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TEC

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


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Journal ArticleDOI
TL;DR: In this paper, the authors investigated the seasonal variation, magnetic local time (MLT) variation, geomagnetic activity dependence, and solar activity dependence of the mid-latitude trough using GPS total electron content (TEC) data from 2000 to 2014.
Abstract: This study statistically investigated the seasonal variation, magnetic local time (MLT) variation, geomagnetic activity dependence, and solar activity dependence of the mid-latitude trough using GPS total electron content (TEC) data from 2000 to 2014. The daily median Kp index was used to characterize the daily geomagnetic activity level. The results showed that the trough minimum position depended primarily on the geomagnetic activity, MLT, and the season. The trough depth depended primarily on the solar flux index (F107) and, to a lesser degree, on MLT. The trough depth increased as F107 increased and as the incidence angle of solar flux decreased. The trough equatorward half-width decreased as the geomagnetic activity increased. These variations in the GPS-TEC trough minimum position were compared with the variations in the TEC trough derived from the International Reference Ionosphere (IRI)-2007 model. The GPS-TEC trough minimum position changed little with respect to F107, whereas the IRI-TEC trough minimum position showed a strong F107 dependence.

35 citations

Journal ArticleDOI
TL;DR: In this paper, an intriguing effect was found while analyzing the small-scale variations of total electron content (TEC) derived from global positioning system (GPS) signals during the recovery phase of the strong magnetic storms on 31 October 2003.
Abstract: An intriguing effect was found while analyzing the small-scale variations of total electron content (TEC) derived from global positioning system (GPS) signals. We found a response in TEC variations to intense global Pc5 pulsations with periods of a few millihertz covering the corrected geomagnetic latitudes ~58°–75° during the recovery phase of the strong magnetic storms on 31 October 2003. Earlier studies demonstrated that the GPS-TEC technique is a powerful method to study the propagation pattern of transient disturbances in the ionosphere, generated by seismic or internal gravity waves. This technique has turned out to be sensitive enough to ULF waves as well. During periods with intense Pc5 geomagnetic wave activity, distinct pulsations with the same periodicity were found in the TEC data from high-latitude GPS receiving stations in Scandinavia. Wavelet and cross-spectral analysis showed a high coherence (~0.9) between the periodic geomagnetic and TEC variations. Moreover, the relative amplitude of TEC periodic fluctuations ΔTEC/TEC was about or even larger than the relative amplitude of geomagnetic variations ΔB/B. So far, the effect of TEC modulation by Pc5 waves is not well understood and is still a challenge for the MHD wave theory. Various possible modulation mechanisms have been estimated, but no mechanism has been firmly identified.

35 citations

Proceedings ArticleDOI
24 Apr 2006
TL;DR: In this paper, the authors quantified the impact of the background ionosphere on a L-band interferometric synthetic aperture radar (SAR) mission using a combination of simulation, modeling, Global Positioning System (GPS) data collected during the last solar maximum, and existing spaceborne SAR data.
Abstract: We have quantified the impact that the ionosphere would have on a L-band interferometric synthetic aperture radar (SAR) mission using a combination of simulation, modeling, Global Positioning System (GPS) data collected during the last solar maximum, and existing spaceborne SAR data. Using the Jet Propulsion Laboratory's Global Ionospheric Maps (GIM) total electron content (TEC) estimates derived from the worldwide array of GPS stations, we determined that the sun synchronous orbit which would minimize TEC at the time of imaging has dawn and dusk equator crossings. Such an orbit also avoids the equatorial post-sunset irregularities. We used the GIM data to examine the day-to-day variability in the background ionosphere and to quantify the impact of the background ionosphere on single pass SAR performance. With the exception of Faraday rotation related effects on single polarization systems, degradation due to the background ionosphere can be avoided if a reasonable model for the ionosphere is used during processing. Our studies reveal that Faraday rotation angles rarely exceeded the 10/spl deg/ threshold that impacts biomass retrieval and that repeat pass interferometric SAR decorrelation due to variations in the background ionosphere causing variable Faraday rotations is a negligible effect. Even a dawn-dusk orbit will not avoid high latitude ionospheric irregularities. We evaluated the strength of the ionospheric irregularities using GPS scintillation data collected at Fairbanks, Alaska and modeled the impact of these irregularities on azimuth resolution, azimuth displacement, peak sidelobe ratio (PSLR), and integrated sidelobe ratio (ISLR). Our examination of ionospheric artifacts in InSAR data has revealed that the artifacts occur primarily in the polar cap data, not auroral zone data as was previously thought.

