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 precipitation pattern is fixed in relation to the direction to the aim. Therefore, a station of the surface of the earth, as f.inst. Godhavn, will move beneath different parts of the pattern as it follows the rotation of the earth. о This is obvious in .the 6300 A record of the meridian scanning photometer, shown in Pig.5. Here a southward shift of the 350 R contour from latitudes north of Godhavn to latitudes south of Godhavn is recorded between 00 and 01 UT (22.5 and 23.5 MLT). A shift of similar magnitude, but now from south to north, takes place at ab. 04 UT (02.5 MLT). As mentioned above the diffuse о 6300 A emission coincides with the zone of enhunced electron precipitation. The latitudinal shift of the 350 R contour therefore illustrates the varying position'of the poleward boundary of the precipitation belt over the magnetic meridian through Godhavn. The course of the 350 R contour between 00 and 05 UT (22.5 and 03.5 MLT) is in agreement with the shape of the polar cap boun dary during the same quiet interval (Pig.4, circles). The rapid poleward _ О shift of the 6300 A emission ab.03 MLT is a common phenomenon on quiet nights (Lassen et al.,1981). It has already been mentioned that there is a close relationship between the electron precipitation pattern and the distribution of visible discrete auroral forms. This is illustrated in Pig.6, in which Pig.4 has been overlaid a polar graph showing the distribution of discrete auroras observed by the camera network in Greenland when Kp=0 (Danielsen,1980). The narrow nighttime maximum, visible at 70° between 19 and 03 MLT, is cleraly connected w i t h the outer high-energy belt. The dominating daytime maxima at 75°-80° are situated poleward of the transition line, which is thus separating the nighttime auroral distribution from the daytime auroras. We have defined the polar cap boundary as the location where the decrees- ft ? — 1 ing value of the electron number flux drops to 10 el (cm s ster) after crossing of the contiguous precipitation belt. This boundary is seen to be reasonably well related to the isofrequency lines at the poleward edge of the auroral distribution. At the very quiet level studied here auroras are rather frequent at latitudes above 85° in agreement with the observation of spikes of electrons at these latitudes. These polar cap forms may be related to the Pig. 6. Polar graph showing both the electron precipitation boundaries from Pig.4 and the distribu tion of discrete auroras observed by the camera n e t work in Greenland 1973-74 for К =0. no