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Earth Planets Space, Vol. 64 (No. 6), pp. 467-471, 2012
doi:10.5047/eps.2011.10.014

A comparison of the equatorial spread F derived by the International Reference Ionosphere and the S4 index observed by FORMOSAT-3/COSMIC during the solar minimum period of 2007-2009

G. Uma1, J. Y. Liu1,2,3, S. P. Chen1, Y. Y. Sun2, P. S. Brahmanandam1, and C. H. Lin4

1Institute of Space Science, National Central University, Jhongli City 32001, Taiwan
2Center for Space and Remote Sensing Research, National Central University, Jhongli City 32001, Taiwan
3National Space Organization, Hsin-Chu City 30078, Taiwan
4Plasma and Space Science Center, No. 1, University Road, Tainan City 701, Taiwan

(Received June 3, 2010; Revised September 3, 2011; Accepted October 25, 2011; Online published July 27, 2012)

Abstract: The latest version of the International Reference Ionosphere (IRI-2007) model includes an option for spread-F occurrence prediction for the first-time. The IRI-2007 spread-F occurrence is a function of solar 10.7 cm radiation flux, F10.7. In this paper, an attempt is made to cross-examine the spread-F occurrence derived by the IRI-2007 and the ionospheric scintillations in terms of the maximum value of the S4 index (S4max) between 150-350-km altitudes, calculated from fluctuations of the signal-to-noise ratio (SNR) intensity in the L1 channel of GPS radio occultation signals using FORMOSAT-3/COSMIC (F3/C) satellites during the low solar activity years 2007-2009. It is found that S4max maintains a fairly good consistency with spread-F occurrence simulated by IRI-2007 in the Brazilian region. Thus, the global S4 index statistics can be considered as a viable source of database to be incorporated into the global IRI spread-F prediction scheme owing to fact that the F3/C satellites can provide an unprecedented global database including the S4 index.
Key words: GPS RO technique, S4 index, IRI-2007, spread-F.


Corresponding author E-mail: jyliu@jupiter.ss.ncu.edu.tw


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