Physics of auroral phenomena : proceedings of the 34th Annual seminar, Apatity, 01 - 04 March, 2011 / [ed.: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 231 с. : ил.

KB. Belakhovsky et al. 2. Data The data from VHF EISCAT radar is used in this study complemented by the data from IMAGE magnetometer network. The data from IRIS imaging riometer is used for monitoring precipitation of energetic electrons. The data from the LANL-01 geostationary spacecraft is used for monitoring trapped particles. The parameters of the solar wind are taken from the OMNI database. 3. Observations The event 29 April 2001 was considered when the geomagnetic Pc5 pulsations were observed at the latitudinal profile of magnetic observatories of the IMAGE network. During the event the solar wind velocity was 650 km/s, the solar wind density was 6 rrf3, and Bz-component of IMF was about -5 nT. The SYM-H index value was about -40 nT. The magnetic activity was not large during this day. Figure 1 presents the Pc5 pulsations observed at the meridian profile SOD-IVA-BJN-HOP The maximum amplitude of geomagnetic Pc5 pulsations was observed at HOP station. The spectral analyze shows the decrease of the frequency of geomagnetic Pc5 with increase of the geomagnetic latitude. At the lower-latitude stations SOD and IVA the spectral maximum was observed approximately at the frequency o f 2.9 mHz, whereas at the higher-latitude stations 5J7Vand HOP the spectral maximum was observed at the frequency of 1.5 mHz. The latitudinal distance between the lower- and higher- latitude stations (IVA and BIN) is about 4° of geomagnetic latitude. So that, there is an abrupt change of the resonant frequency observed between these stations. The decrease of frequency of geomagnetic Pc5 pulsations is indeed seen from the visual inspection of the magnetograms. There was observed one more manifestation of the resonance properties of the pulsations in this event, namely the change of the phase and ellipticity during passage thought the resonance region (not shown). 28 A pril 2001 UT Fig. 1. The variations of the ^-component of geomagnetic filed at the stations of IMAGE profile. We determined the azimuthal wave number m for the geomagnetic Pc5 pulsations using the azimuthal pare of stations ABK-IVA. The cross-correlation method was used to determine the m. The m was determined by the formula m=/A/-360°/AA, w e re /is the frequency of pulsations determined from the spectral analyze, At is the time shift corresponding to the maximum of correlation coefficient, and ДА - the longitudinal distance in deg between ABK and IVA (ДЯ=6.75°). The frequency of Pc5 pulsations in 06.00-08.30 UT at the ABK-IVA stations was /=3.2 mHz, the time shift between ABK and IVA stations during this time interval was Д/=20 sec (r = 0.98). The phase shift was A<p=23.04° 72