35 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of CD40 ligand ligation on IL-15 production in human tubular epithelial cells (TEC) was investigated, and it was shown that activation with CD40-expressing cells (CD40L cells) resulted in an additive effect.
Abstract: Interleukin-15 (IL-15) is a potent T-cell growth factor and activator. Acute rejection of kidney allografts strongly correlated with elevated IL-15 mRNA in the graft. A role in the rejection process is also suggested for the interaction between CD40 ligand (CD154) expressed on membranes of activated T cells and its receptor (CD40). The effect of CD40 ligation on IL-15 production in human tubular epithelial cells (TEC) was investigated. TEC were co-cultured with a cell line genetically engineered to express CD154. CD154-expressing cells (CD40L cells) bind to TEC. Addition of the CD40L cells to the TEC culture resulted in elevated IL-15 levels. This enhanced production was not observed with control cells, when anti-CD154 antibody was added, and when direct contact between CD40L-cells and TEC was prevented with the use of a Trans-well system. CD40 activation resulted in a twofold increase of IL-15 mRNA transcripts as measured by reverse transcription-PCR and a concordant elevation in IL-15 protein production as measured by specific enzyme-linked immunosorbent assay. The intensity of activation by CD154 was linearly dependent on cell number, reaching plateau when the effector/target-ratio was 1:1. The increase of IL-15 levels was similar to that produced by stimulation with interferon-gamma (IFN-gamma). Combination of IFN-gamma and activation with CD154 resulted in an additive effect. To conclude, activated T cells may enhance IL-15 expression in two ways: by secreting IFN-gamma and by cell to cell contact using CD154. Each signal alone induces IL-15 in similar magnitudes, and both signals are additive. Because IL-15 is a major T-cell activator, this interaction may contribute to graft rejection.

35 citations

Journal ArticleDOI
TL;DR: In this article, temperature and wind data from the TIMED satellite during the years 2002-2007 were used to describe the seasonal variations of the westward propagating 6.5-day planetary wave in the mesosphere and lower thermosphere (MLT).
Abstract: . In the current work, temperature and wind data from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite during the years 2002–2007 were used to describe the seasonal variations of the westward propagating 6.5-day planetary wave in the mesosphere and lower thermosphere (MLT). Thermospheric composition data from the TIMED satellite and ionospheric total electron content (TEC) from the International Global Navigation Satellite System (GNSS) Service were then employed to carry out two case studies on the effect of this dissipating wave on the thermosphere/ionosphere. In both cases, there were westward anomalies of ~ 30–40 m s−1 in zonal wind in the MLT region that were caused by momentum deposition of the 6.5-day wave, which had peak activity during equinoxes. The westward zonal wind anomalies led to extra poleward meridional flows in both hemispheres. Meanwhile, there were evident overall reductions of thermospheric column density O / N2 ratio and ionospheric TEC with magnitudes of up to 16–24 % during these two strong 6.5-day wave events. Based on the temporal correlation between O / N2 and TEC reductions, as well as the extra poleward meridional circulations associated with the 6.5-day waves, we conclude that the dissipative 6.5-day wave in the lower thermosphere can cause changes in the thermosphere/ionosphere via the mixing effect, similar to the quasi-two-day wave (QTDW) as predicted by Yue and Wang (2014).

35 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023303
2022578
2021284
2020321
2019293
2018272