Some average properties of auroral electron precipitation as determined from satellite observations

Abstract

The total energy flux of electrons precipitating on the auroral zones has been measured by particle detectors aboard a low-altitude, polar-orbiting satellite for the 5-day period from October 30 to November 4, 1963. The observations were made at local times of approximately 0100 and 1300 hours. Precipitating electrons were observed on almost every transit of the auroral zone. Parameters are defined characterizing the intensity, the angular distribution, and the energy distribution of the precipitating electrons. The relationships among these parameters and their dependence on Kp are examined. The averaged total precipitated energy flux was found to be approximately 5 times more intense on the night side than on the day side of the auroral zone, and the averaged energy distribution was found to be softer on the night side. The averaged angular distributions were found to be generally anisotropic, peaking at the higher pitch angles. The intensity of the precipitation was found to increase, the angular distribution became more isotropic, and the averaged spectral hardness increased as Kp increased. The averaged energy and angular distributions were also found to undergo significant changes that occurred on a global scale and persisted for many hours, thus indicating that large-scale, rather than local, processes were responsible for these changes. The total auroral-zone energy input is computed for the period of the experiment, and by comparison with published measurements for the average solar wind properties, an ‘efficiency’ of the auroral mechanism is calculated. This efficiency varies approximately from 0.01% to 0.2% as Kp varies from 0 to 5.