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This paper presents the results of model calculations of the behavior of the ionosphere during a complex space-weather event that occurred in September 2017. The main attention is paid to the analysis of the response of an integral characteristic of the ionosphere—global electron content (GEC)—to geomagnetic storms on September 7–8. Comparison of the temporal behavior of the model and experimental GEC showed there to be a good qualitative agreement between the temporal variations of hydroelectric power stations associated with geomagnetic storms. At the same time, the absence in the results of model calculations of positive hydroelectric disturbances observed on September 7, 8, and 11 is noted. It is hypothesized that these positive disturbances of the GEC on the indicated days may be associated with the observed solar-proton events and precipitation of protons from the magnetosphere, but not taken into account in model calculations. [ABSTRACT FROM AUTHOR]

In this paper, we discuss perturbations in neutral temperature, total electron content (TEC), and critical frequency of the maximum of the F2 layer (foF2) during the sudden stratospheric warming in January 2009. The calculations were performed using the first version of the EAGLE (Entire Atmosphere Global Model), which is a combination of the models of the low-middle atmosphere (HAMMONIA) and the upper atmosphere (GSM TIP). The EAGLE reproduces observed stratospheric warming and related mesospheric cooling in the northern polar cap in January 2009. At thermospheric altitudes, the neutral temperature perturbations have a quasi-wave character with a wavelength of ∼40 km in the vertical direction. Our results indicate that the HAMMONIA model should be used in the EAGLE instead of the GSM TIP model for the neutral temperature calculations in the altitude region from 80 to 120 km. It is shown that the obtained model foF2 and TEC perturbations are mainly related to seasonal variations. The most-pronounced perturbations in the ionospheric electron density due to stratospheric warming are formed near the equator and are basically negative. Our analysis of the neutral temperature and electron density perturbations made it possible to conclude that the dependence of ionospheric parameters on seasonal changes in solar zenith angle is stronger than for the thermosphere parameters. [ABSTRACT FROM AUTHOR]

The study presents the results of the analysis of the F2-layer critical frequency variations obtained for the winter periods of 2008-2010, during which sudden stratospheric warmings were observed. The data were obtained at Kaliningrad ionospheric station (54.6° N, 20° E) with the Parus digital ionosonde in standard sounding mode. The mean daily foF2 values were used in the analysis. The results of spectral analysis based on continuous wavelet transform showed that, during all of the warmings that occurred in 2008-2010, the foF2 time variations demonstrated the presence of wave processes with periods of approximately 5−6 days, as well as more extended processes with periods of ~10−13 and 23−30 days. These periods coincide with the characteristic periods of planetary waves observed in the mesosphere during sudden stratospheric warmings, while the 13- and 30-day periods can be conditioned by the influence of the Sun. [ABSTRACT FROM AUTHOR]