Statistical Analyses of Ionospheric Electron Density Variations resulting from Geomagnetic Storms over Istanbul

Ionospheric parameters, totaling about 72, were measured at ITU-Dynasonde site including F2 region critical frequency and its virtual height from 2012 to 2018. This project utilizes F2 region critical frequency to determine the storm related variations and quantify the storm effects over İstanbul (42N, 29E).  Three strong geomagnetic storm events were selected and the differences in foF2 betwen quiet (non-storm) and active (storm) days were identified. It was found that when a geomagnetic storm occurs, the ionospheric electron densities increase at noon times and decrease during the night times around midnight. These variations were seen to occur during the main phase of the storm and continues during the recovery phase.  During the following days of the storm main phase, increasing electron densities at noon times subsided and even reversed indicating a deficit of electron density. The noon decrease became even stronger after two days following the storm occurrence while the nighttime  variations stayed at the same level.   Strong increases in the solar wind dynamic pressure and strong IMF southward variations were detected in L1 data from WIND spacecraft. The maximum positive electron density difference at noon was obtained to be about 10% while  the storm associated midnight decrease was found to be about 15 %.  While the electron densities in a region can be associated with several physical processes initiated by the magnetic storm in the upper atmosphere, association to neutral atmosphere dynamics were searched by examining the thermospheric neutral density from SWARM satellites at about 500 kms during these storm days in order to bring some understanding on the storm time variations of electron density over Istanbul latitudes.  Some of these findings support those in the literature while some others were reported for the first time here in relation to the magnetic storms. It is intended to expand the analysis to more storm cases from 2012 to 2018 in order to obtain a statistical base.  The results from the preliminary search based on the statistical analyses and the corresponding SWARM neutral density will be presented in order to address on the ionosphere-thermosphere coupling at these latitudes.