Behavior Of Total Electron Content Research Articles

The capability of Artificial Neural Networks as a Model for Predicting Total Electron Content (TEC): A Review

The results of investigations from a complete analysis of ANN application on Total Electron Content (TEC) prediction are presented in this paper. TEC is important in defining the ionosphere and has many everyday applications, for example, satellite navigation, time delay and range error corrections for single frequency Global Positioning System (GPS) satellite signal receivers. The total electron content (TEC) in the ionosphere has been measured using GPS. GPS are not installed in every point on the earth to make global TEC measurements possible. As a result, it is crucial to have certain models that can aid to get data from places where there is not any in order to comprehend the global behavior of TEC. Neural Network (NN) models have been shown to accurately anticipate data patterns, including TEC. The capacity of neural networks to represent both linear and nonlinear relationships directly from the data being modeled is what makes them so powerful. The survey from literature reveals that, Levenberg-Marquardt algorithm is preferred and used mostly because of its speed and efficiency during learning process, and that ANN showed a good prediction of TEC compared to the IRI model. As a result, NNs are suitable for forecasting GPS TEC values at various locations if the model's input parameters are well specified.

Prediction of ionospheric total electron content data using spatio-temporal residual network

Since the ionospheric total electron content (TEC) exhibits complex spatial and temporal behaviour including the seasonal and solar activity dependencies, resulting in large scale differences across different regions of the world, developing an effective deep-learning-based predictive model, capturing the complex behaviour of TEC is much needed. We present a novel deep learning-based model to predict the TEC using the spatio-temporal residual network (ST-ResNet). The TEC data used in the study were obtained from 185 GPS receiver locations, covering the latitude region from 10° N to 80° N and the longitude region from 110° W to 34° E. We considered TEC data of 154 days each corresponding to the solar maximum (2014) and the solar minimum (2020) years for training the network together with the exogeneous interplanetary magnetic field (IMF) data, including the magnetic field components By, Bz, plasma flow speed (Vp), and proton density (Np). A total of 44,352 maps (collected at the rate of 288 maps per day) were pre-processed by grouping them into closeness, period, and trend channels, which associate with the near-time, short-term, and long-term trends in the TEC data, respectively. After training, the model was tested for one day. The objectives of the study are: i) To develop and evaluate the performance of the ST-ResNet model, ii) to assess its performance on TEC data corresponding to mid-latitude region, under different solar conditions and iii) to compare the ST-ResNet model with other predicted models. For the entire study region, the root mean squared error (RMSE) was found to be 3.13 TECU for the solar maximum year and 1.23 TECU for the solar minimum year. Similar trends were observed in the mid-latitude region (30° N-60° N), with RMSE values of 2.31 TECU and 1.58 TECU for the solar maximum and solar minimum years, respectively. ST-ResNet model showed an improved accuracy over the long short-term memory (LSTM) deep learning network by about 23% and 31% for the entire study region and by 49% and 19% for only mid-latitude region, during the solar maximum and minimum years respectively, suggesting the superior performance of ST-ResNet over the LSTM network. A comparative observation of results of ST-ResNet model with those of back propagation and international reference ionosphere-2016 (IRI-2016) model also showed the superiority of the former. Results confirm the suitability of the ST-ResNet model for predicting the spatial and temporal behavior of TEC across different locations during various solar conditions.

Using Deep Learning to Map Ionospheric Total Electron Content over Brazil

The low-latitude ionosphere has an active behavior causing the total electron content (TEC) to vary spatially and temporally very dynamically. The solar activity and the geomagnetic field have a strong influence over the spatiotemporal distribution of TEC. These facts make it a challenge to attempt modeling the ionization response. Single frequency GNSS users are particularly vulnerable due to these ionospheric variations that cause degradation of positioning performance. Motivated by recent applications of machine learning, temporal series of TEC available in map formats were employed to build an independent TEC estimator model for low-latitude environments. A TEC dataset was applied along with geophysical indices of solar flux and magnetic activity to train a feedforward artificial neural network based on a multilayer perceptron (MLP) approach. The forecast for the next 24 h was made relying on TEC maps over the Brazilian region using data collected on the previous 5 days. The performance of this approach was evaluated and compared with real data. The accuracy of the model was evaluated taking into account seasonality, spatial coverage and dependence on solar flux and geomagnetic activity indices. The results of the analysis show that the developed model has a superior capacity describing the TEC behavior across Brazil, when compared to global ionosphere maps and the NeQuick G model. TEC predictions were applied in single point positioning. The achieved errors were 27% and 33% lower when compared to the results obtained using the NeQuick G and global ionosphere maps, respectively, showing success in estimating TEC with small recent datasets using MLP.

