Validation of the STORM response in IRI2000

[1] The latest version of the International reference ionosphere, IRI2000 [Bilitza, 2001], contains a dependence on geomagnetic activity based on an empirical storm-time ionospheric correction model (STORM) [Araujo-Pradere et al., 2002]. The new storm correction in IRI is driven by the previous time history (33 hours) of ap and is designed to scale the normal quiet-time F layer critical frequency (f(o)F(2)) to account for storm-time changes in the ionosphere. An extensive validation of IRI2000 has been performed during geomagnetic storm conditions to determine the validity of the new algorithms. The quality of the storm-time correction has been evaluated by comparing the model with the observed ionospheric response during all the geomagnetic storms with ap > 150 in 2000 and 2001, a total of 14 intervals. The model output was compared with the actual ionospheric response for all available ionosonde stations for each storm. The comparisons show that the model captures the decreases in electron density particularly well in summer and equinox conditions. To quantify the improvement in IRI2000, the root-mean-square error has been evaluated and compared with the previous version of IRI, which had no geomagnetic dependence. The results indicate that IRI2000 has almost a 30% improvement over IRI95 during the storm days and is able to capture more than 50% of the increase in variability, above quiet times, due to the storms.