Correlated Disturbances of the Upper and Lower Ionosphere from Synchronous Measurements of Parameters of GNSS Signals and VLF Radio Signals

This is a study of the spatiotemporal distribution of midlatitude disturbances of the upper and lower ionosphere in the European zone during a strong geomagnetic storm and strong X-ray flare using data of synchronous measurements of the parameters of global navigation satellite system (GNSS) signals and very low-frequency (VLF) radio signals. It has been shown that the contribution of electron concentration at different altitudes to the total electron content of the ionosphere can vary significantly depending on the type of heliogeophysical disturbances. A combined analysis of GNSS signals and VLF radio signals makes it possible to study the mechanisms of coupling between the upper and lower ionospheric disturbances and the dynamics of ionospheric disturbances in the horizontal and vertical directions.