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

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.

Recurrence plot analysis of GPS ionospheric delay time series in extreme ionospheric conditions

With provision of Positioning, Navigation, and Timing (PNT) services, satellite navigation systems have become a pillar of modern society. These services lay the foundations of a growing number of technological and socio-economic systems and constitute a key enabling technology for transportation systems, services and components. Mitigation of disruptions and degradation of Global Navigation Satellite System (GNSS) positioning performance and operation quality become critical issues for satellite navigation advancement and adoption. Ionospheric conditions are the single prime natural cause of GNSS positioning performance disruptions and degradations. Complex, non-linear and random nature of the ionospheric effects on GNSS positioning performance adds to the challenges of the suitable mitigation processes development. Here a contribution to the understanding of the ionospheric effects on GNSS positioning performance is provided through a study of Total Electron Content (TEC) and GNSS pseudorange measurement errors time series in the selected cases of characteristic ionospheric conditions, using the Recurrence Plot Analysis (RPA), a common procedure for studying general time series. Based on experimental GPS observations, this study found good alignment of TEC and TEC-rate time series with several characteristic schemes of dynamical behaviour, thus allowing for classification of ionospheric conditions and related TEC behaviour based on their dynamical properties. Further to this, the study identified several RPA predictors as precursors of developing ionospheric storm and the consequent disruptions and degradation of GNSS positioning performance. The study stressed the importance of TEC time series assessment, and initiates research challenges for consideration of TEC time series RPA predictors for mitigation, correction, and forecasting model development of GNSS pseudorange measurements, and GNSS position estimation errors, thus contributing to GNSS resiliency development against space weather and ionospheric effects.

Demarcation of solar cycle 24 and characterization of ionospheric GPS-TEC towards the western part of India

We analyze the behavior of Total Electron Content (TEC) in the Ionosphere using the GPS data between 2009 and 2017 towards the western part of India. The GPS data used in the present study consists of 22 Continuously Operating Reference Sites (CORS), bounded between 200- 240 N Latitude and 680 - 740 E Longitude. All the GPS data used in the study are generated using the Leica 1200 receivers and AX1202GG antennas with a sampling interval of 0.03 Hz. The TEC value of this study is calculated using the L-band GPS frequencies L1 (1575.42 MHz) and L2 (1227.36 MHz). The results reveal maximum TEC values during the daytime (03.30–04.30 IST) for all the years and a maximum of 120 TECu (TEC unit) was observed during the year 2014. The reflection of seasonal variation was visible in the time-series of TEC in all the years, while E season (March, April, September and October) observed maximum TEC values in all the stations. The mean monthly TEC values of the present study illustrate the solar cycle-24 and the coefficient of correlation (r2) of 0.74 indicates a close relationship between the sunspot number and TEC values. A fall of 35% TECu was observed on the annular solar eclipse day on 15 January 2010.

