Ionospheric Height Research Articles

Ionosphere Peak Height Prediction Performance of International Reference Ionosphere Model

电离层峰值高度<i>H</i>_m<i>F</i>₂是描述电离层形态的重要参数之一，国际参考电离层模型IRI-2016中融入了大量电离层测高仪和无线电掩星探测数据，用以提升<i>H</i>_m<i>F</i>₂的预测精度.本文利用太阳活动低年（2007—2010年）气象、电离层和气候卫星联合观测系统COSMIC探测数据描述全球范围内COSMIC <i>H</i>_m<i>F</i>₂的三维形态变化，对比分析了IRI-2016与IRI-2012模型的预测结果，同时分析了IRI-2016模型输出<i>H</i>_m<i>F</i>₂的性能.结果表明，IRI模型在中高纬度地区的输出结果高于COSMIC反演结果，而赤道及低纬地区则大都偏低.与IRI-2012模型相比，IRI-2016模型的输出结果在夜间至凌晨时段呈现较为明显的纬向梯度变化且大部分区域输出值偏高，但在白天时段赤道附近区域的输出值大都偏低.上述结果为电离层IRI模型的完善提供了一定参考.

Accuracy assessment of the quiet-time ionospheric F2 peak parameters as derived from COSMIC-2 multi-GNSS radio occultation measurements

The Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2) mission was launched into a low-inclination (24°) orbit on June 25, 2019. Six satellites, each with an advanced Tri-GNSS Radio-Occultation Receiver System (TGRS), provide a global and uniform data coverage of the equatorial region with several thousand electron density profiles daily. The COSMIC-2 electron density profiles, and specifically the derived ionospheric F2 peak parameters, are properly validated in this study with reliable “truth” observations. For this purpose, we used manually scaled ionograms from 29 ground-based ionosondes located globally at low and middle latitudes. For this validation campaign, we considered only geomagnetically quiet conditions in order to establish benchmark level of the new mission’s ionospheric observation quality and to evaluate the operational capability of the COSMIC-2 Radio Occultation (RO) payload at the background of normal day-to-day variability of the ionosphere. For reliable colocations between two independent techniques, we selected only COSMIC-2 RO profiles whose F2 peak point coordinates were within 5° of the closest ionosonde. Our comparison of the ionospheric F2 peak height (hmF2) derived from COSMIC-2 RO and ground-based ionosonde measurements showed a very good agreement, with a mean of ~5 and ~2 km at low and middle latitudes, respectively, while RMS error was of ~23 and ~14 km, respectively. That range corresponds to a deviation of only 6–9% from the reference, ionosonde observations. Examination of representative collocation events with multiple (2–5) simultaneous RO tracks near the same ionosonde with different RO geometry, multi-satellite and multi-GNSS combination give us observational evidence that COSMIC-2 RO-based EDPs derived from GPS and GLONAS links show good self-consistency in terms of the ionospheric F2 peak values and electron density profile shape. We can conclude that COSMIC-2 provides high quality data for specification the ionospheric electron density at the F2 peak region.

Numerical simulation of lower ionospheric reflection parameters by using International Reference Ionosphere (IRI) model and validation with Very Low Frequency (VLF) radio signal characteristics

Sub-Ionospheric Very Low Frequency (VLF) radio wave propagation characteristics are the major tool to study the lower ionospheric heights mainly D-region. Wait’s 2-component exponential model is a well-known mechanism to understand the basic characteristics of this layer based on VLF remote sensing. This model deals with two major ionospheric parameters, namely, ‘steepness parameter’ (β) and ‘effective reflection height’ (h′). ‘International Reference Ionospheric (IRI)’ is a famous model for the terrestrial ionosphere that provides mostly the altitude profile temperature of the electron and ions globally. In this manuscript, we use such electron density profiles based on IRI outcomes during a quiet ionospheric condition. We choose our VLF reception location ‘Ionospheric and Earthquake Research Center & Optical Observatory’ (IERCOO), Sitapur (Lat 22.5° N, Lon 87.48° E) to compute the electron density from IRI model. By using the Wait’s exponential model with a log-linear fitting of electron density, we compute the β and h′ from their fundamental definition. With an automation technique, we repeat this process several times and generate a complete data set of such parameters for different time of the day during the summer and winter seasons of the year 2016. To get a qualitative comparison with the VLF signal amplitude variation with β and h′, we choose the Indian VLF transmitter VTX of frequency 18.2 kHz (Lat 8.26°N and 77.44°E). By computing similar data sets for other four receiving locations in India, we replicate the VLF signal amplitude profiles using Long Wavelength Propagation Capability (LWPC) model which matches with the observed signal profile satisfactorily.

