Middle ultraviolet remote sensing of the equatorial thermosphere during a geomagnetic storm

Abstract. We present measurements of the equatorial middle ultraviolet airglow taken during the week of 21-28 May 2000, including a strong geomagnetic storm on 24 May. Limb spectra were taken by the Ionospheric Spectroscopy and Atmospheric Chemistry (ISAAC) experiment on the Advanced Research and Global Observation Satellite (ARGOS). OII lines near 247.0nm and NII lines near 214.3nm provide a measure of thermospheric O and N₂ changes, respectively. Our results show increases in airglow brightness of both emissions during the storm that we interpret as increases in the concentrations of both species, but the ratio of intensities that correspond to O/N₂ is lower than expected during and after the storm. We also invert the emission profiles using discrete inverse theory, to obtain a measure of thermospheric neutral temperatures during this time. Although temperatures increase after the main phase of the storm, the increases do not correlate with the observed features in the intensity ratio. These data could be explained by vertical winds and tides modifying the equatorial neutral composition during storms, in addition to common heating responses.