Substorm signatures between 10 and 30 earth radii Original Research Article

Based on about two years of Geotail data, we use a superposed epoch approach to study the average behavior of plasma and magnetic fields at different radial distances during 66 substorms in the premidnight sector. Magnetic field dipolarization is first seen inside of 16 RE around substorm onset and subsequently moves tailward at a rate of 0.4 RE/min. Fast earthward and tailward ion bulk flows in the central plasma sheet indicate that the near-Earth neutral line is first located around 21 RE, but later moves a bit tailward. About 30 min after onset, the tailward moving dipolarization front reaches the near-Earth neutral line at around 26 RE. Thereafter the near-Earth neutral line suddenly disappears beyond 31 RE. This may be the beginning of the recovery phase.