Physics of auroral phenomena : proceedings of the 40th annual seminar, Apatity, 13-17 March, 2017 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2017. - 143 с. : ил., табл.

ТА. Kornilova and I. V. Golovchanskaya An event where periodic auroral restructuring before To is not observed by optical data is illustrated in Fig. 2. Our working hypothesis was that an apparent latitudinal motion of the phase o f oscillations always occurs inside Alfven field-lined resonance layer. However, in the case of weak events the associated field-aligned currents may be not sufficient to produce the optical effect of periodic auroral restructuring before To. 30.12.2002 Tumanny (b) a C l ) N Ои 5 Ъ ■8 j о о (С) Figure 2. The same set of data as in Fig. 1 but for substorm on 30 December 2002, as observed at Tumanny station (TUM, 65.2°, 115.9° CGM coordinates). First, as a characteristic of the ‘strength’ of event, we used the value of magnetic bay observed after To by the ground- based magnetometers, meaning that fluctuations inside a ‘strong’ Alfven resonance must spoil the conductance in the magnetospheric current sheet more readily and thus divert more of the cross-tail current into the ionosphere. While, indeed, the average value ofmagnetic bay (~ 230 nT) for 13 substorms, where there were periodic auroral restructuring before To, appeared to be somewhat larger than that (~ 186 nT) for 6 substorms lacking the auroral restructuring before To, the discrepancy was not so large. Then, a more precise analysis has been performed consisting in a direct comparison of the amplitude of Alfvenic (flapping) fluctuations in the boundary plasma sheet before To (those presumably connected to the FLR) by in situ spacecraft measurements with the presence or absence of conjugate auroral restructuring in the ionosphere. In the event o f 05 March 2008 shown in Fig. 3, the auroral restructuring before To took place (Fig. 3b) and was associated with fluctuations in the boundary plasma sheet observed by THEMIS P3 (THD) spacecraft (Fig. 3c). The amplitude of fluctuations in the magnetic Bx component was as high as 7-10 nT. The Alfvdnic (flapping) nature o f those fluctuations was previously demonstrated by Kornilov et al. [2015]. Note that the period o f auroral restructuring (~ 2-3 min) in the ionosphere (Fig. 3b) is close to the period of the field oscillations in the plasma sheet (~ 2 min at 05:57-06:04 UT, Fig. 3c). 05:20 05:40 06:00 06:20 06:40UT .J L-. I, ---------- ■- - - - T --- 10 г . , ;5 THEMTSP3 I 20 I Bx V../, : г ' -30 05-48 05:51 05:54 05:57 06:00 UT 05.03.2008 Gillam (a) a Figure 3. Original (a) and filtered (b) N-S keograms constructed by all-sky auroral observations at Gillam station £ (GILL, 66.18°, 332.78° GM coordinates) for the event o f 5 о ' March, 2008 and (c) conjugate magnetic field Bx-component ° measured by THEMIS P3 probe in the boundary plasma sheet. In Fig. 3b the P3 footprint at 110 km altitude obtained by T96 model and designed to the central meridian o f the GILL camera field of view is indicated by circle. cz 28