Relativistic magnetospheric electrons: Lower ionospheric conductivity and long-term atmospheric variability

Abstract

Long-term (1979–88) observations of relativistic electrons in the earth's outer magnetosphere show a strong solar cycle dependence with a prominent intensity maximum during the approach to solar minimum (1983–85). This population therefore corresponds to the presence of high-speed solar wind streams emanating from solar coronal holes. Using a numerical code, we have calculated the precipitating electron energy deposition in the earth's upper and middle atmosphere. Observed events (typically persisting several days) would have maximum effect in the 40–60 km altitude range. We suggest that this electron population could play an important long-term role in modulating lower D-region ionization and middle atmospheric ozone chemistry. We describe methods of observing middle atmospheric and lower ionospheric effects of the electrons. A particularly promising approach may involve the monitoring of global Schumann resonance modes which are sensitive to global changes in the properties of the earth-ionosphere cavity. Ongoing work indicates that Schumann resonance properties are moderately correlated with the flux of precipitating relativistic electrons thus offering the possibility of continuously monitoring this aspect of magnetosphere-atmosphere coupling.