Average Total Electron Content Research Articles

Impact of Tonga volcanic eruption on the ionosphere based on ground-based GNSS and COSMIC occultation data

The eruption of large volcanoes may potentially disturb the upper atmosphere, causing disturbances in ionospheric plasma and triggering irregular changes in the Total Electron Content (TEC). The GNSS ionospheric inversion method has been used to analyze ionospheric anomalies caused by the volcano, while it was limited to the spatial distribution of ground-based GNSS. The joint observation with space-based GNSS can further improve the spatio-temporal distribution of ionospheric monitoring. The Tonga volcano erupted on January 15th, 2022, is the largest volcanic eruption since the beginning of the 21st century and generated intense acoustic, atmospheric gravity waves and ionospheric disturbance. In this paper, we used the GIM products, ground-based GNSS station data around the volcanic eruption point and COSMIC occultation data to analyze the short-term TEC change. The experiments showed that: the average TEC of GIM grid data on eruption day dropped by 7.5 TECu compared to the last day which was substantially larger than other three days. The TEC extracted from nearby tracking stations was smaller than GIM and the difference was inversely proportional to the distance between the station and the volcanic eruption site. The average daily ionospheric TEC obtained from the nearest TONG station was the biggest, as much as 3.44 TECu lower. The peak electron density of COSMIC occultation data gradually diminished and then recovered with TEC about 7.32 TECu lower than GIM products. The experments showed that there was a good consistency in the TEC obtained from space-based and ground-based GNSS, the Tonga volcano produced a huge TEC change over 10 TECu or even bigger. As a global grid product, GIM underestimated ionospheric changes due to its limited spatial resolution, which needs further improvement.

Exploring ionospheric dynamics: a comprehensive analysis of GNSS TEC estimations during the solar phases using linear function model

Abstract The modeling and forecasting of Total Electron Content (TEC) play a major role in influencing signals from satellite-based navigation systems and impact the performance of diverse satellite-dependent technologies. The intensity of solar ionizing radiation and the state of geomagnetic field activity influence the Global Navigation Satellite System (GNSS)-TEC. This paper uses a Linear TEC Function (LTF) climatology model to understand ionospheric behavior under solar and geomagnetic activities that cause variations in the electron distribution of the ionosphere medium. The LTF model integrates representations of solar EUV photon (MgII) and geomagnetic (SYMH) activities, incorporating solar-modulated oscillations (periodic variations) at four seasonal cycles and a linear trend. The LTF model examined the time series of GPS-TEC at a location (geographic 34.95° N, 134.05° E) with a time resolution of 1 h, from 1997 to 2016, covering solar cycles 23 and 24. The Root Mean Square Deviation (RMSD) and correlation coefficient between the GNSS-TEC and model TEC (LTF) was 5.30 TECU and 95 %. The results indicate that solar components, as well as annual and semi-annual variations, have a significant impact on the daily average TEC. Solar activity appears to be the predominant determining factor of TEC during the solar phases of cycles 23 and 24. In contrast, periodic influences primarily outline TEC during periods characterized by minimal solar activity. The geomagnetic component presents an increased influence, particularly during storm periods. The model demonstrates superior performance in Total TEC modeling compared to other state-of-the-art approaches.

A comparison of ionospheric TEC between the South Atlantic anomaly region and the Indian Ocean region based on TIEGCM simulations in 2002

Using the Thermosphere-Ionosphere-Electrodynamic General Circulation Model (TIEGCM), a comparison of the ionospheric total electron content (TEC) between the South Atlantic anomaly (SAA) and the Indian Ocean (IO) at solar maximum is performed in this study. The results show that the average total electron content in the SAA is greater than that in the Indian Ocean in general. In order to further analyze the difference between the two regions, the empirical orthogonal function (EOF) are used to investigate the temporal and spatial characteristics of TEC. The empirical orthogonal function method separate part of the global four-peak structure (an equatorial ionization anomaly structure, distributed in Southeast Asia, South America, Africa, and central Pacific) and spatial variations in both regions. Moreover, the first mode of EOF shows the different distribution of Equatorial ionization anomaly in South America and central Pacific caused by deviation of geomagnetic field and tides between two regions, and the enhancement of TEC in SAA region at dusk is emphasized, but the enhancement of TEC in IO region at dawn is emphasized. The second mode performs the distribution of EIA in Africa related to solar radiation and E×B drift. The third mode indicates the similar spatiotemporal variations from the geomagnetic field. Besides, the correlation between TEC and Dst in two regions indicate that there are some deficiencies in simulation to the specificity of SAA, and the deficiencies are likely caused by the model’s inaccurate simulation of the magnetic field and particle deposition in the SAA region.