Detection of high-latitude ionospheric structures using GNSS

For detection of rather large ionospheric structures (such as high-latitude ionospheric troughs, main ionospheric trough, etc.) using Global Navigation Satellite Systems (GNSS) we suggest employing the analysis of anomalous deviations in behavior of the absolute slant total electron content (TEC) on particular “GNSS receiver - GNSS satellite” lines of sight (LOSs). Using data of four high-latitude GNSS-stations, the proposed method allowed us to detect the 5 May 2013 high-latitude ionospheric trough (HLIT), determine its location and size, and follow the dynamics. The HLIT was located on the dayside within 25-185°E. Initially (04:40–06:00 UT), the HLIT equatorial wall and bottom were within 68-78°N and 70-80°N, respectively. The trough northern wall was not registered at this time, most likely due to insufficient number of LOSs. During the next hour (06:00–07:00 UT), the trough has moved 2-4° southward. Its bottom lay near 68-76°N; equatorial and polar walls were within 67-74°N and 77-78°N, respectively. The trough width was about 4°. At 07:00–08:00 UT, the HLIT structure and location remained almost the same. To interpret the observation results, we used the model for ionosphere-plasmasphere coupling (developed at the Institute of Solar-Terrestrial Physics SB RAS) to simulate the high-latitude ionosphere conditions on 4–6 May 2013. This simulation showed that on 5 May 2013, a high-latitude trough was formed on the dayside at 40-200°E and 78-85°N. The most likely reason for the formation of HLIT both in model calculations and in reality was a change in the magnetospheric convection in the high-latitude ionosphere caused by the moderate geomagnetic disturbances (substorms) on 4–5 May 2013. The trough location determined from the analysis of anomalous TEC deviations on particular LOSs was in good agreement with location of the high-latitude ionospheric trough obtained from numerical simulation. Thus, the analysis of anomalous deviations in TEC behavior on particular LOSs expands the GNSS potential in detecting large-scale irregularities in the ionosphere.

On Global Ionospheric Maps based winter-time GPS ionospheric delay with reference to the Klobuchar model

Modelling of the ionospheric Total Electron Content (TEC) represents a challenging and demanding task in Global Navigation Satellite Systems (GNSS) positioning performance. In terms of satellite Positioning, Navigation and Timing (PNT), TEC represents a significant cause of the satellite signal ionospheric delay. There are several approaches to TEC estimation. The Standard (Klobuchar) ionospheric delay correction model is the most common model for Global Positioning System (GPS) single-frequency (L1) receivers. The development of International GNSS Service (IGS) Global Ionospheric Maps (GIM) has enabled the insight into global TEC dynamics. GIM analyses in the Northern Adriatic area have shown that, under specific conditions, local ionospheric delay patterns differ from the one defined in the Klobuchar model. This has been the motivation for the presented research, with the aim to develop a rudimentary model of the TEC estimation, with emphasis on areas where ground truth data are not available. The local pattern of the ionospheric delay has been modelled with wave functions based on the similarity of waveforms, considering diurnal differences in TEC behavior from defined TEC patterns. The model represents a spatiotemporal winter-time ionospheric delay correction with the Klobuchar model as a basis. The evaluation results have shown accurate approximation of the local pattern of the ionospheric delay. The model was verified in the same seasonal period in 2007, revealing it successfulness under pre-defined conditions. The presented approach represents a basis for the further work on the local ionospheric delay modelling, considering local ionospheric and space weather conditions, thus improving the satellite positioning performance for single-frequency GNSS receivers.

Possibilities of the usage of the total electron content in a low-latitude zone

Last years, the small quantity of ionosondes at low latitudes could not give a sufficient picture of behavior of the ionosphere in these areas. Now, reception of experimental data, their analysis and detection of total electron content (TEC) variations at low latitudes are an actual problem. When moving from describing the state of the ionosphere using vertical sounding parameters to describing using TEC, it is important to identify similarities and differences in their behavior in order to assess the possibilities of using TEC. This paper carries out research on four ways of TEC usage in low-latitude zone: (1) research of climatological peculiarities of the TEC behavior, (2) validation of up-to-date TEC models, (3) foF2 calculation according to observational TEC, and (4) peculiarities of TEC behavior during geomagnetic disturbances. Results for station Hainan show the following. 1. In addition to previous investigation it is shown, that the empirical global and local models of TEC provide the values close to observational ones, however climatological features of TEC behavior described by various models may still differ from each other and from the experimental data showing in this case TEC maxima of diurnal variation in the afternoons, seasonal variations in March and October, some slight winter anomaly. 2. In contrast to previous investigation it is shown that the closest to the experimental values of TEC are provided by the IRI-Plas model, while this model overestimates values, and the model NeQuick underestimates values compared to the observational ones. 3. For the first time, the ionospheric equivalent slab thickness τ, which plays the role of the coefficient of proportionality between TEC and NmF2, was compared for the IRI, IRI-Plas, NeQuick models with the experimental median τ(med) and it was shown, that the usage of observational TEC data and τ(med) for calculation of critical frequencies foF2 allows improving correspondence with experimental data by 1.2–2 times compared to the models. 4. Comparison of foF2 and TEC behavior has a particular importance during disturbances. Using the example of 15 strong magnetic storms (Dst < −50 nT), it was shown that, despite its global nature, the details of the TEC response strongly depend on the region. So, the peculiarities of δTEC in comparison with the mid-latitude region are the predominance of the positive phase, and a smaller value of response. The synchronism of variations δTEC and δfoF2 was very high, although there are cases of mismatch. Using the median τ(med) allows determining foF2 during disturbances and filling data gaps.

