An auroral-zone electron precipitation event and its relationship to a magnetic bay

The relationship of an auroral-zone electron precipitation event to a magnetic bay has been examined using simultaneous observations of X-ray intensity at balloon altitudes, ionospheric absorption of cosmic radio noise, geomagnetic micropulsations in the 5- to 30-sec period range, and variations in the geomagnetic elements H, D, and Z. These observations show that an intense electron bombardment of the upper atmosphere was in progress prior to the bay and suggest that the current system of the bay was ‘triggered’ by the sudden intensification and expansion of the electron precipitation. The motion of the current system of the westward electrojet and the electrons precipitating on the atmosphere was toward the north, indicating that processes well out of the lines of force through the auroral zone, rather than local field conditions, were responsible for the movement.