Middle atmosphere ionization from auroral particle precipitation as observed by the SSUSI satellite instruments

Solar, auroral, and radiation belt electrons enter the atmosphere at polar regions leading to ionization and affecting its chemistry. Climate models usually parametrize this ionization and the related changes in chemistry based on satellite particle measurements. Precise measurements of the particle and energy influx into the upper atmosphere are difficult because they vary substantially in location and time. Widely used particle data are derived from the POES and GOES satellite measurements which provide electron and proton spectra.

We present electron energy and flux measurements from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) satellite instruments on board the Defense Meteorological Satellite Program (DMSP) satellites. This formation of now four satellites observes the auroral zone in the UV from which electron energies and fluxes are inferred in the range from 2 keV to 20 keV. We use these observed electron energies and fluxes to calculate ionization rates and electron densities in the upper mesosphere and lower thermosphere (≈ 70–200 km). We present an initial comparison of these rates to other models and compare the electron densities to those measured by the EISCAT radar. This comparison shows that with the current standard parametrizations, the SSUSI inferred auroral (90–120 km) electron densities are larger than the ground-based measured ones by a factor of 2–5. It is still under investigation if this difference is due to collocation (in space and time) and EISCAT mode characteristics or caused by incompletely modelling the ionization and recombination in that energy range.