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.

The upper pannel, which is typical for very quiet periods, was recorded from 0421 to 0441 UT, i.e. while B z was positive and e low. The precipitation profile ia similar to the preceding crossing (Fig.3), exoept that the poleward boundaries of the region of low-energy electrons have moved to still higher latitude. Irregular bursts of precipitation (spikes) are occurring all over the polar cap. The second panel was obtained from 0602 to 0622 UT. The substorm onset took place during this crossing, while the satellite was situated over the central polar cap. A comparison of the two profiles finds that a strong contr action of the lower-energy zone has taken place in the dawn sector before 0б0б-0б08 UT, while the adjacent polar cap is found to be void of spikes several minutes before the substorm onset at 0612 UT in agreement with the ground-based observations. In contrast to this result Fig.9 shows that the shape of the dusk precip itation zone was not essentially changed several minutes after the substorm onset. CONCLUSION. Ground-based optical measurements combined with electron precipitation data obtained during a very quiet interval (KpaOo) on Nov.29, 1984 confirm the statistical configuration of the quiet polar cap boundary (Lassen *t al.,1986). At mid-night the boundary is near 75° corr.geom.lat. At about 03 MLT the latitude changes rapidly to about 84° in the dawn sector. At noon, the latitude may be e little lower, increasing again to ab.84° in the duek sector. At 21-22 MLT the latitude decreases rapidly to the midnight position at 75°. It should be noticed that the polar cap boundary described here has been defined as the location where the value of the electron number flux after 6 2 -1 crossing of the contiguous precipitation belt drops to ab.10 el (cm s ster) . Spikes of flux as well аяauroral arcs are abundant poleward of the boundary of the quiet polar cap. A sudden increase of the energy input rate 6 , which occurred at 0510 UT, waa followed by a moderate substorm onset in the midnight sector at 0612 UT. 10-20 minutes after the increase photometer measurements indicate a thinning of the number of aporadio intensity increases (auroras) in the low- energy particle belt near the polar cap boundary. A few minutes before 0600 UT i.e. 10-20 minutes before substorm onset, the boundary had moved equatorward by ab.7°. The equatorward border of the dawn sector of the auroral oval did not change ita position until after the substorm onset, when it began to move towards equator. Consequently, the total width of the electron precipitation zones was reduced by more than 7° in the dawn sector- prior to the substorm onset. The satellite observation obtained at 0602 to 0622 UT shows that a corresponding reduction had not taken place in the duak sector several minutes after the substorm onset. Thus, in thla particular case the expansion of the polar cap occurred earlier at dawn than at duek. Ourstudy has confirmed the reault of Makita et al.(1985) that an increaseofthe polar oap aets in after the increase of the e parameter, but priorto the corresponding increase of the AE index. In the particular case studiedherethe firet signature of a change of the boundary position is observed 10-20 minutes after the £ increase, while a rapid shift of the boundarytakes place ab.45 minutes after thedecrease and ab.15 minutes before theeubBtorm onoet. II3