Measurement-Level Target Tracking Fusion for Over-the-Horizon Radar Network Using Message Passing

Tracking an unknown number of targets based on multipath measurements provided by an over-the-horizon radar (OTHR) network with a statistical ionospheric model is complicated, which requires solving four subproblems: Target detection, target tracking, multipath data association, and ionospheric heights identification. A joint solution is desired since the four subproblems are highly correlated, but suffering from the intractable inference problem of high-dimensional latent variables. In this article, a unified message passing (MP) approach, combining belief propagation (BP) and mean-field (MF) approximation, is developed for simplifying the intractable inference. Based upon the factor graph corresponding to a factorization of the joint probability density function (PDF) of the latent variables and a choice for a separation of this factorization into BP region and MF region, the posterior PDFs of target kinematic state and ionospheric heights, are approximated by MF due to its simple MP update rules for conjugate-exponential models. The posterior PDFs of target visibility state and multipath data association which contains one-to-one frame (hard) constraints (i.e., at each time, a measurement is either originated from one target via a particular path or it is clutter, and each target generates at most one measurement under a particular path) are approximated by BP. Finally, the approximated posterior PDFs are updated iteratively in a closed-loop manner, which is effective for dealing with the coupling issue among latent variables. Meanwhile, the proposed approach has the measurement-level fusion architecture due to the direct processing of the raw multipath measurements from an OTHR network, which is beneficial to improving tracking fusion performance. Its performance is demonstrated on a simulated OTHR network multitarget tracking scenario.

OTHR multitarget tracking with a GMRF model of ionospheric parameters

The ionosphere is the propagation medium for radio waves transmitted by an over-the-horizon radar (OTHR). Ionospheric parameters, typically, virtual ionospheric heights (VIHs), are required to perform coordinate registration for OTHR multitarget tracking and localization. The inaccuracy of ionospheric parameters has a significant deleterious effect on the target localization of OTHR. Therefore, to improve the localization accuracy of OTHR, it is important to develop accurate models and estimation methods of ionospheric parameters and the corresponding target tracking algorithms. In this paper, we consider the variation of the ionosphere with location and the spatial correlation of the ionosphere. We use a Gaussian Markov random field (GMRF) to model the VIHs, providing a more accurate representation of the VIHs for OTHR target tracking. Based on expectation-conditional maximization and GMRF modeling of the VIHs, we propose a novel joint optimization solution, namely ECM-GMRF, to perform target state estimation, multipath data association and VIHs estimation simultaneously. In ECM-GMRF, the measurements from both ionosondes and OTHR are exploited to estimate the VIHs, leading to a better estimation of the VIHs which improves the accuracy of data association and target state estimation, and vice versa. The simulation indicates the effectiveness of the proposed algorithm.

