Структура и динамика полярных токовых систем : материалы международного симпозиума «Полярные геомагнитные явления», 25-31 мая, Суздаль, СССР / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : [б. и.], 1988.

Klnter P.M., Kelley U.C., Sharp R.D., Ghielmetti A.G., Temerin М., Cattell C., Mizera P.P., Fennell J.P. Simultaneous observations of energetic keV upstreaming ions and electrostatic hydrogen cyolotron waves. - J.Geophys. Res., 84, 7201,1979. Moser P.S., Cattell C.A., Hudson M.K., Lysak R.L., Tamerin М., Torbert R.G. Satellite measurements and theories cf low altitude auroral particle acceleration. - Space Sci,Rev., 27, 155, 1980. Pashin A.B., Glassmeier K.-H., Baumjohann \V., Raspopov O.M., Yahnin A . G . , Opgenoorth H.J., Pellinen R.J. Pi2 magnetic pulsationo, auroral break-ups, and the substorm current wedge: A oase study, - J.Geophys., 51, 223, 1982. Yamada М., Seiler S., Hendel H.W., Ikezi H. Electrostatic ion cyolotron instabilities driven by parallel ion beam injection. - Phye.Fluids, 20, 450, 1977. J.Kangas, A.Aikio, T.Pikkarainen, A.Parmer, J.V.Olson, T.Turunen EFFECTS OF SUDDEN IMPULSES (SI) AND SUBST0RM3 ON Pel MAGNETIC PULSATION SPECTRUM ABSTRACT. We present some examples of magnetic pulsation spectra measured at the north-south chain of pulsation magnetometers in Finland where the ongoing Pel wave activity is interrupted by a sudden impulse or magnetospheric substorm. We show that Si's induce most prominent changes in the Pel spectrum at auroral latitudes. This is shown to be mostly in agreement with model calculations where the growth rate of ion-cyclotron waves is changed by an increase in the ambient magnetic field and in anisotropy of the plasma pressure. The substorm onset induces an upward sweep of Pel frequency and a typical IPDP pulsation event is observed. We show that this is associated with an ehhanoed southward drift of plasma measured by the EISCAT radar. We oonolude that the increase in frequency is due to the S x l drift of the wave source in the magnetosphere. INTRODUCTION. Both Si's (Sudden Impulses) and magnetospheric substorms generate ion-cyclotron waves in the magnetosphere which are observed also on the ground. S i’s are often followed by Pel magnetic pulsations which may last for hours (Troitskaya et al., 1968; Kokubun and 0guti,1968j Olson and Lee, 1983| Kangas et al.,1986). During subatorms, IPDP type wave events (Intervals of Pulsations of Diminishing Periods) occur mainly in the evening-to-midnight sector of the sub-auroral zone (Fukuniahi, 1969; Heacock,1971; Pikkarainen et al.,1983). They are delayed with respect to the onset of substorm and they last typically for an hour. In both oases, the generation of ion-cyclotron waves are associated with the changes in magnetospheric fields and plasma populations. These changes modify the conditions for wave growth. The most useful way to investigate these modifications i B to study the caees whore the activity is in progress when an 31 or an onset of substorm occurs. It is the aim of the present study to analyse such events in order to determinate the main factors which modify the wave amplification and the ULF pulsation speotrum recorded on the ground. 95