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.

maximum dimension of the polar cap was found to approximately coincide with the period of the maximum AE value. The dimension of the polar cap was deri ved from electron precipitation data obtained by combining observations from the DMSP-F2 and F3 satellites. Thereby it became possible to determine the precipitation boundaries with time resolution of about 30 minutes on the average. The observed locations of the boundaries were normalized to that of the 1800 and 0600 MLT by assuming a circular distribution with the center shifted by 4°.2 from the geomagnetic pole towards the 0015 MLT. IMP B 2 and € data were obtained from the ISEE-3 satellite. There was about 1 hr time delay for the solar wind to propagate between the ISEE-3 location and the magnetosphere. Recent studies have demonstrated that the assumption of a circular shape of the poleward electron precipitation boundary is not valid during quiet periods (Lassen et al.,1986). Therefore, normalization of the poleward boun dary locations to fixed hours may in some cases be doubtful. Similarly, the time delay of about 1 hr may introduce uncertainties in the result. I n the study on which we are going to report here we have been able to check the t i m e .sequence of disturbance signatures reported by Makita et al. wi t h an improved time resolution and with reduced uncertainty originating fi'om the above-mentioned sources. The present study is a case study, in which we have observed the config uration of the quiet electron precipitation belt during an interval of ma g n etic calm (K = Oo) during the first five hours of November 29,1984 as well as the change of this pattern resulting from a sudden change in the solar wind parameters. This particular night has been chosen for a detailed study, because we happened to operate the Incoherent Scatter Radar at Sondre Strom- fjord with a good time resolution just at the time of the event. The observed quiet configuration is shown to be in agreement with the statistical patt ern reported earlier (Lassen et al., 1986 ). IMF and 6 data obtained from AMPTE/IRM satellite are shown in Fig,1. The satellite left the magneto- sheath ab.03-04 UT so that the data shown refer to a satellite position in the solar wind immediately outside the bow shock. At about 0510 UT В . z B z and В change drastically, resul ting in a steep rise in e . The change is observed as a sudden impulse in the geomagnetic field at all latitudes (Fig.2), There is no obvious time delay, in agreement with the proximity of the satellite to the magnetosphere. The slight depres sion of H at Pamatai near equator and the corresponding gradually Fig. 1. Variation of the components of the IMP' observed by the .AMPTE/IRM satellite immediately outside the bow shock on Nov.29,1984. Bottom:e -param eter (Akasofu,1979). 106