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.

Figure 11. The ваше aa in F i g . 10 but for December 31» 1980 (a) and December 31, 1981 (b). 8-9°. If the equatorward boundary is drawn through the southernmost auroral area or along the background luminosity boundary, the correlation coefficient for curves 1 a n d 2 is 0.89. The magnetic activity in the midnight sector of the auroral zone w a s inconsiderable. A minor magnetic disturbance at about 0730 UT did not have any explicit effect on the dynamics of auroras. The December 31, 1981 case. Fig. 11 (b) shows the IMF B z -component vari- ations, the position of auroras' inferred fr om the Heiss Island ascafilms, and the variations of the magnetic field horizontal component at Churchill. During the 0300-0400 UT interval, the value of the IMF B z -component changed from +5 nT to -4 nT. In the respective period of time the boundary of the discrete auroral forms shifted to a 70° latitude, i.e. the variations of the position of the discrete aurora equatorward boundary repeated the B z -component intensity v a r iation pattern. During the 0 4 0 0 - 0 6 0 0 U T interval the B z -component got positive and its value reached 8-10 nT. The northward turn of the IMF vertical component was accompanied by a shift of the ray^d forms to latitudes of 74-75° and by their eventual disappearance. At the same time the auroras in the form of individual rays appeared at latitudes of 79-81° and were observed there throughout the B z > 0 period. A n abrupt change of the B 2-component fr o m posi tive to negative occurred at about 0 6 0 0 UT, w h e reupon the vertical component remained negative until 0900 UT. The position of the luminosity region suffered respective variations, namely, the equatorward boundary of lumino sity shifted in latitude f r o m ~ 79° to ~ 73°. Dtiring the 0000-0800 UT interval the magnetic field on the Earth's dark side was relatively quiet. A n intensive storm ( ~ 1 0 0 0 nT, as inferred fr o m the A E - i n d e x ; ~ 500 nT, as inferred fr o m the Churchill magnetogram in the maximum) commenced at 0810 UT. The substorm expansion phase was accompanied by a n additional equatorward-shift of the daytime auroras, although the southward B„ value slightly decreased. Unfortunately, the additional shift of the eqvurtorward boundary cannot be evaluated because it falls outside the all-sky camera field of view. Figure 12 presents the correlation coefficient b etween the IMF B 0 - I36