The Mean Temperatures of CME-Related Dimming Masses

Abstract

AbstractSun-as-a-star EUV spectroscopy from EVE (the Extreme-ultraviolet Variability Experiment, on board SDO, the Solar Dynamics Observatory) frequently shows striking irradiance reductions following major solar flares. These coincide with dimming events as seen in EUV and X-ray images, involving the evacuation of large volumes of the corona by the associated coronal mass ejections. The EVE view of the dimming process is precise and quantitative, whereas difference imaging in the EUV reveals the structures to be full of complicated detail due most likely to unrelated activity. We have studied a sample of 11 events, mostly GOES X-class flares, all of which were associated with coronal mass ejections. For a set of nine lines of Fe ions at stages viii – xiii, corresponding to nominal peak formation temperatures below $\log (T/\mathrm{K}) = 6.3$ log ( T / K ) = 6.3 , we have compared the emission-measure-weighted temperature of the preflare global corona and that of the dimming mass, defined by the deficit at the time of greatest dimming. We find similar temperatures by this measure, but with a distinctly narrower variation in the preflare samples. For higher ionization states, weak emission commonly appears during the dimming intervals, consistent with residual late-phase flare development. The dimming depths do not appear to correlate with the preflare state of the global corona.