Thermospheric nitric oxide at higher latitudes: Model calculations with auroral energy input

摘要

The nitric oxide (NO) density in the lower thermosphere has been calculated by a photochemical model for NOx and compared with measured NO densities from Student Nitric Oxide Explorer (SNOE). At higher latitudes the most important contributor for NO density increases is energetic electron precipitation. The electron energy is estimated in two ways, from auroral ultraviolet (UV) and X-ray measurements obtained from Ultraviolet Imager (UVI) and Polar Ionospheric X-ray Imaging Experiment (PIXIE) on board the Polar satellite and from ground magnetometer measurements. For the time intervals when the Polar satellite was not above the northern hemisphere, a parameterization of the electron energy flux from ground magnetic measurements was used. This parameterization was based on data from the SuperMAG database compared to UVI/PIXIE derived electron energy fluxes. The negative perturbation in the northward ground magnetic component is found to be linearly related to the precipitating electron energy flux. The 4-day period studied is from 30 April (day 120) until 4 May 1998, where the onset of a geomagnetic storm occurred 2 May (day 122). The results of the comparisons show an overall larger modeled nitric oxide density at auroral latitudes than what was measured by SNOE. The largest discrepancies were for the day of the storm onset, when the background atmosphere was more distorted by Joule heating. The next day the agreement between the model and the observations was far better, which might be due to less amount of Joule heating this day.