Seasonal Variability of Relationship between Main Ionospheric Characteristics and Solar/Geomagnetic Indices via Graphical Models of Conditional Independences

We investigated seasonal variations of relationships between main ionospheric characteristics and solar and geomagnetic indices in longitudinal perspective. We consider statistically significant differences in connections of ionospheric response to the F10.7cm, R, and Kp indices on seasonal time-scales during years 1975 – 2010 covering 21^st – 23^rd Solar Cycles. The periods of 21 days before and after Winter/Summer Solstices and Vernal/Autumnal Equinoces are considered as season. The foF2 time series in our analysis represent measurements of daily observational data which were obtained using mid-latitude (41.4°N – 54°N) ionosondes (Chilton, Slough RL052/SL051, Juliusruh/Rugen JR055, Boulder BC840). We used local time noon 5-hour foF2 averages. For the investigation, we used seasonal differences method of conditional independence graphs (CIG) models. Significant seasonal variations are visible during ascending and descending phases of Solar cycles.