Enhanced proton parallel temperature inside patches of switchbacks in the inner heliosphere

¹ Department of Physics, The Blackett Laboratory, Imperial College London, London, UK
e-mail: l.woodham@imperial.ac.uk
² Space Sciences Laboratory, University of California, Berkeley, CA, USA
³ Physics Department, University of California, Berkeley, CA, USA
⁴ School of Physics and Astronomy, Queen Mary University of London, London, UK
⁵ Mullard Space Science Laboratory, University College London, Dorking, UK
⁶ Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA
⁷ Smithsonian Astrophysical Observatory, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
⁸ Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA
⁹ LESIA, Observatoire de Paris, Université PSL, Meudon, France

Received: 13 September 2020
Accepted: 12 October 2020

Abstract

Context. Switchbacks are discrete angular deflections in the solar wind magnetic field that have been observed throughout the heliosphere. Recent observations by Parker Solar Probe (PSP) have revealed the presence of patches of switchbacks on the scale of hours to days, separated by ‘quieter’ radial fields.

Aims. We aim to further diagnose the origin of these patches using measurements of proton temperature anisotropy that can illuminate possible links to formation processes in the solar corona.

Methods. We fitted 3D bi-Maxwellian functions to the core of proton velocity distributions measured by the SPAN-Ai instrument onboard PSP to obtain the proton parallel, T_p,∥, and perpendicular, T_p,⊥, temperature.

Results. We show that the presence of patches is highlighted by a transverse deflection in the flow and magnetic field away from the radial direction. These deflections are correlated with enhancements in T_p,∥, while T_p,⊥ remains relatively constant. Patches sometimes exhibit small proton and electron density enhancements.

Conclusions. We interpret that patches are not simply a group of switchbacks, but rather switchbacks are embedded within a larger-scale structure identified by enhanced T_p,∥ that is distinct from the surrounding solar wind. We suggest that these observations are consistent with formation by reconnection-associated mechanisms in the corona.