Influence of Solar Rotation Influence on Ionospheric/Thermospheric Parameters: Modeling and Observations for Case Studies

We investigated the effect of ~27 day solar rotation on the thermosphere-ionosphere system at different latitudes using both model results and multi-instrumental observation data. Considered ionospheric stations (ionosondes, GPS receivers, ISR radars) were located from the middle to high latitudes in Northern hemisphere. We analyzed also TIMED/GUVI variations of the O/N2 ratio in the thermosphere. Three different temporal periods were considered: December 2012-January 2013; January 2014; June-July 2014. The Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) were used for interpretation of coupled processes in the thermosphere-ionosphere system during one solar rotation cycle. There is a distinct response of daytime ionospheric electron density to the ~27-day variation in solar flux (F10.7). Using comparative and correlative analysis we revealed a delay in variation of modeled daytime critical frequency (foF2) and total electron content (TEC) with respect to F10.7 variation. According to model results variations in O/N2 ratio seems to be the main possible mechanism for this delay. Some model/data disagreement was discussed in context of importance of atmosphere-ionosphere coupling and geomagnetic control of ionospheric variability. Seasonal changes and difference between ~27-day variation in foF2 and TEC were discussed.