In situ observations of large amplitude Alfv\'en waves heating and accelerating the solar wind

TL;DR

This study uses in situ spacecraft data to demonstrate that large amplitude Alfvén waves significantly contribute to heating and accelerating the solar wind between the Sun's corona and Venus's orbit.

Contribution

It provides direct observational evidence linking Alfvén wave damping to solar wind heating and acceleration in the inner heliosphere.

Findings

Alfvén waves are present and energetic in the inner heliosphere.

Wave damping correlates with plasma heating and acceleration.

Alfvén wave energy is sufficient to power observed solar wind dynamics.

Abstract

After leaving the Sun's corona, the solar wind continues to accelerate and cools, but more slowly than expected for a freely expanding adiabatic gas. We use in situ measurements from the Parker Solar Probe and Solar Orbiter spacecrafts to investigate a stream of solar wind as it traverses the inner heliosphere. The observations show heating and acceleration of the the plasma between the outer edge of the corona and near the orbit of Venus, in connection to the presence of large amplitude Alfv\'en waves. Alfv\'en waves are perturbations in the interplanetary magnetic field that transport energy. Our calculations show the damping and mechanical work performed by the Alfv\'en waves is sufficient to power the heating and acceleration of the fast solar wind in the inner heliosphere.