TEC

About: TEC is a research topic. Over the lifetime, 5119 publications have been published within this topic receiving 84696 citations.

Analysis of ionospheric scintillation spectra and TEC in the Chinese low latitude region

Abstract: GPS L-band scintillations and total electron content (TEC) were recorded at Sanya (18.33°N, 109.52°E) during the period July 2004–July 2005. Automatic recorded raw digital scintillation data are analyzed to obtain the spectral characteristics of irregularities producing ionospheric scintillations and to estimate the correlation between amplitude scintillation and power spectral density. Concurrent measurements of TEC are used to analyze ROTI, defined as the standard deviation of the rate of change of TEC. The statistical results of S4 indices and power spectral indices indicate that the power spectral indices increase with S4 indices for weak scintillation (0.1 ≤ S4 < 0.3), but for moderate and strong scintillation, spectral indices tend to be saturated. In the analyzed data set, the ratio of ROTI/S4 is found to vary between 0.3 and 6, and the variation in estimated zonal drift velocities during geomagnetic quiet days (K p < 3) shows that the motion of the irregularities is highly variable in the initial phase of irregularity development. After about 22:00 LT, the estimated drift velocities tend to follow the same pattern.

The GPS Segment of the AFRL-SCINDA Global Network and the Challenges of Real-Time TEC Estimation in the Equatorial Ionosphere

Abstract: The estimation of Total Electron Content (TEC) in the equatorial ionosphere using GPS presents a number of challenges due to the presence of strong spatio-temporal density gradients and scintillation of the satellite signals caused by F-region irregularities. In this paper we describe a methodology for real-time calibrated TEC estimation in the presence of scintillation and a highly structured ionosphere. The inter-frequency biases of the GPS satellites are assumed known; we use estimates provided by the Center for Orbit Determination in Europe (CODE). The inter-frequency bias associated with a particular receiver is estimated late at night when the ionosphere is minimally structured, using an iterative approach that minimizes the variance of verticalized TEC measured along the different satellite links. The nightly estimated receiver bias is shown to be insensitive to the assumed centroid height used in the single-layer approximation of the ionosphere. It is also relatively stable on a night to night basis, deviating from its running average most when nighttime gradients in density are largest (commonly associated with geomagnetic activity and/or equatorial spread F). A 14 day running average of the bias is used to minimize the effect of this variability on the calibrated TEC. The effectiveness of the technique is illustrated by comparing the calibrated TEC estimated using two GPS receivers connected to the same antenna. During quiescent ionospheric conditions the difference in TEC estimated with the two receivers is generally less than a couple of TECU, despite their substantially different internal biases. During scintillating conditions, the TEC from the two receivers exhibit substantial differences due to receiver errors in the measurement of pseudorange and phase, unless strict quality control techniques are applied to exclude this data from the analysis. Methods for the automated detection of receiver error due to scintillation are presented and are shown to yield reliable TEC estimates.

Attribution of interminima changes in the global thermosphere and ionosphere

Abstract: We present a statistical attribution analysis of the changes in global annual average thermospheric mass density and ionospheric total electron content (TEC) between the cycle 22/23 solar minimum (which occurred at epoch 1996.4) and the prolonged cycle 23/24 minimum (2008.8). The mass density data are derived from orbital drag, and the TEC data are derived from ground-based GPS receivers. The interminima change in mass density was −36% relative to the 1996.4 yearly average. Considering each multiplicative forcing independently, lower average geomagnetic activity during the cycle 23/24 minimum produced an interminima density change of at least −14%, solar extreme ultraviolet (EUV) irradiance forcing produced a density change of −1% to −13%, and changes in thermospheric CO2 concentration produced a density change of −5%. There was essentially no interminima change in global TEC derived from ground-based GPS receivers or space-based altimeters, even though past behavior suggests that it should have changed −3% (0.2 TEC units (1 TECU = 1016 el m−2)) in response to lower geomagnetic activity and −1% to −9% (0.1–0.8 TECU) in response to lower EUV irradiance. There is large uncertainty in the interminima change of solar EUV irradiance; the mass density and TEC data suggest a plausible range of 0% to −6%.

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 2004–2006. 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 F2 plasma frequency (foF2) 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.