Diurnal, seasonal and solar activity pattern of ionospheric variability from Irkutsk Digisonde data

From 2003-2012 dataset of the Irkutsk DPS-4 Digisonde (52.3°N, 104.3°E), we obtained the diurnal, seasonal and solar activity pattern of the F2 peak density (NmF2) variability for both high- and low-frequency parts of the variability. The high-frequency part (periods from 0.5 to 6 h) is mainly caused by traveling ionospheric disturbances associated with internal gravity waves. The low-frequency part with periods more than 6 h is related to long-term variability. The year-to-year (solar cycle) variations of the total daytime variability were used to estimate the geomagnetic and meteorological activity contributions into the NmF2 variability. An explanation of the obtained variability pattern is proposed in terms of the geomagnetic, meteorological and wave activity contributions, and the sensitivity of the ionospheric electron density to the geomagnetic and meteorological impacts.