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.

We conclude that the increase in Pel frequency after the onset of sub storm is related to the inward drift of the source of pulsations. We believe that we have been able for the first time to shov/ the direct experimental evidence for such a process. SUMMARY AND DISCUSSION. We have shown experimental data to illustrate the changes in Pel magnetic pulsations which are induced by sudden impulses and magnetospheric substorms. The main conclusions of this analysis are: 1) The most prominent new features induced by Si's are observed at auro ral latitudes. New frequency bands of emissions may occur. 2) The meridional profile of the Pel spectrum is more variable than that of ordinary Pci's. 3) The substorm onset results in a gradual increase of the Pel frequency and an IPDP type plasma wave event appears. This increase is associated with an increase of the westward component of the magnetospheric electric field. Sudden impulses are associated with the compression of the magnetospheric cavity. Olson and Lee (1983) have presented some model calculations of the growth rate of ion-cyclotron waves for such situations. In their model the magnetopause i s m o v e d from 11 to 8 Rg. It is shown that the anisotropy in the plasma pressure measured by A=(Wj. /W„ - 1) increases significantly at high latitudes. Olson and Lee (1983) concluded that the shift of the Pel frequency induced by the SI comes primarily from the increase in the ambient magnetic field as well as in the anisotropy A. We feel that the observations presented in this study support the main conclusions of these model calculations. However, as the poleward boundary of Pel source region definitely exists other necessary plasma conditions which are met probably in the plasmapause region are also to be taken into account. The L-dependence of wave spectrum indicates that there are simaltaneous separate plasma regions where favourable conditions for wave amplification may develop as a result of sudden impulse. During eubstorm fresh energetic plasma is injected into the magnetosphere. Protons will drift from the midnight sector to the evening sector due to gradient and inertial forces. Protons generate ion-cyclotron waves when favourable plasma conditions prevail. The frequency shift in IPDP events have been explained by both the azimuthal and radial drift of protons. Bo t h mo v e ments have been observed (see, e.g. Pikkarainen et al.,1983). The radial drift should dominate near the midnight sector, i.e. e.g. in the case reported in this paper. This is supported by our electric field measurements. Such a drift increases the anisotropy A and transports the interactin protons to a stronger magnetic field. It is interesting that the first part of the IPDP event can be due to the inward drift of preexisting protons and the enhancement associated with fresh substorm particles occurs later. This means that the beginning of the IPDP type event does not always signify the arrival time of substorm-associated protons. ACKNOWLEDGEMENTS. Part of this work was begun during Pinniii-American Auroral Workshops sponsored jointly by the Academy of Finland and the National Science Foundation. A.Aikio and J.Kangas were supported by grants from the Akademy of Finland. The EISCAT Scientific Association is supported by the Centre National de la Rescherche Scientifique of France, Suomen Akatemia of Finland, Max-Planck Geaellschaft of West Germany, Norges Almenvitenskaplige ForskningsrSd of Norway, Naturvetenskapliga ForskningsrSdet of Sweden and Engineering Research Council of the United Kingdom. I00