X-Ray Observations and Interpretations

Abstract

The presence of soft X-rays in the stratosphere at high latitudes was first reported in 1956, and correctly identified as due to Bremsstrahlung from energetic auroral electrons entering the atmosphere. Balloon X-ray measurements provide the most direct means of monitoring auroral electron precipitation both day and night from a relatively fixed location, and for long periods of time. Further, no time constants are involved in the Bremsstrahlung process, and the approximate electron spectrum and flux can be obtained quite readily. X-ray measurements however, do suffer severe limitations. The Bremsstrahlung process is very inefficient and this, plus atmospheric attenuation of the X-rays, makes the method useful only in the energy range 20 to 200 keV. Further, due to the isotropic emission of X-rays by the source and subsequent scattering in the atmosphere, detectors at balloon altitudes provide only a spatially averaged picture of the electron precipitation.