Time Empirical Ionospheric Correction Model (STORM) response in IRI2000 and challenges for empirical modeling in the future

IRI2000 [Bilitza, 2001] now contains a geomagnetic activity dependence based on the Time Empirical Ionospheric Correction Model (STORM) [Araujo-Pradere and Fuller-Rowell, 2002; Araujo-Pradere et al., 2002]. The storm correction is driven by the previous time history of a(p) and is designed to scale the quiet time F layer critical frequency (f(o)F(2)) to account for storm-time changes in the ionosphere. The quality of the storm-time correction was recently evaluated by comparing the model with the observed ionospheric response during all the significant geomagnetic storms in 2000 and 2001. The model output was compared with the actual ionospheric response at 15 stations for each storm. These quantitative comparisons using statistical metrics showed that the model captures the decreases in electron density particularly well in summer and equinox conditions, but is not so good during winter conditions. To further assess the capabilities of the model, STORM has been compared in detail with observations during the Bastille Day storm in July 2000. This storm, considered to be on the extreme end of the statistical scale of storm magnitude, highlights two main areas were challenges remain for the empirical storm-time ionospheric model. The first is the rapid onset of the positive storm phase; the second is the regional composition changes that can affect one longitude sector at the expense of another for a particular storm. Both these challenges, although appreciated during the development of STORM, remain to be addressed.