Ionospheric Conditions Research Articles

An Assessment of HF Radio Wave Propagation in Antarctica for a Radio Link Between McMurdo and South Pole Station

AbstractIn this work, we analyze data collected by an HF transmitter/receiver radio link, operating as an oblique ionosonde between the McMurdo Station (transmitter) and South Pole Station (receiver) at 4.1, 5.1, 6.0, 6.4, and 7.2 MHz between 28 February and 14 March 2019. To help contextualize the link's data we have performed numerical raytrace simulations to help understand the observations. By considering both the data and simulations, we have identified both single‐ and two‐hop E‐ and F‐region propagation modes in the data, where the multi‐hop modes were observed in the hours around sunrise and sunset in the 4.1 and 5.1 MHz channels. This is an unexpected result given the accepted wisdom that multi‐hop modes, which require a ground scatter component, cannot be supported in Antarctica because of the highly absorptive ice covering much of the continent. Our results show that multi‐hop propagation modes can be supported in the region under specific ionospheric conditions—around sunrise and sunset—if the mode's ground scatter component is collocated with the Transantarctic Mountains. The mountains are located along the great‐circle path between the link's transmitter and receiver. However, the combination of favorable ionospheric and ground scattering conditions makes the detection of the multi‐hop mode a rare occurrence in the data set analyzed here. These findings are critical to data analysis efforts of any current or future oblique ionosonde systems operating in Antarctica and other regions such as the Arctic.

Graph-enabled spatio-temporal transformer for ionospheric prediction

The ionosphere, crucial for satellite navigation and radio communication, is highly sensitive to solar and geomagnetic activities. Traditional ionospheric prediction models often struggle to capture its complexities. This paper introduces a Graph-Enabled Spatio-temporal transformer (GEST) model, designed to predict the Total electron content (TEC) in the ionosphere with higher accuracy. The GEST model innovatively integrates six dynamic space weather parameters, including the Kp index, and refines grid distances and weights in the Global ionospheric maps (GIM). Leveraging the efficiency of the Transformer architecture in processing spatio-temporal data, the GEST model adapts to varying ionospheric conditions and provides superior precision. Our evaluations, based on data from the Center for orbit determination in Europe (CODE), demonstrate that the GEST model significantly outperforms traditional methods and other intelligent algorithms such as conv-LSTM. It shows marked improvements in Mean absolute error (MAE), Root mean square error (RMSE), Pearson correlation coefficient (CC), and Mean absolute percentage error (MAPE), particularly during periods of intense solar and geomagnetic activity. These advancements highlight the GEST model’s substantial contributions to the field of ionospheric prediction technology, offering a robust tool for enhancing the reliability of satellite-based systems.

Tropospheric delay retrieval using cost-effective single-frequency GNSS receivers with established reference stations

This study explores the feasibility of using single-frequency (SF) receivers to achieve Zenith Total Delay (ZTD) retrievals with existing reference stations via the Satellite-specific Epoch-differenced Ionospheric delay (SEID) model. Over 30 days, data from a low-cost SF receiver was collected under varying ionospheric conditions. Two reference network configurations were tested: scheme 1 with an average inter-station distance of 138 km and scheme 2 with a distance of 431 km. The GPS-only solution exhibited Root Mean Square (RMS) of 4.2 mm and 11.3 mm for schemes 1 and 2, respectively. Incorporating GLONASS data had minimal impact on scheme 1 but increased the mean bias in scheme 2, likely due to residual ionospheric delays over the larger area. ZTD estimates from reanalysis products fell between those of the two schemes. This study demonstrates the viability of cost-effective, single-frequency receivers for precise ZTD estimation, advocating for network expansion through additional low-cost receivers.

LOFAR PL610 Station Data Product Specification

ABSTRACT Since 2017, the Space Research Centre of the Polish Academy of Sciences in Warsaw, Poland, has measured and gathered over 35,000 hours of observations with the use of the LOw Frequency ARray (LOFAR) radio telescope. This paper outlines the Standard Data Product acquired from the LOFAR PL610 station located in Borówiec, Poland. Within this context, we detail the data products that are accessible, provide metadata descriptions for them, and include an example of the data under both quiet and disturbed ionospheric conditions.

