A short-term ionospheric forecasting empirical regional model (IFERM) to predict the critical frequency of the F2 layer during moderate, disturbed, and very disturbed geomagnetic conditions over the European area

摘要

A short-term ionospheric forecasting empirical regional model (IFERM) has beendeveloped to predict the state of the critical frequency of the F2 layer(foF2) under different geomagnetic conditions.IFERM is based on 13 short term ionospheric forecasting empirical local models(IFELM) developed to predict foF2 at 13 ionospheric observatories scattered aroundthe European area. The forecasting procedures were developed by taking intoaccount, hourly measurements of foF2, hourly quiet-time reference values offoF2 (foF2_QT), and the hourly time-weighted accumulation series derived fromthe geomagnetic planetary index ap, (ap(τ)), for each observatory.Under the assumption that the ionospheric disturbance indexln(foF2/foF2_QT) is correlated to the integrated geomagnetic disturbance indexap(τ), a set of statistically significant regression coefficients wereestablished for each observatory, over 12 months, over 24 h, and under 3different ranges of geomagnetic activity. This data was then used as inputto compute short-term ionospheric forecasting of foF2 at the 13 local stationsunder consideration.The empirical storm-time ionospheric correction model (STORM) was used to predictfoF2 in two different ways: scaling both the hourly median prediction providedby IRI (STORM_foF2_MED,IRI model), and the foF2_QT values (STORM_foF2_QT model) fromeach local station.The comparison between the performance of STORM_foF2_MED,IRI,STORM_foF2_QT, IFELM, and the foF2_QT values, was made on the basis of root mean squaredeviation (r.m.s.) for a large number of periods characterized by moderate,disturbed, and very disturbed geomagnetic activity.The results showed that the 13 IFELM perform much better thanSTORM_foF2,sub>MED,IRI and STORM_foF2_QT especially in the eastern part of the European areaduring the summer months (May, June, July, and August) and equinoctialmonths (March, April, September, and October) under disturbed and verydisturbed geomagnetic conditions, respectively. The performance of IFELM is alsovery good in the western and central part of the Europe during the summermonths under disturbed geomagnetic conditions. STORM_foF2_MED,IRI performsparticularly well in central Europe during the equinoctial months undermoderate geomagnetic conditions and during the summer months under verydisturbed geomagnetic conditions.The forecasting maps generated by IFERM on the basis of the results provided bythe 13 IFELM, show very large areas located at middle-high and high latitudeswhere the foF2 predictions quite faithfully match the foF2 measurements, andconsequently IFERM can be used for generating short-term forecasting maps offoF2 (up to 3 h ahead) over the European area.