Stream structure and coronal sources of the solar wind during the May 12th, 1997 CME

Abstract

We report on our efforts to model the ambient solar wind out to 1 AU around the time of the May 12, 1997 halo coronal mass ejection (CME) and to identify its coronal source regions. We use the simple physics and empirical based Wang–Sheeley–Arge (WSA) model driven by two different sets of updated photospheric field synoptic maps to accomplish this: daily updated maps from Mount Wilson Solar Observatory and updated SOHO/MDI maps constructed with the Schrijver et al. flux transport data assimilation algorithm. The results generated by the WSA model are then compared with the WIND satellite observations near Earth, as well as with each other. We find that the model describes the observed ambient solar wind stream structure around the time of the May 12, 1997 CME generally well, except for the ejecta itself. Our results suggest that the source of the high-speed stream that followed the CME is a coronal hole extension located south of the Sun's equator. We conclude that the northern active region associated with the May 12th CME did not play a role in the formation of the small southern coronal hole extension that produced the high-speed stream, which followed and eventually compressed the ICME from behind. Overall, this analysis suggests how the solar wind context of CME-related events can be analyzed and understood using coronal and solar wind models.