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We study the coronal dimming caused by the fast halo CME (deprojected speed v = 1250 km s−1) associated with the C3.7 two-ribbon flare on 2012 September 27, using Hinode/EIS spectroscopy and Solar Dynamics Observatory (SDO)/AIA Differential Emission Measure (DEM) analysis. The event reveals bipolar core dimmings encompassed by hook-shaped flare ribbons located at the ends of the flare-related polarity inversion line, and marking the footpoints of the erupting filament. In coronal emission lines of log T [K] = 5.8–6.3, distinct double-component spectra indicative of the superposition of a stationary and a fast upflowing plasma component with velocities up to 130 km s−1 are observed at these regions, which were mapped by the scanning EIS slit close in time to their impulsive dimming onset. The outflowing plasma component is found to be of the same order as and even dominant over the stationary one, with electron densities in the upflowing component of 2 × 109 cm−3 at log T [K] = 6.2. The density evolution in core-dimming regions derived from SDO/AIA DEM analysis reveals impulsive reductions by 40%–50% within ≲10 minutes and remains at these reduced levels for hours. The mass-loss rate derived from the EIS spectroscopy in the dimming regions is of the same order as the mass increase rate observed in the associated white-light CME (1 × 1012 g s−1), indicating that the CME mass increase in the coronagraphic field of view results from plasma flows from below and not from material piled up ahead of the outward-moving and expanding CME front. [ABSTRACT FROM AUTHOR]

Coronal mass ejections are often associated with coronal dimmings, i.e., transient dark regions that are most distinctly observed in Extreme Ultra-violet wavelengths. Using Atmospheric Imaging Assembly (AIA) data, we apply Differential Emission Measure 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 minutes after the flare start and does not recover for at least 10 hr later, whereas the secondary dimming tends to be more gradual and starts to replenish after 1–2 hr. 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 and 193 Å 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. [ABSTRACT FROM AUTHOR]