A Study of the Different classes of Poleward-Moving Auroral Forms

Abstract:

During periods when the z-component of the interplanetary magnetic field (IMF) becomes negative, the dayside auroral oval moves equatorward [Feldstein and Starkov, 1967; Horrwitz and Akasofu, 1977]. During these expansion periods poleward-auroral moving forms (PMAFs) are observed. PMAFs are also observed during periods when the auroral oval is expanded. PMAFs are not observed when the dayside auroral oval moves poleward of 79° [Lockwood et al., 1989]. Past studies of PMAFs show that they drift poleward and fade [Vorobjev et al., 1975; Horwitz and Akasofu, 1977; Sandholt et al., 1986, 1989, 1990; Rairden and Mende, 1989; Lockwood, 1991], rebrighten as they drift into the polar cap [Fasel et al., 1992, 1994; Fasel, 1995], or rebrighten and slow down while moving into the polar cap, eventually stopping while maintaining their luminosity at least 10 minutes [Fasel, 1995; Fasel et al., 1995]. Fasel [1995] classified these three types of PMAFs as PMAF1, PMAF2, PMAF3 events, respectively.

This study looks at the three classes of PMAF events. The study will show the brightening histories of the PMAF events and their evolution as they move into the polar cap. PMAF1 events usually do not drift as far poleward as PMAF2 and PMAF3 events. The lifetime of PMAF1 events are shorter than those of PMAF2 and PMAF3 events. At least two rebrightenings are observed in PMAF2 and PMAF3 events as they drift into the polar cap.