SH054-06
Enhanced Proton Parallel Temperature in ‘Patches’ of Alfvénic Switchbacks
Wednesday, 16 December 2020: 12:12
Virtual
Lloyd David Woodham1, Timothy Simon Horbury1, Lorenzo Matteini2, Thomas Woolley2, Ronan Laker1, Stuart D Bale3, Georgios Nicolaou4, Julia E Stawarz1, David Stansby5, Heli Hietala6, Justin Christophe Kasper7, Davin E Larson3, Roberto Livi8, Kelly E Korreck9, J. L. Verniero3, Michael McManus3 and the PSP FIELDS & SWEAP teams, (1)Imperial College London, Department of Physics, London, SW7, United Kingdom, (2)Imperial College London, Department of Physics, London, United Kingdom, (3)University of California Berkeley, Space Sciences Laboratory, Berkeley, CA, United States, (4)University College London, Mullard Space Science Laboratory, Dorking, United Kingdom, (5)University College London, Mullard Space Science Laboratory, London, United Kingdom, (6)Imperial College London, Physics, London, SW7, United Kingdom, (7)University of Michigan, Climate and Space Sciences and Engineering, Ann Arbor, MI, United States, (8)Space Sciences Laboratory, University of California Berkeley, Berkeley, CA, United States, (9)Smithsonian Astrophysical Observatory, Cambridge, MA, United States
Abstract:
Switchbacks in the solar wind have been observed throughout the heliosphere with increasing prominence closer to the Sun [e.g., Horbury et al. 2018]. These Alfvénic structures consist of a rapid reversal in the direction of the magnetic field as well as plasma jets with enhanced velocity over the background flow. Parker Solar Probe (PSP) observations at 35 solar radii have revealed the presence of ‘patches’ of switchbacks separated by intervals of radial fields [Bale et al. 2019; Kasper et al. 2019], likely related to their formation in the solar corona.
In this study, we fit 3D bi-Maxwellian functions to the core of proton velocity distributions measured by SPAN-Ai over PSP’s second encounter. We obtain proton core temperature anisotropy measurements for times when the distributions are not obscured by the spacecraft heatshield. We find that the perpendicular temperature, T⊥, maintains the familiar correlation with solar wind speed [e.g., Perrone et al. 2018]. In contrast, the parallel temperature, T∥, shows enhancements that correlate with the presence of ‘patches’ of Alfvénic switchbacks. We find that these patches also correspond to a deflection of the transverse flow away from the radial direction.
These results are consistent with the hypothesis that patches arise from flux tubes connected to exhaust outflows from magnetic reconnection in coronal plumes and jets. Switchbacks embedded within these patches may then form in the expanding solar wind from low-amplitude outward-propagating Alfvénic fluctuations [e.g., Squire et al. 2020]. We also discuss the possible mechanisms that may lead to the observed enhancements in T∥.
