Two spacecraft observations of a reconnection pulse during an auroral breakup

Abstract

At 1130 UT on November 28, 1995, two spacecraft, Interball‐Tail and Geotail, were in a favorable position to study the plasma sheet activity and an auroral breakup observed on the ground near the spacecraft ionospheric footpoints. Both spacecraft were near the neutral sheet, and they were nearly aligned along the magnetic meridian. During the auroral breakup observed at the equatorward half of the auroral oval (also registered as an AKR burst at Interball) both spacecraft simultaneously detected signatures of a reconnection pulse: The earthward plasma streaming and magnetic field dipolarization were observed at 12 RE at Interball, while the tailward energetic ion beam, then the tailward flow and the passage of a plasmoid were observed at 28 RE at Geotail. This pulse seem to proceed inside of the plasma sheet closed field lines, in the region of small (∼1 nT) background magnetic field at the neutral sheet. At Interball position the onset of fast earthward ion flow, likely initiated by the reconnection pulse, was followed by other manifestations (dipolarization, enhancements of the magnetic turbulence and the energetic particle flux, the intensification of field‐aligned currents). Auroral observations showed initial brightening delayed an approximately l min after the commencement of the reconnection pulse. The auroral intensification was not accompanied by a significant magnetic disturbance on the ground, and therefore the event can be classified as the pseudobreakup. We estimate magnetic flux transport characteristics and possible location of the onset region in the plasma sheet. We conclude that observations during this event are consistent with the initiation of an auroral breakup by some disturbance (e.g., Alfven wave) generated by the reconnection pulse that commenced in the neutral sheet at ∼15 RE distance.