IRI-2001 model efficiency in ionospheric radiowave propagation forecasting

Results of data analysis referring to two type of experimental investigations are presented: (i) oblique chirp-sounding (OS) on two perpendicular paths: Inskip(GB)-IZMIRAN (∼2500 km) and Cyprus-IZMIRAN (∼2300 km) and (ii) vertical sounding at their common point (IZMIRAN). These investigations were performed in the vernal equinox periods of 2002–2007 covering like that a wide range of solar activity, for example, the mean sunspot number for March varied from 112.0 at the maximum (2002) to 4.6 at the minimum (2007). In order to improve the quality of the short-term radio wave propagation forecasting, an attempt was made to consider this combined set of experimental data from the point of view of its description made by IRI-2001 empirical model, and to examine a proposed procedure to adapt the model to the current geophysical conditions. The aim of the paper was to quantify the root-mean-square (RMS) error for two different descriptions of the behavior of maximum usable frequency (MUF) 1F2 mode: long-term – monthly averaged dependence and short-term – diurnal dynamics. These estimates are obtained as in the case of classic way of the model input parameters assignment (monthly mean sunspot number) so when solar radio flux data was considered as an additional information about the solar activity. Special emphasis is focused on the estimation of the accuracy of the short-term description, when current solar radio flux and F2-layer peak data is used as input parameters for the IRI-2001 model in the proposed procedure of its adaptation. It is shown that relative RMS error in 10% is the bottom estimation of an accuracy of MUF 1F2 in the long- and short-term forecasts, at least, for March. This limitation, apparently, is caused by a considerable discrepancy between the F1-layer electron density values obtained from the model and from the observed N(h)-profiles.