Plasma diagnostics of coronal dimming events

TL;DR

This study uses EUV data and DEM diagnostics to analyze plasma density and temperature changes in coronal dimming regions associated with CMEs, revealing plasma evacuation as the main cause and differences between core and secondary dimmings.

Contribution

It provides detailed plasma diagnostics of coronal dimming events, distinguishing between core and secondary regions and their plasma evolution during CMEs.

Findings

Core dimming density decreases by 50-70% within 20-30 min.

Secondary dimming density decreases by 10-45% and begins to recover after 1-2 hours.

Temperature drops are less significant than density decreases, confirming plasma evacuation.

Abstract

Coronal mass ejections (CMEs) are often associated with coronal dimmings, i.e. transient dark regions that are most distinctly observed in Extreme Ultra-violet (EUV) wavelengths. Using Atmospheric Imaging Assembly (AIA) data, we apply Differential Emission Measure (DEM) diagnostics to study the plasma characteristics of six coronal dimming events. In the core dimming region, we find a steep and impulsive decrease of density with values up to 50-70%. Five of the events also reveal an associated drop in temperature of 5-25%. The secondary dimming regions also show a distinct decrease in density, but less strong, decreasing by 10-45%. In both the core and the secondary dimming the density changes are much larger than the temperature changes, confirming that the dimming regions are mainly caused by plasma evacuation. In the core dimming, the plasma density reduces rapidly within the first 20-30 min after the flare start, and does not recover for at least 10 hrs later, whereas the secondary dimming tends to be more gradual and starts to replenish after 1-2 hrs. The pre-event temperatures are higher in the core dimming (1.7-2.6 MK) than in the secondary dimming regions (1.6-2.0 MK). Both core and secondary dimmings are best observed in the AIA 211 \AA\ and 193 \AA\ filters. These findings suggest that the core dimming corresponds to the footpoints of the erupting flux rope rooted in the AR, while the secondary dimming represents plasma from overlying coronal structures that expand during the CME eruption.