Metis Observations of Alfv\'{e}nic Outflows Driven by Interchange Reconnection in a Pseudostreamer

TL;DR

This paper reports on Metis observations of Alfvénic outflows from a pseudostreamer, revealing helical structures likely caused by interchange reconnection and nonlinear torsional Alfvén waves, with results consistent with MHD simulations.

Contribution

First detailed observation of Alfvénic outflows driven by interchange reconnection in a pseudostreamer using Metis data, linking observations with MHD simulations.

Findings

Helical structures observed up to 3 solar radii.

Helix inclination decreases with height.

Similarity between observed structures and MHD simulation images.

Abstract

This study presents observations of a large pseudostreamer solar eruption and, in particular, the post-eruption relaxation phase, as captured by Metis onboard the Solar Orbiter on October 12, 2022, during its perihelion passage. Utilizing total brightness data, we observe the outward propagation of helical features up to 3 solar radii along a radial column that appears to correspond to the stalk of the pseudostreamer. The helical structures persisted for more than 3 hours following a jet-like coronal mass ejection associated with a polar crown prominence eruption. A notable trend is revealed: the inclination of these features decreases as their polar angle and height increase. Additionally, we measured their helix pitch. Despite a 2-minute time cadence limiting direct correspondence among filamentary structures in consecutive frames, we find that the Metis helical structure may be interpreted as a consequence of twist (nonlinear torsional Alfv\'{e}n waves) and plasma liberated by interchange reconnection. A comparison was performed of the helix parameters as outlined by fine-scale outflow features with those obtained from synthetic white-light images derived from the high-resolution magnetohydrodynamics simulation of interchange reconnection in a pseudostreamer topology by Wyper et al. (2022). A remarkable similarity between the simulation-derived images and the observations was found. We conjecture that these Metis observations may represent the upper end in spatial and energy scale of the interchange reconnection process that has been proposed recently as the origin of the Alfv\'{e}nic solar wind.