Observation of repeated intense near-Earth reconnection on closed field lines with Cluster, Double Star, and other spacecraft
Sauvaud, J. -A.; Zhang, T. L.; Glassmeier, K. -H.; Lucek, E.; Penz, T.; Nakamura, R.; Baumjohann, W.; Cao, J. B.; Sergeev, V.; Runov, A.; Daly, P.; Angelopoulos, V.; Frey, H.; Kubyshkina, M.; Ivanova, V.; Singer, H.; Semenov, V.
Russia, Austria, Germany, United States, France, China, United Kingdom
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 (E R ∼ 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.