Variations of total electron content during geomagnetic disturbances: A nlodel/olmervation comparison

This paper studies the ionospheric response to a major geomagnetic storm of October 18-19, 1995, using the thermosphere-ionosphere electrodynamics general circulation model (TIEGCM) simulations and the global ionospheric maps (GIM) of total electron content (TEC) observations from the Global Positioning System (GPS) worldwide network. The TIE-GCM results, which utilize the realistic time-dependent ionospheric convection and auroral precipitation derived from the assimilative mapping of ionospheric electrodynamics (AMIE) procedure as the inputs at the upper boundary, shows a good agreement with the GPS-GIM in terms of simulating storm-time TEC disturbances over the polar regions as well as variations in hemisphere-integrated TEC. The model simulation indicates that the increase of electron density, especially in the highlatitude E and lower F regions below 200 km, is directly related to the magnetospheric energy inputs (through Joule heating and auroral precipitation) to the ionosphere. A goocl correlation is found between the percent increase in TEC and auroral precipitation during the main phase of the storm. The simulation also shows that the decrease of TEC, on the other hand, is mainly due to the increase in 02 and N2 in the upper F region above 200 km. During the recovery phase, both