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

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    Variations of ionospheric slab thickness over the magnetic equator of Southeast Asia
    (2016-09-06)
    Jamjareegulgarn, P.
    ;
    Supnithi, P.
    ;
    Watthanasangmechai, K.
    ;
    Yokoyama, T.
    ;
    Tsugawa, T.
    In this paper, the diurnal and seasonal variations of the ionospheric slab thickness in an ionosonde chain over magnetic equator of Southeast Asia are studied. Three ionosonde stations of SEALION project located along the magnetic meridian of 100°E are selected to investigate, including two stations in Thailand, namely Chumphon and Chiang Mai, and one station in Indonesia, namely Kototabang. The monthly hourly medians of the foF2 from three ionosonde stations in 2010 are used to compute the observed NmF2. Refer to the TEC data; it can be obtained directly from GPS receiver at Chumphon station since the TEC data in 2010 were observed completely. In contrast, the TEC data at Chiang Mai station lost extremely and those at Kototabang station were unavailable. Hence, the TEC data used for these two stations are obtained from the International GNSS service (IGS). Our results show that 1) for all seasons, the NmF2 values during daytime have the successive decreasing values from Chiang Mai, Kototabang, and Chumphon. While the NmF2 values at three stations are almost identical during nighttime; 2) for all seasons at these three stations, the TEC values in the daytime are larger than those in the nighttime and their maximum values in the equinox and winter are higher than those in the summer; 3) the slab thickness values in all seasons during nighttime are generally larger than those during daytime for all three stations. Meanwhile, during daytime for all seasons, the slab thickness at Chumphon station is the highest among these three stations due to the fountain effect over magnetic equator.
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    Comparison of observed TEC values with IRI-2007 TEC and IRI-2007 TEC with optional foF2 measurements predictions at an equatorial region, Chumphon, Thailand
    (2013-11-15)
    Kenpankho, P.
    ;
    Supnithi, P.
    ;
    Nagatsuma, T.
    In this research, as part of working towards improving the IRI over equatorial region, the total electron content (TEC) derived from GPS measurements and IRI-2007 TEC predictions at Chumphon station (10.72 N, 99.37 E), Thailand, during 2004-2006 is analyzed. The seasonal variation of the IRI-2007 TEC predictions is compared with the TEC from the IRI-2007 TEC model with the option of the actual F2 plasma frequency (foF2) measurements as well as the TEC from the GPS and International GNSS service (IGS). The Chumphon station is located at the equatorial region and the low latitude of 3.22 N. For a declining phase of the solar cycle (2004-2006), the study shows that the IRI-2007 TEC underestimates the IRI-2007 TEC with the foF2 observation at the nighttime by about 5 TECU. The maximum differences are about 15 TECU during daytime and 5 TECU during nighttime. The overestimation is more evident at daytime than at nighttime. When compared in terms of the root-mean square error (RMSE), we find that the highest RMSE between GPS TEC and IRI 2007 TEC is 14.840 TECU at 1230 LT in 2004 and the lowest average between them is 1.318 TECU at 0630 LT in 2006. The noon bite-out phenomena are clearly seen in the IRI-2007 TEC with and without optional foF2 measurements, but not on the GPS TEC and IGS TEC. The IRI TEC with optional foF2 measurements gives the lowest RMSE values between IRI TEC predicted and TEC measurement. However, the TEC measurements (GPS TEC and IGS TEC) are more correct to use at Chumphon station. © 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.
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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.