Auroral-zone X-ray events and their relation to polar magnetic substorms

Abstract

The general relationship between auroral-zone X-ray events produced by precipitating electrons, and magnetic bay activity, has been studied. Every X-ray event, irrespective of the local time at which it was observed, could be associated with a negative disturbance in the geomagnetic H-component in the midnight sector of the auroral zone. And in most cases, a polar magnetic substorm of global character could be identified. X-ray events observed in the local midnight sector are prompt with respect to the associated magnetic disturbance, but it has been found that those which occur later tend to be delayed, and those observed after 0600 hr LMT are always delayed. The average delay increases with increasing separation of the region of electron precipitation from the instantaneous midnight sector, which is interpreted as an effect of drift of electrons in the magnetosphere, from an acceleration region on the night side of the Earth. Reasons are given for assuming that the acceleration region is usually rather narrow in latitude, and may extend from about magnetic midnight to dawn.