Reconstruction of ionospheric VTEC using empirical orthogonal function and its performance during extreme geomagnetic storm

This paper demonstrates that the spatial distribution of the ionospheric TEC over the Indian region can be reconstructed with appreciable accuracy using minimal numbers of empirical orthogonal functions as a basis. These basis functions were derived using the Singular Value Decomposition of a matrix composed of pragmatic vertical Total Electron Content (VTEC) values collected across varied ionospheric conditions and measured over the region of interest. The reconstruction was achieved by linearly combining the appropriately chosen significant bases with corresponding weight factors. The reconstruction accuracy of the algorithm was found to be better than 4 TECU (TECU = 1016 electrons/m2) for more than 99.9 % of the time when tested over the complete year of 2016 with only eight basis vectors. The containment factor, defined here, indicates the goodness of the chosen bases in representing the arbitrary VTEC distributions and is found to remain typically high, aiding in improved algorithm performance. The performance, however, was found to be sensitive to the seasons and geomagnetic conditions. Deteriorated performance was observed when tested for the St. Patrick's Day storm data. The deterioration was attributed to the structural alteration of the ionospheric plasma density and the presence of atypical modes during the storm. The results ascertain the prospect of a faithful representation of the spatial distribution of the ionospheric VTEC using limited parametric variables, which may find utility in navigation, radar, and various other applications.

New Expression of the Field‐Line Integrated Rayleigh‐Taylor Instability Growth Rate

AbstractAn expression of Rayleigh‐Taylor (R‐T) instability growth rate based on the field‐line integrated theory is newly established. This expression can be directly utilized in ionosphere models with magnetic flux tube structure based on Modified Apex Coordinates. The R‐T instability growth rates are calculated using the thermospheric and ionospheric conditions based on the coupled Whole Atmosphere Model and Ionosphere Plasmasphere Electrodynamic model (WAM‐IPE). The parameters used in this calculation include the field‐line integrated conductivities and currents, which consider the Quasi‐Dipole Coordinates and the modifications to the equations of electrodynamics. Detailed description of the new formulas and comprehensive analyses of diurnal, longitudinal, and seasonal variations of the R‐T instability growth rate are carried out. The dependencies of growth rates on pre‐reversal enhancement (PRE) vertical drifts and solar activity are also examined. The results show that pronounced R‐T growth rates are captured between 18 and 22 local time (LT) when strong PRE occurs in the equatorial ionosphere. The simulated R‐T growth rate increases with increasing solar activity levels and demonstrates strong correlations with the angle between the sunset terminator and the geomagnetic field line. These results are consistent with plasma irregularity occurrence rates shown in various satellite observations, suggesting that the newly developed R‐T growth rate calculation can effectively capture the probability of irregularities by considering the changes along magnetic flux‐tubes in the ionosphere. Since the WAM‐IPE is running in operation at National Oceanic and Atmospheric Administration Space Weather Prediction Center, the new calculations can be potentially implemented in the near future to provide forecasted information of the R‐T growth rate.

Ionospheric contributions to the excess power in high-redshift 21-cm power-spectrum observations with LOFAR