Multi-Experiment Observations of Ionospheric Disturbances as Precursory Effects of the Indonesian Ms6.9 Earthquake on August 05, 2018

Taking the 2018 Ms6.9 Indonesia earthquake as a case study, the ionospheric perturbations in very low frequency (VLF) transmitters recorded by China Seismo-Electromagnetic Satellite (CSES) were mainly investigated, as well as the multi parameters of the plasma and electromagnetic field. The characteristics of electron density (Ne), GPS TEC, ULF electric field, ion drift velocity, and ionosphere height were extracted and compared with the features of the signal-noise ratio (SNR) from VLF transmitters of NWC at the southern hemisphere and JJI at the northern hemisphere. Most disturbances in VLF radio waves occurred along the orbits near the epicenter within 10 days before the earthquake. Along these orbits, we observed simultaneous modulations in the Ne and ULF electric field, as well as the changed ion drifting directions. There was also high spatial correspondence between both SNR and ionospheric height anomalies over the epicentral and its magnetic conjugate regions. Combined with the multi observations, these results suggest that the genesis of perturbations in signals emitted by VLF transmitters on satellite was more likely related to the overlapped electric field in the preparation area of the earthquake.

ЕЛЕКТРОМАГНІТНІ ЕФЕКТИ АКУСТИКО-ГРАВІТАЦІЙНИХ ХВИЛЬ У ПРИЗЕМНІЙ АТМОСФЕРІ

Purpose: Acoustic and atmospheric gravity waves (AAGW) are generated by many natural and anthropogenic sources. The AAGW propagation at ionospheric heights is accompanied by the generation of disturbances in the magnetic and electric fields. The plasma presence plays a crucial role. The mechanisms for generating electrical and magnetic disturbances in the near-Earth atmosphere by the AAGW have been studied much worse. Therefore, the validation of the capability to generate electromagnetic disturbances in the near-Earth atmosphere by the AAGW is an urgent problem. The purpose of this paper is to describe the mechanism for generating disturbances in the electric and magnetic fields in the near-Earth atmosphere under the action of AAGW and to estimate the amplitudes of these disturbances for various AAGW sources. Design/methodology/approach: The impact of a series of highenergy sources often results in the generation of synchronous disturbances in the acoustic and geoelectric (atmospheric) fields, when an approximate proportionality between the pressure amplitude and the amplitude of the disturbances in the atmospheric electric field is observed to occur. Based on the observational data and making use of the Maxwell equations, the theoretical estimates of the disturbances in the electric and magnetic fields have been obtained. Findings: Simplified expressions have been obtained for estimating the amplitudes of the electric and magnetic fields under the action of the AAGW generated by natural and manmade sources. The amplitudes of the electric and magnetic fields generated by the AAGW of natural and manmade origin, which travel in the near-Earth atmosphere, have been calculated. The amplitudes of the AAGW generated electric and magnetic fields are shown to be large enough to be detected with the existing electrometers and fluxmeter magnetometers. The magnitudes of the amplitudes of the electric and magnetic fields generated in the near-Earth atmosphere under the action of AAGW are large enough to trigger coupling between the subsystems in the Earth–atmosphere–ionosphere–magnetosphere system. Conclusions: The estimates and not numerous observations are in good agreement. Key words: acoustic and atmospheric gravity waves, near-Earth atmosphere, volume charge, atmospheric pressure disturbances, electric field, magnetic field

Assessment of IRI-2016 hmF2 model predictions with COSMIC observations over the African region

With significant advancement in the climatological nature of the International Reference Ionosphere (IRI) through a series of editions, the ionospheric community now focuses on possible improvements in the IRI Real-Time Assimilative Model (IRTAM) for describing the real-time weather conditions in the ionosphere. In line with the focuses of the global research community, the present study intends improving the critical ionospheric electron density height (hmF2) predictions in the latest version of the IRI model (IRI-2016) through a comparative analysis with the hmF2 derived from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric occultation profiles over the African region under various solar and geomagnetic conditions. As the existing operational ionosondes (only five in number) are not evenly distributed across the African region, the dense COSMIC soundings offer an excellent opportunity for assessing the IRI hmF2 model performance over the region. The study includes a comparative study of observed COSMIC hmF2 values with IRI-2016 predictions, almost covering the whole solar cycle (2007 to 2017). The comparison is based on statistical model validation metrics for datasets under various solar and geomagnetic conditions. The average performance of the IRI hmF2 model over Africa is similar during quiet geomagnetic conditions under both low and high solar activity periods. However, the average performance declines during disturbed geomagnetic conditions and for night-time values, while the best average performance is noticed in the daytime hmF2 predictions. The SHU-2015 model option in IRI-2016 manifests the least prediction error, best model efficiency, and correlation with the COSMIC hmF2 values, justifying the use of a large number of COSMIC profiles in the development of the SHU-2015 model. Finally, the study suggests the suitability of the SHU-2015 IRI hmF2 option over the African region when and where there are no or limited COSMIC profiles. Additionally, the research work suggests further improvements in the IRI hmF2 predictions, especially for night-time values over the African region.

