A local ionospheric model for forecasting the critical frequency of the F2 layer during disturbed geomagnetic and ionospheric conditions

Abstract. An ionospheric forecasting empirical local model over Rome (IFELMOR) has been developed to predict the state of the critical frequency of the F2 layer (foF2) during geomagnetic storms and disturbed ionospheric conditions. Hourly measurements of foF2 obtained at the Rome observatory, hourly quiet-time values of foF2 (foF2_QT), and the hourly time-weighted accumulation series derived from the geomagnetic planetary index a_p (a_p(τ)), were considered during the period January 1976–December 2003. Under the assumption that the ionospheric disturbance index log(foF2/foF2_QT) is correlated to the integrated geomagnetic index a_p(τ), statistically significant regression coefficients are obtained for different months and for different ranges of a_p(τ) and used as input to calculate the short-term ionospheric forecasting of foF2. The empirical storm-time ionospheric correction model (STORM) was used to make comparisons with the IFELMOR model. A few comparisons between STORM's performance, IFELMOR's performance, the median measurements and the foF2_QT values, were made for significant geomagnetic storm events (a_p>150) occurring from 2000 to 2003. The results provided by IFELMOR are satisfactory, in particular, for periods characterized by high geomagnetic activity and very disturbed ionospheric conditions.