Abstract This study investigates ionospheric responses to geomagnetic storms of 21–24 March and 15–17 April 2025 using GNSS‐derived total electron content (TEC), magnetometer observations, and thermospheric O/N 2 measurements at low and mid‐latitudes across the Northern Hemisphere of the Europe–Africa sector. The March storm reached a SYM‐H minimum of −72 nT, driven by a CME with a brief southward IMF‐Bz interval followed by a high‐speed stream (HSS). Low‐latitude African stations recorded night‐time TEC enhancements of +85% to +168%, attributed to prompt penetration electric fields (PPEFs) driving night‐time upward E × B plasma transport, while mid‐latitude European stations exhibited mixed deviations. Elevated daytime O/N 2 ratios indicate reduced molecular recombination in the F region during the daytime, consistent with positive daytime ionospheric responses at low latitudes. The April storm reached a SYM‐H minimum of −150 nT, from a compound CME–HSS interaction sustaining southward IMF‐Bz conditions. During 16–17 April, mid‐latitude European stations experienced TEC reductions of −52% to −69% in the main phase, while low‐latitude stations displayed alternating responses. O/N 2 ratios decreased to 0.6–0.8 across the sector, consistent with enhanced molecular recombination and negative ionospheric responses at mid‐latitudes. Magnetometer observations revealed storm‐time perturbations after sudden commencement, consistent with prompt penetration electric fields, followed by latitudinal disturbances during late main and recovery phases. Magnetic signatures for disturbed ionospheric currents Diono, negative at low latitudes and positive at mid‐latitudes, agree with the polarity predicted by the disturbance dynamo model of Blanc and Richmond (1980, https://doi.org/10.1029/ja085ia04p01669 ). These results demonstrate how storm evolution and solar‐wind forcing shape ionospheric variability within the Europe–Africa sector.

Predicting ionospheric conditions is becoming increasingly important towards the operational efficiency of both ground-based and space-borne radio communication systems with a view to compensate for the effects of space weather. This study focuses on predicting ionospheric irregularities in the complex and variable equatorial ionosphere which is deemed critical for optimal space-based application. We utilized the Long-Short-TermMemory (LSTM) deep learning algorithm to develop a predictive model for forecasting disturbances in the equatorial ionization anomaly (EIA) region using Global Navigation Satellite Systems (GNSS) data. We utilized fifteen-year worth of data (2005-2020) to train, validate and test the performance of the model and assessed the results against a baseline model relying on daily and hourly Rate of Change of TEC Index (ROTI) values and utilized evaluation metrics such as correlation (R), determination coefficient (R2), and mean squared error (MSE). Remarkably, the LSTM Predictive Model consistently outperformed the Baseline Model across various stations, demonstrating higher R and R2 values and significantly lower MSE. These results indicate the LSTM model's superior accuracy in forecasting ionospheric disturbances, essential for space-based applications. The distribution analysis of residual errors highlighted the LSTM model's ability to better capture underlying patterns and variability in the target variable. This study contributes to enhancing ionospheric forecasting models for space applications, ensuring the dependability of space-based systems.

In this paper, we investigate and propose the application of an unsupervised machine learning clustering method to characterize the spatial and temporal distribution of ionospheric plasma irregularities over the Western African equatorial region. The ordinary Kriging algorithm was used to interpolate the rate of change of the total electron content (TEC) index (ROTI) over gridded 0.5° by 0.5° latitude and longitude regional maps in order to simulate the level of ionospheric plasma irregularities in a quasi-real-time scenario. K-means was used to obtain a spatial mean index through an optimal stratification of regional post-processed ROTI maps. The results obtained could be adapted by appropriate K-means algorithms to a real-time scenario, as has been performed for other applications. This method could allow us to monitor plasma irregularities in real time over the African region and, therefore, lead to the possibility of mitigating their effects on satellite-based location systems in the said region.

