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.

- coincidence of the regions with enhanced field-aligned currents and discrete aurorae and electron precipitations! - evidence for the electric current flow in the ionosphere in middle latitudes at the time of SC*; - existence of a toroidal magnetic field within the ionosphere in the equatorial region on the dusk side, caused by an upward electric current above the dip equator and its associated current circulation in the meridional plane; and • - global antisunward net current of a few million Amperes flowing below the MAGSAT level during the developing stage of magnetospheric storms. The magnetic field measurements by many previous satellites have contrib uted to the demonstration of the field configuration around the earth, espec ially its quantitative deviation from a dipole magnetic field. Magnetometers on board the synchronous-orbit satellites showed a sudden transition from a tail-like magnetic field to a dipolar configuration near the midnight meridian at the onset of magnetic substorms, which is associated with a disruption of westward tail current, i.e. its conversion into the ionospheric current connected with a pair of field-aligned currents in the magnetosphere. INTRODUCTION. Since 1958 (when the Sputnik III was launched with flux- gate magnetometers), a great number of artificial satellites or planets contributed to the study of magnetic field around the earth. In the meantime the techniques for measuring magnetic field, especially the three-component measurement, have greatly advanced. This enabled us to know the electric current pattern in the earth's environmental space through the analysis of magnetic field measured at various altitudes by space vehicles. Magnetometers on board some high-apogee satellites or artificial planets detected the shock front and the magnetosheath over the earth's magnetosphere on the sunlit side, and a long magnetotail with the neutral sheet near the equatorial on the night side. This was an experimental verification of the spatial magnetic field configuration around the earth that had been inferred to some extent from the ground observation of geomagnetic field and its time-variations. Because of the non-uniqueness in assigning the equivalent overhead current- system for ground magnetic variations (Fukushima, 1969), the in situ observ ation of the geomagnetic field by satellites is indispensable for knowing the exact pattern of electric currents flowing in the apace around the earth. A recent low-altitude satellite MAGSAT wa3 devoted to a very accurate three-component measurement of the global magnetic field (Langel et al.,1982); it was launched with the inclination angle of 96.76° (initial apogee 561 km and perigee 352 km) to keep its orbit always confined to the dawn-dusk meridian plane throughout its operative period of November 1979 - June 1980. Although the MAGSAT project objectives were (1) to carry out accurate vector measure ments of the near-earth magnetic field and (2) to use these measurements to *■ identify and model the main (core) and crustal fields, it was also possible to study the electric currents flowing in and above the ionosphere at the dawn and dusk. This subsidary investigation took the advantage of repeated measurements by MAGSAT at the two selected local times; otherwise the spatial and temporal variations are inseparable in the data obtained by flying space craft. Magnetometers on board some synchronous satellites provided us with use ful information on the time-variation of the magnetic field on the equatorial plane at 6.6 earth radii. At this altitude the observed magnetic field is slightly deviated from that of a geocentric dipole; it is compressed on the 75