Comparison of GPS TEC measurements with IRI TEC prediction at the equatorial latitude station, Chumphon, Thailand

Abstract

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][2005][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• N, 99.37• E) is located at the equatorial latitude and the dip latitude of 3• N. The TEC from the IRI-2007 model is based on the actual F 2 plasma frequency ( f o F 2 ) 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.

Impacts of solar activity on performance of the IRI-2012 model predictions from low to mid latitudes

“…The largest discrepancy (overestimation) in the IRI-2012 model TEC with the IRI-2001 topside has been observed during the daytime hour in equatorial and low-latitude regions (NTUS, CUSV, and KUNM). One possible cause for the daytime discrepancy in the IRI-2012 model may be the daytime ionospheric expansion, and as a result, a larger slab thickness is covered at around noon time as compared to other times (Kenpankho et al 2011). This expansion is larger at low latitudes as compared to mid latitudes.…”

Variations in Electron Content Ratio and Semi-thickness Ratio during LSA and MSA periods and some Cyclone Genesis Periods using COSMIC satellite observations

“…All these effects are proportional to the Integrated Electron Content (IEC) which in turn intimately depends on Ne distribution along the ray-path, connecting satellite to receivers. However, IEC delivers one of the most important quantitative characteristic (Kenpankho et al, 2011) about the vertical framework of ambient ionosphere. DasGupta et al (2007) have reported that large spatial gradient in Total Electron Content (TEC; 1TECU = 10 16 el/m 2 ) variations exist in the equatorial ionosphere.…”

The influence of space weather on ionospheric total electron content during the 23rd solar cycle

“…The IRI model permits, among other things, the reconstruction of the electron density profiles up to plasmaspheric heights and the TEC prediction. However, many studies compared the TEC derived from IRI and GNSS and show systematic bias in the IRI-TEC (e.g., Kenpankho et al 2011;Orús et al 2002). These discrepancies are interpreted by the lack of knowledge of the upper part of the ionosphere (e.g., Iwamoto et al 2002) and lead to a focus on the improvement of the topside ionospheric models in IRI (Bilitza et al 2006).…”