SATELLITE AND ROCKET STUDIES OF RELATIVISTIC ELECTRONS AND THEIR INFLUENCE ON THE MIDDLE ATMOSPHERE

Magnetospheric electrons from hundreds of keV to over 10 MeV in energy have been systematically measured at geostationary altitude (6.6 R(E) ) for well over a decade. We find evidence of significant diurnal, sol ar-rotational (27-day), annual, and solar-cycle (11-yr) variations in the fluxes of the relativistic electron component. We have also used l ow-altitude satellite data and sounding rocket measurements to charact erize the location and strength of the relativistic electron precipita tion into the atmosphere. We conclude that the magnetospheric electron s, when dumped into the middle atmosphere, represent a very significan t ionization source which affects the pattern of conductivity, electri c fields, and atmospheric chemistry. These measurements-when combined with global atmospheric modeling-suggest that relativistic electrons p rovide a robust coupling mechanism to impose long-term solar wind and magnetospheric variability onto the Earth's deep atmospheric regions. A strong 11-yr cycle of relativistic electron effects is found in avai lable atmospheric data sets.