Observation of repeated intense near-Earth reconnection on closed field lines with Cluster, Double Star, and other spacecraft

Abstract

We report strong repeated magnetic reconnection pulses that occurred deep inside closed plasma sheet flux tubes at r ≤ 14Re. They have been observed with a fortuitous spacecraft constellation during three consecutive turbulent magnetic dipolarizations, accompanied by localized auroral brightenings near the equatorward edge of a wide auroral oval. The reconnection separatrix was mapped to ∼64° CGLat in the ionosphere, where a very energetic and narrow energy-dispersed ion injection with unusually steep dispersion slope was observed. Reconstruction of the reconnection rate from magnetic waveforms at Cluster provided a reconnection pulse duration (∼1 min) and peak strength (ER ∼ 8 mV/m) consistent with direct observations in the reconnection outflow region. The magnetic activity was rather weak, although the concurrent solar wind flow pressure was above the norm. We suggest that near-Earth reconnection events may be a phenomenon more frequent than generally thought. We also confirm that reconnection and the growth of strong turbulence in the near tail are strongly coupled together in near-Earth reconnection events. Copyright 2007 by the American Geophysical Union.