ESA Science & Technology - Study of near-Earth reconnection events with Cluster and Double Star

Publication date: 06 June 2008

Authors: Sergeev, V. et al.

Journal: J. Geophys. Res.
Volume: 113
Issue: A07
ID: A07S36
Year: 2008

Copyright: American Geophysical Union

Observations made by a unique constellation of Cluster (at 14-16 R_E), TC2, Goes10, and LANL spacecraft (near 6.6 R_E) have allowed us to study the details of three reconnection events in the middle of a thick plasma sheet with the reconnection X-line located unusually close to Earth (10-12 R_E). We use mapping along field lines with magnetospheric models adapted to magnetic field observations to confirm that the reconnection region mapped onto localized auroral brightenings. Using simultaneous observations in the inflow and outflow regions, we describe an encounter with a localized tailward Alfvénic jet produced by a short isolated reconnection pulse. A good correlation between intense E and ion [BV] indicates that the concurrent strong turbulence could not destroy the frozen-in ion behavior in the reconnection outflow. We find that a steady quadrupole-like distribution of the magnetic B_y component in the turbulent reconnection outflow extended far beyond the ion diffusion region and existed for several minutes. We demonstrate an apparent V_x flow reversal, formed owing to the reappearance (switch-on) of reconnection at another location, rather than to a continuous motion of the active X-line. Using the Liouville mapping technique, we show that the acceleration of outflow electrons, after the particles passed a potential drop of 180 V, is consistent with Fermi/betatron acceleration. We also suggest another interpretation of the energetic particle bursts at the onsets, to emphasize the role of seed population and explain the sudden burst as a consequence of changing magnetic topology.