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Showing papers on "TEC published in 2016"


Journal ArticleDOI
TL;DR: In this article, a new improved design portable asymmetrical solar still has been designed, fabricated and tested over six typical summer days (between 27/08/2014 and 07/09/2014) under the real climatic conditions of Semnan (35°33′N, 53°23′E), Iran.

121 citations


Journal ArticleDOI
TL;DR: In this paper, during the 17 March 2015 great storm, the observed TEC, NmF2, and electron temperatures of the stormenhanced density (SED) over Millstone Hill (42.6°N, 71.5°W, 72° dip angle) show a quiet different picture.
Abstract: Ionospheric F2 region peak densities (NmF2) are expected to have a positive correlation with total electron content (TEC), and electron densities usually show an anticorrelation with electron temperatures near the ionospheric F2 peak. However, during the 17 March 2015 great storm, the observed TEC, NmF2, and electron temperatures of the storm-enhanced density (SED) over Millstone Hill (42.6°N, 71.5°W, 72° dip angle) show a quiet different picture. Compared with the quiet time ionosphere, TEC, the F2 region electron density peak height (hmF2), and electron temperatures above ~220 km increased, but NmF2 decreased significantly within the SED. This SED occurred where there was a negative ionospheric storm effect near the F2 peak and below it, but a positive storm effect in the topside ionosphere. Thus, this SED event was a SED in TEC but not in NmF2. The very low ionospheric densities below the F2 peak resulted in a much reduced downward heat conduction for the electrons, trapping the heat in the topside in the presence of heat source above. This, in turn, increased the topside scale height so that even though electron densities at the F2 peak were depleted, TEC increased in the SED. The depletion in NmF2 was probably caused by an increase in the density of the molecular neutrals, resulting in enhanced recombination. In addition, the storm time topside ionospheric electron density profiles were much closer to diffusive equilibrium than the nonstorm time profiles, indicating less daytime plasma flow between the ionosphere and the plasmasphere.

109 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the response of the ionosphere (F region) in the Brazilian sector during extreme space weather event of 17 March 2015 using a large network of 102 GPS-total electron content (TEC) stations.
Abstract: We studied the response of the ionosphere (F region) in the Brazilian sector during extreme space weather event of 17 March 2015 using a large network of 102 GPS- total electron content (TEC) stations. It is observed that the vertical total electron content (VTEC) was severely disturbed during the storm main and recovery phases. A wavelike oscillation with three peaks was observed in the TEC diurnal variation from equator to low latitudes during the storm main phase on 17–18 March 2015. The latitudinal extent of the wavelike oscillation peaks decreased from the beginning of the main phase toward the recovery phase. The first peak extended from beyond 0°S to 30°S, the second occurred from 6°S to 25°S, whereas the third diurnal peaks was confined from 13°S to 25°S. In addition, a strong negative phase in VTEC variations was observed during the recovery phase on 18–19 March 2015. This ionospheric negative phase was stronger at low latitudes than in the equatorial region. Also, two latitudinal chains of GPS-TEC stations from equatorial region to low latitudes in the east and west Brazilian sectors are used to investigate the storm time behavior of the equatorial ionization anomaly (EIA) in the east and west Brazilian sectors. We observed an anomalous behavior in EIA caused by the wavelike oscillations during the storm main phase on 17 March, and suppression of the EIA, resulting from the negative phase in VTEC, in the storm recovery phase.

106 citations


01 Mar 2016
TL;DR: A statistical framework for estimating global navigation satellite system (GNSS) non-ionospheric differential time delay bias is presented and a new method is found to produce estimates of receiver bias that have reduced day-to-day variability and more consistent coincident vertical TEC values.
Abstract: . We present a statistical framework for estimating global navigation satellite system (GNSS) non-ionospheric differential time delay bias. The biases are estimated by examining differences of measured line-integrated electron densities (total electron content: TEC) that are scaled to equivalent vertical integrated densities. The spatiotemporal variability, instrumentation-dependent errors, and errors due to inaccurate ionospheric altitude profile assumptions are modeled as structure functions. These structure functions determine how the TEC differences are weighted in the linear least-squares minimization procedure, which is used to produce the bias estimates. A method for automatic detection and removal of outlier measurements that do not fit into a model of receiver bias is also described. The same statistical framework can be used for a single receiver station, but it also scales to a large global network of receivers. In addition to the Global Positioning System (GPS), the method is also applicable to other dual-frequency GNSS systems, such as GLONASS (Globalnaya Navigazionnaya Sputnikovaya Sistema). The use of the framework is demonstrated in practice through several examples. A specific implementation of the methods presented here is used to compute GPS receiver biases for measurements in the MIT Haystack Madrigal distributed database system. Results of the new algorithm are compared with the current MIT Haystack Observatory MAPGPS (MIT Automated Processing of GPS) bias determination algorithm. The new method is found to produce estimates of receiver bias that have reduced day-to-day variability and more consistent coincident vertical TEC values.

