Drivers for different behaviors in storm-time thermospheric O/N2 ratio and nitric oxide density

Geomagnetic storms lead to significant depletion/enhancement in O/N2 column density and enhancement in nitric oxide (NO) in the thermosphere.  The O/N2 depletion is generally anti-correlated with NO enhancement on a global scale. However, the NO enhancement often extends beyond the equatorward edge of O/N2 depletion in latitude and/or the range of O/N2 depletion in longitude on a local scale. These behaviors are most likely driven by the storm-time equatorward wind that brings the O/N2 depleted and NO enhanced air from high to low latitudes, as well as zonal wind perturbations. On the other hand, the equatorward wind also depends on altitudes. Note that the peak NO density locates at an altitude around 110 km while the O/N2 column density is mostly contributed by local O andN2 density around 140 km and above. The different behaviors between NO and O/N2 are likely due to the altitude variations of the meridional winds during storms as revealed by TIEGCM simulations. The downward advection by vertical winds associated with storm-time meridional circulation perturbations may also contribute to the difference.