scholarly journals Variation of Vertical Total Electron Content (TEC) Over West Africa during Geomagnetic Storms

2020 ◽  
pp. 52-63
Author(s):  
Kingsley Chukwudi Okpala ◽  
Ernest Benjamin Ugwu ◽  
Okwudili Joseph Attah ◽  
Dominic Obiegbuna ◽  
Rose Chigoziri Anamezie ◽  
...  
Keyword(s):  
West Africa ◽  
Total Electron Content ◽  
Geomagnetic Storms ◽  
The Other ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Spatial Evolution ◽  
Quiet Time ◽  
Total Electron ◽  
Present Understanding

Changes in vertical total electron content (VTEC) over West Africa which were associated with four geomagnetic storms in 2015 have been studied. The spatial evolution of the quiet time TEC over West Africa for four months (vis; March, June, October and December) which may give rise to unique features of the storm TEC were also evaluated. Quiet-time VTEC (i.e Sq VTEC) was obtained using the hourly means of the international quietest days for each month when a storm of interest occurred. The change in TEC ( ) was obtained after removing the quiet time VTEC from the storm day VTEC.  A significant latitudinal variation in VTEC was observed at 22:00LT over West Africa and this was accompanied by the usual broad peak at about 14-17UT. The latitudinal disparity observed in the Sq  at 22.00LT was likely driven by the intesification of the fountain effect. The maximum   observed during the storms in 2015 were of the other of 16 TECU. These results have important implications for our present understanding of TEC evolution during a geomagnetic and its direct effect on the technologies that depend on it.

scholarly journals Total electron content responses to HILDCAAs and geomagnetic storms over South America

2017 ◽  
Vol 35 (6) ◽  
pp. 1309-1326 ◽  
Author(s):  
Patricia Mara de Siqueira Negreti ◽  
Eurico Rodrigues de Paula ◽  
Claudia Maria Nicoli Candido
Keyword(s):  
Solar Wind ◽  
South America ◽  
Total Electron Content ◽  
Geomagnetic Storm ◽  
Electric Fields ◽  
Geomagnetic Storms ◽  
Time Variability ◽  
Electron Content ◽  
Quiet Time ◽  
Total Electron

Abstract. Total electron content (TEC) is extensively used to monitor the ionospheric behavior under geomagnetically quiet and disturbed conditions. This subject is of greatest importance for space weather applications. Under disturbed conditions the two main sources of electric fields, which are responsible for changes in the plasma drifts and for current perturbations, are the short-lived prompt penetration electric fields (PPEFs) and the longer-lasting ionospheric disturbance dynamo (DD) electric fields. Both mechanisms modulate the TEC around the globe and the equatorial ionization anomaly (EIA) at low latitudes. In this work we computed vertical absolute TEC over the low latitude of South America. The analysis was performed considering HILDCAA (high-intensity, long-duration, continuous auroral electrojet (AE) activity) events and geomagnetic storms. The characteristics of storm-time TEC and HILDCAA-associated TEC will be presented and discussed. For both case studies presented in this work (March and August 2013) the HILDCAA event follows a geomagnetic storm, and then a global scenario of geomagnetic disturbances will be discussed. Solar wind parameters, geomagnetic indices, O ∕ N2 ratios retrieved by GUVI instrument onboard the TIMED satellite and TEC observations will be analyzed and discussed. Data from the RBMC/IBGE (Brazil) and IGS GNSS networks were used to calculate TEC over South America. We show that a HILDCAA event may generate larger TEC differences compared to the TEC observed during the main phase of the precedent geomagnetic storm; thus, a HILDCAA event may be more effective for ionospheric response in comparison to moderate geomagnetic storms, considering the seasonal conditions. During the August HILDCAA event, TEC enhancements from  ∼  25 to 80 % (compared to quiet time) were observed. These enhancements are much higher than the quiet-time variability observed in the ionosphere. We show that ionosphere is quite sensitive to solar wind forcing and considering the events studied here, this was the most important source of ionospheric responses. Furthermore, the most important source of TEC changes were the long-lasting PPEFs observed on August 2013, during the HILDCAA event. The importance of this study relies on the peculiarity of the region analyzed characterized by high declination angle and ionospheric gradients which are responsible for creating a complex response during disturbed periods.

Inter-hemispheric comparison of the ionosphere-plasmasphere system from multi-instrumental/model approach.