ABSTRACT The turbulent ionosphere causes phase shifts to incoming radio waves on a broad range of temporal and spatial scales. When an interferometer is not sufficiently calibrated for the direction-dependent ionospheric effects, the time-varying phase shifts can cause the signal to decorrelate. The ionosphere’s influence over various spatiotemporal scales introduces a baseline-dependent effect on the interferometric array. We study the impact of baseline-dependent decorrelation on high-redshift observations with the Low Frequency Array (LOFAR). Data sets with a range of ionospheric corruptions are simulated using a thin-screen ionosphere model, and calibrated using the state-of-the-art LOFAR epoch of reionization pipeline. For the first time ever, we show the ionospheric impact on various stages of the calibration process including an analysis of the transfer of gain errors from longer to shorter baselines using realistic end-to-end simulations. We find that direction-dependent calibration for source subtraction leaves excess power of up to two orders of magnitude above the thermal noise at the largest spectral scales in the cylindrically averaged autopower spectrum under normal ionospheric conditions. However, we demonstrate that this excess power can be removed through Gaussian process regression, leaving no excess power above the 10 per cent level for a $5~$ km diffractive scale. We conclude that ionospheric errors, in the absence of interactions with other aggravating effects, do not constitute a dominant component in the excess power observed in LOFAR epoch of reionization observations of the North Celestial Pole. Future work should therefore focus on less spectrally smooth effects, such as beam modelling errors.

Investigation of the Contribution of Five Broadcast Ionospheric Models (GPSK, NTCMG, NEQG, BDGIM, and BDSK) and IRTG to GNSS Positioning During Different Solar Activities in Solar Cycle 25

AbstractAdditional ionospheric information is essential for mitigating errors in single‐frequency (SF) Global Navigation Satellite Systems (GNSS) positioning. The increasing number of low‐cost dual‐frequency (DF) receiver users faces limitations in tracking DF observables compared to traditional geodetic receivers. Consequently, ionospheric correction algorithms (ICAs) are also essential for low‐cost DF devices in hybrid‐frequency positioning. To evaluate the performance of commonly used ICAs during solar cycle 25, our study presents a global statistical investigation of the contribution of five broadcast ionospheric models (BIMs) and the International GNSS Service (IGS) combined real‐time global ionospheric maps (IRTG) to the positioning domain, covering both quiet and perturbed ionospheric conditions. The BIMs investigated include the GPS Klobuchar (GPSK), Galileo NequickG (NEQG), NTCM‐GlAzpar (NTCMG), BDS‐2 Klobuchar (BDSK), and BeiDou Global Ionospheric delay correction Model (BDGIM). Experimental results from standard point positioning indicate that IRTG demonstrates superior overall accuracy compared to all BIMs, with a mean 3D root mean squared (RMS) of 2.76 m during perturbed period. Specifically, GPSK, NTCMG, NEQG, BDGIM, and BDSK exhibit RMS values of 2.03, 1.67, 1.72, 1.62, and 2.36 m during quiet conditions, and 4.02, 3.17, 2.86, 3.14, and 4.44 m during perturbed conditions, respectively. Among the BIMs, NEQG demonstrates superior performance at middle and high latitudes but exhibits lower accuracy than NTCMG and BDGIM at low latitudes during daytime under quiet conditions. BDGIM performs slightly better than NTCMG at low latitudes but slightly worse at high latitudes. BDSK shows notable improvement for high‐ and mid‐latitude regions since 3 June 2020.

Автоматическая интерпретация ионограмм наклонного зондирования на основе гибридных алгоритмов

The paper presents a method of interpreting data on oblique ionosphere sounding (OS) with a continuous chirp signal. Hybrid algorithms for automatic interpretation of ionograms by selected points with significant amplitude obtained during secondary data processing for various heliogeophysical conditions have been developed and implemented. For the conditions of the two-layer ionosphere, an interpretation method has been worked out which involves analyzing histograms for the distribution of points with significant amplitude, which fall into a model mask constructed from the results of modeling of the distance-frequency characteristic for propagation when it moves over the ionogram. For the multilayer ionosphere, the interpretation is based on the study of the ionogram amplitude relief. The algorithms for extracting tracks of signals reflected from sporadic layers are examined separately. We report the results of interpretation of ionograms obtained on the network of chirp sounding radio paths in the northeastern region of Russia.