Reference responses of regional electron content to strong geomagnetic events

The paper presents an analysis of reference responses of regional electron content to strong geomagnetic events identified by the AE-index. As an ionospheric characteristic, we used the regional electron content (REC), which is the average total electron content (TEC) for five latitude zones in the corrected geomagnetic coordinate system: the mid-latitude zones in both hemispheres, the high-latitude zones in both hemispheres, and the equatorial zone. The relative (percentage) deviation of observed values from the 27-day running average REC was used to calculate disturbances of REC (ΔREC). The reference response was calculated by averaging ΔREC using the superimposed epoch method with key moments corresponding to the AE maximum for the winter, spring, summer and autumn storms. The paper discusses storm-time behavior, seasonal dependence and interhemispheric asymmetry of the REC responses to strong geomagnetic events.

Anomalous Disturbance of the Ionosphere in the East Asia Region During the Geomagnetically Quiet Day on 1 November 2016

AbstractIn this study, multiple data sets from Beidou geosynchronous Earth orbit (GEO) satellite, ionosonde, magnetometer, Swarm satellite, and meteor radar were used to investigate an anomalous disturbance of the ionosphere in East Asia on 1 November 2016. During 03:00–08:00 universal time (UT), the total electron content (TEC) observed by the Beidou GEO satellite decreased by up to 8.17% at low latitudes and increased by up to 140.19% at middle to low latitudes in East Asia compared to the average TEC on the reference days. The F2 peak electron density (NmF2) measured by ionosondes decreased by 16.00% at Sanya (109.4°E, 18.3°N) and increased by 51.96% and 53.97% at Wuhan (114.4°E, 30.5°N) and Shaoyang (111.3°E, 27.1°N), respectively. The equatorial electric field (EEF) observed by the Swarm satellite at 06:59 UT on 1 November was approximately 77.57% higher than on 4 November. The variations of equatorial electrojet near 100°E and 120°E on 1 November presented an east‐west asymmetry in which there was a significant enhancement in the east while there was no obvious increase in the west. The TEC enhancement derived by the Center for Orbit Determination in Europe also showed the same east‐west asymmetry in the two longitudes. Based on the comprehensive analysis of multiple observational data, the increase in EEF caused the ionospheric TEC and NmF2 to decrease at low latitudes and increase at middle to low latitudes in East Asia during 03:00–08:00 UT on 1 November 2016. The lower atmospheric tidal forcing could contribute to the enhancement of the EEF.

Persistent Eastward EEJ Enhancement During the Geomagnetic Storm Recovery Phases

AbstractRecent case studies disclosed that sometimes the dayside ionospheric equatorial electric field underwent persistent long‐duration (>4 hr) eastward enhancements during geomagnetic storm recovery phases, rather than anticipated decrease or reversal. However, it is still unknown the occurrence and morphology of the persistent enhancement as well as its impact on the low‐latitude ionospheric plasma distribution. For the first time, we examined the issue with superposed epoch analyses of equatorial electrojet (EEJ) and GNSS total electron content (TEC) responses in the American (49°W) and Indian (78°E) sectors. The occurrence rates of the persistent enhancement during storm recovery phases are more than 30%, with higher occurrence rates in second to fourth days of the recovery phase, equinoxes, and American sector. The corresponding averaged EEJ and TEC responses were disclosed and compared with those storm samples without the persistent enhancement. On the first day of recovery phase, the dayside equatorial ionosphere was dominated by the prevalent westward electric field and causative inhibited equatorial fountain. In contrast, after the first day, the dayside morphologies showed different patterns: (a) for the persistent cases, the large eastward EEJ and TEC enhancement indicated the enhanced eastward electric field at forenoon and causative intensified equatorial fountain. (b) For the storms without the persistent cases, the general westward EEJ and equatorial TEC enhancements were dominated. Our study indicates that dayside eastward enhancement is an important disturbed pattern of equatorial ionospheric electric field during the late recovery phases, and the enhancement generally causes the intensification of equatorial ionization anomaly.

