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.

a n d thua of magnetic energy i n the magnetotail (e.g.Feldstein,1972; Makita et al.,1985). Following this interpretation, the optical and geomagnetic data recorded i n the period 1130-1210 U T seem like signatures of the growth phase (cf.Starkov an d F e l d s t e i n , 1 9 7 1 ; Vorobjev et al.,1975, 1976; Rostoker et al., 1980; B a k e r et a l . ,1 9 8 1 j Co w l e y , 1982). We express our reservation concerning the determination of the substorn onset time, wh i c h is based on observations from the Alaska sector only (cf«Fig.2b). Notice that this was a n isolated substorm, proceeded b y ve r y quiet conditions. It is reasonable to suggest that the observed substorm expantion onset was triggered by the IM P no r t h w a r d turning at 1210 UT (see. arrow i n the left panel of Pig.2a) (cf.Rostoker, 1983). Spikes in the magnetic recording at 1140 and 1150 UT are due. to bow- shock encounters. The poleward (dawnward) movement w i t h i n the polar cap of the afternoon arc at a p p r . 1300 UT ie the direct response to a northward and counter-clock wise rotation of the IMP vector (Pig,2a). This mo t i o n is similar to the observed dawn-dusk mo t i o n of Ѳ -aurora i n the polar cap, i n response to IMP В changes (of.Prank et a l . ,1985,1986). J The December 13. 1983 c a s e . Significant southward movements of day- and nightside aurores b etween ~ 0915 and ~ 0930 UT occurred at the time of large negative IM P B B . Three distinct auroral break-ups above Alaska we r e not ob served to have immediate effects on the dayside aurora. Poleward motions of the m a i n dayside arc during the intervals 1045-1100 UT an d 1115-1135 U T could be delayed responses to the auroral s u bstorm intensifications at 0950 end ~ 1030 UT, respectively. The December 10. 1983 c a s e . A most remarkable feature is the r e lation ship b etween the l ocation of the poleward bo rder of the mi d d a y luminosity and the magnetosheath B 2 component. W e notice clear responses to the IMP n o r t h ward and southward transitions at 0855 and 1003 UT, respectively (Fig.4a). A similar response i n the poleward boundary of the dayside aurora occurred on January 4,1984 at appr.0840 U T (of. Pig.6a). P r o m the day- a n d nightside auroral data we infer a significant polar cap expansion during the pre-onset period 0750-0815 UT, similar to the previ ous examples. The poleward mov i n g luminosity structure on the dayside between 0815 and 0823 UT (Figures 4a and 4b) could be the optical signature of a flux transfer event (PTE). It appears as a n intensification at the equatorward b o undary of the pre-existing ousp auroral display, indicating an initial l o cation at the boundary between closed a n d op e n field lines. Then it mo v e s aoross the cusp aurora before disappearing o n the poleward side of the cusp. All - s k y pioturea of the phenomenon r eveals that it appears i n the south-east, then moving towards nort h w e s t , - i n agreement w i t h the statistical convection p attern for IMP B y > 0 (e.g. Reells,i984). I n the actual case m a g n e t osheath B y " 2 0 nT. A more extensive discussion of similar events is given i n Sandholt et al. (1985 and 1986b). The January 17. 1985 c a s e . Movements in latitude of the dayaide aurora were well correlated w i t h nightside magnetic activity i n this caae (Pig.5a). The IMF information is incomplete due to data gap. Thus the possibility that the geomagnetic a ctivity w a s directly driven b y IMP variations cannot be disregarded. N otice the series of individual auroral structures mo v i n g into the polar cap (cf. Fig.5b) during the period of equatorward shift of the m a i n belt of I28