Impacts of Intense Geomagnetic Storms on NavIC / IRNSS System

The Total Electron Content (TEC) of Navigation with the Indian Constellation (NavIC)/ Indian Regional Navigation Satellite System (IRNSS) was examined under the influence of an intense geomagnetic storm occurred on 8 September, 2017, in the low latitudes of the Indian re- gion. One week (3 September, 2017 to 9 September, 2017) data from five stations located in the equatorial region and in the Equatorial Ionization Anomaly (EIA) area in India are collected from Accord NavIC/IRNSS dual-frequency (L5 and S-band) receivers for the investi- gation. The diurnal TEC comparison between IRI-2007 empirical model and NavIC/IRNSS dual frequency model is done. Through a com- parative study, of TEC at the five locations, we clearly observed geomagnetic storms using dual-frequency NavIC/IRNSS receivers, while the diurnal TEC behavior of the IRI-2017 model was the same on all observation days. On the intense stormy day, we observed an increase of about 19 TECU for the area near the equator and decrease of about 20 TECU in the EIA region compared to other observed quiet days. As a result, positive correlation between TEC and storm occurrence were found in the equatorial region, while a negative one in EIA re- gion. In order to support dramatic change in TEC during intense geomagnetic storm, geomagnetic indices and solar wind/IMF parameters maps are added. The results have been further validated using TEC map from IGS data and thermosphere O/N2 ratio map from Global UV Imager (GUVI).

Effects of the Solar Eclipse of March 20, 2015 on the Total Electron Content over Europe

The effect of the solar eclipse of March 20, 2015 on variations of the total electron content (TEC) in the ionosphere over Europe is analyzed based on GPS/GLONASS measurements at EUREF network stations. The specific feature of this eclipse is that it occurred under conditions of geomagnetic disturbance remaining after a strong geomagnetic storm on March 17, 2015. This made it more difficult to identify the effects of the solar eclipse. To detect these effects, diurnal TEC variations at individual stations were analyzed. The effect manifested itself as a TEC depression with the minimum close to the time of the maximum phase of the eclipse over the observation station. The effect was more pronounced in TEC variations along the individual passes of the satellites, appearing as a trough-like TEC depression. The diurnal variation of the TEC on the day of the eclipse was significantly different from the nearest control days, which made it difficult to determine the absolute magnitude of the eclipse effect. The space–time behavior of the TEC was represented in the form of TEC maps for the European region. For this purpose, concurrent GPS/GLONASS observations at more than 150 stations were used. A high space–time resolution of the maps made it possible to reveal the dynamics of TEC behavior over Europe during the event under consideration. The eclipse led to a clear change in the structure of the latitudinal and longitudinal TEC gradients. TEC maps generated with a 5-min resolution demonstrate the dynamics of the spatiotemporal behavior of the TEC during the eclipse.

