The Inconvenient Truth About Coronal Dimmings

TL;DR

This study uses high-resolution spectral imaging to analyze coronal dimmings caused by CMEs, revealing dynamic non-thermal broadening linked to Alfven waves and suggesting dimmings temporarily act as solar wind sources, impacting CME modeling.

Contribution

It provides new insights into the evolution of non-thermal line broadening during CME-driven coronal dimmings and proposes a link to Alfven wave dynamics affecting CME propagation.

Findings

Non-thermal broadening increases during dimming events.

Coronal dimmings behave like temporary solar wind sources.

Rapid thermodynamic transition may impulsively influence CME dynamics.

Abstract

We investigate the occurrence of a CME-driven coronal dimming using unique high resolution spectral images of the corona from the Hinode spacecraft. Over the course of the dimming event we observe the dynamic increase of non-thermal line broadening in the 195.12Angstrom emission line of Fe XII as the corona opens. As the corona begins to close, refill and brighten, we see a reduction of the non-thermal broadening towards the pre-eruption level. We propose that the dynamic evolution of non-thermal broadening is the result of the growth of Alfven wave amplitudes in the magnetically open rarefied dimming region, compared to the dense closed corona prior to the CME. We suggest, based on this proposition, that, as open magnetic regions, coronal dimmings must act just as coronal holes and be sources of the fast solar wind, but only temporarily. Further, we propose that such a rapid transition in the thermodynamics of the corona to a solar wind state may have an impulsive effect on the CME that initiates the observed dimming. This last point, if correct, poses a significant physical challenge to the sophistication of CME modeling and capturing the essence of the source region thermodynamics necessary to correctly ascertain CME propagation speeds, etc.