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.

(Uozth pole) (South pole) 12 OfILT H i Cuzzent into ionosphete A-В CD a 8 „ quotient negative 0 MLT E D Cuzzent ow<ri hom ionosphete B-C &8„ gzaofient positive 1 18 Pig. 2. Spatial distribution of field-aligned currents and дB M gradients for 9 consecutive paths on 13 November 1979 in. the northern and southern polar regions (Iijima et al., 1982). In the analysis of MAGSAT data, the reference magnetic field originating from the earth'B interior (denoted here by B Q , Yrtiich can ba given by a sum of lower-order spherical harmonics) is subtracted in advance from the observed vector magnetic field B. The difference A В (observed Вminus B Q ) consists of A B „ and ABi , the components parallel and perpendicular to the refer ence permanent magnetic field at each point of observation. ABX °an be further decomposed into two components, for example to the component in the sun-earth direction and that in the dawn-dusk meridional plane. The density of field- aligned sheet currents can be obtained from the spatial gradient of observed ABj. , whereas A B (| is uninfluenced by field-aligned currents but contains an effect from the current flowing perpendicularly to the magnetic field, which is practically the Hall current in the ionosphere in h i g h latitudes. The altitudes of magnetic field measuremente by previous satellites were so high that A B „ were undetectable because of its rapid decrease with the distance from the ionosphere. MAGSAT data have a great advantage that they show not only ABx but also aB,i with a significant magnitude, as shown in Fig.3. Hance one can study with the aid of MAGSAT data the interaction between the field-aligned currents and the auroral electrojet (in which the Hall current is predominant), for example, as done by Zanetti et al. (1983). During the period of MAGSAT flight, there were some intervals with a steady strong northward interplanetary magnetic field (B 0), e.g. on 9-10 May 1960. In such an interval, the MAGSAT data in the region near the geomagn etic pole showed the appearance of a nev/ field-aligned current pair, which consists of the current into the ionosphere on the dusk side and the outflow ing current on the morning side (called NB2 current system), as reported by Iijima (1984), Iijima et al.(1984), Araki et al.(1984b) and Zanetti et al. (1984). One may state that the cusp current in Fig.1 (the field-aligned currents into and out from the ionosphere along the 80° invariant latitude circle) becomes enhanced when B z> 0 condition persists for several hours (Iijima and Potemra, 1976b). The ground magnetic variation associated with 77