The global efficiency of relativistic electron production in the Earth's magnetosphere

Data from sensors on board the Polar, Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX), and other Earth-orbiting spacecraft show that h igh-energy electron intensities vary in a global, coherent way throughout t he outer trapping zone of the terrestrial magnetosphere. Long-term measurem ents of very energetic trapped electrons provide a comprehensive view of th e large variability of intensities on timescales less than I day to times c orresponding to the 11-year sun-spot cycle. The average density of relativi stic electrons within the outer magnetospheric trapping region (2.5 <L <6.5 ) is calculated in this paper during a 7-year observing period. The total e nergy content and power dissipation in this relativistic electron component are then compared on a yearly basis to the solar wind energy that impacts the magnetosphere during the same time. The overall efficiency of relativis tic electron production is thereby computed and is found consistently to be similar to1% throughout the entire observing interval. Such efficiencies a re important and potentially useful in scaling electron acceleration in oth er, more remote solar, planetary, and cosmic systems. The results presented here suggest that a range of different processes are involved in producing very energetic electrons in various astrophysical plasmas.