Электродинамические процессы в высоких широтах: материалы междунарордного симпозиума «Полярные геомагнитные явления», 25-31 мая 1986 г., Суздаль, СССР / Междунар. геодез. и геофиз. союз, Междунар. ассоц. геомагнетизма и аэрономии ; Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т ; [редкол.: О. М. Распопов (отв. ред.). и др.]. - Апатиты : Кольский филиал АН СССР, 1988.

1 'igure 1 a. The geophysical situation on 16.B . 1974. In the upper lefthand c o m e r the daily m e a n values of Det. The Ap and the Kp values are shown for five days wit h the day of the event under study in the center. B e l o w m e a n hourly valuea are given for the AE and Dst-index the density a nd the veloc i t y of the solar wind, the amplitude and the Bz-component of the interplanetary magnetic field in dependence on universal time. The duration of the АА-ѳѵепѣ in Scandinavia is m a r ke d by ve rt i cal lines. midnight sector the onset eeemo to ocour n e ar l y simultaneously from midnight to late m o r n i n g (within a f ew minutes). Since simultaneous magnetograms and ionograma from nearby stations in the m or ning sector show ver y quiet undiBturbed trends it must be concluded that there is no p r e cipitation of softer electrons in the SVA-region. Fur-flier there seems to be no remarkable injection of hi gh energy ions Into the inner magnetosphere: Dst remains positive and shows no considerable decrease. There are man y details in the pioture fox- the six SVA-events, w h i c h are hard to inderstand under the assumption that they are all due to a cloud of drifting electrons wh i c h have b e e n injected ne ar midnight. On the other hand Collis and Korth, 1985 have analyzed GE0S-2 observations of hi g h energy ele ctrons for two SVA-events and were able to show that the electron flux ch ar a cteristics were consistent w i t h gradient-curvature drift fro m a source near midnight. B ut these questions will be discussed later in another paper. 4.2. Examples for events in the evening to afternoon sector. 4.2.1. August 17, 1974: 13.00-18.00 UT. This event occurred in relation wi t h a very isolated substorm (Fig.2a). Before that magnetic substorm A E w as about zero, Dst positive for a long time, and Bz(IMF) had only some short southward excursions before 12.00 UT. The onset of a magnetic substorm is seen at about 13.00 UT n e a r magnetic m i d night (Fig.2b) (at College <2.5 MLT) at 13.10 UT). The onset of the AA-event occurs some m i nutes later in the Alaska chain. Looking fro m the Alaska sta- o tions via Churchill to Narssar s s ua q and Qodthab in this case one has the impression that the p r e cipitation m a y be due to the drift of a cloud of injected electrons. On the evening side (20 MLT) after a mi no r increase at about the same time as in Fort Yukon, No r ilsk eees a ver y strong increase of 92