Observations of an active thin current sheet
Dandouras, I.; Lucek, E.; Fazakerley, A. N.; André, M.; Klecker, B.; Vaivads, A.; Owen, C. J.; Nakamura, R.; Sergeev, V. A.; Baumjohann, W.; Amm, O.; Runov, A.; Frey, H.; Alexeev, I.
Austria, United States, Russia, Finland, United Kingdom, Sweden, France, Germany
Abstract
We analyze observations of magnetotail current sheet dynamics during a substorm between 2330 and 2400 UT on 28 August 2005 when Cluster was in the plasma sheet at [-17.2, -4.49, 0.03] RE (GSM) with the foot points near the IMAGE ground-based network. Observations from the Cluster spacecraft, ground-based magnetometers, and the IMAGE satellite showed that the substorm started in a localized region near midnight, expanding azimuthally. A thin current sheet with a thickness of less than 900 km and current density of about 30 nA/m2 was observed during 5 min around the substorm onset. The thinning of the current sheet was accompanied by tailward plasma flow at a velocity of -700 km/s and subsequent reversal to earthward flow at Vx ≈ 500 km/s coinciding with a Bz turning from -5 to +10 nT. The analysis of magnetic and electric fields behavior and particle distributions reveals signatures of impulsive (with ∼1 min timescale) activations of the thin current sheet. These observations were interpreted in the framework of transient reconnection, although the data analysis reveals serious disagreements with the classical 2.5-D X line model.