Sequential observations of flux transfer events, poleward-moving auroral forms, and polar cap patches

Abstract:

The solar wind-magnetosphere coupling often occurs in a localized and transient manner, modifying the responses of the magnetosphere-ionosphere system. Among various types of transient phenomena, one of the most common and important processes is transient dayside reconnection. This leads to the generation of flux transfer events (FTEs) and their ionospheric manifestation, poleward-moving-auroral forms (PMAFs). Decaying of PMAFs has been related to localized structures of enhanced F-region plasma density, propagating into and over the polar cap, so-called polar cap patches. Although previous studies reported a portion of this link, the driving solar wind-transient reconnection-FTEs-PMAFs, the complete sequence of these dynamic processes and full picture of the solar wind-dayside magnetopause-ionosphere coupling have rarely been reported and examined. We report the observation of solar wind-magnetosphere-ionosphere interactions using a series of FTEs observed by MMS located near the dayside magnetopause. The FTEs were observed to propagate duskward and either southward or slightly northward, as predicted under duskward and southward IMF. Near the MMS footprint, a series of PMAFs occurred almost simultaneously with those FTEs. They propagated poleward and westward, consistent with the modeled FTE propagation. The intervals between FTEs, relatively consistent with those between PMAFs, strongly suggest a one-to-one correspondence between the dayside transients and ionospheric responses. The FTEs were, however, embedded in continuous reconnection observed by MMS. Corresponding PMAFs individually occurred during persistent auroral activity recorded by an all sky imager strongly indicate that those FTEs/PMAFs resulted from the temporal modulation of the reconnection rate during continuous reconnection. With the decay of the PMAFs associated with the FTEs, patch-like plasma density enhancements were detected to form and propagate poleward and then dawnward. Propagation to the dawn was also suggested by the SuperDARN convection and GPS total electron content data. We relate the temporal variation of the driving solar-wind and magnetospheric mechanism to that of the high-latitude and polar ionospheric responses and estimate the response time.