Ionospheric peak parameter foF2 and its variation trend observed by GPS

Knowledge of the ionospheric peak parameter foF2 (the critical frequency of F2 layer) is one of key essential factors for predicting ionospheric characteristics and delay correction of satellite positioning. However, the foF2 was almost estimated using an empirical model of International Reference Ionosphere (IRI) or other expensive observing techniques, such as ionosondes and scatter radar. In this paper, the ionospheric peak parameter foF2 is the first observed by ground-based GPS with all weather, low-cost and near real time properties. Compared with the IRI-2001 and independent ionosondes at or near the GPS receiver stations, the foF2 obtained from ground-based GPS is in better agreement, but closer to the ionosonde. However, during nighttime, the IRI model overestimated the GPS observed values during winter and equinox months.Furthermore, seasonal variation trend of the foF2 in 2003 is studied using foF2 monthly median hourly data measured over South Korea. It has shown that the systematic diurnal changes of foF2 are apparent in each season and the higher values of foF2 are observed during the equinoxes (semiannual anomaly) as well as in mid-daytime of each season.