Automatic interpretation of oblique sounding ionograms based on hybrid algorithms

The paper presents a method of interpreting data on oblique ionosphere sounding (OS) with a continuous chirp signal. Hybrid algorithms for automatic interpretation of ionograms by selected points with significant amplitude obtained during secondary data processing for various heliogeophysical conditions have been developed and implemented. For the conditions of the two-layer ionosphere, an interpretation method has been worked out which involves analyzing histograms for the distribution of points with significant amplitude, which fall into a model mask constructed from the results of modeling of the distance-frequency characteristic for propagation when it moves over the ionogram. For the multilayer ionosphere, the interpretation is based on the study of the ionogram amplitude relief. The algorithms for extracting tracks of signals reflected from sporadic layers are examined separately. We report the results of interpretation of ionograms obtained on the network of chirp sounding radio paths in the northeastern region of Russia.

Analysis of Ionospheric VTEC Retrieved from Multi-Instrument Observations

This study examines the Vertical Total Electron Content (VTEC) estimation performance of multi-instruments on a global scale during different ionospheric conditions. For this purpose, GNSS-based VTEC data from Global Ionosphere Maps (GIMs), COSMIC (F7/C2)—Feng–Yun 3C (FY3C) radio occultation (RO) VTEC, SWARM–VTEC, and JASON–VTEC were utilized. VTEC assessments were conducted on three distinct days: geomagnetic active (17 March 2015), solar active (22 December 2021), and quiet (11 December 2021). The VTEC values of COSMIC/FY3C RO, SWARM, and JASON were compared with data retrieved from GIMs. According to the results, COSMIC RO–VTEC is more consistent with GIM–VTEC on a quiet day (the mean of the differences is 4.38 TECU), while the mean of FY3C RO–GIM differences is 7.33 TECU on a geomagnetic active day. The range of VTEC differences between JASON and GIM is relatively smaller on a quiet day, and the mean of differences on active/quiet days is less than 6 TECU. Besides the daily comparison, long-term results (1 January–31 December 2015) were also analyzed by considering active and quiet periods. Results show that Root Mean Square Error (RMSE) values of COSMIC RO, FY3C RO, SWARM, and JASON are 5.02 TECU, 6.81 TECU, 16.25 TECU, and 5.53 TECU for the quiet period, and 5.21 TECU, 7.07 TECU, 17.48 TECU, and 5.90 TECU for the active period, respectively. The accuracy of each data source was affected by solar/geomagnetic activities. The deviation of SWARM–VTEC is relatively greater. The main reason for the significant differences in SWARM–GIM results is the atmospheric measurement range of SWARM satellites (460 km–20,200 km (SWARM A, C) and 520 km–20,200 km (SWARM B), which do not contain a significant part of the ionosphere in terms of VTEC estimation.

A novel piecewise linear transformation to moderate regional boundary effect on Real-Time regional ionospheric map (RT-RIM)

RT-RIM with high accuracy and dense spatiotemporal resolution of the ionospheric total electron content is crucial to diverse real-time GNSS applications. However, the uneven ionospheric pierce points distribution and boundary effect severely restrict the RT-RIM accuracy. We dedicate to the rapid and straightforward method to address the limited accuracy issue caused by the two crucial challenges. A novel piecewise linear transformation-adjusted spherical cap harmonic (PLT-ASCH) method is proposed to moderate the localized accuracy decrease in various latitudes areas for both active and stable ionospheric conditions. Especially, in the active ionospheric condition, the RMS improvements referring to IGS products are about 38.85%, 17.04%, 16.73% in Europe and 53.12%, 4.36%, 4.35% in South America, comparing to the inverse distance weighting, ASCH, and adjusted spherical harmonics adding Kriging methods. Moreover, the RMS improvements referring to differential slant TEC are about 48.11%, 16.53%, 16.99% in Europe and 61.01%, 4.87%, 4.33% in South America.