This study examines the occurrences rate of geomagnetic storms during the solar cycles (SCs) 20-24. It also investigates the solar sources at SCs 23 and 24. The Disturbed storm time (Dst) and Sunspot Number (SSN) data were used in the study. The study establishes that the magnitude of the rate of occurrences of geomagnetic storms is higher (lower) at the descending phases (minimum phases) of solar cycle. It as well reveals that severe and extreme geomagnetic storms (Dst <-250 nT) seldom occur at low solar activity but at very high solar activity and are mostly associated with coronal mass ejections (CMEs) when occurred. Storms caused by CME + CH-HSSW are more prominent during the descending phase than any other phase of the solar cycle. Solar minimum features more CH-HSSW- asso-ciated storms than any other phase. It was also revealed that all high intensity geomagnetic storms (strong, severe and extreme) are mostly associated with CMEs. However, CH-HSSW can occasionally generate strong storms during solar minimum. The results have proven that CMEs are the leading cause of geomagnetic storms at the ascending, maximum and the descending phases of the cycles 23 and 24 followed by CME + CH-HSSW. The results from this study indicate that the rate of occurrence of geomagnetic storms could be predicted in SC phases. (c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

Perturbations from thunderstorms can play a notable role in the dynamics of the ionosphere. In this work, ionospheric perturbation effects due to thunderstorms were extracted and studied. Thunderstorm-associated lightning activities and their locations were detected by the World-Wide Lightning Location Network (WWLLN). The mechanical components of ionospheric perturbations due to thunderstorms were extracted from the total electron content (TEC), which was measured at selected thunderstorm locations using the polynomial filtering method. Further analyses were conducted using wavelet analysis and Discrete Fourier Transform (DFT) to study the frequency modes and periodicities of TEC deviation. It was revealed that the highest magnitudes of TEC deviations could reach up to ~2.2 TECUs, with dominant modes of frequency in the range of ~0.2 mHz to ~1.2 mHz, falling within the gravity wave range and the second dominant mode in the acoustic range of >1 mHz to <7.5 mHz. Additionally, a 20–60 min time delay was observed between the sprite events, the other high-energy electrical discharges, and the time of occurrence at the highest peak of acoustic-gravity wave perturbations extracted from TEC deviations. The possible mechanism responsible for this phenomenon is further proposed and discussed.

It has been a concern of space scientists and engineers for many decades to have a well-defined proxy to characterize the fluctuations experienced by radio-based signals propagating through the ionosphere. Scintillation indices were deduced using the signal intensity to show the level of fluctuations in phase and amplitude of radio signal passing through the ionosphere. Subsequently, more than two decades now, the rate of change of Total Electron Content (TEC) index (ROTI) was as well used to characterize the level of fluctuations associated to ionospheric irregularities on radio signals. This paper examines the level of relationship between the rate of change of TEC index (ROTI) and the ionospheric amplitude scintillation (S4) within the belt of equatorial ionization anomaly of West African sector. The study was carried out using the Scintillation Network Decision Aid (SCINDA) Global Positioning System (GPS) data obtained from ground-based stations located at Dakar (Senegal) and Cape Verde. The comparative analysis of ROTI and S4 was done with normalized ROTI. The results obtained have shown that the magnitude of normalized ROTI and S4 corresponds very well, higher in Cape Verde compared to Dakar. It was observed that the correlation coefficient could be -0.6 when all the satellites are used. However, the relationship increases with individual satellite in which the coefficient of correlation could be up to -0.97 and R2 - 0.94. It can be concluded that the relationship between the S4 and ROTI depends on the location and the level of ionospheric disturbance condition as observed in this work. & COPY; 2022 Published by Elsevier B.V. on behalf of COSPAR.

&lt;p&gt;Regional Total Electron Content (TEC) Maps proffer better mitigation effects in ionospheric models which are needed to resolve ionospheric TEC gradient errors associated with space-based technologies such as Global Navigation Satellite Systems (GNSS) and Space-Based Augmentation Systems (SBAS). EGNOS (European Geostationary Navigation Overlay System) is a European SBAS system that provides integrity, accuracy, continuity and availability to critical GNSS applications like aviation and others over ECAC (European Civil Aviation Conference) area. The EGNOS Ionospheric model is built with the concept of the ordinary Planar fit technique. This paper focuses on modified Planar fit, ordinary Kriging and modified Kriging techniques to validate the EGNOS algorithm during different geophysical (geomagnetically quiet and disturbed) conditions. The structure of EGNOS was strictly adhered to during the study and only publicly available GNSS ground-based stations over the ECAC area are engaged in the study. The preliminary results obtained show that adapting modified Planar fit and Kriging techniques could improve the EGNOS services over the ECAC area, most especially the northern part near the high latitudes and the southern part near the low latitude regions.&lt;/p&gt;

