More of the Inconvenient Truth About Coronal Dimmings

TL;DR

This study uses high-resolution imaging to analyze the evolution of coronal dimmings caused by CMEs, revealing dynamic changes in non-thermal line broadening linked to magnetic and plasma conditions, supporting the idea that dimmings are transient sources of the solar wind.

Contribution

It provides detailed observational evidence of the temporal evolution of non-thermal broadening during a CME-driven coronal dimming, linking it to magnetic and plasma dynamics.

Findings

Non-thermal broadening increases during CME release.

Broadening levels reach those typical of coronal holes.

Refilling of the corona reduces non-thermal broadening.

Abstract

We continue the investigation of a CME-driven coronal dimming from December 14 2006 using unique high resolution imaging of the chromosphere and corona from the Hinode spacecraft. Over the course of the dimming event we observe the dynamic increase of non-thermal line broadening of multiple emission lines as the CME is released and the corona opens; reaching levels seen in coronal holes. As the corona begins to close, refill and brighten, we see a reduction of the non-thermal broadening towards the pre-eruption level. The dynamic evolution of non-thermal broadening is consistent with the expected change of Alfven wave amplitudes in the magnetically open rarefied dimming region, compared to the dense closed corona prior to the CME. The presented data reinforce the belief that coronal dimmings must be temporary sources of the fast solar wind. It is unclear if such a rapid transition in the thermodynamics of the corona to a solar wind state has an effect on the CME itself.