On the physical nature of auroral breakup precursors as observed in an event on 5 March 2008

作者：Kornilov I A^*; Kornilova T A; Golovchanskaya I V

来源：Geomagnetism and Aeronomy, 2015, 55(2): 210-218.

DOI：10.1134/S0016793215020103

Using coordinated THEMIS spacecraft and all-sky imager observations, we studied an auroral breakup event on 5 March 2008, where auroral activities for 30-40 min before T (0) were all of the East-West (E-W) orientation, and found that their dynamics infers a wave process. For the event under study, there were conjunctive measurements (with 3 s time resolution) of plasma, energetic particles, magnetic B and electric E fields by four THEMIS probes, positioned approximately along the tail. The THEMIS probe measurements, bandpass-filtered in the range 12-120 s, revealed the low-frequency wave activity in the considered time interval. The out-of-phase relation between variations in the magnetic and plasma pressures, along with a positive correlation between -a,Bx/a,t and z GSM component of ion velocity (flapping), indicated the ballooning mode. Considering the similarity of the wave-like characteristics derived from ground-based auroral and THEMIS spacecraft observations, we argue that the E-W auroral features preceding onset may be related to ballooning waves propagating in the plasma sheet, their wavefronts inclined at relatively small angles to the azimuthal direction. The implications for mechanisms of substorm triggering are discussed.

• 出版日期2015-3