Smithsonian Astrophysical Observatory, Cambridge, MA 02138, USA
¹³ School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
¹⁴ Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA
¹⁵ BWX Technologies, Inc., Washington, DC 20002, USA
¹⁶ Solar System Exploration Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA

Received: 30 October 2020
Accepted: 15 January 2021

Abstract

Context. The first encounters of Parker Solar Probe (PSP) with the Sun revealed the presence of ubiquitous localised magnetic deflections in the inner heliosphere; these structures, often called switchbacks, are particularly striking in solar wind streams originating from coronal holes.

Aims. We report the direct piece of evidence for magnetic reconnection occurring at the boundaries of three switchbacks crossed by PSP at a distance of 45 to 48 solar radii to the Sun during its first encounter.

Methods. We analyse the magnetic field and plasma parameters from the FIELDS and Solar Wind Electrons Alphas and Protons instruments.

Results. The three structures analysed all show typical signatures of magnetic reconnection. The ion velocity and magnetic field are first correlated and then anti-correlated at the inbound and outbound edges of the bifurcated current sheets with a central ion flow jet. Most of the reconnection events have a strong guide field and moderate magnetic shear, but one current sheet shows indications of quasi anti-parallel reconnection in conjunction with a magnetic field magnitude decrease by 90%.

Conclusions. Given the wealth of intense current sheets observed by PSP, reconnection at switchback boundaries appears to be rare. However, as the switchback boundaries accomodate currents, one can conjecture that the geometry of these boundaries offers favourable conditions for magnetic reconnection to occur. Such a mechanism would thus contribute in reconfiguring the magnetic field of the switchbacks, affecting the dynamics of the solar wind and eventually contributing to the blending of the structures with the regular wind as they propagate away from the Sun.