Vertical plasma transport in the ionosphere over Irkutsk during St. Patrick’s Day geomagnetic storm: Observations and modeling

The St. Patrick’s Day storm being the strongest geomagnetic storm of Solar Cycle 24 caused strong changes in ionospheric and thermospheric dynamics. The paper presents a study of vertical plasma transport in the ionosphere during the St. Patrick’s Day storm with using both observations and modeling. The observations give the ionospheric peak height obtained with the chirp vertical sounding ionosonde and the neutral wind velocities obtained with the Fabry-Perot interferometer. The ionospheric peak height is an indicator of the total vertical plasma transport, while meridional wind and electromagnetic drift are the two main drivers of the vertical plasma transport. The Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere used in this study gives the total set of ionospheric and thermospheric parameters including F2-layer peak height, neutral wind velocities, electric field, and neutral composition. The model/data comparison allows us to obtain two main results. The first one is an estimation of the model prediction possibilities under storm conditions. The second result is an indirect assessment of the neutral wind and electric field contribution into the changes in the ionospheric peak height in the case of the St. Patrick’s Day geomagnetic storm.

On the link between the topside ionospheric effective scale height and the plasma ambipolar diffusion, theory and preliminary results

Over the years, an amount of models relying on effective parameters were implemented in the challenging issue of the topside ionosphere description. These models are based on different analytical functions, but all of them depend on a parameter called effective scale height, that is deduced from topside electron density measurements. As their names state, they are effective in reproducing the topside electron density profile only when applied to the analytical function used to derive them. Then, in principle, they do not have any physical meaning. It is the goal of this paper to mathematically link the effective scale height modeled through the Epstein layer to the vertical scale height theoretically deduced from the plasma ambipolar diffusion theory. Firstly, effective and theoretical scale heights are linked through a mathematical relation by showing that they tend to each other in the topside ionosphere. Secondly, their connection is preliminarily demonstrated by calculating effective scale height values from the entire COSMIC/FORMOSAT-3 radio occultation dataset. Thirdly, a possible connection between the vertical gradient of the topside scale height (as obtained by COSMIC/FORMOSAT-3 satellites) and the electron temperature (as obtained by ESA Swarm B satellite) is studied by highlighting corresponding similarities in the diurnal, seasonal, solar activity, and latitudinal variability.

Comparison of ionospheric reflection heights for LEMPs produced by lightning return strokes of different polarity

Apparent ionospheric reflection heights estimated using electric field waveforms of negative and positive cloud-to-ground lightning return strokes (-CGs and +CGs) that occurred during the same thunderstorms have been compared. We analyzed electric field waveforms of 101 -CGs and 74 +CGs that were recorded in August 2016 in Florida. For daytime conditions, the mean ionospheric reflection height for lightning electromagnetic pulses (LEMPs) produced by + CGs is larger than that for LEMPs produced by -CGs for either first or subsequent strokes, although the difference is statistically significant only for subsequent strokes. For nighttime conditions, the trend is the same, but the sample sizes are too small to draw meaningful conclusions. For daytime conditions, the mean ionospheric reflection height for subsequent strokes in -CGs is smaller than that for first strokes, while for + CGs the mean reflection heights for first and subsequent strokes are essentially the same. This disparity is related to the fact that subsequent strokes in –CGs usually develop in the channel of the first stroke, while subsequent strokes in +CGs usually form new terminations on ground and, hence, are similar to first strokes. In our dataset, NLDN-reported peak currents for + CGs tend to be higher than for –CGs for both daytime and nighttime conditions and for either first or subsequent strokes.