TEC behavior over the Mexican region

With the advent of the Navigation Satellites the Total Electron Content (TEC) has become one of the main parameters of the ionosphere. This is the result of a continuous TEC monitoring and rather dense network of GPS receivers. For Mexican region having no ionosondes the use of TEC for ionospheric conditions studies and monitoring has a special value. To study the behaviour of TEC and for its applied aspects two types of source-files are used worldwide: IONEX (global maps) and RINEX (local data) depending on the task solved. Magnetometer and satellite data from CHAMP and DMSP were involved in the analysis. First, benefits and limitations of TEC derived from both types of files are discussed in regard to the estimation of the ionosphere state in the Mexican region. Second, using both methods the specific features of diurnal, seasonal and annual patterns in TEC behaviour over Mexico were revealed, among which are the shift of the diurnal maximum to 14 LT, dependence on solar activity, high probability of night-time enhancements, presence of annual and winter anomalies. Third, it was revealed that the positive short-lived TEC enhancements are characteristic for Mexican region. They may occur even under quiet conditions. The answer is given what part of the ionosphere is responsible for TEC change during these positive disturbances. The results for Mexico were compared to the neighboring regions and South-East zone.

Features of TEC behaviour over the low-latitude North-American region during the period of medium solar activity

The study is focused on Total Electron Content (TEC) behavior in low-latitude North-American region within the twelve-year period from 2005 to 2016. The obtained systematic (regular) TEC variations (diurnal, seasonal patterns) conform to the known tendencies described by climatological TEC models. TEC variations during disturbances have a number of distinctive features. The majority of positive TEC enhancements occur already with Dst <−30nT. The intensity of TEC change does not depend on Dst-index minimum value. Almost all cases of day-time TEC disturbances are accompanied by night-time disturbances with the possibility of relative night-time deviations being larger that is confirmed by data of low-orbit satellites CHAMP and DMSP. The simultaneity of changes of critical frequencies of the ionosphere with changes of TEC during disturbances was observed at Ramey (Puerto Rico) and Eglin (U.S.A.) stations when ionosonde data was available. This proves that TEC reflects the character of ionospheric disturbances. Spatial non-synchronism of TEC change that was sometimes observed can be explained by local character of the area covered with positive TEC disturbance. It was shown the potential provided by local GNSS networks for the detailed analysis of TEC variations over the considered region and estimation of the ionosphere state in near-real time.

Analysis of ionospheric TEC from GNSS observables over the Turkish region and predictability of IRI and SPIM models

The present study investigates the ionospheric Total Electron Content (TEC) variations in the lower mid-latitude Turkish region from the Turkish Permanent GNSS Network (TPGN) and International GNSS Services (IGS) observations during the period from January 2015 to December 2015. The corresponding TEC predicted by the International Reference Ionosphere (IRI 2012) and Standard Plasmasphere-Ionosphere Model (SPIM), and interpolated from Global Ionosphere Maps (GIMs) are evaluated to realize their reliability over the region. We studied the diurnal and monthly behavior of TEC and the relative TEC deviations along with the upper and lower quartiles to represent its spatio-temporal variability. The diurnal variation of GNSS-derived TEC indicates its maximum peak value around 10.00 UT which decreases gradually to attain minimum value after midnight. The monthly maximum value of TEC is observed in March followed by May and August, and the lowest value is seen during September. Studies show that the monthly relative deviation of TEC variability lies in the range of −1 to 4 units for all stations with the maximum difference between positive and negative variability remaining around 5. The studies also cover seasonal variation, grand-mean of ionospheric TEC and TEC intensity from the TPGN. The seasonal ionospheric VTEC pattern over all stations depicts slight increment in VTEC distribution during March equinox compared to September equinox. The December solstice perceived relatively higher VTEC than June solstice. The overall of VTEC values enhanced at all stations towards end of the year 2015 compare to mid of year due the high solar activity. The maximum grand-mean of VTEC is registered in March equinox while the lowest value is seen in September irrespective of all stations. The measured grand-mean intensity variations of VTEC values are in ascending phase during March, May, August and November months, but in descending phase during February, April, June and September months. The latitudinal study shows daytime TEC slowly decreasing with latitudes with a latitudinal gradient range of 0.1–0.2 TECU/degree. Additionally, the TEC analysis during the strong geomagnetic storm period (07–11 September 2015; SYM-H −120 nT) infers relatively better predictability of the SPIM model compared to the IRI 2012 model. The outputs of this study would complement towards a complete understanding of the lower mid-latitude ionospheric dynamics and its effects on radio propagations, particularly over the Turkish region.

