Coronal dimmings , localized regions of reduced emission in the EUV and soft X-rays , are interpreted as density depletions due to mass loss during the CME expansion .
They contain crucial information on the early evolution of CMEs low in the corona .
For 62 dimming events , characteristic parameters are derived , statistically analyzed and compared with basic flare quantities .
On average , coronal dimmings have a size of 2.15 \times 10 ^ { 10 } km ^ { 2 } , contain a total unsigned magnetic flux of 1.75 \times 10 ^ { 21 } Mx , and show a total brightness decrease of -1.91 \times 10 ^ { 6 } DN , which results in a relative decrease of \sim 60 % compared to the pre-eruption intensity level .
Their main evacuation phase lasts for \sim 50 minutes .
The dimming area , the total dimming brightness , and the total unsigned magnetic flux show the highest correlation with the flare SXR fluence ( c \gtrsim 0.7 ) .
Their corresponding time derivatives , describing the dimming dynamics , strongly correlate with the GOES flare class ( c \gtrsim 0.6 ) .
For 60 % of the events we identified core dimmings , i.e .
signatures of an erupting flux rope .
They contain 20 % of the magnetic flux covering only 5 % of the total dimming area .
Secondary dimmings map overlying fields that are stretched during the eruption and closed down by magnetic reconnection , thus adding flux to the erupting flux rope via magnetic reconnection .
This interpretation is supported by the strong correlation between the magnetic fluxes of secondary dimmings and flare reconnection fluxes ( c = 0.63 \pm 0.08 ) , the balance between positive and negative magnetic fluxes ( c = 0.83 \pm 0.04 ) within the total dimmings and the fact that for strong flares ( > M1.0 ) the reconnection and secondary dimming fluxes are roughly equal .