The huge number of researches is devoted to formation of additional layers in F-region of equatorial ionosphere, first of which has been published more 60 years ago. Originally the occurrence of such layers has received the name “stratification of equatorial F2-layer”. However, in the middle of 90-s' years of the last century it has been shown, that the additional maximum above F2-layer maximum in the equatorial ionosphere exists regular enough and at the certain Local Time. From this point onwards it was named by F3-layer, and instead of the term “stratification of equatorial F2-layer” the most of researches began to speak about formation of the F3-layer. The theoretical and experimental researches which have been carried out last 20 years, have shown, that the F3-layer is formed by zonal component of electric field with assistance of meridional component of thermospheric wind. However, it is necessary to notice, that till now there is no precisely formulated physical mechanism of F3-layer formation. The given research is devoted to detailed investigation of the formation mechanism of F3-layer in quiet geomagnetic conditions and its variations during geomagnetic disturbances. These researches are based on calculation results obtained with use of the model GSM TIP and experimental data of Interkosmos-19 satellite and digital ionosondes. The research is carried out at financial support of the Russian Foundation for Basic Research (Grant №08-05-00274).

Earlier we have carried out the researches of behavior of ionosphere F-region parameters during geomagnetic storm sequence on September 9-14, 2005. These researches have been executed with use of the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) and experimental data of digital ionosondes, incoherent scatter radars and GPS receivers. The comparison of ionospheric effects of geomagnetic storms obtained in modeling calculations, with experimental data has revealed the satisfactory agreement. In the given work the results of researches of this storm sequence effects in the external ionosphere are presented. The comparison of calculation results of electron concentration and electron temperature with experimental data of DMSP F13 and F15 satellites (height of ~830 km) is carried out. Besides on the basis of model calculation results the global maps of disturbances of various parameters of the external ionosphere during geomagnetic storms are constructed and physical interpretation of the obtained effects is submitted. The research is carried out at financial support of the Russian Foundation for Basic Research (Grant №08-05-00274).