Role of poleward moving auroral forms in the dawn-dusk auroral precipitation asymmetries induced by IMF B-y

In a case study we document the detailed spatial/temporal structure of the aurora in the 0900–1500 magnetic local time (MLT) sector during an interval of steady southeast IMF orientation. Emphasis is placed on ground-based observations of structure that is often averaged out in large statistical studies. A central feature is the phenomenon of poleward moving auroral forms (PMAFs), an ionospheric manifestation of pulsed magnetopause reconnection in the form of flux transfer events, FTEs, whose evolution in both prenoon and postnoon MLTs can be monitored under similar interplanetary conditions. Differences in auroral precipitation associated with PMAFs about the noon meridian related to IMF By are documented. While the prenoon PMAFs develop in three stages spanning a latitude range of ≥500 km, the highest-latitude stage is absent in postnoon PMAFs for By \u3e 0, which, after the initial intensification, progressively fade. We suggest that this auroral precipitation asymmetry is closely related to the different field-aligned current configuration in PMAFs/prenoon and PMAFs/postnoon and the underlying plasma convection pattern. We detail the association between the high-latitude component of PMAFs in the prenoon sector (By \u3e 0) and a channel of plasma convection located in the dawnside convection cell. The latter convection channel, located in the regime of old open flux, represents an aspect of the Svalgaard-Mansurov effect which is not included in the traditional description. The auroral and plasma convection data are placed in the context of recent work on solar wind-magnetosphere interconnection topology for a southward pointing IMF with a strong By-component