A study of geoelectromagnetic disturbances in Quebec. II. Detailed analysis of a large event

For pt. I see ibid., vol.13, p.1251-6 (1998). As part of investigations of geomagnetically induced currents in the Hydro-Quebec power system, the geoelectromagnetic field was recorded at five sites in western Quebec in 1992 to 1994. A description of the measurements and some general results are presented in an accompanying paper. This paper concentrates on an analysis of a disturbance on February 21, 1994, that produced one of the largest electric fields recorded. The magnetic recordings are used to determine the intensity, location, and orientation of the auroral electrojet that is the cause of the disturbance. By tracking these parameters we show that dB/dt is due to both the changing intensity of the electrojet and due to movement of the electrojet. The resulting electric fields are found to be anti-parallel (parallel) to the electrojet when the magnetic field is increasing (decreasing).