Ionospheric Plasma Response to the Anomalous Minimum of the Solar Cycle 23/24: Modeling and Comparison with IRI-2012

The work inspects the ionospheric plasma response to the last minimum of solar activity (minimum 23/24, years 2008-2009), which was extremely low and prolonged. Characterized by unprecedented features in space era, the last minimum represents then a unique natural window to study the ionospheric plasma behaviors in such extreme conditions. The work is organized in two main parts. The first one focuses on the analysis of the relationships between the parameter foF2 and five widely used solar activity indices: F10.7, Lym-α, MgII, R and EUV0.1-50. Using the long and continuous dataset of the mid-latitude station of Rome (41.8°N, 12.8°E, Italy) and applying a 1-year running mean to both foF2 and solar indices, it is found that a second order polynomial fit represents the best choice to describe the relationships (foF2 vs Index) and that the index MgII is the best one to describe and forecast the variations of foF2. The application of these outcomes to the European regional model SIRM produced an improvement of the corresponding performances. The second part investigates the differences between the last solar minimum and the previous ones, and evaluates the performances of the IRI-2012 model for the parameters NmF2 and hmF2, using data from four ionosondes: Rome, Gibilmanna (37.9°N, 14°E, Italy), Tucumán (26.9°N, 294.6°E, Argentina) and São José dos Campos (23.1ºS, 314.5ºE, Brazil). The inter-minima analysis reveals a decrease for both NmF2 and hmF2 for the last minimum with respect to the previous ones, with more pronounced decreases at low latitudes. The comparison between ionosonde data and IRI outputs shows that: (1) the model does not worsen its performances for the last minimum; (2) it works better at mid latitudes than at low latitudes; (3) it slightly overestimates (~10%) hmF2 at both latitudes.