Comparison among IRI, GPS-IGS and ionogram-derived total electron contents

In this paper, we compare the ionogram-derived total electron content (ITEC) obtained at the low latitude station Hainan (geographical coordinates 19.4°N, 109.0°E; Dip = 22.8°), China with that derived from GPS signals produced by the International GPS Services for Geodynamics (TECigs) and the TEC data obtained by the altimeter on TOPEX satellite when it passed over nearby Hainan. We also compare them with the results produced by the current International Reference Ionosphere model (IRI2001) TECiri. Data used for the present comparison study are both the daily hourly and monthly median values for the 12 months of the descending solar activity year 2003. Our study showed that (1) in general ITEC is in agreement with TOPEX-TEC, although there are exceptions; (2) the total electron contents produced by all techniques (TECigs, ITEC and TECiri) can reproduce quiet well the remarkable semi-annual variation behavior of the total electron content; (3) the variation trends of ITEC and TECigs are generally in good agreement, however during nighttime to pre-sunrise hours ITEC is systematically lower than TECigs, whereas during daytime hours around local noontime ITEC is usually larger than TECigs. The absolute difference between ITEC and the TECigs (|▵TEC1| = |ITEC-TECigs|) of the monthly median data is usually under the limit of 10–15 TECu (1 TECu = 1016 el/m2) during the diurnal variation, except for the time period 09–16UT(∼17–24LT) in September and October when the value of |▵TEC1| is larger than 15 TECu, fluctuating between about 15–25 TECu; (4) during nighttime hours TECiri is generally larger than TECigs, whereas during daytime hours TECiri is generally smaller than TECigs except for the months June and July when TECiri is slightly larger than TECigs; (5) the difference between ITEC and TECigs (ΔTEC1) and that between TECiri and TECigs (ΔTEC2) are almost reverse in their positive/negative signs at a given local time, however, the magnitudes of the maximum absolute values of |▵TEC1| and |▵TEC2| are comparable.