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.

space current below the MAGSAT orbit is always antlsunward during magnetic storms or aubstorm3, very often exceeding one million Amperes in good correl ation with the AE-index. The calculated space current value is given only as an average value during one MAGSAT revolution of 94 minutes. It has been well known that the depression of the horizontal intensity of the geomagnetic field in low latitudes during magnetic storms is greater on the dusk side than on the dawn side, especially during the developing stage of magnetic storms. This longitudinal inequality is revealed also in the analysis of MAGSAT data (Kane and Trivedi,1985; Uaeda et al.,1985; Suzukiet al.,1985). Combining this fact and the existence of the antisunward space current below the MAGSAT altitude, it will be quite reasonable to introduce a global-scale current-system of Fig.9, which consists of a symmetric ring current and a partial one combined with field-aligned currents in the magnetosphere and the horizontal current (mainly Pedersen current) in the ionosphere (Kamide and Fukuahima,1972; Fukushima and Kamide,1973a). The intensity ratio of partial/ symmetric ring current is calculated to be only 10-20 % (Suzuki and Fukushima, 1984; Suzuki et al.,1985). The picture of Fig.9 is, of course, too simplified; e.g., the antisunward field-aligned current will not at all be a simple line- current, but it must be at least a sheet current over a wide range of longi tude. The ring current in the ejuatorial plane is also a simplified substitu tion for the westward flowing current in the entire magnetosphere resulting from all the motions (diamagnetic gyration, north-south bouncing across the equator, and westward or eastward drifting) of all charged particles trapped in the magnetosphere, as proposed first by Singer (1957). The author is however aware of a fundamental comment on the partial ring current model that the dawn-dusk asymmetry in the ground magnetic field depression doee not necessarily require the current closure with a partial ring in the magnetosphere, because the dawn-dusk asymmetry caused predominantly by the antisunward field-aligned currents in the magnetosphere (Fukushima and Kamide,1973b; Crooker and Siscoe,1981). This argument does not at all destroy the whole idea of a partial ring current, but it puts emphasis on the role of antisunward field-aligned currents in the magnetosphere. DISRUPTION OF THE MAGNETOSPHERIC TAIL CURRENT DURING SUBSTORMS OBSERVED BY SYNCHRONOUS SATELLITES. At the time of substorm onset, magneto meters on board the synchronous satellites at 6.6 earth radii show an abrupt transition of the observed magnetic field from a tail-like configuration to a more dipolar one. This change is resulted from a conversion of the magneto spheric tail current near the midnight meridian into a field-aligned current pair connected with a westward ionospheric current along the auroral oval. This has been known since the early launching of a synchronous satellite Fig. 9. A simplified model of electric current circuit with a partial ring current, which accounts for the dawn-dusk дН asymmetry and an antisunward space current during magnetic storms (Suzuki and Fukushima,1984; Suzuki et a l . ,1985). 83