Simultaneous observations of auroral zone electrodynamics by two satellites: Evidence for height variations in the topside ionosphere

The S3-2 and S3-3 satellites were launched with identical orbit inclinations and with apogees of 1500 and 8000 km respectively. By comparing a few cases when the satellites were crossing the auroral zone at approximately the same universal time and location, altitude variations in the electrodynamics of the auroral zones can be separated from universal and local time variations. Such comparisons show that there are times when the field aligned current per unit of flux in the auroral zone measured by magnetic field deflections at the two satellites is the same at both altitudes. There are also times when the field aligned current per unit of flux is larger at high altitudes then at low altitudes. This requires convection electric field at the two altitudes show that the electric field does not always map as though field lines were were equipotentials. In addition, intense, small scale (0.1 deg) electric fields perpendicular to the magnetic field observed at high altitudes are usually not seen in simultaneous low altitude observations.