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

TL;DR

This study investigates the nature of switchback patches in the solar wind, revealing that they are associated with enhanced proton parallel temperatures and likely formed through reconnection processes in the solar corona.

Contribution

The paper provides new evidence linking switchback patches to increased proton parallel temperature and suggests a formation mechanism involving magnetic reconnection in the corona.

Findings

Switchback patches show transverse magnetic and flow deflections.

Enhanced proton parallel temperature is associated with patches.

Patches may form through reconnection processes in the solar corona.

Abstract

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. 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. 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, $T_{p,\perp}$, temperature. 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 $T_{p,\perp}$ remains relatively constant. Patches sometimes exhibit small proton and electron density enhancements. 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.