91 citations


Journal ArticleDOI
Junhui Li1, Xiaorui Zhang1, Can Zhou1, Jingan Zheng1, Dasong Ge1, Wenhui Zhu1 
TL;DR: In this paper, an automatic system based on thermoelectric cooler (TEC), a microfan, and microcontroller is first applied to thermal management of high-power light-emitting diodes (LEDs).
Abstract: An automatic system based on thermoelectric cooler (TEC), a microfan, and microcontroller is first applied to thermal management of high-power light-emitting diodes (LEDs). Its hardware is composed of microcontroller as a control core, K-type thermocouples as acquisition devices, and TEC and a microfan with heatsink as cooling vehicles. The experiment confirms that the LEDs substrate temperature can be controlled effectively, and indicates that the LED chips are operating reliably. Specifically, in high-temperature environments of 43 °C, the system can automatically drop to the low set temperature (30 °C) due to thermoelectric effect driven by TEC. Heat transfer analysis shows that maximum LED power cooled by the system is 106.7 W, and the total power consumption of the automatic cooling system is only 8.85 W. The automatic cooling system has a high cooling efficiency.

87 citations


Journal ArticleDOI
TL;DR: In this article, a statistical framework for estimating global navigation satellite system (GNSS) non-ionospheric differential time delay bias is presented, which is based on the differences of measured line-integrated electron densities (total electron content: TEC) that are scaled to equivalent vertical integrated densities.
Abstract: . We present a statistical framework for estimating global navigation satellite system (GNSS) non-ionospheric differential time delay bias. The biases are estimated by examining differences of measured line-integrated electron densities (total electron content: TEC) that are scaled to equivalent vertical integrated densities. The spatiotemporal variability, instrumentation-dependent errors, and errors due to inaccurate ionospheric altitude profile assumptions are modeled as structure functions. These structure functions determine how the TEC differences are weighted in the linear least-squares minimization procedure, which is used to produce the bias estimates. A method for automatic detection and removal of outlier measurements that do not fit into a model of receiver bias is also described. The same statistical framework can be used for a single receiver station, but it also scales to a large global network of receivers. In addition to the Global Positioning System (GPS), the method is also applicable to other dual-frequency GNSS systems, such as GLONASS (Globalnaya Navigazionnaya Sputnikovaya Sistema). The use of the framework is demonstrated in practice through several examples. A specific implementation of the methods presented here is used to compute GPS receiver biases for measurements in the MIT Haystack Madrigal distributed database system. Results of the new algorithm are compared with the current MIT Haystack Observatory MAPGPS (MIT Automated Processing of GPS) bias determination algorithm. The new method is found to produce estimates of receiver bias that have reduced day-to-day variability and more consistent coincident vertical TEC values.

87 citations


Journal ArticleDOI
TL;DR: In this article, the authors deploy the TIEGCM and GPS total electron content (TEC) observations to identify the principle mechanisms for storm-enhanced density (SED) and the tongue of ionization (TOI) through term-byterm analysis of the ion continuity equation and also identify the advantages and deficiencies of theTIEGCM in capturing high-latitude and subauroral latitude ionospheric fine structures for the two geomagnetic storm events occurring on 17 March 2013 and 2015.
Abstract: There are still uncertainties regarding the formation mechanisms for storm-enhanced density (SED) in the high and subauroral latitude ionosphere. In this work, we deploy the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) and GPS total electron content (TEC) observations to identify the principle mechanisms for SED and the tongue of ionization (TOI) through term-by-term analysis of the ion continuity equation and also identify the advantages and deficiencies of the TIEGCM in capturing high-latitude and subauroral latitude ionospheric fine structures for the two geomagnetic storm events occurring on 17 March 2013 and 2015. Our results show that in the topside ionosphere, upward E × B ion drifts are most important in SED formation and are offset by antisunward neutral winds and downward ambipolar diffusion effects. In the bottomside F region ionosphere, neutral winds play a major role in generating SEDs. SED signature in TEC is mainly caused by upward E × B ion drifts that lift the ionosphere to higher altitudes where chemical recombination is slower. Horizontal E × B ion drifts play an essential role in transporting plasma from the dayside convection throat region to the polar cap to form TOIs. Inconsistencies between model results and GPS TEC data were found: (1) GPS relative TEC difference between storm time and quiet time has “holes” in the dayside ion convection entrance region, which do not appear in the model results. (2) The model tends to overestimate electron density enhancements in the polar region. Possible causes for these inconsistencies are discussed in this article.

