On Streamer-Blowout CMEs That Aren’t Really CMEs: How the Corona Makes Slow Flux Rope-Like ICMEs Without an Explosive Release of Free Magnetic Energy

Abstract:

We present a 3D numerical MHD simulation of the 2008 Jun 2 gradual streamer blowout CME that had virtually no identifiable low coronal signatures. We energize the field by simple footpoint shearing along the source region’s polarity inversion line and model the background solar wind structure using an ~2MK isothermal wind and a low-order potential field source surface representation of the CR2070 synoptic magnetogram. Our results show that the CME “initiation” is obtained by slowly disrupting the quasi-steady-state configuration of the helmet streamer, resulting in the standard eruptive flare picture that ejects the sheared/twisted fields -- very slowly and on a relatively large scale -- with virtually no decrease in the global magnetic energy. We obtain a relatively slow CME eruption of order the background solar wind speed (Vcme ~ 300 km/s by 15 Rs). We argue that these very slow, expansion-driven “eruptions” are merely the natural and gradual response of the large-scale corona to the accumulation of global-scale stress (e.g. differential rotation). We present comparisons of the CME propagation through the corona (≤15Rs) in synthetic white-light images derived from the simulation density structure with multi-spacecraft coronagraph data from STEREO/SECCHI and SOHO/LASCO. We show a favorable comparison between the simulation’s ICME flux rope structure with the in situ STEREO observations.