The May 13, 2005 eruption: Observations, data analysis and interpretation

In this study, we present detailed description and analysis of the May 13, 2005 eruption, the corresponding coronal mass ejection (CME) and intense geomagnetic storm observed near the Earth on May 15, 2005. This isolated two-ribbon M8.0 flare and the very fast CME occurred in a relatively simple magnetic configuration during a quiet period of solar activity, which enabled us to reliably associate the solar surface event with its counterpart observed in the Earth magnetosphere. In our study, we utilized (i) various tools to analyze a multi-wavelength data set that includes ground (BBSO vector magnetograms, Hα) and space (SOHO, TRACE, RHESSI and ACE) based data; (ii) linear force-free modeling to reconstruct the coronal field above the active region and (iii) erupting flux rope (EFR) model to simulate a near-Sun halo CME and a near-Earth interplanetary CME (ICME). Our findings indicate that persisting converging and shearing motions near the main neutral line could lead to the formation of twisted core fields and eventually their eruption via reconnection. In the discussed scenario, the in situ formed erupting loop can be observed as a magnetic cloud (MC) when it reaches the Earth. The EFR model was able to produce both a model halo CME and ICME providing a good global match to the overall timing and components of the magnetic field in the observed MC. The orientation of the model ICME and the sense of the twist, inferred from the EFR model, agree well with the orientation and the magnetic helicity found in the source active region.