Energetic electron precipitation and the NO abundance in the upper atmosphere: A direct comparison during a geomagnetic storm

Abstract

Nitric oxide (NO) densities at heights between 96 and 150 km in the Earth's upper atmosphere are directly compared with the energy deposition from precipitating energetic electrons. The comparisons are done for the beginning of a geomagnetic storm event on 2 May 1998. The electron energy is derived from X‐ray bremsstrahlung observations from the Polar Ionospheric X‐ray Imaging Experiment (PIXIE) on board the Polar spacecraft. Measurements of the NO density are performed by the Student Nitric Oxide Explorer (SNOE) on the dayside by measuring airglow spectral features of the NO γ‐band. Since a significant part of the electron precipitation takes place during the night, and considering the long lifetime of NO, we have accumulated the X‐ray data in geographical boxes. This enables us to follow the development of the total energy deposition over a specific area during the night and morning hours. In agreement with theoretical predictions we find an increase in NO at higher latitudes due to electron precipitation. At 106 km altitude, which is found to be the average altitude of the peak values of both NO intensity and precipitating electron energy, ∼83% of the NO density is produced by electron precipitation. At this altitude we find that the electron precipitation results in the production of ∼8 NO molecules per keV deposited energy. The comparison of the data also shows effects of a horizontal neutral wind. Above 100 km the peak in NO density is displaced equatorward of the peak in electron energy deposition.