The inconvenient truth about coronal dimmings

We investigate the occurrence of a coronal mass ejection (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 nonthermal line broadening in the 195.12 Å emission line of Fe XII as the corona opens. As the corona begins to close, refill and brighten, we see a reduction of the nonthermal broadening toward the pre-eruption level. We propose that the dynamic evolution of the nonthermal broadening is the result of the growth of Alfvén 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.