Simulation of Nighttime Medium‐Scale Traveling Ionospheric Disturbances in the Midlatitude Ionosphere During Stormtime

AbstractThe generation of medium‐scale traveling ionospheric disturbances (MSTIDs) in the mid‐latitude F region ionosphere, particularly in the presence of sporadic E (Es) layers or geomagnetically conjugate features, has been the focus of extensive investigation using both observational and numerical modeling approaches. Recent observations have revealed the occurrence of nighttime MSTIDs over the continental US during storm conditions even without invoking the Es instability. While this phenomenon is considered to be electrified and likely associated with the Perkins instability, the influences of storm‐enhanced density (SED), electric fields, and winds on the excitation of nighttime MSTIDs remain a complicated issue and require further quantitative analysis. In this study, we develop a two‐dimensional numerical model of the nighttime ionospheric electrodynamics at midlatitudes using the ionospheric ion continuity equation and the electric field Poisson equation to investigate the characteristics of MSTIDs in the SED base region during storm conditions. We demonstrate that the magnetic inclination effect can explain the lower latitude preference of the MSTIDs during magnetic storms, while the development of MSTIDs is primarily influenced by intense storm electric fields under the background ionospheric condition of large density gradients associated with SED. However, the impact of neutral winds on the MSTIDs growth varies, depending on their specific direction determined by the strongly dynamic spatiotemporal variation of the thermosphere and ionosphere during storms. Therefore, the MSTIDs stormtime scenario results from a combination of multiple important factors.

Monitoring the ionospheric conditions during the annular solar eclipse December 2019: A case study

This study investigates the ionospheric response to the December 26, 2019 annular solar eclipse over the southern tip of the Asia region, focusing on Malaysia, Sumatra, and Singapore. Utilizing data from GPS stations and ionosondes along the eclipse path, variations in Total Electron Content (TEC) and ionospheric foF2 parameters were analysed to assess the eclipse's impact. Results indicate a slight northward depletion of TEC, possibly linked to the Equatorial Ionization Anomaly (EIA), with up to −30% of depletions observed across all sites. Time delays in TEC and foF2 parameter responses suggest the influence of recombination and photochemical processes. Differences in depletion percentages between TEC and foF2 parameters may stem from production rate reductions during the eclipse. Post-sunset enhancements in TEC and foF2 parameters suggest the formation of ionospheric plasma blobs associated with Travelling Ionospheric Disturbances (TIDs) during the eclipse. While consistent with trends observed in prior studies, the study's findings highlight regional variations in ionospheric effects. This study enhances our understanding of ionospheric dynamics during solar eclipses and paves the way for further exploration in this area.

Travelling Ionospheric Disturbances detection: a statistical study of detrending techniques, induced period error and near real-time observables

Due to advances in remote sensing of the Earth's Ionosphere through Total Electron Content (TEC) estimates by Global Navigation Satellite System (GNSS) receivers, it is possible to detect and characterize Travelling Ionospheric Disturbances (TIDs) in both post-processing and, to some extent, in near real-time (NRT). A reliable and precise TEC filtering technique must be adopted to characterize waves accurately. Specifically, TEC detrending is widely adopted to extract the amplitude and period of the detected ionospheric waves from the background ionospheric conditions. Therefore, this study aims to understand and compare how different TEC detrending techniques and their settings impact the ability to extract such parameters. We highlight that the novel Fast Iterative Filtering (FIF) and the Savitzky-Golay filter (SGOLAY) techniques are the most reliable overall compared with moving average (MA), multi-order numerical difference (DD), polynomial detrending (POLY) and Finite Impulse response (FIR) band-pass filter (BUTF). Moreover, the impact of general algorithm settings on the extracted TID period is investigated, such as the Ionospheric Piercing Point (IPP) height and elevation cut-off angle, showing that such parameters drastically impact the retrieved period, especially for slower TIDs. Finally, due to the growing interest in real-time (RT) detection and classification of TIDs, the study proposes techniques for accurately estimating the TID amplitude in an NRT scenario. Such NRT techniques are then compared with the widely used post-processing products, such as the calibrated vertical TEC (vTEC), showing a difference that is mostly lower than the typical noise level of GNSS receivers (0.05 TECu).

