Ground-based observations of field-aligned currents in auroral zone - Methods and results

Some methods for reconstructing the three-dimensional current flow in the auroral zone from ground magnetic and from ionospheric electric field observations have been developed. The basic features of the algorithm of Kamide et al. (1981) and Mishin et al. (1979) and of the Untiedt (1983) algorithm, and forward modeling procedure are described. The three-dimensional current flow derived using these methods is analyzed. Particular attention is given to global field-aligned current flow during the maximum phase of a substorm, field-aligned current flow within the Harang discontinuity, eastward drifting auroral omega bands, westward travelling surges, and temporal oscillations of field-aligned currents during substorm onset. It is observed that the Harang discontinuity, omega bands, and westward travelling surge represent stationary patterns and the EISCAT data combined with these methods are useful for studying field-aligned currents in the auroral zone.