Photospheric magnetic field observations during the May 12, 1997 CME and their implications for modeling that event

Flares and Coronal Mass Ejections (CMEs) are two major manifestations of solar activity displaying eruptive releases of energy but on significantly different spatial scales. Although the relationship between flares and CMEs is still controversial, it is generally believed that they are magnetically driven. The energy released during these eruptions is suggested to be originally stored in the stressed magnetic fields in the solar atmosphere. It is thus expected that magnetic field changes will occur during eruptive events. In this paper, we present evidence of changes in both small-scale and large-scale magnetic fields during the 1997 May 12 flare/CME, an event selected for modeling and detailed analysis by SHINE, CISM and MURI working groups. The small-scale changes are indicated by magnetic shear calculated from the photospheric fields of the active region. The large-scale changes are inferred from a modeled coronal magnetic field, computed from the observed photospheric magnetic field. The latter result implies that the magnetic fields calculated from field observations can reflect transient-related variations. This study suggests that observation-based force-free-field models of the active region fields, and potential field models of the large-scale fields, may provide the necessary configurations to initiate or drive realistic MHD models of flares and CMEs.