Estimation of Ionospheric Electrodynamic Parameters Using Ionospheric Conductance Deduced from Bremsstrahlung X-Ray Image Data

摘要

Various ionospheric electrodynamic parameters are calculated by using ground magnetic records from a total of 88 stations in the northern hemisphere. For this purpose, an instantaneous conductance distribution deduced from the DMSP-F6 bremsstrahlung X-ray image data is utilized. It is a unique opportunity to examine some of the inherent ambiguity in the magnetogram-inversion technique based on a statistically-derived conductance model. Important conclusions are: (1) The pole-ward portion of the westward electrojet in the morning sector is dominated by electric field, while its equatorward portion is dominated by the ionospheric conductance. (2) During a quiet or moderately disturbed period, the major electric potential pattern is roughly circumscribed by the auroral zone conductance belt. (3) The global pattern of the equivalent current system resembles the electrical potential distribution. (4) The electric potential distribution consists generally of a smooth and well-defined two-cell convection pattern without any significantly localized structure. (5) A sunward convection flow is clearly identified over the polar cap region. (6) During strongly northward IMF periods, significant currents and joule dissipation are observed in the polar cap region, indicating that the magnetosphere is far from its ground state. (7) The regions of intense joule heating are generally confined to relatively narrow belts. (8) The Region 2 upward current in the morning hemisphere is roughly collocated with the enhanced conductance region. (9) The presently available statistical conductance models can be used, as a first approximation, to study global-scale polar ionospheric electrodynamics. Aurorae. (jhd)