Changes of Electron Density Profiles during Extreme Manifestation of Solar Activity
Boska, J.; Sauli, P.; Buresova, D.
Institute of Atmospheric Physics ASCR

During periods of extreme solar events rapid changes of electron concentration profiles of the Ionosphere lead to the high degradation of the satellite navigation system precision. This contribution deals with changes in the Ionosphere during most extreme events of solar activity during years 1986 till 2007. Studied events are selected according to the Dst index (Events with Dst excceding -200 nT are involved). Our results show that the most pronounced effects in the Ionosphere were observed during winter time in the period of solar minimum. Extreme events of this type were observed 8 February, 1986 and 20 November, 2003. During solar maximum, greatest event occured in March 1989. Comparison of the ionospheric effects during the analysed events shows that influence/effects of solar maximum events on the Ionosphere were substantialy lower compare to the events occuring during solar minimum especially during winter. Changes of the electron density profiles are very fast and sharp and therefore difficult to be predicted. This contribution demonstrates the importance of the direct ionospheric measuremets in the navigation systems.