Spectroscopic analysis of interaction between an EIT wave and a coronal upflow region

TL;DR

This study uses spectroscopic data to analyze how an EIT wave interacts with a nearby upflow region, revealing changes in plasma velocities and magnetic field orientation during the wave's passage.

Contribution

It provides new spectroscopic evidence of plasma dynamics and magnetic field changes during an EIT wave interaction, supporting the field-line stretching model.

Findings

Weak blueshift observed in wave front plasma lines

Sudden decrease in upflow and non-thermal velocities after wave passage

Indications of magnetic field reorientation during the interaction

Abstract

We report a spectroscopic analysis of an EIT wave event that occurred in active region 11081 on 2010 June 12 and was associated with an M2.0 class flare. The wave propagated near circularly. The south-eastern part of the wave front passed over an upflow region nearby a magnetic bipole. Using EIS raster observations for this region, we studied the properties of plasma dynamics in the wave front, as well as the interaction between the wave and the upflow region. We found a weak blueshift for the Fe XII {\lambda}195.12 and Fe XIII {\lambda}202.04 lines in the wave front. The local velocity along the solar surface, which is deduced from the line of sight velocity in the wave front and the projection effect, is much lower than the typical propagation speed of the wave. A more interesting finding is that the upflow and non-thermal velocities in the upflow region are suddenly diminished after the transit of the wave front. This implies a significant change of magnetic field orientation when the wave passed. As the lines in the upflow region are redirected, the velocity along the line of sight is diminished as a result. We suggest that this scenario is more in accordance with what was proposed in the field-line stretching model of EIT waves.