Study of Spatial and Temporal Variations of Ionospheric Total Electron Content in Japan, during 2014-2019 and the 2016 Kumamoto Earthquake.

There are a large number of excellent research cases in Global Navigation Satellite System (GNSS) positioning and disaster prediction in Japan region, where the simulation and prediction of total electron content (TEC) is a powerful research method. In this study, we used the data of the GNSS Earth Observation Network (GEONET) established by the Geographical Survey Institute of Japan (GSI) to compare the performance of two regional ionospheric models in Japan, in which the spherical cap harmonic (SCH) model has the best performance. In this paper, we investigated the spatial and temporal variations of ionospheric TEC in Japan and their relationship with latitude, longitude, seasons, and solar activity. The results show that the TEC in Japan increases as the latitude decreases, with the highest average TEC in spring and summer and the lowest in winter, and has a strong correlation with solar activity. In addition, the observation and analysis of ionospheric disturbances over Japan before the 2016 Kumamoto earthquake and geomagnetic storms showed that GNSS observing of ionospheric TEC seems to be very effective in forecasting natural disasters and monitoring space weather.

Comparison of seasonal and longitudinal variation of daytime MSTID activity using GPS observation and GAIA simulations

The total electron content (TEC) data derived from the GAIA (Ground-to-topside model of Atmosphere Ionosphere for Aeronomy) is used to study the seasonal and longitudinal variation of occurrence of medium-scale traveling ionospheric disturbances (MSTIDs) during daytime (09:00–15:00 LT) for the year 2011 at eight locations in northern and southern hemispheres, and the results are compared with ground-based Global Positioning System (GPS)-TEC. To derive TEC variations caused by MSTIDs from the GAIA (GPS) data, we obtained detrended TEC by subtracting 2-h (1-h) running average from the TEC, and calculated standard deviation of the detrended TEC in 2 h (1 h). MSTID activity was defined as a ratio of the standard deviation to the averaged TEC. Both GAIA simulation and GPS observations data show that daytime MSTID activities in the northern and southern hemisphere (NH and SH) are higher in winter than in other seasons. From the GAIA simulation, the amplitude of the meridional wind variations, which could be representative of gravity waves (GWs), shows two peaks in winter and summer. The winter peak in the amplitude of the meridional wind variations coincides with the winter peak of the daytime MSTIDs, indicating that the high GW activity is responsible for the high MSTID activity. On the other hand, the MSTID activity does not increase in summer. This is because the GWs in the thermosphere propagate poleward in summer, and equatorward in winter, and the equatorward-propagating GWs cause large plasma density perturbations compared to the poleward-propagating GWs. Longitudinal variation of daytime MSTID activity in winter is seen in both hemispheres. The MSTID activity during winter in the NH is higher over Japan than USA, and the MSTID activity during winter in the SH is the highest in South America. In a nutshell, GAIA can successfully reproduce the seasonal and longitudinal variation of the daytime MSTIDs. This study confirms that GWs cause the daytime MSTIDs in GAIA and amplitude and propagation direction of the GWs control the noted seasonal variation. GW activities in the middle and lower atmosphere cause the longitudinal variation.

Solar activity dependence of medium-scale traveling ionospheric disturbances using GPS receivers in Japan

