Sun to 1 AU propagation and evolution of a slow streamer-blowout coronal mass ejection

We present a comprehensive analysis of the evolution of the classic, slow streamer blowout CME of 1 June 2008 observed by the STEREO twin spacecraft to infer relevant properties of the pre-eruption source region which includes a substantial portion of the coronal helmet streamer belt. The CME was directed similar to 40 degrees East of the Sun-Earth line and the Heliospheric Imager observations are consistent with the CME propagating essentially radially to 1 AU. The elongation-time J-map constructed from the STEREO-A HI images tracks the arrival of two density peaks that bound the magnetic flux rope ICME seen at STEREO-B on 6 June 2008. From the STEREO-A elongation-time plots we measure the ICME flux rope radial size R-c(t) and find it well approximated by the constant expansion value V-exp = 24.5 km/s obtained from the STEREO-B declining velocity profile within the magnetic cloud. The flux rope spatial orientation, determined by forward modeling fits to the STEREO COR2 and HI1 data, approaches the observed 1 AU flux rope orientation and suggests large-scale rotation during propagation, as predicted by recent numerical simulations. We compare the ICME flux content to the PFSS model coronal field for Carrington Rotation 2070 and find sufficient streamer belt flux to account for the observed ICME poloidal/twist flux if reconnection during CME initiation process is responsible for the conversion of overlying field into the flux rope twist component in the standard fashion. However, the PFSS model field cannot account for the ICME toroidal/axial flux component. We estimate the field strength of the pre-eruption sheared/axial component in the low corona and the timescales required to accumulate this energized pre-eruption configuration via differential rotation and flux cancelation by supergranular diffusion at the polarity inversion line. We show that both mechanisms are capable of generating the desired shear component over time periods of roughly 1-2 months. We discuss the implications for slow streamer-blowout CMEs arising as a natural consequence of the corona's re-adjustment to the long term evolutionary driving of the photospheric fields.