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.

intensity increased abruptly while the green line intensity decreased. A noticeable rise of the •сбЗО.О/,'[557.7 r a 't^° i Q indicative of a rapid softening of the precipitating electron flux. The ionospheric data indicate the occur rence of the apread-Pg reflections wh i c h were recorded during the entire period w h e n th$ ra y e d arcs mo v i n g polewards were observed. The m e a n liftime of the ra y e d arcs is 10 min; they are located w i t h i n the red luminosity region. The area are formed at the equatorward boundary of the 630.0 n m luminosity reg i o n w i t h about 4 m i n recurrence . A ba n d of enhanced 557.7 n m e m ission intensity appeared after 0700 UT near the equatorward boundary inside the red luminosity region. This i s the band of relatively harder electron precipitations w h i c h expanded i n time pole wa r d s and reached the station ssenith at about 0800 UT. Cur i n g that period the ^бзо.о/3^ ? . ? ratio decreased substantially at the zenith. The 0800-0900 UT ionospheric data show the spread-Fg reflections and are indicative of the appearance of a n o n - s c reening sporadic E 0r layer w i t h fairly h i g h limiting frequences. After 0915 UT the aurorae of a nother mo rphological type (bright homoge neous arcs) were observed. Their m o t i o n direction coincided w i t h the shift direction of the luminosity re g i o n as a whole. The occurrence of various morphological types of auroras in the dayside hemisphere is described i n de tail b y Yo r o b j e v et al,(1976). I n the dusk-type auroras the ratio Igj0 0/ I 5 5 7 . 7 " 1 * ionospheric data fo r that period show the presence of a fairly dense E 0r layer w h i c h screens the ionospheric Fg-layer completely. The luminosity structure in the transient re g i o n b etween the auroras of the daytime a n d dusktime types w a s studied i n detail b y H e zhenov et a l . ( 1 9 7 9 ) and Vorobjev et al.(1981) using the data f r o m a longitudinal chain of a l l sky cameras. The most interesting events were observed during the period of enhanced DP - 2 current system w h e n the oval aa the whole shifted equatorwards. During that period, the discrete forms of the auroras of the two types mo v e d oppositely to ea c h other. The short-lived ra y e d arcs of the daytime type shifted polewards a n d eastwards, while the homogeneous dusktime-type arcs m o v e d equatorwards a n d westwards. I n the r e g i o n where the m o t i o n directions changed, the daytime-type arc is overlapped by 10-15° of longitude w i t h the dusktime-type arc a n d w a s located equatorwards f r o m the latter in all the cases examined. The re g i o n of the direction change of the meridional motion of the discrete forme w a s found in the 1200-1700 IffiE interval. The position of the re g i o n changes f r o m case to case. I n individual periods the aurorae of the two types w e r e observed to be separated by 15-20° of longitude w i t h the diffuse luminos ity region. Such separation wa s observed in the December 30,1984 case presented i n P i g . 9. The D e cember E. 1978 сазе. Figure 10 (a) shows the IMP B z component variations (curve 1) inferred fr o m the ISBE-3 data, the position of the equatorward bou n d a r y of auroras at the geomagnetic mer i d i a n in the 0810-1000 UT interval inferred fr o m the He i s s Island a sk a f i l m data (curve 2), a n d the variations of the magnetic field horizontal component i n the midnight sector at Churchill (curve 3). D uring the examined interval the magnetic variations at Churchill did not exceed 30 nT. At College the magnetic fi eld wa s in practice quiet. The auroras we r e observed to be of the f o r m of a single rayed arc w h i c h defined the equatorward boundary of the auroral oval. Sometimes the discrete forms disappeared or their brightness decreased to below the all-sky camera sen- 134