Authors: Christopher Smithtro
Affiliation: Center for Atmospheric and Space Science, Utah State University;
United States Air Force
It is well established that solar EUV radiation is responsible for the formation of the ionosphere, and this irradiance in fact varies considerably on timescales of minutes (solar flares) to years (solar cycle). We examine the resulting sensitivity of the ionosphere over the same timescales using the Time-Dependant Ionospheric Model (TDIM) as well as a new coupled Global Average Ionosphere/Thermosphere (GAIT). In lieu of continuous direct measurements, empirical models are used to represent the solar irradiance. We compare electron density profiles computed using these EUV representations over the course of the solar cycle, and see up to a factor of two spread in the peak electron density as a result of differences between the models. On a much shorter timescale, solar flares can dramatic increase the solar XUV flux (1-30 nm) resulting in increased ionization, especially in the lower E region. The Solar EUV Experiment (SEE) instrument on the TIMED spacecraft has measured representative spectra during a number of flares. These data are used to investigate the ionospheric response to such solar variability.