TEC

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

TEC response during severe geomagnetic storms near the crest of equatorial ionization anomaly

Abstract: The responses of the ionosphere near equatorial anomaly crest as observed at Bhopal (geographic 23.2°N, 77.4°E, and magnetic latitude 14.2°N), India for geomagnetic storms during 15 May 2005 (SSC: 0239 hrs UT, SymH: -305 nT) and 24 August 2005 (SSC: 0615 hrs UT, SymH: -179 nT) has been studied using total electron content (TEC). TEC data is recorded by GPS Ionospheric Scintillation and TEC Monitor (GISTM) GSV4004A at Bhopal. The temporal variations of vertical total electron content (VTEC) during these storms were analysed. Fifteen minute average of VTEC is considered for analysis. More than +68% and +70% deviation in VTEC was observed for 15 May 2005 and 24 August 2005 storms, respectively, relative to average of five quiet days of the respective months. Significant deviations in VTEC during the main phase of the storms were found to be associated with the prompt penetration of electric fields which originate due to the under-shielding and over-shielding conditions. Peaks like structure in EIA region were observed for both the storms. Peaks like structure well before the fountain effect in EIA region were observed for 15 May 2005. Latitudinal enhancement of anomaly peak in EIA region was also observed for both the storms. Suppressed equatorial electrojet strength and consequently VTEC, observed on 25 August 2005 during recovery phase of the storm, are mainly due to the thermospheric composition changes and also possibly due to the delayed disturbance dynamo electric fields in this region. The range error is also discussed in the present paper.

An examination of the Galileo NeQuick model:comparison with GPS and JASON TEC. GPS Solutions

Abstract: We evaluate the performance of Galileo broadcast NeQuick model by comparing it with GPS broadcast Klobuchar and the original NeQuick2 models. The broadcast coefficients of Galileo NeQuick model are computed from 23 globally distributed tracking stations of the International GNSS Service (IGS), by ingesting the Global Positioning System (GPS)-derived ionospheric total electron content (TEC) into the original NeQuick2 model. The accuracy of the three ionospheric models is evaluated over both the continental and oceanic regions for the year 2013. In continental regions, ionospheric TEC derived from 34 IGS stations is used as references for comparison. In oceanic regions, where the IGS stations are sparse, high-quality vertical TEC sources provided by JASON-1&2 altimeters are used as references. The evaluation results show that in continental regions, GPS broadcast Klobuchar and the original and broadcast NeQuick can mitigate the ionospheric delay by 56.8, 63.3 and 72.4 %, respectively. In oceanic regions, the three models can correct for 51.1, 61.2 and 68.6 % of the ionospheric delay. Galileo broadcast NeQuick model outperforms Klobuchar by 15.6 and 17.5 % over the continental and oceanic regions, respectively, for the test period. The broadcast NeQuick model can provide accurate ionospheric error corrections when Galileo begins full operational capability.

A new technique for spectral analysis of ionospheric TEC fluctuations observed with the Very Large Array VHF system: From QP echoes to MSTIDs

Abstract: [1] We have used a relatively long, contiguous VHF observation of a bright cosmic radio source (Cygnus A) with the Very Large Array (VLA) through the nighttime, midlatitude ionosphere to demonstrate the phenomena observable with this instrument. In a companion paper, we showed that the VLA can detect fluctuations in total electron content (TEC) with amplitudes of ≤ 10−3 TECU and can measure TEC gradients with a precision of about 2 × 10− 4 TECU km−1. We detail two complementary techniques for producing spectral analysis of these TEC gradient measurements. The first is able to track individual waves with wavelengths of about half the size of the array (∼20 km) or more. This technique was successful in detecting and characterizing many medium-scale traveling ionospheric disturbances (MSTIDs) seen intermittently throughout the night and has been partially validated using concurrent GPS measurements. Smaller waves are also seen with this technique at nearly all times, many of which move in similar directions as the detected MSTIDs. The second technique allows for the detection and statistical description of the properties of groups of waves moving in similar directions with wavelengths as small as 5 km. Combining the results of both spectral techniques, we found a class of intermediate and small scale waves which are likely the quasi-periodic (QP) echoes that have been observed to occur within sporadic-E (Es) layers. We find two distinct populations of these waves. The members of one population are coincident in time with MSTIDs and are consistent with being generated within Es layers by the E–F coupling instability. The other population seems more influenced by the neutral wind, similar to the predominant types of QP echoes found by the Sporadic-E Experiments over Kyushu (SEEK). We have also found that the spectra of background (i.e., isotropic) fluctuations can be interpreted as the sum of two turbulent components with maximum scales of about 300 km and 10 km.

Ionospheric total electron content variations observed before earthquakes: possible physical mechanism and modeling

Abstract: The GPS derived anomalous TEC disturbances before earthquakes were discovered in the last years using global and regional TEC maps, measurements over individual stations as well as measurements along individual GPS satellite passes. For strong mid-latitudinal earthquakes the seismo-ionospheric anomalies look like local TEC enhancements or decreases located in the vicinity of the forthcoming earthquake epicenter In case of strong low-latitudinal earthquakes there are effects related with the modification of the equatorial F2-region anomaly: deepening or filling of the ionospheric electron density trough over the magnetic equator. We consider that the most probable reason of the NmF2 and TEC disturbances observed before the earthquakes is the vertical drift of the F2-region ionospheric plasma under the influence of the zonal electric field of seismic origin. To check this hypothesis, the model calculations have been carried out with the use of the Upper Atmosphere Model. The electric potential distribution at the near-epicenter region boundary required for the electric field maintenance has been proposed. The upper atmosphere state, presumably foregone a strong earthquake, has been modeled. The results of the corresponding numerical model calculations have revealed a fine agreement with TEC anomalies observed before strong earthquakes at the middle and low latitudes both in spatial scales and in amplitude characteristics.