79 citations


Journal ArticleDOI
TL;DR: A ten-parameter Klobuchar-like model, which describes the nighttime term as a linear function of geomagnetic latitude, is finally proposed for GNSS single-frequency ionospheric corrections.

77 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the ionospheric effects of the geomagnetic storm that occurred during 17-19 March 2015 in the American and European sectors using available ground-based ionosonde and GPS TEC data.
Abstract: The current study aims at investigating and identifying the ionospheric effects of the geomagnetic storm that occurred during 17–19 March 2015. Incidentally, with SYM-H hitting a minimum of −232 nT, this was the strongest storm of the current solar cycle 24. The study investigates how the storm has affected the equatorial, low-latitude, and midlatitude ionosphere in the American and the European sectors using available ground-based ionosonde and GPS TEC (total electron content) data. The possible effects of prompt electric field penetration is observed in both sectors during the main phase of the storm. In the American sector, the coexistence of both positive and negative ionospheric storm phases are observed at low latitudes and midlatitudes to high latitudes, respectively. The positive storm phase is mainly due to the prompt penetration electric fields. The negative storm phase in the midlatitude region is a combined effect of disturbance dynamo electric fields, the equatorward shift of the midlatitude density trough, and the equatorward compression of the plasmapause in combination with chemical compositional changes. Strong negative ionospheric storm phase is observed in both ionosonde and TEC observations during the recovery phase which also shows a strong hemispherical asymmetry. Additionally, the variation of equatorial ionization anomaly as seen through the SWARM constellation plasma measurements across different longitudes has been discussed. We, also, take a look at the performance of the IRI Real-Time Assimilative Mapping during this storm as an ionospheric space weather tool.

72 citations


Journal ArticleDOI
TL;DR: Anticoagulation was protective against TEC and resulted in a reduction of TEC risk by 2.5 TEC per 100 patient-years, without a significant increase in bleeding risk.

68 citations


Journal ArticleDOI
TL;DR: In this article, the authors used data from ground-based GNSS-receivers located in southern Chile to study the ionospheric total electron content response to two eruptions of the Calbuco volcano that occurred on 22-23 April 2015.
Abstract: Using data from ground-based GNSS-receivers located in southern Chile, we study the ionospheric total electron content (TEC) response to two eruptions of the Calbuco volcano that occurred on 22-23 April 2015. In both cases, the TEC response showed quasi-periodic signals with several consecutive wave-trains. The averaged amplitude of the observed co-volcanic TEC-perturbations amounted 0.45 TECU for the first eruption and 0.16 TECU for the second one. We compare amplitudes of the TEC response to volcano eruptions of different intensity from our and previously published data, and we show that both the intensity and the background ionospheric conditions define the amplitude of ionospheric co-volcanic disturbances (CVID). The relative contribution, however, scales with the eruption intensity. The travel-time diagrams allowed to estimate the propagation speed of the observed co-volcanic TEC perturbations as ~900-1200 m/s, which is close to the acoustic (or shock-acoustic) waves speed at the ionospheric height. The spectrograms are consistent with the conclusion on the acoustic nature of the observed TEC perturbations. Finally, we use the approximation of a spherical wave propagating at a constant velocity from a point source and, for the first time, we calculate the location of the volcanic source and the onset time of the volcano eruption from ionospheric measurements. We show that even from 30-sec ionospheric GPS data it is possible to “localize” the eruptive source within several degrees of latitude/longitude.

Journal ArticleDOI
TL;DR: In this article, the amplitude spectrum of the TEC time series showed peaks at 3.7 mHz, 4.8 mHz and 6.8mHz, and wavelet analysis showed that harmonic oscillations started at ∼16:25 UT and continued for ∼2.5 h.

Journal ArticleDOI
TL;DR: In this paper, the applicability of three mapping functions for low earth orbit (LEO) satellite-based TEC conversion is examined for ground-based global navigation satellite system (GNSS) observations, and the results illustrate that the F&K (Foelsche and Kirchengast) geometric mapping function together with the ionospheric effective height (IEH) from the centroid method is more suitable for the LEO-based TSEC conversion.
Abstract: The mapping function is commonly used to convert slant to vertical total electron content (TEC) based on the assumption that the ionospheric electrons concentrate in a layer. The height of the layer is called ionospheric effective height (IEH) or shell height. The mapping function and IEH are generally well understood for ground-based global navigation satellite system (GNSS) observations, but they are rarely studied for the low earth orbit (LEO) satellite-based TEC conversion. This study is to examine the applicability of three mapping functions for LEO-based GNSS observations. Two IEH calculating methods, namely the centroid method based on the definition of the centroid and the integral method based on one half of the total integral, are discussed. It is found that the IEHs increase linearly with the orbit altitudes ranging from 400 to 1400 km. Model simulations are used to compare the vertical TEC converted by these mapping functions and the vertical TEC directly calculated by the model. Our results illustrate that the F&K (Foelsche and Kirchengast) geometric mapping function together with the IEH from the centroid method is more suitable for the LEO-based TEC conversion, though the thin layer model along with the IEH of the integral method is more appropriate for the ground-based vertical TEC retrieval.

