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. observed the gradual change of the sense of rotation of the wave polarization from the pure left-handed to the pure right-handed. It can be interpreted as the approaching the VLF wave ionosphere exit point to KAN station. We suppose that it can be a result of the progressive plasmapause replacing with geomagnetic activity change. According to the satellite observations [e.g., Bezrukikh et al., 2001; Laakso and Jarva, 2001] the response time of the dayside plasmapause to changes in geomagnetic activity is very rapid. The same was concluded by analysing of the simultaneous temporal change of the Pc4 geomagnetic pulsations spectra. The statistical behaviour of ground Pc4 pulsations is well documented in the past [e.g., Orr and Matthew, 1971; Kopytenko et al., 1972, Hayakawa and Sazhin, 1992]. The Pc4 amplitude peaks at magnetic latitudes below ~60°. The same results were obtained in ourobervations. The THEMIS data [Liu et al., 2009] showed that the Pc4 wave activities were observed as soon as the satellite moved away from plasmasphere, suggesting that the plasmapause location can play a role in the occurrence rate of the Pc4 ULF waves. Here we found that in the first Pc4 wave packet (04.45-05.02 UT), the resonance frequency was 12 mHz and in the second one (near 05.30 UT), it decreased to ~10.5 mHz. In both events the spectral maximum was observed at the same latitude area. According to a number of authors [e.g., Milling et al., 2001; Menk et al., 2004], this resonant frequency change can be interpreted as an increasing the plasma density in the resonance region. It can be a result of the plasmapause replacing to the higher L-values. We would like to note that the time of the temporal change of the Pc4 resonant frequency (Fig. 6 ) coincided with the time of reversal of the VLF hiss polarization vector. 4. Conclusion Thus, temporal dynamics of the polarization behavior of VLF hiss as well as the change of the Pc4 resonant geomagnetic pulsation spectra can be a result of the temporal dynamics of the plasmapause location. Acknowledgements. This work was supported by the Program №22 of the Russian Academy of Sciences. References Bezrukikh V. V., Verigin М. I., Kotova G. A., Lezhen L. A.,.Venediktov Y. I, Lemaire J. (2001), Dynamics of the plasmasphere and plasmapause under the action of geomagnetic storms, J. Atmos. Sol. Terr.Phys., 63, 1179-1184. Hayakawa М., and S. S. Sazhin (1992), Mid-latitude and plasmaspheric hiss: A review, Planet. Space Sci., 40, 1325-1338. Inan U. S. and Т. E. Bell (1977), The Plasmapause as a VLF guide, J.Geophys. Res, 82, 2819-2827. Kennel C. F., and H. E. Petschek (1966), Limit on stably trapped particle fluxes, J. Geophys. Res., 71, 1-28. Kleimenova N.G., Troitskaya V.A., Vigneron J. 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