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.

magnetic field at the equator have been evaluated for a certain time of the year and universal time and projeoted along the magnetic field lines down to the ionosphere. The ovals may be labeled by the radius at the equator estima ted from Rg = where HQ is the intensity of the dipolo magnetic field at the equator of the earth. COMPARISON OP OVALS. The auroral oval, especially the equatorward border, can be approximated with nearly circular patterns in corrected geomagnetic coordinates displaced towards midnight by a few degrees in latitude. Peldstein and'Starkov (1967) found a displacement of about 4 degrees for low magnetic activity. Similar values of the displacement has been found in many other studies. Whalen (1983) studied the energy flux at E-layer altitudes by means of ionospheric sounders and obtained a displacement of 4.2°. Auroral observ ations from the ISIS-2 satellite of 630 nm emission (Shepherd,1979) showed a displacement for the 500 R contour at noon and midnight of about 4 degrees. The auroral orientation curves based on statistical studies of the orientation of uuroral area show a pattern that is displaced 5 . 5 °during sunspot- maximum and 4.5° during aunapot minimum (Gustafseon et al.,1969). These studies show that there iu a number of aurora-related phenomena that show patterns displa ced about 4 degrees in latitude towards the night side of the earth. The projection of the constant magnetic field (constant-B) contour at the equator down to the ionosphere using the magnetic field model has been shown in Figure 1. The В-value of the magnetic field has been selected to give an oval that is located near the equatorward border of the Peldstein and Starkov auroral oval. The equatorward border haa been chosen in order to avoid the uncertainties in the field model near the dayside magnetopause. The calcu lated oval, taking into account external currents with parameters correspond ing to rather quiet magnetic conditions, shows an offset of 2.5 degrees of latitude relative the magnetic pole. Comparing this result with the above ovals based on observations, shows that the constant-B oval is displaced about 1.5 degrees less from the magnetic pole than the other ovals. Varying the parameters of the field model within reasonable limits for a quiet magneto sphere changes the center by less than 0.5 degrees. О SUN 0.600UT J-vA С. I уI □ u 0600 UT, with center at 79 . 0 °of latitude} 2 - auroral orientation curve, center at 76„0°j 3 ~ corrected geomagnetic latitude for 70 °, center at 81.5°. Pig. 1. Three ovals displayed in a geocentric coordinate system. 1 - oval based on thi 3 study for December 21,1980 at 103