Forecasting 24‐Hr Total Electron Content With Long Short‐Term Memory Neural Network

AbstractAn accurate prediction of the ionospheric state is important for correcting ionospheric propagation effects on Global Navigation Satellite Systems (GNSS) signals used in precise navigation and positioning applications. The main objective of the present work is to find a total electron content (TEC) model which gives a good estimate of ionospheric state not only during quiet but also during perturbed ionospheric conditions. For this, we implemented several long short‐term memory (LSTM)‐based models capable of predicting TEC up to 24 hr ahead. For the first time, we used the solar wind forcing parameters Wprot (a measure of the ionospheric disturbance during storm time) and Econv (measure of the solar wind parameters) as driver parameters. We found that using external drivers does not improve the accuracy of TEC predictions significantly. The final model is trained with data from the last two solar cycles using TEC from the rapid UQRG global ionosphere maps (GIMs). Data from the years 2015 and 2020 were excluded from the training data set and used for testing. The performance of the LSTM‐based TEC model is tested for near real‐time (RT) cases as well by using RT products (IRTG GIMs) as historical TEC inputs. We compared the performance of the LSTM‐based model to a quiet‐time feed forward neural network (FNN)‐based model and the Neustrelitz TEC model (NTCM). The results indicate that the LSTM‐based model proposed here is outperforming the FNN‐based model and NTCM in both cases, that is, using the UQRG or the IRTG GIMs as input for the historical TEC.

A Comparative Analysis of the Effect of Orbital Geometry and Signal Frequency on the Ionospheric Scintillations over a Low Latitude Indian Station: First Results from the 25th Solar Cycle

The equatorial post-sunset ionospheric irregularities induce rapid fluctuations in the phase and amplitude of global navigation satellite system (GNSS) signals which may lead to the loss of lock and can potentially degrade the position accuracy. This study presents a new analysis of L-band scintillation from a low latitude station at Guntur (Geographic 16.44°N, 80.62°E, dip 22.18°), India, for the period of 18 months from August 2021 to January 2023. The observations are categorized either in the medium Earth-orbiting (MEO) or geosynchronous orbiting (GSO) satellites (GSO is considered as a set of the geostationary and inclined geosynchronous satellites) for L1, L2, and L5 signals. The results show a higher occurrence of moderate (0.5 < S4 ≤ 0.8) and strong (S4 > 0.8) scintillations on different signals from the MEO compared to the GSO satellites. Statistically, the average of peak S4 values provides a higher confidence in the severity of scintillations on a given night, which is found to be in-line with the scintillation occurrences. The percentage occurrence of scintillation-affected satellites is found to be higher on L1 compared to other signals, wherein a contrasting higher percentage of affected satellites over GSO than MEO is observed. While a clear demarcation between the L2/L5 signals and L1 is found over the MEO, in the case of GSO, the CCDF over L5 is found to match mostly with the L1 signal. This could possibly originate from the space diversity gain effect known to impact the closely spaced geostationary satellite links. Another major difference of higher slopes and less scatter of S4 values corresponding to L1 versus L2/L5 from the GSO satellite is found compared to mostly non-linear highly scattered relations from the MEO. The distribution of the percentage of scintillation-affected satellites on L1 shows a close match between MEO and GSO in a total number of minutes up to ~60%. However, such a number of minutes corresponding to higher than 60% is found to be larger for GSO. Thus, the results indicate the possibility of homogeneous spatial patterns in a scintillation distribution over a low latitude site, which could originate from the closely spaced GSO links and highlight the role of the number of available satellites with the geometry of the links, being the deciding factors. This helps the ionospheric community to develop inter-GNSS (MEO and GSO) operability models for achieving highly accurate positioning solutions during adverse ionospheric weather conditions.

Radiation of twisted waves from a phased array of loop antennas in a resonant magnetoplasma

A study is made of the radiation from a phased array of circular loop antennas in a resonant magnetoplasma. The loops are assumed to have a finite radius and be located on a circumference in such a manner that their axes are aligned with a static magnetic field superimposed on the plasma. The emphasis is placed on determining the total radiated power of such an array and the partial powers going to different azimuthal field harmonics. For these quantities, rigorous integral representations are obtained using an expansion of the excited field in terms of cylindrical vector eigenfunctions of a magnetized plasma medium. Numerical results are reported for the radiation characteristics of the phased array in the whistler frequency range under conditions of the Earth's ionosphere. It is shown that an appropriately phased array is capable of selectively exciting waves with the desired helicity of the phase front and can be useful as a source of twisted whistler-mode waves in a magnetoplasma.

