Morphology of electron precipitation during auroral substorms

A Study of auroral substorms using coordinated measurements of a number of parameters at Ft. Churchill, Manitoba (L = 8) in October 1963 has yielded interesting conclusions on the electron precipitation close to the northern auroral boundary, the morphology of which appears to follow closely the working model proposed by Akasofu. Extensions to this model are suggested that include high energy electron precipitation (>30 keV) as determined from X-ray measurements at balloon altitudes. During surges and auroral substorms near local midnight, very localized precipitation of electrons with a wide spectrum of energies produced a sharp northern optical and radio absorption border which moved rapidly northwards and contained the auroral electrojet. During the decay phases of the substorms, a region of high energy precipitation receded southwards in advance of the northern border of luminous aurora and appeared to be accompanied by the ionospheric electric current. In contrast to this, the optical northern border produced no noticeable auroral absorption or magnetic activity on its southward overhead passage later in the substorm. Systematic spectral changes near the border indicated a softening of the electron spectrum above 40 keV with increasing northward position (or increasing L value), in agreement with satellite observations. Highly structured enhancements of precipitation of high energy electrons occurred at times when small scale folds in auroral bands were reported during break-up and at times of occurrence of Type B aurora.