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We present two case studies in the night and evening sides of the auroral oval, based on plasma and ®eld measurements made at low altitudes by the AUREOL-3 satellite, during a long period of stationary magnetospheric convection (SMC) on November 24, 1981. The basic feature of both oval crossings was an evident double oval pattern, including (1) a weak arctype structure at the equatorial edge of the oval/polar edge of the diuse auroral band, collocated with an upward ®eld-aligned current (FAC) sheet of 1.0 lA m, (2) an intermediate region of weaker precipitation within the oval, (3) a more intense auroral band at the polar oval boundary, and (4) polar diuse auroral zone near the polar cap boundary. These measurements are compared with the published magnetospheric data during this SMC period, accumulated by Yahnin et al. and Sergeev et al., including a semi-empirical radial magnetic ®eld pro®le BZ in the near-Earth neutral sheet, with a minimum at about 10±14 RE. Such a radial BZ pro®le appears to be very similar to that assumed in the ``minimumB/cross-tail line current'' model by Galperin et al. (GVZ92) as the ``root of the arc'', or the arc generic region. This model considers a FAC generator mechanism by Grad-Vasyliunas-BostroÈ m-Tverskoy operating in the region of a narrow magnetic ®eld minimum in the near-Earth neutral sheet, together with the concept of ion non-adiabatic scattering in the ``wall region''. The generated upward FAC branch of the double sheet current structure feeds the steady auroral arc/inverted-V at the equatorial border of the oval. When the semiempirical BZ pro®le is introduced in the GVZ92 model, a good agreement is found between the modelled current and the measured characteristics of the FACs associated with the equatorial arc. Thus the main predictions of the GVZ92 model concerning the ``minimum-B'' region are consistent with these data, while some small-scale features are not reproduced. Implications of the GVZ92 model are discussed, particularly concerning the necessary conditions for a substorm onset that were not ful®lled during the SMC period.

Stationary magnetospheric convection on November 24, 1981. 1. A case study of “pressure gradient/minimum-