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.

К.Lassen, C.Danielsen, Т.3.Jorgensen, C.-I.Meng CONFIGURATION OF THE QUIET POLAR CAP AND ITS RESPONSE TO A SUDDEN INCREASE OF THE ENERGY INPUT RATE fi ABSTRACT. Following a geomagnetically quiet period of ab. 17 hours duration a sudden increase of the solar wind-magnetosphere energy coupling function £ to above 10 11 W occurred at 0510 UT on Nov.29, 1964, and a moderate substorm onset was observed in the midnight sector of the aurox'al oval at 0612 UT. Ground-based optical measurements combined with electron precipitation data obtained during the very quiet interval are used to determine the shape and position of the boundary of the polar cap during quiet conditions. Next the influence of the sudden disturbance on the boundary О position is studied. 10-20 minutes after the solar wind disturbance 6300 A photometer measurements show evidence of a decrease in the number of sporadic ocouring auroras (spikes) in the precipitation belt near the polar cap bound ary in the dawn sector. 10-20 minutes before substorm onset this boundary had been shifted equatorward by ab. 7°. In the same sector the equatorward boundary of the auroral oval began to move equatorwards at the time of the substorm onset. In the dusk sector the equatorward shift of the polar cap boundary is not observed until at least 5 minutes after the onset. It is concluded that an equatorward shift of the polar cop boundary caused by an increase in the energy input rate £ may be observed at part of the boundary essentially earlier than the corresponding shift of the auroral oval. The shift may take place at different hours in different sectors of the polar cap with time differences of at least 20 minu tes between dav/n and dusk. INTRODUCTION. The statistical precipitation pattern of auroral electrons measured during magnetically quiet intervals has the shape of an annular belt surrounding the polar cap. The belt is composed by two parts. The outer belt is produced by electrons with average energy above 500 eV, the inner belt by electrons with average energy below 500 eV (Ilakita et al.,1983). The outer belt includes the classical quiet (Feldstein) auroral oval. The inner low energy belt is mainly daytime belt, usually observed from 03 to 21 MLT. The daytime discrete auroras are embedded in this belt (Lassen et al.,1986). Makita et al. (1985) and Makita and Meng (1984) discussed the position of the poleward and equatorward boundaries of the belts as a function of geo magnetic activity and interplanetary magnetic field, and Makita et al.(1985) presented models showing the variation of the double-belt in relation to the energy input rate в and AE index. Assuming that the polar cap bpundary can approximately be identified as the boundary of the intense precipitation region of the low energy electrons these authors found an increase in the dimension of the polar cap beginning about 30-60 minutes after the southward turning of the corresponding increase of the AE index. The period of the I05