Letter to the Editor

Energetic particle behavior in near-Sun magnetic field switchbacks from PSP

¹ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
e-mail: riddhib@princeton.edu
² Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA
³ Bartol Research Institute, University of Delaware, Newark, DE 19716, USA
⁴ University of Arizona, Tucson, AZ 85721, USA
⁵ University of New Hampshire, Durham, NH 03824, USA
⁶ Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
⁷ Southwest Research Institute, San Antonio, TX 78238, USA
⁸ University of Texas at San Antonio, San Antonio, TX 78249, USA
⁹ Physics Department, University of California, Berkeley, CA 94720-7300, USA
¹⁰ Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450, USA
¹¹ The Blackett Laboratory, Imperial College London, London, SW7 2AZ, UK
¹² School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK
¹³ LPC2E, CNRS and University of Orléans, Orléans, France
¹⁴ School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
¹⁵ Solar System Exploration Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁶ Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA
¹⁷ BWX Technologies, Inc., Washington DC 20002, USA
¹⁸ Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA
¹⁹ Smithsonian Astrophysical Observatory, Cambridge, MA 02138, USA

Received: 30 October 2020
Accepted: 9 February 2021

Abstract

Context. The observation of numerous magnetic switchbacks and associated plasma jets in Parker Solar Probe (PSP) during its first five orbits, particularly near the Sun, has attracted considerable attention. Switchbacks have been found to be systematically associated with correlated reversals in the direction of the propagation of Alfvénic fluctuations, as well as similar reversals of the electron strahl.

Aims. Here we aim to see whether the energetic particles change direction at the magnetic field switchbacks.

Methods. We use magnetic field data from the MAG suite’s fluxgate magnetometer instrument to identify switchback regions. We examine the radial anisotropy of the energetic particles measured by the EPI-Lo instrument of the IS⊙IS suite.

Results. We find that energetic particles measured by EPI-Lo generally do not preferentially change their directionality from that of the background magnetic field to that of the switchbacks.

Conclusions. A reasonable hypothesis is that particles with smaller gyroradii, such as strahl electrons, can reverse direction by following the magnetic field in switchbacks, but that larger gyroradii particles cannot. This provides the possibility of setting a constraint on the radius of the curvature of the magnetic field in switchbacks, a property not otherwise observed by PSP. We expect that particles at higher energies than those detectable by EPI-Lo will also not respond to switchbacks. The observed reversals of radial energetic particle flux are separate phenomena, likely associated with source locations or other propagation effects occurring at greater radial distances.