Abstract
In this study, an empirical model constructed using data of FORMOSAT3/COSMIC (F3/C) from 29 June, 2006, to 17 October, 2009, retrieves altitude profiles of electron density (Ne). The model derives global Ne profiles from 150 to 590 km altitude as functions of the solar EUV flux, day of year, local time and location under geomagnetically quiet conditions (Kp < 4). Ne profiles derived by the model are further compared with those of the International Reference Ionosphere (IRI). Results show that the F2 peak altitude hmF2 and the electron density NmF2, as well as the electron density above, derived by the model are lower than those of the IRI model. The F3/C model reproduces observations of F3/C well at 410-km altitude while the IRI model overestimates them. The overestimation of the IRI model becomes large with decrease of EUV flux. It is found that the topside vertical scale height of the F3/C model shows high values not only magnetic dip equator but also middle latitude. The results differ significantly from those of IRI, but agree with those observed by topside sounders, Alouette and ISIS satellites.
Highlights
The International Reference Ionosphere (IRI) has been developed since 1978 (Rawer et al, 1978) and is established as the most standard and reliable ionospheric empirical model
We describe the methodology in constructing the model and compare the empirical model based on F3/C observations with the IRI model
In order to estimate the accuracy of the F3/C model, the root-mean-square error (RMS) is calculated as follows, RMS =
Summary
The International Reference Ionosphere (IRI) has been developed since 1978 (Rawer et al, 1978) and is established as the most standard and reliable ionospheric empirical model. Since a large amount of ionosonde data has been used, IRI derives a relatively accurate electron density (Ne) profile below the F2 peak. The IRI model might still have some shortcomings in the topside ionosphere, because very limited satellite data are included. Kakinami et al (2008) found an in-situ Ne observation at a 600-km altitude with the Hinotori satellite which differed from the IRI Ne. Kakinami et al (2008) found an in-situ Ne observation at a 600-km altitude with the Hinotori satellite which differed from the IRI Ne This shortcoming results in a difference between the Total Electron Content (TEC) reproduction and real observations, because the TEC is calculated using an integration of the Ne profile. The IRI model overestimates the TEC in the equatorial region (Bilitza and Williamson, 2000) during high solar activity, while the IRI model overestimates and underestimates the TEC over Taiwan (24◦N 120◦E) during low and high solar activity, respectively (Kakinami et al, 2009)
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