Physics of auroral phenomena : proceedings of the 35th Annual seminar, Apatity, 28 Februaru – 02 March, 2012 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2012. - 187 с. : ил., табл.

J. Manninen et al. After ~05.15 UT, the wave polarization gradually turned to a strong right-hand direction, which can indicate that the ionospheric exit point of wave was nearly overhead. 11-13 APR 2011 Fig-1 Solar wind and IMF data In the previous day (11 Apr. at -16 UT) the very high solar wind dynamic pressure (up to 14 nPa) was observed and strongly compressed the magnetosphere. The result of the analysis of the wave arrival direction is presented in Fig.2 (bottom panel). The angles were determined as the direction of the minor axes of the polarization ellipses, which makes it possible to determine only the direction, but not the vector of arrival of the waves. This means that it can be argued that the waves came, for example, from the north-south direction, but it remains unknown whether the waves came from the north or the south. It is seen that the waves arrived mostly from the north-south direction (the angles are <~60° and >~140°). The continuous emissions with arrival angle ~ 130° are the industrial power lines signals. It is seen that and left-hand (L) polarized waves, observed at ~04-05 UT, came from South or from Nord while the right-hand (R) ones at -05-06 UT came from both directions. 2. In the discussed time interval (04-06 UT) there were no strong magnetic substorms (Fig.3), however, at -05 UT the growth phase of substorm started at the night side (Fig.4). The magnetic field lines started to stretch in the tail. At that time the hiss polarization and the arrival angles changed (Fig. 2). 3. The considered hiss burst was accompanied by geomagnetic Pc4 pulsation observed at Scandinavian IMAGE stations (Fig.5). The pulsations demonstrated the resonant nature. The first pulsation burst was observed in the time of the left-hand polarized hiss and the second one - in the time of the right-hand polarized hiss. It is seen that both pulsation bursts modulated the hiss amplitude. The spectral analysis of pulsations (Fig. 6 ) showed that the pulsations can be classificated as Pc4 type, but the wave spectra during the first and the second bursts were different. The strongest maximum (12 mHz) in the first wave packet spectrum was observed at the geomagnetic latitudes -57-59° (MEK-NUR) and in the second packet, the maximum shifted to -10.5 mHz, and it was observed at the same area with strongest magnetude at HAN (58.6°). The second maximum at 9 mHz, recorded in botn bursts, also shifted to higher latitude (from SOD to KEV). That can be a result or the shift of the resonant field lines to the higher latitudes. Total 12 APRIL 2011 KAN 04 05 UT 06 07 Fig.2. Spectrogram of VLF hiss: the upper panel - the total power; the middle ones - the power of the right-hand (R) and left-hand (L) polarized wave power; the bottom panel - the variation of the wave arrival angle. 68