Ionospheric TEC disturbance study over seismically region in China

Using data of Crustal Movement Observation Network of China (CMONOC) and IGS (International GNSS Service), we attempt to give a statistical behavior of the total electron content (TEC) perturbation before 30Mw6.0+ earthquakes from 2000 to 2010 in China. Results show that TEC anomalies are detected before 20 earthquakes, nearly 67%. The anomalies represent positive before most events and occur mostly within 2–6days before the shocks, significantly during the afternoon period, 12–20LT. To verify the reliability of the anomalous behavior of TEC detected in the statistical study, we analyze variations of TEC over two regions during a period of low solar and geomagnetic activity in April-October 2008. In southwest China, during that time, six large earthquakes with magnitude M≧6.0 occurred. And a ‘check-region’ with same geomagnetic latitudes as the epicentral area is selected. Known that the decisive role in the ionosphere state is performed by space weather effects, we compare the TEC variations with time series of EUV solar radiation, Bz component of the interplanetary magnetic field (IMF), index of geomagnetic activity Dst and planetary index Kp, respectively. It is found that, both in the two regions, the observed anomalies in the regional TEC are in good correlation with the variations of above index. We detect different levels of TEC anomalies before the 6 earthquakes, and most of them are amost certainly dominated by space weather expect for Wenchuan case. The work illustrates the difficulties of searching precursors of earthquake in the ionosphere, but also, it reminds the importance for considering the effect of atmospheric waves on the ionosphere as well as the applicability of statistical approach.

Multifractal detrended fluctuation analysis of ionospheric total electron content data during solar minimum and maximum

The spatio-temporal variations in ionospheric vertical total electron content (TEC) data, which often reflect their scale invariant properties, can well be studied with multifractal analysis. We discuss the multifractal behaviour of TEC recorded at a total of 27 stations confined to a narrow longitude band (35°W-80°W) spanning from equator to high-latitude regions (30°S to 80°N) (geographic coordinates) during solar minimum (2008) and solar maximum (2014), using multifractal detrended fluctuation analysis (MFDFA). MFDFA provides an understanding of the multifractal scaling behaviour of a signal using the multifractal singularity spectra and the generalised Hurst exponents as diagnostic tools. The objectives of this study are to (i) understand the latitudinal dependence of the multifractal behaviour of TEC, (ii) compare the multifractal behaviour of TEC corresponding to the well-known 27-day variation (solar rotation period) and its harmonics and the 1-day (solar diurnal) periodicities, during 2008 and 2014 and (iii) understand the lunar tidal influence on TEC. Results indicate that except for the 1-day period, the TEC at all other periods shows a higher degree of multifractality during solar maximum compared to solar minimum. Further, irrespective of the solar activity, the degree of mutifractality in general decreases with increase in period for all latitude zones for periods of 27-day and its harmonics. However, the 1-day period exhibits monofractal behaviour regardless of the solar activity. The influence of semi-lunar tidal effects (having a periodicity of about 14.5 days) as a function of latitude is clearly seen in the 13.5-day periodicity (i.e., the 2nd harmonic of 27-day variation) of TEC. It manifests in the form of decreasing differences in the widths of the multifractal singularity spectra corresponding to the years 2008 and 2014, with increase in latitude. Results are discussed in the light of these observations.

Dynamics of the level of total electron content disturbance at high and middle latitudes according to GPS data

We study the level of total electron content (TEC) disturbance in ionospheric mid-latitude and high-latitude regions, which occurred during 2013. TEC behavior is calculated using data from two GPS stations: MOND (Mondy) and NRIL (Norilsk). TEC variations are estimated from dual-frequency phase measurements for all radio signal paths. We analyze the TEC variations in two time ranges: 10 and 40 min. These ranges correspond to medium- and large-scale ionospheric disturbances respectively. The TEC disturbance level is characterized using a special index WTEC. It allows us to receive multi-day continuous series of average TEC variation intensity. We reveal that at high latitudes WTEC variations correlate well with AE ones. The correlation between WTEC and Dst variations is much lower. The minimum level of TEC disturbance is independent of the season in the Arctic region; diurnal WTEC variations are more pronounced for medium-scale ionospheric disturbances than for large-scale ones. At mid-latitudes, the WTEC variation concurs with Dst and Kp variations only during strong magnetic storms. The minimum level of TEC disturbance is higher in summer than in winter. At middle latitudes, the sunset terminator generates gravity waves. In the Arctic region, terminator-induced waves are not observed.

