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Author: search.filters.author.Supnithi, P.Subject: search.filters.subject.GPS TEC

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    Comparison of GPS TEC measurements with IRI TEC prediction at the equatorial latitude station, Chumphon, Thailand
    (2011-01-01)
    Kenpankho, P.
    ;
    Watthanasangmechai, K.
    ;
    Supnithi, P.
    ;
    Tsugawa, T.
    ;
    Maruyama, T.
    We have analyzed the total electron content (TEC) derived from dual-frequency GPS receivers (GPS TEC) at the Chumpon station, Thailand, during the period 2004-2006. The diurnal, monthly, and seasonal variation in the measured TEC is compared with the TEC derived from the IRI-2007 model as well as the TEC obtained from the International GNSS service (IGS). To date, TEC data at equatorial latitudes are limited. The Chumphon station (10.72 <sup>°</sup>N, 99.37<sup>°</sup>E) is located at the equatorial latitude and the dip latitude of 3<sup>°</sup>N. The TEC from the IRI-2007 model is based on the actual F<inf>2</inf> plasma frequency (f<inf>o</inf>F<inf>2</inf>) measurement. The results of our study show that the TEC derived from the IRI-2007 model agrees with the GPS TEC data mostly in the morning hours, but that it generally underestimates the GPS TEC. The maximum differences are about 15 TECU during the daytime and 5 TECU during the nighttime. The underestimation is more evident at daytime than at nighttime. The noon-bite out phenomena are clearly seen for the IRI-2007 TEC, but not on the IGS TEC and GPS TEC. The general underestimation of the IRI-2007 model can be explained from the exclusion of the plasmasphere, whereas the large difference during noon bite-outs is caused by the difference in the slab thickness in the ionosphere between the IRI-2007 model and the actual measurement. When compared with the TEC from the IGS model, the TEC measurements at Chumpon appear to be quite similar. Copyright © The Society of Geomagnetism and Earth.
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    Variation of ionospheric slab thickness observations at Chumphon equatorial magnetic location
    (2011-01-01)
    Kenpankho, P.
    ;
    Supnithi, P.
    ;
    Tsugawa, T.
    ;
    Maruyama, T.
    This study presents the diurnal and seasonal variations of slab thickness at the equatorial magnetic latitudes in Thailand during 2004-2006, corresponding to the declining part of low solar activity. The GPS-derived total electron content (TEC) and the maximum electron density of the F-region (N <inf>m</inf>F<inf>2</inf>) are used to compute the slab thickness (&tau) at the Chumphon station (10.72<sup>°</sup>N, 99.37<sup>°</sup>E), located near the magnetic equator. The results show that large peaks of slab thickness exist during the pre-sunrise hours in all three seasons at Chumphon when compared with other latitudes. The maximum value of slab thickness occurs when the peak electron density in the F<inf>2</inf> region is at the lowest level. During daytime, the slab thickness ranges from 200 kilometers to 580 kilometers for all seasons. During nighttime, the maximum value of slab thickness is 1250 kilometers in the summer of 2004. Moreover, the diurnal variation shows two minima that appear around 0900 LT and 1900 LT, during the post-sunrise and sunset hours. The seasonal variations show that the average slab thickness daily value is greater during summer and winter than those during equinox. Our study finds that the slab thickness at Chumphon located near the equatorial latitude is much larger than those found at low, mid, and high latitudes. The difference in slab thickness between the equatorial latitude and other zones is explained by the lack of plasma flow from the plasmasphere to the F<inf>2</inf> region at the magnetic equator. Copyright © The Society of Geomagnetism and Earth.