Ionospheric Response to Geomagnetic Storms of Different Intensity in the Eastern North Atlantic Mid-Latitudinal Zone (Iberian Peninsula, Azores and Madeira)—Part 1: Solar and Geomagnetic Drivers

The ionospheric response to a geomagnetic storm depends on several factors, including the strength of a storm, commencement type, solar origin of a geomagnetic storm (as, coronal mass ejections or high-speed solar wind streams), and observational site location. In this work, we present the results of a statistical analysis of 80 moderate to major geomagnetic storms that took place during the declining phase of the 24th solar cycle from 2015 to 2019. We performed an analysis of the ionospheric response to these storms using the total electron content (TEC) data obtained from three geodetic receivers located in Portugal: Lisbon (Continental Portugal), Furnas (Azores), and Funchal (Madeira). Statistical analysis of the observed TEC variations allowed detection of specific patterns in the ionospheric response to storms with different characteristics. We found that the type of geomagnetic storm commencement (gradual or sudden) is a statistically significant predictor of the ionospheric response amplitude and duration. Also, specific patterns in the ionospheric response to geomagnetic storms were found for the most southern location (Madeira), which are likely related to its proximity to the northern boundary of the equatorial ionization anomaly.