Journal ArticleDOI
TL;DR: In this article, a combined solution of thermoelectric cooler (TEC) and mini-channel heat sink was proposed to remove the hotspot of the chip in the electronic equipment.

Journal ArticleDOI
TL;DR: Ionospheric weather maps using the total electron content (TEC) monitored by ground based GNSS receivers over South American continent, TECMAP, have been operationally produced by INPE´s Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial, EMBRACE) since 2013.
Abstract: Ionospheric weather maps using the total electron content (TEC) monitored by ground based GNSS receivers over South American continent, TECMAP, have been operationally produced by INPE´s Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial, EMBRACE) since 2013. In order to cover the whole continent, 4 GNSS receiver net-works, RBMC/IBGE, LISN, IGS and RAMSAC, in total ~140 sites, have been used. TECMAPs with a time resolution of 10 minutes are produced in 12 hour time delay. Spatial resolution of the map is rather low, varying between 50 and 500 km depending on the density of the observation points. Large day to day variabilities of the equatorial ionization anomaly (EIA) have been observed. Spatial gradient of TEC from the anomaly trough (TECu 80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles (IPB), their seeding and development, could be monitored.These plasma density (spatial and temporal) variability causes not only the GNSS based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC Mapping becomes an important issue for Space Weather concern for high technology positioning system and telecommunication.

Journal ArticleDOI
TL;DR: In this paper, a physics-based Cauer-type thermal equivalent circuit (TEC) was constructed for an insulated-gate bipolar transistor (IGBT) module based on its geometry.
Abstract: A physics-based Cauer-type thermal equivalent circuit (TEC) can be constructed for an insulated-gate bipolar transistor (IGBT) module based on its geometry. In the conventional Cauer-type TEC, each layer of the IGBT module is modeled as a lump with the uniformly distributed temperature. However, this method oversimplified the transient thermal behavior of the IGBT module, leading to unsatisfactory transient junction temperature estimation. Based on a new concept of lumped-capacitance approximation error, this letter proposes a method to determine the number of sublayers that a layer in an IGBT module should be subdivided. For the bulky-baseplate layer, an analytical expression of its thermal impedance is derived and simplified to a first-order transfer function, which can be represented by a thermal resistance and capacitance pair in the TEC. The proposed Cauer-type TEC model is much more accurate than the conventional Cauer-type TEC model for the transient junction temperature estimation of IGBT modules with a slightly increased order only. The improvement of the proposed model over the conventional Cauer-type TEC model is validated by comparing with a finite element analysis model for a commercial IGBT module using simulation studies.

Journal ArticleDOI
TL;DR: In this paper, the top-side ionospheric total electron content (TEC) observations from multiple low-Earth orbit (LEO) satellites have been used to investigate the local time, altitudinal, and longitudinal dependence of the topside ionosphere storm effect during both the main and recovery phases of the March 2015 geomagnetic storm.
Abstract: Topside ionospheric total electron content (TEC) observations from multiple low-Earth orbit (LEO) satellites have been used to investigate the local time, altitudinal, and longitudinal dependence of the topside ionospheric storm effect during both the main and recovery phases of the March 2015 geomagnetic storm. The results of this study show, for the first time, that there was a persistent topside TEC depletion that lasted for more than 3 days after the storm main phase at most longitudes, except in the Pacific Ocean region, where the topside TECs during the storm recovery phase were comparable to the quiet time ones. The observed depletion in the topside ionospheric TEC was relatively larger at higher altitudes in the evening sector and greater at local times closer to midnight. Moreover, the topside TEC patterns observed by MetOp-A (832 km) were different from those seen by other LEO satellites with lower orbital altitudes during the storm main phase and at the beginning of the recovery phase, especially in the evening sector. This suggests that the physical processes that control the storm time behavior of topside ionospheric response to storms are altitude-dependent.

