A model study of the mid-latitude ionospheric response to a strong geomagnetic storm of September 25, 1998

From September 25 to 27, 1998, a strong geomagnetic storm occurred, during which the planetary index of geomagnetic activity Kp was as high as similar to8.5, and Dst was similar to-207 nT. During the concerned storm, the Irkutsk Incoherent Scatter Radar measured height-time variations of electron density, electron and ion temperatures and plasma drift line-of-sight velocities. An interpretation of the measurements involved comparing them with results of calculations in terms of a numerical model of the ionosphere and plasmasphere. It was shown that the measured variations of such ionospheric parameters as the electron density, electron and ion temperatures, as well as ion fluxes along the geomagnetic field are reasonably accurately reproduced in model calculations. Furthermore, the ionospheric response to the magnetic storm under consideration was controlled mainly by a disturbance in the composition of the neutral atmosphere. The enhancement of the horizontal wind left the ionospheric response essentially unaffected as a consequence of what occurred in the morning hours when the ion production sources were insufficiently intense.