Drifting airglow patches in relation to tail reconnection

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Abstract
In this study we present optical ground‐based signatures of drifting airglow patches in the polar ionospheric F‐layer, in the evening/nighttime MLT sector. The patches were observed under predominately IMF BZ < 0, IMF BY > 0 conditions, which are favorable for high‐density sunlit plasma to be entrained into the polar cap with the large afternoon cell in the northern hemisphere. The patch morphology, such as altitude, meridional convection speed, and repetition rate was investigated using a meridian scanning photometer, and put into the context of activity changes in the auroral substorm. It was found that the meridional patch speed was modulated by the ongoing substorms, and that the patches crossed the open/closed field line boundary (OCB), even during late recovery, and subsequent growth phase. We take this as an indication of ongoing tail reconnection, and we therefore propose that the patches can be used as a tracer for tail reconnection when they cross the OCB and enter the nighttime auroral oval.

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