A case study test of Araki's physical model of geomagnetic sudden commencement

This paper tests the Araki [1994] computational model of the Earth-ionosphe re system during geomagnetic sudden commencement (sc). In particular, we te st the model's ability to predict the signs of the preliminary and main imp ulses, given the latitude and the magnetic local time (MLT), using a case s tudy of an sc which occurred at 0949 UT on November 22, 1997. Data from a g lobal network of magnetometer stations and from satellites are used. Model predictions compare well with the case study data at high latitudes (above similar to 72 degreesN Altitude Adjusted Corrected Geomagnetic Coordinates (AACGM)), less well for lower latitudes, particularly on the nightside. In addition, the position of the footprints of the field-aligned currents (FAC s) associated with the sc ground signature varies with MLT, contrary to the model. Data from satellites in polar and geostationary orbits suggest that the FACs for both the preliminary and the main impulses map to gradients i n magnetospheric plasma concentration, such as the outer radiation belt and the plasmapause.