VARIATIONS OF TOTAL ELECTRON-CONTENT DURING GEOMAGNETIC DISTURBANCES - A MODEL OBSERVATION COMPARISON/

This paper studies the ionospheric response to the major geomagnetic s torm of October 18-19, 1995, using the NCAR TIE-GCM simulations and th e global ionospheric maps (GIM) of total electron content (TEC) observ ations from the worldwide network of Global Positioning System (GPS) r eceivers. The TIE-GCM results show a good agreement with the GPS-GIM i n terms of simulating storm-time TEC disturbances over the polar regio ns. The model indicates that the increase of electron density in the h igh-latitude E and lower F regions below 200 km is directly related to the magnetospheric energy input through auroral precipitation to the ionosphere, while the decrease of TEC is mainly due to the increase in O-2 and N-2 densities in the upper F region above 200 km. During the recovery phase, both the TIE-GCM and GPS-GIM reveal a distinct hemisph eric asymmetry in the TEC integrated above \50 degrees\ magnetic latit ude, with a 20% decrease in the southern (summer-like) hemisphere and a 30% increase in the northern (winter-like) hemisphere.