Magnetic Source Region Characteristics Influencing the Velocity of Solar Eruptions in the Corona

The velocity of coronal mass ejections (CMEs) is one of the primary parameters determining their potential geoeffectiveness. The great majority of very fast CMEs receive their main acceleration already in the corona. We study the magnetic source region structure for a complete sample of 15 very fast CMEs (v > 1500 km/s) during 2000-2006, originating within 30 deg from central meridian and find a correlation between CME speed and the decay index profile of the coronal field estimated by a PFSS extrapolation. Such a correlation is not found for a comparison sample of slower CMEs. We also study how the decay index profile is related to the structure of the photospheric field distribution. This is complemented by a parametric simulation study of flux rope eruptions using the analytic Titov-Demoulin active-region model for simple bipolar and quadrupolar source regions, which provide simple relationships between the photospheric field distribution and the coronal decay index profile. Very fast, moderate-velocity, and even confined eruptions are found. Detailed, data-constrained MHD modeling of a very fast and a relatively slow CME, including a comparison of their source region characteristics, will also be presented. Support by NSF and NASA's LWS program is acknowledged.