Study of the foF2 and vTEC variations at the Ionospheric Observatory of Rome during the last solar minimum, in relation to the geomagnetic activity

In this study we investigate the variations of the hourly observations at the Ionospheric Observatory of Rome (41.82° N, 12.51° E) during the last minimum of solar activity. The values of the critical frequency of the F2 layer (foF2) manually scaled from the ionograms recorded by the AIS-INGV ionosonde, and the vertical Total Electron Content (TEC) acquired by the Rome GNSS receiver during the years 2018-2020 (between solar cycles 24 and 25) are analysed in order to detect ionospheric anomalies. Each hourly deviation of foF2 greater than ±15% with respect to a background level defined by 27-days running median values is here considered anomalous, while the Interquartile Range (IQR) method is used to define vTEC anomalies. All the found anomalies are classified according to their sign and the geomagnetic activity during their occurrence up to 24 hours in advance on the base of the ap geomagnetic index values, according to the NOAA Space Weather Scales (from G0 to G5, https://www.swpc.noaa.gov/noaa-scales-explanation), and defining an additional class considered representative of actually quiet conditions. The top level of geomagnetic activity reached during 2018 was G3, and G2 for 2019-2020. Some cases of anomalies occurred under geomagnetic storm conditions or magnetically quiet conditions are further investigated in order to discuss the existence of different types of ionospheric anomalies, related to different physical processes in the ionosphere.