In order to reveal solar activity dependence of the medium-scale traveling ionospheric disturbances (MSTIDs) at midlatitudes, total electron content (TEC) data obtained from a Global Positioning System (GPS) receiver network in Japan during 22 years from 1998 to 2019 were analyzed. We have calculated the detrended TEC by subtracting the 1-h running average from the original TEC data for each satellite and receiver pair, and made two-dimensional TEC maps of the detrended TEC with a spatial resolution of 0.15° × 0.15° in longitude and latitude. We have investigated MSTID activity, defined as delta I/overline{I}, where delta I and overline{I} are standard deviation of the detrended TEC and the average vertical TEC within the area of 133.0°–137.0° E and 33.0°–37.0° N for 1 h, respectively. From each 2-h time series of the detrended TEC data within the same area as the MSTID activity, auto-correlation functions (ACFs) of the detrended TEC were calculated to estimate the horizontal propagation velocity and direction of the MSTIDs. Statistical results of the MSTID activity and propagation direction of MSTIDs were consistent with previous studies and support the idea that daytime MSTIDs could be caused by atmospheric gravity waves, and that nighttime MSTIDs were caused by electro-dynamical forces, such as the Perkins instability. From the current long-term observations, we have found that the nighttime MSTID activity and occurrence rate increased with decreasing solar activity. For the daytime MSTID, the occurrence rate increased with decreasing solar activity, whereas the MSTID activity did not show distinct solar activity dependence. These results suggest that the secondary gravity waves generated by dissipation of the primary gravity waves propagating from below increase under low solar activity conditions. The mean horizontal phase velocity of the MSTIDs during nighttime did not show a distinct solar activity dependence, whereas that during daytime showed an anticorrelation with solar activity. The horizontal phase velocity of the daytime MSTIDs was widely distributed from 40 to 180 m/s under high solar activity conditions, whereas it ranged between 80 and 200 m/s, with a maximum occurrence at 130 m/s under low solar activity conditions, suggesting that gravity waves with low phase velocity could be dissipated by high viscosity in the thermosphere under low solar activity conditions.

Ionospheric Modeling and Forecasting Services of GNSS

The study of ionospheric variability is vital for refining and predicts services of GNSS (Global Navigation Satellite System) applications. The GNSS service provides an explicitly obtainable resource GNSS information, goods and services in support of the earthly reference structure. GNSS is provides an Earth observation, navigation, positioning, timing and other applications that an assistance Society and Science. To investigate the variations in the daily averaged TEC (Total Electron Content) by taking several model components such as solar activity component, geomagnetic activity and periodic components at different latitudes ranging from 10˚N to 26˚N for the year 2018. The presented results would be useful to download, processing and analysis the IGS (International GNSS Service) data. MSSA model can reproduce quite well the observed values of GPS-TEC by utilizing only the first 4 singular modes and constitutes 99% of the total variance. The data is transformed into the singular values which are used for forecasting a noiseless time series. The proposed system results show that higher accuracy is achieved by MSSA (Multivariate Singular Spectrum Analysis) based model. It can also be noted that the training of MSSA is much faster and achieves higher learning accuracy, lowest training time. MSSA is effective even the space weather conditions are active during different solar phase periods.

Variation of the TEC at a dip equatorial station, Trivandrum and a mid latitude station, Hanle during the descending phase of the solar cycle 24 (2014–2016)

Morphological variations in the Total Electron Content (TEC) of the ionosphere at a dip equatorial station, Trivandrum (8.47°N, 76.91° E) and a mid latitude station, Hanle (32.78° N, 78.95° E) during the period 2014–2016 is studied using the GPS TEC measurements from the InSWIM (Indian Network for Space Weather Impact Monitoring) network of stations. The variation of the TEC at Hanle, which is located in the same longitude sector as that of Trivandrum, is presented here for the first time. At Hanle, the TEC peaks at local noontime while its peak appears with a delay (1600 LT) at Trivandrum. The minima in the TEC at both stations appear during the early morning hours. Nighttime enhancements in the TEC are seen at Trivandrum during the equinoctial months while at Hanle they appear in the summer months. The TEC at both the stations exhibit semi-annual anomaly and equinoctial asymmetry. However, the winter anomaly is seen only at Trivandrum. The TEC at both Trivandrum and Hanle is seen to display strong solar activity dependence with the average TEC decreasing as solar activity decreases. We surmise that the observed diurnal/seasonal/annual variations in the TEC at the dip equatorial station, Trivandrum is controlled by the processes induced by electrodynamics while the TEC variations at the mid latitude station, Hanle is mostly affected by the neutral dynamical processes. The morphological comparison between the TEC at Trivandrum derived from the IRI 2012 model and GPS TEC measurements shows only a qualitative agreement. The IRI 2012 model is found to overly underestimate the daytime as well as nighttime TEC at the dip equatorial station, Trivandrum while it is well in agreement with the TEC measurements at the mid latitude station, Hanle.