2020 ◽  
Author(s):  
Nicolas Bergeot ◽  
John Bosco Habarulema ◽  
Jean-Marie Chevalier ◽  
Tshimangadzo Matamba ◽  
Elisa Pinat ◽  
...  
Keyword(s):  
South African ◽  
Total Electron Content ◽  
Geomagnetic Storms ◽  
Global Navigation Satellite Systems ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Hemispheric Differences ◽  
Total Electron ◽  
Precise Knowledge

<p>An increasing demand for a better modelling and understanding of the Ionosphere-Plasmasphere system (I/Ps) is required for both scientific and public practical applications using electromagnetic wave signals reflecting on or passing through this layer. This is the case for the Global Navigation Satellite Systems (GNSS, i.e. GPS, GLONASS, Galileo) and for spacecraft designers and operators who need to have a precise knowledge of the electron density distribution.</p><p>Additionally, despite the long-term ionospheric studies that have been on-going for many decades, a number of aspects are still complicated to understand and forecast accurately even in mid-latitude regions during quiet conditions. Performing inter-hemispherical climatological studies in European and South African regions should highlight differences/similarities in I/Ps response during different phases of solar activity and geophysical conditions.</p><p>In that frame, the Royal Observatory of Belgium (ROB) and the South African National Space Agency (SANSA) started a collaboration named “Interhemispheric Comparison of the Ionosphere-Plasmasphere System” (BEZA-COM). The goal is to provide inter-hemispheric comparison of the I/Ps implying: (1) a characterization of the climatological behavior of the Total Electron Content (TEC) in the I/Ps, over European, South African, Arctic and Antarctica regions; (2) an identification of the mechanisms that regulate inter-hemispheric differences, asymmetries and commonalities in the I/Ps from low to high-latitudes, (3) study of the different responses of the I/Ps during extreme solar events and induced geomagnetic storms in the two hemispheres.</p><p>In this paper, we reprocessed the GNSS data (GPS+GLONASS) of the dense EUREF Permanent GNSS Network (EPN) and South African TRIGNET networks as well as IGS stations for the period 1998-2018. The output consists in vertical Total Electron Content (vTEC), estimated every 15 min., and covering the central European and South African regions. The vTEC is then extracted at two conjugated locations and used to constrain empirical models to highlight the climatological behavior of the ionospheric vTEC over Europe and South Africa. From the results, we will show that the differences are quite significant. To give first answers on these differences, we also compared these models with ionosondes long-term data based models (for foF2 and hmF2) at two conjugated locations (Grahamstown and Průhonice) as well as long-term NRLMSISE O/N<sub>2</sub> ratio.</p>

scholarly journals The Feature of Ionospheric Mid-Latitude Trough during Geomagnetic Storms Derived from GPS Total Electron Content (TEC) Data

2022 ◽  
Vol 14 (2) ◽  
pp. 369
Author(s):  
Na Yang ◽  
Tao Yu ◽  
Huijun Le ◽  
Libo Liu ◽  
Yang-Yi Sun ◽  
...  
Keyword(s):  
North America ◽  
Total Electron Content ◽  
Geomagnetic Storms ◽  
Electron Content ◽  
Quiet Time ◽  
Ionospheric Storm ◽  
Total Electron ◽  
Total Electron Content Data ◽  
Storm Effects ◽  
Storm Effect

This study aims to investigate the features of the ionospheric mid-latitude trough over North America by using the MIT total electron content data obtained during three geomagnetic storms that occurred in August 2018, September 2017, and March 2015. The mid-latitude trough position sharply moves equatorward from the quiet-time subauroral latitude to mid-latitude with the decrease in SYM-H during geomagnetic storms. We find that the ionospheric behavior of TEC around the mid-latitude trough position displays three kinds of ionospheric storm effect: negative ionospheric storm effect, unchanged ionospheric behavior, and positive ionospheric storm effect. These ionospheric storm effects around the mid-latitude trough position are not always produced by the mid-latitude trough. The ionospheric storm effects produced by the mid-latitude trough are limited in the narrow mid-latitude trough regions, and are transmitted to other regions with the movement of the mid-latitude trough.

scholarly journals Analysis of Ionospheric Vertical Total Electron Content before the 2014 Mw8.2 Chile Earthquake

2017 ◽  
Author(s):  
Weiping Jiang ◽  
Yifang Ma ◽  
Xiaohui Zhou ◽  
Zhao Li ◽  
Xiangdong An ◽  
...  
Keyword(s):  
Total Electron Content ◽  
Electric Fields ◽  
Geomagnetic Storms ◽  
Meridional Wind ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Equatorial Anomaly ◽  
Total Electron ◽  
Seasonal And Diurnal Variations ◽  
Chile Earthquake

This paper studies ionospheric vertical total electron content (VTEC) variations before the 2014 Mw8.2 Chile earthquake. VTEC derived from 14 GPS (Global Positioning System) stations and GIM (Global Ionospheric Map) were used to analyze ionospheric variations before the earthquake using the sliding interquartile range method, and results showed that significant positive VTEC anomalies occurred on 28 March. To explore possible causes of these anomalies, effects of solar and geomagnetic activities were examined, and VTEC variations during 17 March to 31 March in 2009-2013 were cross-compared. Also, VTEC for a full year before the earthquake was investigated. Results indicated that these anomalies were weakly associated with high solar activities and geomagnetic storms and that these anomalies were not normal seasonal and diurnal variations. An analysis of the spatial distribution of the observed anomalies was also presented, and it demonstrated that anomalies specifically appeared around the epicenter on 28 March. It suggests that observed anomalies may be associated with the subsequent Chile earthquake. Equatorial anomaly variations were analyzed to discuss the possible physical mechanism, and results showed that the equatorial anomaly unusually increased on 28 March, which indicates that anomalous electric fields generated in the earthquake preparation area and the meridional wind are possible causes of the observed ionospheric anomalies.

