Vertical variations in the N₂ mass mixing ratio during a thermospheric storm that have been simulated using a coupled magnetosphere-ionosphere-thermosphere model

The Center for Integrated Space Weather Modeling's (CISM) suite of models was run together to simulate the passage of an idealized coronal mass ejection (CME) from the Sun's corona to geospace. The resulting interplanetary magnetic field (IMF) pattern included a period during which B_z was southward. The effects of this CME were then propagated through the Lyon-Fedder-Mobarry (LFM) model of the magnetosphere to study its influence on the Earth's ionosphere and thermosphere. The effect of these changes on the thermosphere ionosphere nested grid (TING) model was to drive a large ionospheric and thermospheric storm. This storm had higher potentials than one would expect from the magnitude of the southward excursion of B_z. Changes in N ₂ mmrs were analyzed to investigate their height variations rather than attempting to make any detailed comparison with data. Several conclusions were drawn from this study: (1) The results were consistent with previous data and modeling studies of composition changes on a horizontal surface; (2) neutral composition was severely affected by this storm with large increases in the relative densities of the molecular species first being seen in the high and middle latitudes of the night and early morning sectors and later at all local times; (3) the observed changes were larger than might be expected from the IMF; (4) most upwelling occurred in the dayside auroral oval; far less upwelling occurred in the nightside auroral oval; (5) the large-scale circulation of the storm on the nightside created an overturning in the middle latitudes; (6) this overturning was primarily the result of molecular-rich air being transported horizontally over air that was not as rich in the molecular species; (7) the overturning acted as a diffusive barrier that prevented molecular diffusion from driving recovery to the thermosphere's quiet time compositional distribution; (8) the large-scale circulation has the potential to directly mix the thermosphere on relatively short timescales.