A Method for Separating Coronal Mass Ejections from the Quiescent Corona

A method for separating coronal mass ejections (CMEs) from the quiescent corona in white-light coronagraph images is presented. Such a separation allows the study of CME structure, as well as enabling a study of the quiescent coronal structure, without contamination by the CME. The fact that the large-scale quiescent corona is very close to radial, whilst CMEs are highly non-radial, enables the separation of the two components. The method is applied to Large Angle Spectrometric Coronagraph/Solar and Heliospheric Observatory C2 and C3 observations, and is successful in revealing CME signal, faint CMEs and blobs, and dark rarefactions within a CME. The success of the separation is tested at solar minimum, a time when streamers are in general most non-radial. The technique is also compared to other commonly used methods. The separation method enables (1) the study of extremely faint CME structure, down to almost the noise level of the coronagraphs, (2) paves the way for automated categorization of CME internal structure, and (3) provides a cleaner basis for tomography of the quiescent corona, without contamination from CMEs.