Multipoint in situ and ground-based observationsduring auroral intensifications

摘要

[1] Analysis of in situ and ground-based observations is performed to establish the precisetiming of observed signatures during two successive auroral activations. The first, minoractivation was interpreted as a pseudobreakup, while the second, major one was classifiedas a substorm. Timing of observations aboard four of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes situated in the plasma sheetin the tail-aligned conjunction indicates initial activity at XGSM —15 RE. Magnetic fieldvariations, tailward fast, flows, and signatures in particle behavior observed by twoTHEMIS probes in the midtail plasma sheet suggest magnetic reconnection as the sourceof the first activation. The substorm onset, detected 6 min after the pseudobreakup, wasfound to be associated with the rapid decrease of the magnetic field strength,dipolarization, and increase of plasma density and pressure, i.e., signatures of the cross-tailcurrent reduction (disruption), observed in the near-Earth plasma sheet at XGsm > —10 RE.Thus, in this case, reconnection in the midtail preceded the near-Earth current reduction.A scenario based on a model of the near-Earth breakup triggered by the fastearthward flow, generated by preceding reconnection, is proposed.