We present for the first time the climatology of medium-scale traveling ionospheric disturbances (MSTIDs) by using Global Positioning System (GPS) receiver networks on geomagnetically quiet days (Kp ≤ 3) over the North African region during 2008-2016. The MSTIDs appear frequently as oscillating waves or wave-like structures in electron density induced by the passage of Atmospheric Gravity Waves (AGW) propagating through the neutral atmosphere and consequently, causing fluctuation in the ionospheric Total Electron Content (TEC). The TEC perturbations (dTEC) data are derived from dual frequency GPS-measurements. We have statistically analyzed the occurrence rate, diurnal and seasonal behavior as well as the annual MSTID occurrence characteristics. The results show a local and latitude dependence of nighttime and daytime MSTIDs. The propagation direction is predominantly towards the South (equatorward), MSTIDs event period is (10 ≤ period ≤ 43 mins), and amplitude (0.08 ≤ amp ≤ ~5.0 TECU), with a velocity higher at nighttime than daytime. The amplitudes for daytime and nighttime MSTIDs increase with solar activity. On the average, the local MSTIDs Spatio-temporal heat map for the Mid-latitude reveals variability in disturbance occurrence time to be dominant within the hours of 0900 - 1600 LT in December solstice (winter) and 1900–0400 LT in June solstice (summer) for daytime and nighttime respectively. While the low latitude reveals the disturbance occurrence time to be dominant within the hours of 1100 - 1800 LT in December solstice (winter) and 2000–0200 LT in equinox months and June solstice (summer) for daytime and nighttime respectively. The time series MSTIDs regional distribution map is also generated. Atmospheric gravity waves (AGW) might be responsible for the excitation mechanism for daytime MSTIDs.

This paper examines the accuracy of the Global Positioning System (GPS) within the African low-latitude sector. We evaluated the vertical and horizontal of the single-point positioning (SPP) accuracy of GPS and critically analysed the effects of the equatorial ionospheric anomaly (EIA) over the region of study. Our results imply that using single-frequency GPS for any application could give a positioning error up to 45.00 m vertically and similar to 25.00 m horizontally. The study revealed that 54% of GNSS positioning errors during the night-time could be linked to ionospheric plasma irregularities. Also, positioning errors are higher in western Africa than in the eastern region. The influence of geomagnetic activities is not consistent with GPS positioning accuracy. However, positioning errors are lower during geomagnetically disturbed conditions in comparison to quiet conditions. The unique phenomena of the EIA can severely limit GPS services at night-time for positioning in the study area.

The ionosphere model is essential to satellite-based systems to accurately correct the ionospheric error encountered by satellite signals en route. The Levenberg–Marquardt backpropagation (LMBP) algorithm in the artificial neural network (ANN) was used in this work to predict the total electron content (TEC) within the trough of equatorial ionization anomaly (EIA) over Nigeria. Two sets of data were used over the period of three consecutive years (2011–2013) of high solar activity. The first set was used as an input to the ANN model and the second set of data was used as a target. Seventy percent of the data sets were used to train the network, 15% of the data were used for validation, and 15% used for testing. The performance of the model was assessed during specific quiet and disturbed geomagnetic conditions. The regression analysis of the model output was optimized by minimizing a cost function of the mean square error (MSE). The results of the errors, regression, and comparative analyses have revealed that the ANN model is able to predict accurate and reliable TEC that compares well with the actual experimental data at any geophysical conditions. Hence, this model would be useful to forecast TEC over Nigeria to a reliable threshold.

Anomalous propagation conditions may cause multipath fading and strong signal enhancement on terrestrial line of sight links or interference on transhorizon paths. In detecting this conditions, spatial distribution of vertical refractivity gradient and ducting index were estimated across Nigeria using atmospheric data obtained from Era5 archive of European Centre for Medium‐Range Weather Forecasts (ECMWF). Refractivity and refractivity gradient were calculated from the obtained temperature, relative humidity, and pressure data using International Telecommunication Union (ITU) recommendation expression. Vertical refractivity gradient (VRG) and ducting index (Di) were deducted from refractivity gradient and modified the refractivity gradient. Correlation between vertical refractivity gradient, Di, and latitude were also computed. The result shows that the VRG values range between −5 and −65 N units/km in the Coastal and Guinea Savannah regions, and between −30 and −95 N units/km in the Midland and Sahelian regions. The Di values range between 10 and 60 in the Coastal and Guinea Savannah regions, between −10 and 110 in Midland and Sahelian region. Likewise, superrefraction and ducting are more prominent in the northern part, while superrefraction with minor subrefraction were noticed in the south. The Di performed better than VRG in detecting propagation conditions. Correlation between VRG and latitude ranges between −0.75 and −0.92. Correlation between Di and latitude is between 0.84 and 0.95. The values of VRG decrease northward, while those of the Di increase northward. Both VRG and Di revealed high variability in the dry months than in the wet months.