Journal ArticleDOI
TL;DR: In this paper, the authors present results for state-of-the-art imaging using ground-based and spaceborne ionospheric measurements and coupled atmosphere-ionosphere modeling of ionosphere total electron content (TEC) perturbations.
Abstract: Natural hazards including earthquakes, volcanic eruptions, and tsunamis have been significant threats to humans throughout recorded history. Global navigation satellite systems (GNSS; including the Global Positioning System (GPS)) receivers have become primary sensors to measure signatures associated with natural hazards. These signatures typically include GPS-derived seismic deformation measurements, coseismic vertical displacements, and real-time GPS-derived ocean buoy positioning estimates. Another way to use GPS observables is to compute the ionospheric total electron content (TEC) to measure, model, and monitor postseismic ionospheric disturbances caused by, e.g., earthquakes, volcanic eruptions, and tsunamis. In this paper, we review research progress at the Jet Propulsion Laboratory and elsewhere using examples of ground-based and spaceborne observation of natural hazards that generated TEC perturbations. We present results for state-of-the-art imaging using ground-based and spaceborne ionospheric measurements and coupled atmosphere-ionosphere modeling of ionospheric TEC perturbations. We also report advancements and chart future directions in modeling and inversion techniques to estimate tsunami wave heights and ground surface displacements using TEC measurements and error estimates. Our initial retrievals strongly suggest that both ground-based and spaceborne GPS remote sensing techniques could play a critical role in detection and imaging of the upper atmosphere signatures of natural hazards including earthquakes and tsunamis. We found that combining ground-based and spaceborne measurements may be crucial in estimating critical geophysical parameters such as tsunami wave heights and ground surface displacements using TEC observations. The GNSS-based remote sensing of natural-hazard-induced ionospheric disturbances could be applied to and used in operational tsunami and earthquake early warning systems.

Journal ArticleDOI
TL;DR: In this paper, the authors used an ensemble Kalman filter constructed with the Data Assimilation Research Testbed and the Thermosphere Ionosphere Electrodynamics General Circulation Model.
Abstract: Ionospheric storms can have important effects on radio communications and navigation systems. Storm time ionospheric predictions have the potential to form part of effective mitigation strategies to these problems. Ionospheric storms are caused by strong forcing from the solar wind. Electron density enhancements are driven by penetration electric fields, as well as by thermosphere-ionosphere behavior including Traveling Atmospheric Disturbances and Traveling Ionospheric Disturbances and changes to the neutral composition. This study assesses the effect on 1 h predictions of specifying initial ionospheric and thermospheric conditions using total electron content (TEC) observations under a fixed set of solar and high-latitude drivers. Prediction performance is assessed against TEC observations, incoherent scatter radar, and in situ electron density observations. Corotated TEC data provide a benchmark of forecast accuracy. The primary case study is the storm of 10 September 2005, while the anomalous storm of 21 January 2005 provides a secondary comparison. The study uses an ensemble Kalman filter constructed with the Data Assimilation Research Testbed and the Thermosphere Ionosphere Electrodynamics General Circulation Model. Maps of preprocessed, verticalized GPS TEC are assimilated, while high-latitude specifications from the Assimilative Mapping of Ionospheric Electrodynamics and solar flux observations from the Solar Extreme Ultraviolet Experiment are used to drive the model. The filter adjusts ionospheric and thermospheric parameters, making use of time-evolving covariance estimates. The approach is effective in correcting model biases but does not capture all the behavior of the storms. In particular, a ridge-like enhancement over the continental USA is not predicted, indicating the importance of predicting storm time electric field behavior to the problem of ionospheric forecasting.

Journal ArticleDOI
TL;DR: In this paper, two temperature controls for TEC are proposed and compared to prevent condensation on CPU and save energy, and the performance of TEC with and without temperature control and passive water cooling is investigated under variable operating conditions at severe environment.
Abstract: In this paper, water-cooled thermoelectric cooler (TEC) for central processing unit (CPU) is developed. Two temperature controls for TEC are proposed and compared to prevent condensation on CPU and save energy. Performances of TEC with the two temperature controls are experimentally investigated under different operating conditions and environmental temperatures. Effects of air velocity and water mass flow rate for the heat sink are investigated under severe environment. Dynamic performance comparisons of three cooling methods, including TEC with and without temperature control and passive water cooling, are investigated under variable operating conditions at severe environment. Experimental results show that temperature of CPU (T cpu ) for SC is lower than that for OC when T cpu is lower than the set temperature. A higher COP can be kept when air velocity and water mass flow rate is 0.8 ms −1 and 0.042 kg s −1 , respectively. The largest temperature variation of T cpu s is lower than 1.5 °C under variable operating conditions at severe environment.

