Storm-time variations in aurora and thermospheric compositions

A space based spectrographic imager TIMED/GUVI measures auroral and dayglow emissions. During geomagnetic storms, the energy input from the magnetosphere to the polar ionosphere enhances, increase auroral intensities and extend auroral activity to lower latitudes. This leads to significant changes in the thermospheric O/N2 ratio and nitric oxide (NO) density. The coincident O/N2 ratio and NO column density maps from GUVI reveal two major features: (1) Storm-time O/N2 depletion and NO enhancement extend from high to mid and low latitudes. They are anti-correlated on a global scale, (2) the NO enhancement covers a wider longitude and latitude region than O/N2 depletion on a local scale. Possible mechanisms for the features will be discussed. These observations are important as predictors of times when neutral density models will not be able to correctly predict the amount of satellite drag, especially for vehicles in low-altitude, dipping orbits or those that need accurate predictions of low altitude drag in order to schedule orbit changes to avoid debris.