Linear time series modeling of GPS-derived TEC observations over the Indo-Thailand region

This paper proposes a linear time series model to represent the climatology of the ionosphere and to investigate the characteristics of hourly averaged total electron content (TEC). The GPS–TEC observation data at the Bengaluru international global navigation satellite system (GNSS) service (IGS) station (geographic $$13.02^{\circ }\hbox {N}$$ , $$77.57^{\circ }\hbox {E}$$ ; geomagnetic latitude $$4.4^{\circ }\hbox {N}$$ ) have been utilized for processing the TEC data during an extended period (2009–2016) in the $$24{\mathrm{th}}$$ solar cycle. Solar flux F10.7p index, geomagnetic Ap index, and periodic oscillation factors have been considered to construct a linear TEC model. It is evident from the results that solar activity effect on TEC is high. It reaches the maximum value ( $$\sim $$ 40 TECU) during the high solar activity (HSA) year (2014) and minimum value ( $$\sim $$ 15 TECU) during the low solar activity (LSA) year (2009). The larger magnitudes of semiannual variations are observed during the HSA periods. The geomagnetic effect on TEC is relatively low, with the highest being $$\sim $$ 4 TECU (March 2015). The magnitude of periodic variations can be seen more significantly during HSA periods (2013–2015) and less during LSA periods (2009–2011). The correlation coefficient of 0.89 between the observations and model-based estimations has been found. The RMSE between the observed TEC and model TEC values is 4.0 TECU (linear model) and 4.21 TECU (IRI2016 Model). Further, the linear TEC model has been validated at different latitudes over the northern low-latitude region. The solar component (F10.7p index) value decreases with an increase in latitude. The magnitudes of the periodic component become less significant with the increase in latitude. The influence of geomagnetic component becomes less significant at Lucknow GNSS station $$(26.76^{\circ }\hbox {N}, 80.88^{\circ }\hbox {E})$$ when compared to other GNSS stations. The hourly averaged TEC values have been considered and ionospheric features are well recovered with linear TEC model.

CEDAR‐GEM Challenge for Systematic Assessment of Ionosphere/Thermosphere Models in Predicting TEC During the 2006 December Storm Event

AbstractIn order to assess current modeling capability of reproducing storm impacts on total electron content (TEC), we considered quantities such as TEC, TEC changes compared to quiet time values, and the maximum value of the TEC and TEC changes during a storm. We compared the quantities obtained from ionospheric models against ground‐based GPS TEC measurements during the 2006 AGU storm event (14–15 December 2006) in the selected eight longitude sectors. We used 15 simulations obtained from eight ionospheric models, including empirical, physics‐based, coupled ionosphere‐thermosphere, and data assimilation models. To quantitatively evaluate performance of the models in TEC prediction during the storm, we calculated skill scores such as RMS error, Normalized RMS error (NRMSE), ratio of the modeled to observed maximum increase (Yield), and the difference between the modeled peak time and observed peak time. Furthermore, to investigate latitudinal dependence of the performance of the models, the skill scores were calculated for five latitude regions. Our study shows that RMSE of TEC and TEC changes of the model simulations range from about 3 TECU (total electron content unit, 1 TECU = 1016el m−2) (in high latitudes) to about 13 TECU (in low latitudes), which is larger than latitudinal average GPS TEC error of about 2 TECU. Most model simulations predict TEC better than TEC changes in terms of NRMSE and the difference in peak time, while the opposite holds true in terms of Yield. Model performance strongly depends on the quantities considered, the type of metrics used, and the latitude considered.

Long‐term trends in the total electron content

AbstractThe total electron content (TEC) is important among others for Global Navigation Satellite Systems/GPS signal propagation and applications. However, there is only one comprehensive analysis of TEC trends, and the resulted trends are not consistent with trends in other ionospheric parameters. Here we use the TEC data of Lean et al. (2011) and the JPL35 homogeneous TEC data series derived by Emmert et al. (2017). This analysis results in three main conclusions: (1) Too positive TEC trends by Lean et al. (2011) are caused by data problems in 1995–2001, particularly by too low Center for Orbit Determination data. (2) TEC reveals a weak negative trend at the edge of reliability; no trend or trend break is also possible; longer data series than 1994–2015 is required. (3) About 99% of the total variance of yearly average global TEC values is explained by variability of solar activity.