Using total electron content (TEC) data deduced from 18 Global Positioning System (GPS) receivers in Africa and Middle East, we investigated the morphology of the equatorial ionization anomaly (EIA) and its underlying variations before, during and after the 2009 sudden stratospheric warming (SSW) event. A southern EIA crest stronger than the northern EIA crest was observed for most of the days before the SSW event, while the EIA troughs were significantly obliterated after these SSW induced phases. In addition to the observed marked depletion of the hemispheric EIA crests during the SSW peak phase, we observed a terdiurnal variation straddling the northern EIA crests. This background terdiurnal signature is suggested to be partly responsible for the transport of more plasma to the northern hemisphere at the expense of southern hemisphere during the SSW peak phase. The consequences are higher pre-noon and post noon crests in the northern hemisphere compared to a single crest in the southern hemisphere. Contrary to previous modeling and experimental reports that the reductions in ionospheric TEC are due to semidiurnal variations resulting from the SSW peak phase, our results show that a terdiurnal variation was responsible for reducing the EEJ strength and TEC at the E-region and F2-region's topside, respectively. At the southern middle latitudes, an underlying diurnal variation was seen to initiate an increment in TEC during the SSW descending phase.

•Assessment of ionospheric correction models for SBAS applications over African.•The residual error along the IGPs over the region were evaluated models used.•The Bounding errors were as well estimated with the same algorithms.•The models assessed employed NeQuick2 output for case test.

The ability to model the ionosphere accurately for single frequency users in satellite applications has gained some appreciable usage, most especially during quiet conditions in a mild (middle latitudes) ionosphere. However, solving the problem of ionosphere for single frequency user of Global Navigation Satellite Systems (GNSS) in equatorial ionization anomaly (EIA) region is of a great concern for space scientists and engineers. Several methodologies have been used to develop models that describe global or regional maps for ionosphere errors in order to mitigate the effect of the errors on GNSS systems. Global or regional ionosphere Maps have been known to be an efficient tool to monitor the delay introduced by the ionosphere in the satellite signals. This research uses the conventional Planar fit and ordinary Kriging methodologies to assess a regional map for ionosphere correction in equatorial African sector. The result obtained is an indication that modified Kriging methodology describes the EIA ionosphere corrections better compared with ordinary Kriging and Planar fit methodologies.

This study presents the results of plasma irregularities over African equatorial and low-latitude region under various solar-geophysical conditions that gave rise to an east–west longitudinal asymmetry. The data used for this research were obtained from the ground-based GNSS receiver stations within African equatorial ionization anomaly region, for 3 consecutive years (2011–2013) in the ascending phase of solar cycle ♯24. The study considered specific days of different geomagnetic activities in equinoctial month of October 2013. In addition, the five most geomagnetically disturbed and quietest days in each month for the 3 consecutive years and the annual mean for each year were considered in this study. Rate of change of total electron content index (ROTI) was used to access the level of the ionospheric irregularities activity. The presence of ionospheric irregularities was taken when the difference between the local daytime (0600–1800) and nighttime (1900–2400) mean ROTI is above 0.075 TECu/min. The study revealed that African equatorial ionospheric irregularities’ occurrence is larger in the west sector and that irregularities activity could be sometimes 4–40% lowered or inhibited during the disturbed conditions in the African equatorial eastern sector in comparison to the western region. The asymmetry observed in the region could be attributed to transequatorial meridional winds and probably the east–west asymmetry in the strength of the EEJ current in the region.

A Satellite Based Augmentation System (SBAS) is designed to improve Global Navigation Satellite Systems (GNSS) in terms of integrity, accuracy, availability and continuity. The main limitation to SBAS performance optimization is the ionosphere, and this is more critical in low latitude. During geomagnetically disturbed periods the role of storm-time winds is important because they modify the atmospheric composition toward low latitudes. An index of ionospheric disturbance, the relative percentage of deviation of the vertical Total Electron Content (TEC) from the quiet level (DvTEC) at each station was evaluated to study positive and negative phases of the geomagnetic storms. The rate of change of TEC index (ROTI) over all the GNSS stations was estimated to evaluate equatorial ionospheric gradients and irregularities. From the study it is observed that the positive deviations are more frequent than negative ones. The availability map, which is the mean of the combine Vertical Protection Level (VPL) and Horizontal Protection Level (HPL) are used for the SBAS performance. The cases of moderate and minor storms studied during the months of July and October 2013 showed that the SBAS system performance during the disturbed periods depends on the local time in which the storm occurs, geographic longitude and other phenomena that need further study. During the storm-time conditions considered, three out of seven geomagnetic storms indicated good SBAS performance and exceed monthly average of the availability map, three geomagnetic storms reduced the system performance below monthly average while one does not have effect on SBAS system performance in respect to monthly average. The present study indicates ROTI as a better proxy than geomagnetic indices for the assessment of storm-time effects on GNSS-SBAS performance.