Journal ArticleDOI
TL;DR: In this article, a regional 3D ionospheric electron density specification over China and adjacent areas (70°E-140°E in longitude, 15°N-55°N in latitude, and 100-900 km in altitude) is developed on the basis of data assimilation technique.
Abstract: In this paper, a regional 3-D ionospheric electron density specification over China and adjacent areas (70°E–140°E in longitude, 15°N–55°N in latitude, and 100–900 km in altitude) is developed on the basis of data assimilation technique. The International Reference Ionosphere (IRI) is used as a background model, and a three-dimensional variational technique is used to assimilate both the ground-based Global Navigation Satellite System (GNSS) observations from the Crustal Movement Observation Network of China (CMONOC) and International GNSS Service (IGS) and the ionospheric radio occultation (RO) data from FORMOSAT-3/COSMIC (F3/C) satellites. The regional 3-D gridded ionospheric electron densities can be generated with temporal resolution of 5 min in universal time, horizontal resolution of 2° × 2° in latitude and longitude, and vertical resolution of 20 km between 100 and 500 km and 50 km between 500 and 900 km. The data assimilation results are validated through extensive comparison with several sources of electron density information, including (1) ionospheric total electron content (TEC); (2) Abel-retrieved F3/C electron density profiles (EDPs); (3) ionosonde f o F 2 and bottomside EDPs; and (4) the Utah State University Global Assimilation of Ionospheric Measurements (USU-GAIM) under both geomagnetic quiet and disturbed conditions. The validation results show that the data assimilation procedure pushes the climatological IRI model toward the observation, and a general accuracy improvement of 15–30% can be expected. Thecomparisons also indicate that the data assimilation results are more close to the Center for Orbit Determination of Europe (CODE) TEC and Madrigal TEC products than USU-GAIM. These initial results might demonstrate the effectiveness of the data assimilation technique in improving specification of local ionospheric morphology.

Journal ArticleDOI
TL;DR: Ionospheric total electron content (TEC) variations prior to two large earthquakes in Nepal (M= 7.8) and Chile (M = 8.3) in 2015 were analyzed using measurements from global navigation satellite system network with the aim to detect possible ionospheric anomalies associated to these seismic events and describe their main features, by applying statistical and spectral analysis as discussed by the authors.
Abstract: Ionospheric total electron content (TEC) variations prior to 2 large earthquakes in Nepal (M = 7.8) and Chile (M = 8.3) in 2015 were analyzed using measurements from global navigation satellite system network with the aim to detect possible ionospheric anomalies associated to these seismic events and describe their main features, by applying statistical and spectral analysis. It was shown that abnormal TEC variations appeared few days up to few hours before the events lasting up to 8 h, whereas intensified TEC wave-like oscillations with periods 20 and 2–5 min were also identified that could be linked to the impending earthquakes. An unusual modification of the equatorial ionospheric anomaly 5 days before the main shock was also detected. Spectral analysis on TEC satellite measurements proved an effective method for the discrimination between seismically induced ionospheric waves and those of different origin such as the solar terminator transition and geomagnetic storms.

Journal ArticleDOI
06 Apr 2016
TL;DR: It is indicated that both TeC and TVS under-report Trec during steady-state and intermittent exercise in the heat, with TeC predicting Trec with the least accuracy of the telemetry devices.
Abstract: Aim: Intestinal temperature telemetry systems are promising monitoring and research tools in athletes. However, the additional equipment that must be carried to continuously record temperature data limits their use to training. The purpose of this study was to assess the validity and reliability of a new gastrointestinal temperature data logging and telemetry system (e-Celsius™) during water bath experimentation and exercise trials. Materials and Methods: Temperature readings of 23 pairs of e-Celsius (TeC) and VitalSense (TVS) ingestible capsules were compared to rectal thermistor responses (Trec) at 35, 38.5 and 42°C in a water bath. Devices were also assessed in vivo during steady-state cycling (n = 11) and intermittent running (n = 11) in hot conditions. Results: The water bath experiment showed TVS and TeC under-reported Trec (P<0.001). This underestimation of Trec also occurred during both cycling (mean bias vs TVS: 0.21°C, ICC: 0.84, 95% CI: 0.66-0.91; mean bias vs. TeC: 0.44°C, ICC: 0.68, 95% CI: 0.07-0.86, P<0.05) and running trials (mean bias vs. TVS: 0.15°C, ICC: 0.92, 95% CI: 0.83-0.96; mean bias vs. TeC: 0.25, ICC: 0.86, 95% CI: 0.61-0.94, P<0.05). However, calibrating the devices attenuated this difference during cycling and eliminated it during running. During recovery following cycling exercise, TeC and TVS were significantly lower than Trec despite calibration (P<0.01). Conclusion: These results indicate that both TeC and TVS under-report Trec during steady-state and intermittent exercise in the heat, with TeC predicting Trec with the least accuracy of the telemetry devices. It is therefore recommended to calibrate these devices at multiple temperatures prior to use.

Journal ArticleDOI
TL;DR: In this paper, an analysis of ionospheric irregularities at high latitudes during the 2015 St. Patrick's Day storm is presented, which is associated with stormenhanced density (SED) formation at mid-latitudes and further evolution of the SED plume to the polar tongue of ionization (TOI).
Abstract: We present an analysis of ionospheric irregularities at high latitudes during the 2015 St. Patrick’s Day storm. Our study used measurements from ~2700 ground-based GPS stations and GPS receivers onboard five low earth orbit (LEO) satellites—Swarm A, B and C, GRACE and TerraSAR-X—that had close orbit altitudes of ~500 km, and the Swarm in situ plasma densities. An analysis of the rate of TEC index (ROTI) derived from LEO–GPS data, together with Swarm in situ plasma probe data, allowed us to examine the topside ionospheric irregularities and to compare them to the main ionospheric storm effects observed in ground-based GPS data. We observed strong ionospheric irregularities in the topside ionosphere during the storm’s main phase that were associated with storm-enhanced density (SED) formation at mid-latitudes and further evolution of the SED plume to the polar tongue of ionization (TOI). Daily ROTI maps derived from ground-based and LEO–GPS measurements show the pattern of irregularities oriented in the local noon–midnight direction, which is a signature of SED/TOI development across the polar cap region. Analysis of the Swarm in situ plasma measurements revealed that, during the storm’s main phase, all events with extremely enhanced plasma densities (>106 el/cm3) in the polar cap were observed in the Southern Hemisphere. When Swarm satellites crossed these enhancements, degradation of GPS performance was observed, with a sudden decrease in the number of GPS satellites tracked. Our findings indicate that polar patches and TOI structures in the topside ionosphere were predominantly observed in the Southern Hemisphere, which had much higher plasma densities than the Northern Hemisphere, where SED/TOI structures have already been reported earlier. LEO–GPS data (ROTI and topside TEC) were consistent with these results.

Journal ArticleDOI
TL;DR: In this article, the authors studied perturbations in the European-African sector observed in the total electron content (TEC) observed by large-scale traveling ionospheric disturbances (LSTIDs).
Abstract: Strong ionospheric perturbations were generated by the intense geomagnetic storm on 17 March 2015. In this article, we are studying perturbations in the European-African sector observed in the total electron content (TEC). Focal points are wavelike phenomena considered as large-scale traveling ionospheric disturbances (LSTIDs). In the European-African sector, the storm produced three different types of LSTIDs: (1) a concurrent TEC perturbation at all latitudes simultaneously; (2) one LSTID propagating toward the equator, having very large wave parameters (wavelength: ≈3600 km, period: ≈120 min, and speed: ≈500 m/s); and (3) several LSTIDs propagating toward the equator with typical wave parameters (wavelength: ≈2100 km, period: ≈60 min, and speed ≈600 m/s). The third type of LSTIDs is considered to be exited as most LSTIDs either due to variations in the Joule heating or variations in the Lorentz force, whereas the first two perturbation types are rather unusual in their appearance. They occurred during the partial recovery phase when the geomagnetic perturbations were minor and the interplanetary magnetic field turned northward. A westward prompt penetration electric field is considered to excite the first perturbation signature, which indicates a sudden TEC depletion. For the second LSTID type, variations in the Lorentz force because of perturbed electric fields and a minor particle precipitation effect are extracted as possible excitation mechanisms.

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TL;DR: In this paper, the authors present a complete statistical characterization of the ionospheric response to geomagnetic storms for midlatitudes in the North American sector where dense ground receiver coverage is available.
Abstract: Over the last two decades, maps of GPS total electron content (TEC) have improved our understanding of the large perturbations in ionospheric electron density which occur during geomagnetic storms. However, previous regional and global studies of ionospheric storms have performed only a limited separation of storm time, local time, longitudinal, and seasonal effects. Using 13 years of GPS TEC data, we present a complete statistical characterization of the ionospheric response to geomagnetic storms for midlatitudes in the North American sector where dense ground receiver coverage is available. The rapid onset of a positive phase is observed across much of the dayside and evening ionosphere followed by a longer-lasting negative phase across all latitudes and local times. Our results show clear seasonal variations in the storm time TEC, such that summer events tend to be dominated by the negative storm response while winter events exhibit a stronger initial positive phase with minimal negative storm effects. We find no discernable difference between spring and fall equinox events with both being equivalent to the average storm time response across all seasons. We also identify a prominent magnetic declination effect such that stronger dayside positive storm effects are observed in regions of negative declination (i.e., eastern North America). On the nightside, asymmetries in the TEC response are observed near the auroral oval and midlatitude trough which may be attributed to thermospheric zonal winds pushing plasma upward/downward along field lines of opposite declination.