Analysis of ionospheric vertical total electron content before the 1 April 2014 Mw 8.2 Chile earthquake

2017 ◽  
Vol 21 (6) ◽  
pp. 1599-1612 ◽  
Author(s):  
Weiping Jiang ◽  
Yifang Ma ◽  
Xiaohui Zhou ◽  
Zhao Li ◽  
Xiangdong An ◽  
...  
Keyword(s):  
Total Electron Content ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Total Electron ◽  
Chile Earthquake

Validating the impact of various ionosphere correction on mid to long baselines and point positioning using GPS dual-frequency receivers

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Alaa A. Elghazouly ◽  
Mohamed I. Doma ◽  
Ahmed A. Sedeek
Keyword(s):  
Geomagnetic Storms ◽  
Global Navigation Satellite Systems ◽  
Electron Content ◽  
Assessment Procedure ◽  
Vertical Total Electron Content ◽  
Dual Frequency ◽  
Total Electron ◽  
Satellite Systems ◽  
Point Positioning ◽  
The Impact

Abstract Due to the ionosphere delay, which has become the dominant GPS error source, it is crucial to remove the ionospheric effect before estimating point coordinates. Therefore, different agencies started to generate daily Global Ionosphere Maps (GIMs); the Vertical Total Electron Content (VTEC) values represented in GIMs produced by several providers can be used to remove the ionosphere error from observations. In this research, An analysis will be carried with three sources for VTEC maps produced by the Center for Orbit Determination in Europe (CODE), Regional TEC Mapping (RTM), and the International Reference Ionosphere (IRI). The evaluation is focused on the effects of a specific ionosphere GIM correction on the precise point positioning (PPP) solutions. Two networks were considered. The first network consists of seven Global Navigation Satellite Systems (GNSS) receivers from (IGS) global stations. The selected test days are six days, three of them quiet, and three other days are stormy to check the influence of geomagnetic storms on relative kinematic positioning solutions. The second network is a regional network in Egypt. The results show that the calculated coordinates using the three VTEC map sources are far from each other on stormy days rather than on quiet days. Also, the standard deviation values are large on stormy days compared to those on quiet days. Using CODE and RTM IONEX file produces the most precise coordinates after that the values of IRI. The elimination of ionospheric biases over the estimated lengths of many baselines up to 1000 km has resulted in positive findings, which show the feasibility of the suggested assessment procedure.

scholarly journals Neural network based model for global Total Electron Content forecasting

2020 ◽  
Vol 10 ◽  
pp. 11 ◽  
Author(s):  
Claudio Cesaroni ◽  
Luca Spogli ◽  
Angela Aragon-Angel ◽  
Michele Fiocca ◽  
Varuliator Dear ◽  
...  
Keyword(s):  
Neural Network ◽  
Total Electron Content ◽  
Geomagnetic Storms ◽  
Single Point ◽  
Global Scale ◽  
External Input ◽  
Electron Content ◽  
International Gnss Service ◽  
Total Electron ◽  
Grid Points

We introduce a novel empirical model to forecast, 24 h in advance, the Total Electron Content (TEC) at global scale. The technique leverages on the Global Ionospheric Map (GIM), provided by the International GNSS Service (IGS), and applies a nonlinear autoregressive neural network with external input (NARX) to selected GIM grid points for the 24 h single-point TEC forecasting, taking into account the actual and forecasted geomagnetic conditions. To extend the forecasting at a global scale, the technique makes use of the NeQuick2 Model fed by an effective sunspot number R12 (R12eff), estimated by minimizing the root mean square error (RMSE) between NARX output and NeQuick2 applied at the same GIM grid points. The novel approach is able to reproduce the features of the ionosphere especially during disturbed periods. The performance of the forecasting approach is extensively tested under different geospatial conditions, against both TEC maps products by UPC (Universitat Politècnica de Catalunya) and independent TEC data from Jason-3 spacecraft. The testing results are very satisfactory in terms of RMSE, as it has been found to range between 3 and 5 TECu. RMSE depend on the latitude sectors, time of the day, geomagnetic conditions, and provide a statistical estimation of the accuracy of the 24-h forecasting technique even over the oceans. The validation of the forecasting during five geomagnetic storms reveals that the model performance is not deteriorated during disturbed periods. This 24-h empirical approach is currently implemented on the Ionosphere Prediction Service (IPS), a prototype platform to support different classes of GNSS users.

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