foF2 variations measured by the Rome observatory during solar minimum in the last three solar cycles

Abstract

The last three solar cycles have been considered for a study on the variation of the ionospheric parameter foF2 during solar minimum. Hourly observations recorded by the ionospheric station of Rome have been considered for the years 1985, 1986, 1987, 1995, 1996, 1997, 2007, 2008 and 2009. Background values of foF2 have been computed considering a 27-day running median. A variation of foF2 of more than ± 15% over the background level and with a minimum duration of 3 hours, is here considered as an anomaly. For each anomaly, a study of the geomagnetic condition has been carried out, considering the value of the ap index at the time when the anomaly is detected and for the previous 24 hours. The auroral electrojet index AE has also been investigated in relation with each observed foF2 anomaly, considering 6 hours before the occurrence of the anomaly since TADs, related to upsurges of auroral activity, can reach middle latitudes and consequently perturb the F2 layer. A characterization of the observed foF2 anomalies with respect to the related geomagnetic conditions is presented in this work. Two foF2 storms are studied here in detail, analysing the solar sources.