Динамика возмущенности полного электронного содержания в высоких и средних широтах по данным GPS

We study the level of total electron content (TEC) disturbance in ionospheric mid-latitude and high-latitude regions during 2013. TEC behavior is calculated using data from two GPS stations: MOND (Mondy) and NRIL (Norilsk). TEC variations are calculated from two-frequency phase measurements for all radio rays. We analyze the TEC variations in two time ranges: 10 and 40 min. These ranges correspond to middle- and large-scale ionospheric disturbances respectively. The TEC disturbance level is characterized using the special index WTEC. WTEC allows us to receive multi-day continuous series of average TEC variation intensity. We reveal that at high latitudes WTEC variations agree well with AE ones. The correlation between WTEC and Dst variations is much less. The minimum level of TEC disturbance is independent of the season in the Arctic region; diurnal WTEC variations are more pronounced for medium-scale ionospheric disturbances than for large-scale ones. At mid-latitudes, the WTEC behavior agrees well with the Dst and Kp variations only during strong magnetic storms. The minimum level of TEC disturbance is higher in summer than in winter. At mid-latitudes, the sunset terminator generates gravitational waves. In the Arctic region, terminator-generated waves are not observed.

Evaluation of geomagnetic storm effects on the GPS derived Total Electron Content (TEC)

The geomagnetic storm represents the most outstanding example of solar wind- magnetospheric interaction, which causes global disturbances in the geomagnetic field as well as triggers ionospheric disturbances. We study the behaviour of ionospheric Total Electron Content (TEC) during the geomagnetic storms. For this investigation we have selected 47 intense geomagnetic storms (Dst ≤ -100nT) that were observed during the solar cycle 23 i.e. during 1998- 2006. We then categorized these storms into four categories depending upon their solar sources like Magnetic Cloud (MC), Co-rotating Interaction Region (CIR), SH+ICME and SH+MC. We then studied the behaviour of ionospheric TEC at a mid latitude station Usuda (36.13N, 138.36E), Japan during these storm events produced by four different solar sources. During our study we found that the smooth variations in TEC are replaced by rapid fluctuations and the value of TEC is strongly enhanced during the time of these storms belonging to all the four categories. However, the greatest enhancements in TEC are produced during those geomagnetic storms which are either caused by Sheath driven Magnetic cloud (SH+MC) or Sheath driven ICME (SH+ICME). We also derived the correlation between the TEC enhancements produced during storms of each category with the minimum Dst. We found the strongest correlation exists for the SH+ICME category followed by SH+MC, MC and finally CIR. Since the most intense storms were either caused by SH+ICME or SH+MC while the least intense storms were caused by CIR, consequently the correlation was strongest with SH+ICME and SH+MC and least with CIR.

Use of GLONASS for studying the ionosphere

Results of using the Russian Global Navigation Satellite System (GLONASS) to measure absolute values of the ionosphere’s total electron content (TEC) are presented. Specific features of configurations and differences in parameters of GLONASS and GPS are given, and their impact on TEC evaluation is analyzed. The statistical analysis is also carried out for comparing the TEC measurement data obtained from the GPS and GLONASS observations; a high correlation between measurements of both systems is shown. Investigations have revealed that the use of both systems allows of extending the possibilities of their employment for studying the ionosphere’s structure and dynamics. To restore the diurnal behavior of TEC of the ionosphere above the observation station, the phase measurements are proposed to be taken as input data. Their advantage over the group measurements is not only their high accuracy but the fact that they are less subject to the multipath effect. The technique for processing the phase observations implemented for GLONASS is an essential part of the system for monitoring of the ionosphere over the European part of p]Russia, which is under development at the West Department of Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation.