  Coronal mass ejections (CMEs) are often accompanied by coronal dimming
evident in extreme ultraviolet (EUV) and soft X-ray observations. The locations
of dimming are sometimes considered to map footpoints of the erupting flux
rope. As the emitting material expands in the corona, the decreased plasma
density leads to reduced emission observed in spectral and irradiance
measurements. Therefore, signatures of dimming may reflect properties of CMEs
in the early phase of its eruption. In this study, we analyze the event of
flare, CME, and coronal dimming on December 26, 2011. We use the data from the
Atmospheric Imaging Assembly (AIA) on Solar Dynamics Observatories (SDO) for
disk observations of the dimming, and analyze images taken by EUVI, COR1, and
COR2 onboard the Solar Terrestrial Relations Observatories to obtain the height
and velocity of the associated CMEs observed at the limb. We also measure
magnetic reconnection rate from flare observations. Dimming occurs in a few
locations next to the flare ribbons, and it is observed in multiple EUV
passbands. Rapid dimming starts after the onset of fast reconnection and CME
acceleration, and its evolution well tracks the CME height and flare
reconnection. The spatial distribution of dimming exhibits cores of deep
dimming with a rapid growth, and their light curves are approximately linearly
scaled with the CME height profile. From the dimming analysis, we infer the
process of the CME expansion, and estimate properties of the CME.
