Automated Lasco Cme Catalog for Solar Cycle 23 : Are Cmes Scale Invariant ?

In this paper we present the first automatically constructed LASCO CME catalog, a result of the application of the Computer Aided CME Tracking software (CACTus) on the LASCO archive during the interval September 1997-January 2007. We have studied the CME characteristics and have compared them with similar results obtained by manual detection (CDAW CME catalog). On average CACTus detects less than 2 events per day during solar minimum up to 8 events during maximum, nearly half of them being narrow (< 20 •). Assuming a correction factor, we find that the CACTus CME rate is surprisingly consistent with CME rates found during the past 30 years. The CACTus statistics show that small scale outflow is ubiquitously observed in the outer corona. The majority of CACTus-only events are narrow transients related to previous CME activity or to intensity variations in the slow solar wind, reflecting its turbulent nature. A significant fraction (about 15%) of CACTus-only events were identified as independent events, thus not related to other CME activity. The CACTus CME width distribution is essentially scale invariant in angular span over a range of scales from 20 to 120 • while previous catalogues present a broad maximum around 30 •. The possibility that the size of coronal mass outflows follow a power law distribution could indicate that no typical CME size exists, i.e. that the narrow transients are not different from the larger well-defined CMEs. In this paper we discuss an attempt to quantify the detection of coronal mass ejections (CMEs). Coronal mass ejections (CMEs) are episodic expulsions of mass and magnetic field from the solar corona into the interplane-tary medium. A classical CME carries away some 10 15 g of coronal mass and can liberate energies of 10 23 − 10 25 J (Howard et al. 1985; Vourlidas et al. 2002). In broad band white-light coronagraphic images CMEs are seen as bright features moving radially outward. Building a CME catalog basically means listing all occurrences of events, defined as CMEs. CMEs can be very bright and often show evidence of magnetic structure (e.g. twisted flux-rope), but sometimes, no discernible structure is present or the intensity enhancement is only very weak compared to the background corona (e.g. due to projection effects), which makes it very hard to detect and characterize them. Application of the automated CME detection software on the LASCO archive (see next section for a description of the Software) …