Magnetic reconnection as a mechanism to produce multiple protonpopulations and beams locally in the solar wind

TL;DR

This study demonstrates that magnetic reconnection occurring locally in the solar wind can produce multiple proton populations and beams, highlighting a mechanism previously less emphasized compared to coronal processes.

Contribution

It provides observational evidence from Solar Orbiter that local magnetic reconnection in the solar wind generates multiple proton populations and beams, expanding understanding of their origins.

Findings

At least 6 reconnection sites associated with proton populations and beams identified.

Reconnection events constitute about 2% of measured proton distribution functions.

Reconnection at switchback boundaries also produces proton beams.

Abstract

Context. Spacecraft observations early revealed frequent multiple proton populations in the solar wind. Decades of research on their origin have focused on processes such as magnetic reconnection in the low corona and wave-particle interactions in the corona and locally in the solar wind.Aims.This study aims to highlight that multiple proton populations and beams are also produced by magnetic reconnection occurring locally in the solar wind. Methods. We use high resolution Solar Orbiter proton velocity distribution function measurements, complemented by electron and magnetic field data, to analyze the association of multiple proton populations and beams with magnetic reconnection during a period of slow Alfv\'enic solar wind on 16 July 2020. Results. At least 6 reconnecting current sheets with associated multiple proton populations and beams, including a case of magnetic reconnection at a switchback boundary, are found during this day. This represents 2% of the measured distribution functions. We discuss how this proportion may be underestimated, and how it may depend on solar wind type and distance from the Sun. Conclusions. Although suggesting a likely small contribution, but which remains to be quantitatively assessed, Solar Orbiter observations show that magnetic reconnection must be considered as one of the mechanisms that produce multiple proton populations and beams locally in the solar wind.