Performance evaluation of linear time-series ionospheric Total Electron Content model over low latitude Indian GPS stations

Precise modeling of the ionospheric Total Electron Content (TEC) is a critical aspect of Positioning, Navigation, and Timing (PNT) services intended for the Global Navigation Satellite Systems (GNSS) applications as well as Earth Observation System (EOS), satellite communication, and space weather forecasting applications. In this paper, linear time series modeling has been carried out on ionospheric TEC at two different locations at Koneru Lakshmaiah University (KLU), Guntur (geographic 16.44°N, 80.62°E; geomagnetic 7.55°N) and Bangalore (geographic 12.97°N, 77.59°E; geomagnetic 4.53°N) at the northern low-latitude region, for the year 2013 in the 24th solar cycle. The impact of the solar and geomagnetic activity on periodic oscillations of TEC has been investigated. Results confirm that the correlation coefficient of the estimated TEC from the linear model TEC and the observed GPS-TEC is around 93%. Solar activity is the key component that influences ionospheric daily averaged TEC while periodic component reveals the seasonal dependency of TEC. Furthermore, it is observed that the influence of geomagnetic activity component on TEC is different at both the latitudes. The accuracy of the model has been assessed by comparing the International Reference Ionosphere (IRI) 2012 model TEC and TEC measurements. Moreover, the absence of winter anomaly is remarkable, as determined by the Root Mean Square Error (RMSE) between the linear model TEC and GPS-TEC. On the contrary, the IRI2012 model TEC evidently failed to predict the absence of winter anomaly in the Equatorial Ionization Anomaly(EIA) crest region. The outcome of this work will be useful for improving the ionospheric now-casting models under various geophysical conditions.

Spatial and temporal variation of total electron content as revealed by principal component analysis

Abstract. Eleven years of global total electron content (TEC) data derived from the assimilated thermosphere–ionosphere electrodynamics general circulation model are analyzed using empirical orthogonal function (EOF) decomposition and the corresponding principal component analysis (PCA) technique. For the daily averaged TEC field, the first EOF explains more than 89 % and the first four EOFs explain more than 98 % of the total variance of the TEC field, indicating an effective data compression and clear separation of different physical processes. The effectiveness of the PCA technique for TEC is nearly insensitive to the horizontal resolution and the length of the data records. When the PCA is applied to global TEC including local-time variations, the rich spatial and temporal variations of field can be represented by the first three EOFs that explain 88 % of the total variance. The spectral analysis of the time series of the EOF coefficients reveals how different mechanisms such as solar flux variation, change in the orbital declination, nonlinear mode coupling and geomagnetic activity are separated and expressed in different EOFs. This work demonstrates the usefulness of using the PCA technique to assimilate and monitor the global TEC field.

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.

Long-term prediction of the Arctic ionospheric TEC based on time-varying periodograms.

Knowledge of the polar ionospheric total electron content (TEC) and its future variations is of scientific and engineering relevance. In this study, a new method is developed to predict Arctic mean TEC on the scale of a solar cycle using previous data covering 14 years. The Arctic TEC is derived from global positioning system measurements using the spherical cap harmonic analysis mapping method. The study indicates that the variability of the Arctic TEC results in highly time-varying periodograms, which are utilized for prediction in the proposed method. The TEC time series is divided into two components of periodic oscillations and the average TEC. The newly developed method of TEC prediction is based on an extrapolation method that requires no input of physical observations of the time interval of prediction, and it is performed in both temporally backward and forward directions by summing the extrapolation of the two components. The backward prediction indicates that the Arctic TEC variability includes a 9 years period for the study duration, in addition to the well-established periods. The long-term prediction has an uncertainty of 4.8–5.6 TECU for different period sets.

Ionospheric symmetry caused by geomagnetic declination over North America

We describe variations in total electron content (TEC) in the North American sector exhibiting pronounced longitudinal progression and symmetry with respect to zero magnetic declination. Patterns were uncovered by applying an empirical orthogonal function (EOF) decomposition procedure to a 12 year ground‐based American longitude sector GPS TEC data set. The first EOF mode describes overall average TEC, while the strong influence of geomagnetic declination on the midlatitude ionosphere is found in the second EOF mode (or the second most significant component). We find a high degree of correlation between spatial variations in the second EOF mode and vertical drifts driven by thermospheric zonal winds, along with well‐organized temporal variation. Results strongly suggest a causative mechanism involving varying declination with longitude along with varying zonal wind climatology with local time, season, and solar cycle. This study highlights the efficiency and key role played by the geomagnetic field effect in influencing mesoscale ionospheric structures over a broad midlatitude range.