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TL;DR: In this article, the authors present multi-instrument observations of the effects of the crustal magnetic field on the Martian ionosphere at different altitudes and solar zenith angles by Mars Express.

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TL;DR: In this article, the global ionospheric storm in March 2015 was investigated using data from over 3000 GPS stations worldwide, and the results show that, based on the multiple methods above, we all observed that, for the first time, there were three equatorward traveling ionosphere disturbances (TIDs) in the main phase of this storm.
Abstract: The global ionospheric storm in March, 2015 was investigated using data from over 3000 GPS stations worldwide. In this study, Total Electron Content(TEC), Rate of TEC(ROT) and ROT's standard deviation ROTI, as well as the second-order difference operator TECT, were considered as main characteristic methods to distinguish ionosphereic disturbances.The results show that, (1) Based on the multiple methods above, we all observed that, for the first time, there were three equatorward traveling ionospheric disturbances (TIDs) in the main phase of this storm. In North America, the disturbance zone expanded to ~40°N; the disturbance periods and AE peak stages were roughly synchronous. We suggest that these three TIDs were induced by the propagation of AGWs to low latitudes under the action of AE. (2) The most intense positive storm occurred over South America and the South Atlantic (over 300% enhancement; 00:00–05:00 UT March 18), whereas a negative storm was observed in the corresponding region of the NH. Such inverse hemispheric asymmetry in intensity and structure can be explained by the variations of the thermospheric composition, the IMF By component and the geomagnetic intensity. (3) On March 18, a negative storm dominated globally (except at certain low latitudes), and tended to propagate equatorward and decay with time, which could be largely attributed to the storm circulation theory. And the evolution of the negative storm was further characterized by the foF2 variations of ionosondes.

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TL;DR: In this article, an ensemble Kalman filter software developed by the National Center for Atmospheric Research (NCAR), called Data Assimilation Research Testbed, is applied to assimilate ground-based GPS total electron content (TEC) observations into a theoretical numerical model of the thermosphere and ionosphere.
Abstract: The main purpose of this paper is to investigate the effects of rapid assimilation-forecast cycling on the performance of ionospheric data assimilation during geomagnetic storm conditions. An ensemble Kalman filter software developed by the National Center for Atmospheric Research (NCAR), called Data Assimilation Research Testbed, is applied to assimilate ground-based GPS total electron content (TEC) observations into a theoretical numerical model of the thermosphere and ionosphere (NCAR thermosphere-ionosphere-electrodynamics general circulation model) during the 26 September 2011 geomagnetic storm period. Effects of various assimilation-forecast cycle lengths: 60, 30, and 10 min on the ionospheric forecast are examined by using the global root-mean-squared observation-minus-forecast (OmF) TEC residuals. Substantial reduction in the global OmF for the 10 min assimilation-forecast cycling suggests that a rapid cycling ionospheric data assimilation system can greatly improve the quality of the model forecast during geomagnetic storm conditions. Furthermore, updating the thermospheric state variables in the coupled thermosphere-ionosphere forecast model in the assimilation step is an important factor in improving the trajectory of model forecasting. The shorter assimilation-forecast cycling (10 min in this paper) helps to restrain unrealistic model error growth during the forecast step due to the imbalance among model state variables resulting from an inadequate state update, which in turn leads to a greater forecast accuracy.

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TL;DR: An improved DCB estimation method based on the assumption that the LEO-based TEC can reach zero and also optimize the parameter configuration in the commonly used least square method (LSQ method) is proposed.
Abstract: The uncertainty of differential code bias (DCB) is one of the main error sources in the low Earth orbit (LEO) based total electron content (TEC) retrieval, whereas the derivation of the LEO DCB is not systematically studied. In this paper, we propose an improved DCB estimation method (ZERO method) based on the assumption that the LEO-based TEC can reach zero and also optimize the parameter configuration in the commonly used least square method (LSQ method). In the improved ZERO method, the combination of the lower quartile minimum relative TEC during each orbital revolution with the daily minimum relative TEC gives a stable and reliable DCB estimation. For the LSQ method, the 3-TECU cutoff vertical TEC with 10° cutoff elevation is considered to offer a reasonable DCB estimation. Subsequently, Global Positioning System (GPS) observations from multiple LEO satellites at different altitudes are used to study the variability of the LEO DCBs. Our results revealed that the LEO DCBs underwent obvious long-term variation and periodic oscillations of months. Moreover, the CHAMP data illustrated that the long-term variation of LEO DCBs is partly associated with the GPS satellite replacement, and the periodic variation can be attributed to the variation of the hardware thermal status, represented by the receiver CPU temperature in this study.