The electrical and precipitation characteristics of morning sector Sun-aligned auroral arcs

Two sounding rockets launched from Greenland on March 31, 1987, present one of the most detailed pictures of polar cap auroral are dynamics ever obtained. The electrodynamics show a clear picture of energy flux carried by energetic, precipitating electrons accompanied by a comparable magnitude Poynting flux immediately adjacent to the electron precipitation. The result is a W-shaped region of energy flux at the locations of auroral arcs. In addition, the current carried by the energetic, precipitating electrons is somewhat greater than that indicated by the magnetometer measurements, suggesting that the background ionosphere: in the polar cap may have closed the upward electron current with a downward current along the same field fines. The measurements are compared to a model of quasi-static auroral acceleration based on that by Lyons [1981]. It is found that this model reproduces well most of the electrodynamic features; energy flux, electric fields, and parallel currents determined by the model are in generally good agreement with the in situ measurements.