Modeling the formation and evolution of solar wind microstreams: from coronal plumes to propagating Alfv\'enic velocity spikes

TL;DR

This study uses high-resolution MHD simulations to explore how magnetic reconnection and plasmoid formation in the solar corona lead to microstreams characterized by velocity spikes and magnetic switchbacks in the solar wind.

Contribution

It demonstrates the formation of microstreams and velocity spikes from magnetic reconnection processes in the corona using high-resolution 2.5D MHD modeling, linking coronal jets to solar wind microstructures.

Findings

Microstreams last several hours with velocity increases of about 100 km/s.

Velocity spikes occur periodically at roughly 19-minute intervals.

Simulated properties match in-situ measurements by Parker Solar Probe.

Abstract

We investigate the origin of mesoscale structures in the solar wind called microstreams defined as enhancements in solar wind speed and temperature that last several hours. They were first clearly detected in Helios and Ulysses solar wind data and are now omnipresent in the "young" solar wind measured by Parker Solar Probe and Solar Orbiter. These recent data reveal that microstreams transport a profusion of Alfv\'enic perturbations in the form of velocity spikes and magnetic switchbacks. In this study we use a very high-resolution 2.5 MHD model of the corona and the solar wind to simulate the emergence of magnetic bipoles interacting with the pre-existing ambient corona and the creation of jets that become microstreams propagating in the solar wind. Our high-resolution simulations reach sufficiently high Lundquist numbers to capture the tearing mode instability that develops in the reconnection region and produces plasmo\"ids released with the jet into the solar wind. Our domain runs from the lower corona to 20 Rs, this allows us to track the formation process of plasmo\"ids and their evolution into Alfv\'enic velocity spikes. We obtain perturbed solar wind flows lasting several hours with velocity spikes occurring at characteristic periodicities of about 19 minutes. We retrieve several properties of microstreams measured in the pristine solar wind by Parker Solar Probe, namely an increase in wind velocity of about 100 km/s during the streams passage together with superposed velocity spikes of also about 100 km/s released into the solar wind.