Variations of ionospheric profile parameters during solar maximum and comparison with IRI-2007 over Chung-Li, Taiwan

Abstract. This paper studies the seasonal changes in the diurnal variation of ionospheric bottomside slab thickness (B0), based on observations during high solar activities at the equatorial ionization anomaly (EIA) area station of Chung-Li (121.1° E, 24.9° N), Taiwan. The data examined in this investigation are derived from ionograms recorded at Chung-Li in 1999, and are compared with International Reference Ionosphere (IRI-2007) model values. In our data set B0 shows largest values and biggest changes during the daytime (06:00–12:00 LT) particularly in the summer. Moreover, the diurnal variation of B0 shows an abnormal peak during the pre-sunrise period, especially in the winter. The variation in the F-peak height (hmF2) is related to a thermospheric wind traveling toward the equator, which also enhances B0 during the pre-sunrise period. The results of the comparison with the IRI model show that B0 is overestimated, in both the B0-table and the Gulyaeva option, after noon LT in the equinox (B0-table and Gulyaeva average values for the overestimation are 11 and 47 km, respectively) and summer (B0-table and Gulyaeva average values for the overestimation are 23 and 71 km, respectively) periods. Furthermore, the modeled values are underestimated at approximately 31 and 14 km for the table and Gulyaeva option during the daytime in the winter, respectively. The F2-layer maximum electron density (NmF2) data show reasonably favorable agreement with the model for a high correlation coefficient of approximately 0.97, with the major difference observed at approximately noon in the equinox and winter seasons. Regarding the hmF2 data, the model shows agreement with the observed values, and the largest discrepancy (average value is 39 km) was observed in the summer and the smallest (average value is 11 km) in the equinox season. This paper provides a comprehensive discussion on the relationship among B0, the NmF2 and the hmF2 for geomagnetic storm events.