Nelya M. Polekh

The ionosphere under extremely prolonged low solar activity

[1]xa0A critical question in ionospheric physics is the state of the ionosphere and relevant processes under extreme solar activities. The solar activity during 2007–2009 is extremely prolonged low, which offers us a unique opportunity to explore this issue. In this study, we collected the global ionosonde measurements of the F2 layer critical frequency (foF2), E layer critical frequency (foE), and F layer virtual height (h′F) and the total electron content (TEC) maps produced by the Jet Propulsion Laboratory, which were retrieved from dual-frequency GPS receivers distributed worldwide, to investigate the ionospheric phenomena during solar minimum of cycle 23/24, particularly the difference in the ionosphere between solar minima of cycle 23/24 and the preceding cycles. The analysis indicates that the moving 1 year mean foF2 at most ionosonde stations and the global average TEC went to the lowest during cycle 23/24 minimum. The solar cycle differences in foF2 minima display local time dependence, being more negative during the daytime than at night. Furthermore, the cycle difference in daytime foF2 minima is about −0.5 MHz and even reaches to around −1.2 MHz. In contrast, a complex picture presents in global h′F and foE. Evident reduction exists prevailingly in the moving 1 year mean h′F at most stations, while no huge differences are detected at several stations. A compelling feature is the increase in foE at some stations, which requires independent data for further validation. Quantitative analysis indicates that record low foF2 and low TEC can be explained principally in terms of the decline in solar extreme ultraviolet irradiance recorded by SOHO/SEM, which suggests low solar EUV being the prevailing contributor to the unusual low electron density in the ionosphere during cycle 23/24 minimum. It also verifies that a quadratic fitting still reasonably captures the solar variability of foF2 and global average TEC at such low solar activity levels.

Ionospheric effects of St. Patrick's storm over Asian Russia: 17-19 March 2015: IONOSPHERIC EFFECTS OVER RUSSIA

We have carried out a comprehensive analysis of data from the high-frequency coherent radar located near Yekaterinburg, ground-based ionospheric, riometric, and magnetic stations, situated within t ...

Backscattering dynamics during intense geomagnetic storm as deduced from Yekaterinburg radar data: March 17–22, 2015

This paper examines the spatio-temporal dynamics of backscattering signals during St. Patrick’s Day two-step intense geomagnetic storm from the Yekaterinburg Coherent Radar (YeKB radar) data. It is found that a number of ground backscattering signals increased during the initial phase of the storm and decreased during the second step of its main phase and the first two days of its recovery phase. Changes in ionospheric backscattering signals started at the beginning of the main phase. During the first step, there was a six-hour sequence of ionospheric backscattering signals (BSi signals) the range of which decreased while the storm was in progress. During the last 5 hours of the main phase and the first 3 hours of the recovery phase, the YeKB radar observed only signals scattering in the E region of the ionosphere. We conduct a complex analysis of data from the YeKB radar, ground-based ionospheric, riometric, and magnetic stations located within the radar field of view. The analysis shows that the observed backscattering dynamics was caused by the magnetosphere compression, expansion of convection cells, impact ionization, and changes in atmospheric composition during the initial storm phase, first and second steps of the main phase, and the recovery phase respectively.