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.

Change in the spectralfeatures o fQP emissions due to poleward magnetic bay The AMPERE data (Fig. 3), based on simultaneous measurements by the globally distributed 66 low-altitude commercial satellites, showed the development of the magnetic bay-like disturbances and field aligned currents (FAC) at the high latitudes, aligned from Svalbard to the East. It is seen (upper part of Fig. 3) that the centre of the substorm was located far to the North-East from KAN. The Dixon station located near the centre of this substorm recorded the magnetic bay (do not show here) with the amplitude of ~250 nT. Dynamic spectra of the considered emissions. Before and after the substorm (Fig. 2) the QP emissions (Fig. 4) demonstrated the peculiar dynamic spectral structure of the repeated long-lasting (up to two minutes) noise bursts with quickly rising frequency up to ~ 5.5 kHz. A strong ionospheric frequency cut-off at —1.7 kHz is seen. In Fig. 4, one can see that the high frequency part (2.5 - 5.5 kHz) of QPs arrived from the E-W direction (green-colour in the scale of the wave arrival direction distribution), but the low frequency part (1.7 - 2.5 kHz) of QPs - from the N-S direction (red colour). However, the both parts belong to the same element of the considered emissions. There is the question: how the different parts of the same burst could come from the different directions? At 19.25-19.37 UT, i.e. during the substorm (Fig. 2), the low-frequency structure of the emissions suddenly changed and the wave power also occurred at the frequencies lower than the ionospheric frequency cut-off (1.7 kHz). These low-frequency waves arrived at some deviation from the meridian direction. It is clearly seen in Fig. 4. The waves with f < 1.7 kHz were observed only during the poleward substonn and disappeared after the end of substorm. The fine dynamic spectral feature of the considered emissions is presented in Fig. 5, both in 10 min and 2 min time scale. In the 10-min time scale, the signals look like “candles” with a low-frequency “front foot”. However, in the 2- min scale, one can see that each individual element of QP emissions consists of a cluster of two parts of increasing frequency emissions about 1 min duration which separated by the frequency of -2.5 kHz. The small dispersive emissions (“front foot”) in the frequency range of 1.7-2.5 kHz continued as strong dispersive waves in the frequency range o f 2.5-5.5 kHz (“candle”). Both parts of the waves demonstrate the fine periodic modulation structure with approximately 3 s periodicities as it was previously shown in [Manninen et al., 2014]. MDecJOll Figure 4. The QP spectrogram (upper plot) and Figure 5. Fine structure of QP emissions showed in 10 min the wave arrival direction at different frequencies (upper plot) and 2 min (bottom plot) time scales. (bottom plot) at 19.20-19.50 UT. The polar substorm completely changed the dynamic structure of QPs (Fig. 6), but the arrival direction of the different frequency parts did not change and showed the same behaviour as before substorm. The upper plots in Fig. 6 demonstrate five consecutive 2-min spectrograms during the considered poleward substorm. One can see that during the maximum of the substorm (19.35-19.45 UT), the conjunction of the “candles” and “front foots” destroyed, and three “candles” occurred without their “front foots”. It is clearly seen in Fig. 4 too. The construction o f the magnetic field vectors (Fig. 7a) at IMAGE station chain showed the existence o f the counter-clockwise magnetic vortex at the polar geomagnetic latitudes (> 70°) which could be interpreted as the poleward increasing o f the upward FACs, i.e. soft electron precipitation. The vortex onset was accompanied by the burst of Pi3 type geomagnetic pulsations (Fig. 7b) with the amplitude maximum at SOR station (-67°), i.e. northward from KAN. 51