INVERTED-V EVENTS SIMULTANEOUSLY OBSERVED WITH THE FREJA SATELLITE AND FROM THE GROUND

The paper reports data received from the Freja satellite during two pa sses over broad auroral arc systems or inverted-V events above Gillam/ Manitoba when special wide-angle CCD cameras were operated at this loc ation in addition to the CANOPUS network. Detailed comparisons of the visible structures with modulations of the primary electron fluxes are performed. Motions of this fine structures are interpreted in terms o f high-altitude electric fields shielded from the lower ionosphere. Si multaneous readings of current density, accelerating voltage and energ y flux, the latter determined both from particle and auroral brightnes s measurements, are found to be internally consistent. We calculate fr om these data the effective resistance encountered by the electric cur rents and find agreement with the kinetic theory of the mirror impedan ce, if we allow for substantial variations in density and energy of th e source electrons in the magnetosphere.