Validation of ionospheric weather predicted by global assimilation of ionospheric measurements (GAIM) models

The ability of the Utah State University (USU) Global Assimilation of Ionospheric Measurements (GAIM) model to specify the day-to-day variability of the ionosphere is assessed by comparison of specified hourly values of foF2 with observations that were not assimilated by the model. If the specifications are to be an improvement over a climatological model with zero average error, the interdecile width of errors of the specifications at each hour must be less than the interdecile width of the observations. It has been found that the median specified values of foF2 for undisturbed days are quite accurate, and that the interdecile width of errors of the specifications is less than that of the observations most of the time for midlatitude sites, provided there is a GPS TEC site sufficiently close to the ionosonde site. The errors in GAIM values of foF2 for Australian locations tend to be larger for larger distances from a GPS site, and for low latitudes. GAIM also tracks the values of foF2 on disturbed days, but tends to be conservative, not reproducing the full extent of the departures of the disturbed values from the background values.