On the variations in equatorial and low-latitude GPS-TEC and assessment of NeQuick-2, IRI-2016 and IRI-2020 models in the African longitude during solar cycle 24–25

Ionospheric models play a crucial role in understanding, prediction, and mitigation of the effects of ionospheric variability on a wide range of technological and scientific applications relying on space-based services. Conversely, the models need to be routinely updated with newer datasets and specifications to account for the regional discrepancies in the changing ionospheric conditions due to various dominant localized physical and chemical processes. Although there have been ongoing improvements to the extensively utilized empirical model known as the International Reference Ionosphere (IRI), the newly emerged version (IRI-2020) needs to undergo global testing. In this research, we carried out diurnal and seasonal variations in GPS-TEC and the assessment of some ionospheric models such as IRI-2016 and its recently updated version (IRI-2020), alongside the NeQuick-2 model at 2 stations each in the East, West and South in the equatorial and low-latitude African longitudes during different phases of solar cycles 24–25 (2016 – 2021). Also, we carried out statistical analysis between GPS-TEC and the ionospheric models using Root Mean Square Error (RMSE) and Mean Absolute Error (MAE), in order to show the model with the best forecasting capability in the African region. Diurnal, seasonal and solar cycle variations in GPS-TEC, NeQuick-2, IRI-2016 and IRI-2020 were observed, showing higher magnitudes in the West, followed by the East in close range and least in the Southern sector of the African longitudes. TEC Variations in some sectors in the African longitudes show a consistent trend in this research. More importantly, there are observed regional differences within the African longitudes owing to the wider coverage of landmass in the equatorial and low latitudes. However, TEC variations in the Northern sector of Africa are not included in the present research. From our observation, NeQuick-2 and IRI-2016 models either underestimate or overestimate GPS-TEC during different phases of the solar cycles at the three sectors in the African longitudes, whereas IRI-2020 shows mostly underestimating characteristics at the three sectors irrespective of solar activity conditions during the study period. Nevertheless, the underestimation or overestimation of NeQuick-2 and IRI-2016, and the underestimation of IRI-2020 are reflected in the RMSE and MAE values. Regrettably, the predictions from IRI-2020 model are not satisfactory at any of the three sectors in the African longitudes and prompt attention of the modeling community for further investigations towards possible refinements in the model specifications.

Ionospheric Nowcasting Over Italy Through Data Assimilation: A Synergy Between IRI UP and IONORING

AbstractAn accurate modeling of the ionosphere electron density is pivotal to guarantee the effective operation of communication and navigation systems, particularly during Space Weather events. Despite the crucial contribution of empirical models like the International Reference Ionosphere (IRI), their limitations in predicting ionospheric variability, especially under geomagnetically disturbed conditions, are acknowledged. The solution proposed in this work involves integrating real‐time, spatially distributed ionospheric measurements into climatological models through data assimilation. To enhance our predictive capabilities, we present an upgrade of the IRI UP data‐assimilation method, incorporating real‐time vertical total electron content (vTEC) maps from the IONORING algorithm for nowcasting ionospheric conditions over Italy. This approach involves updating the IRI F2‐layer peak electron density description through ionospheric indices, to finally produce real‐time maps over Italy of the ordinary critical frequency of the F2‐layer, foF2, which is crucial for radio‐propagation applications. The IRI UP–IONORING method performance has been evaluated against different climatological and nowcasting models, and under different Space Weather conditions, by showing promising outcomes which encourages its inclusion in the portfolio of ionospheric real‐time products available over Italy. The validation analysis highlighted also what are the current limitations of the IRI UP–IONORING method, particularly during nighttime for severely disturbed conditions, suggesting avenues for future enhancements.