Investigating the effects of the Equatorial Ionization Anomaly (EIA) ionosphere and space weather on Global Navigation Satellite Systems (GNSS) is very crucial, and a key to successful implementation of a GNSS augmentation system (SBAS) over the equatorial and low-latitude regions. A possible ionospheric vertical delay (GIVD, Grid Ionospheric Vertical Delay) broadcast at a Ionospheric Grid Point (IGP) and its confidence bounds errors (GIVE, Grid Ionospheric Vertical Error) are analyzed and compared with the ionospheric vertical delay estimated at a nearby user location over the West African Sub-Saharan region. Since African sub-Saharan ionosphere falls within the EIA region, which is always characterized by a disturbance in form of irregularities after sunset, and the disturbance is even more during the geomagnetically quiet conditions unlike middle latitudes, the need to have a reliable ionospheric threat model to cater for the nighttime ionospheric plasma irregularities for the future SBAS user is essential. The study was done during the most quiet and disturbed geomagnetic conditions on October 2013. A specific low latitude EGNOS-like algorithm, based on single thin layer model, was engaged to simulate SBAS message in the study. Our preliminary results indicate that, the estimated GIVE detects and protects a potential SBAS user against sampled ionospheric plasma irregularities over the region with a steep increment in GIVE to non-monitored after local sunset to post midnight. This corresponds to the onset of the usual ionospheric plasma irregularities in the region. The results further confirm that the effects of the geomagnetic storms on the ionosphere are not consistent in affecting GNSS applications over the region. Finally, this paper suggests further work to be investigated in order to improve the threat integrity model activity, and thereby enhance the availability of the future SBAS over African sub-Saharan region.

Rate of change of TEC (ROT) and its index (ROTI) are considered a good proxy to characterize the occurrence of ionospheric plasma irregularities like those observed after sunset at low latitudes. SBASs (satellite-based augmentation systems) are civil aviation systems that provide wide-area or regional improvement to single-frequency satellite navigation using GNSS (Global Navigation Satellite System) constellations. Plasma irregularities in the path of the GNSS signal after sunset cause severe phase fluctuations and loss of locks of the signals in GNSS receiver at low-latitude regions. ROTI is used in this paper to characterize plasma density ionospheric irregularities in central–western Africa under nominal and disturbed conditions and identified some days of irregularity inhibition. A specific low-latitude algorithm is used to emulate potential possible SBAS message using real GNSS data in the western African low-latitude region. The performance of a possible SBAS operation in the region under different ionospheric conditions is analysed. These conditions include effects of geomagnetic disturbed periods when SBAS performance appears to be enhanced due to ionospheric irregularity inhibition. The results of this paper could contribute to a feasibility assessment of a European Geostationary Navigation Overlay System-based SBAS in the sub-Saharan African region.

Global or regional Maps of the ionospheric Total Electron Content (TEC) are an efficient tool to monitor the delay introduced by the ionosphere in the satellite signals. Ionospheric disturbance periods are of particular interest because these conditions can strongly affect satellite navigation range measurements. This work presents post-processing regional vertical TEC maps over Southern Europe ([35 degrees N-50 degrees N] latitude) obtained by applying Kriging interpolation to GPS derived TEC over more than 100 Global Navigation Satellite System (GNSS) stations. These maps are used to study the behavior of the ionosphere during space weather events and their effects. To validate these maps, hereafter called Southern European Ionospheric Maps (SEIMs), their TEC values have been compared with those obtained from EGNOS Message Server (EMS) and with direct experimental TEC data from GNSS stations. Ionospheric space weather events related to geomagnetic storms of March 17th, 2013, February 19th, 2014 and March 17th, 2015 have been selected. To test the methodology, one period of quiet days has been also analyzed. TEC values obtained by SEIMs in the Ionospheric Grid Points (IGPs) defined by EGNOS are very close to those given by EMS and in the period of major geomagnetic storms the difference does not exceed 6 TEC units. These results confirm the good performance of the technique used for obtaining the SEIMs that can be a useful tool to study the ionosphere behavior during geomagnetic storms and their effects in the region of interest. (C) 2017 COSPAR. Published by Elsevier Ltd. All rights reserved.