Ionosphere response to geomagnetic storms on 7-8 September 2017 over Kharkiv (Ukraine)

Response of middle latitude ionospheric F-region to two sequential geomagnetic storms on 7–8 September 2017 has been studied using the incoherent scatter radar of Institute of Ionosphere $(49.60^{\circ}N, 36.30^{\circ}E)$. The G3-class geomagnetic storm on 7 September and the G4-class geomagnetic storm on 8 September had close intensities. The first geomagnetic storm was accompanied by the positive disturbance during the main phase and the negative disturbance during the recovery phase. Effects of the second geomagnetic storm caused the negative disturbance. The ionosphere was characterized by a largescale variation in critical frequency $fo F2$ (from 6 to 8 MHz and from 6 to 4 MHz), F2-layer peak height $hm F2$ (by 70–80 km) and the vertical plasma drift velocity oscillations (up to 50–80 m/s).