ESTIMATED RELATIONS BETWEEN THE MAIN THERMOSPHERIC NEUTRAL COMPONENTS AT IONOSPHERIC F1-LAYER HEIGHTSABOVE IRKUTSK IN 2014–2017

We have estimated seasonal variations in the main thermospheric gas components [O]/[N₂] and [O₂]/[O] for the period 2014–2017. We have used the well-known authoring technique and electron density measurements made with the Irkutsk digisonde (52° N, 104° E) at ionospheric F1-layer heights under different geomagnetic activity conditions. We have found that at these heights during geomagnetic disturbances in all seasons the molecular component of the neutral composition of the thermosphere increases and the atomic component decreases. In comparison with 2014, [O₂]/[O] values increased by 2017 under quiet and disturbed geomagnetic conditions: up to 30 % and 20 % in summer and spring respectively; up to 10 % in winter and autumn. The [O]/[N₂] ratio decreased by an average of 15 % by 2017. The assumption has been confirmed that in summer under quiet geomagnetic conditions the relative molecular oxygen content [O₂]/[O] increases with decreasing solar activity.

Оценка отношений основных нейтральных составляющих термосферы в 2014–2017 гг. на высотах слоя F1 над Иркутском

We have estimated seasonal variations in the main thermospheric gas components [O]/[N₂] and [O₂]/[O] for the period 2014–2017. We have used the well-known authoring technique and electron density measurements made with the Irkutsk digisonde (52° N, 104° E) at ionospheric F1-layer heights under different geomagnetic activity conditions. We have found that at these heights during geomagnetic disturbances in all seasons the molecular component of the neutral composition of the thermosphere increases and the atomic component decreases. In comparison with 2014, [O₂]/[O] values increased by 2017 under quiet and disturbed geomagnetic conditions: up to 30 % and 20 % in summer and spring respectively; up to 10 % in winter and autumn. The [O]/[N₂] ratio decreased by an average of 15 % by 2017. The assumption has been confirmed that in summer under quiet geomagnetic conditions the relative molecular oxygen content [O₂]/[O] increases with decreasing solar activity.

Estimation of nighttime ionospheric D-region parameters using tweek atmospherics observed for the first time in the North African region

Dispersive wave modes called tweek atmospherics produced by lightning strokes were observed using Stanford University designed AWESOME VLF receiver system installed at the University of Tunis El Manar, Tunisia (Geog. lat. 36.50° N; lon. 10.08° E). About 84 tweek atmospherics were analyzed during geomagnetically quiet days to provide important clues for estimating the effective ionospheric reflection height and electron density using the cut-off frequency of first modes. Variations of nighttime Wait ionospheric parameters (h′ and β) have been studied using tweeks observed for the first time at the low latitude station in the North African region. The distance of the lightning located in a range of 500–5000 km and the accuracy obtained by single-site technique had been estimated by a comparison with independent data from the World-Wide Lightning Location Network (WWLLN).

Target State and Markovian Jump Ionospheric Height Bias Estimation for OTHR Tracking Systems

Ionospheric heights provided by ionosondes are vital for over-the-horizon radar (OTHR) target tracking. However, biases contained in the provided ionospheric heights definitely cause degradation of the tracking performance. This paper is concerned with the joint estimation problem of the target state and the ionospheric height bias for OTHR target tracking subject to multipath and cluttered measurements. A Markovian jump ionospheric height bias model is presented by simultaneously considering the intermittent and abrupt ionosphere changes. Meanwhile, a set of stochastic variables are adopted to depict association uncertainties among measurements, clutters, and propagation modes so that association is embedded in the resultant measurement model with random coefficients. Through such modeling transformation from association uncertainties to parameter randomness, the coupling processing of data association and state estimate is equivalent to pure state estimate subject to stochastic parameters. Furthermore, an optimal linear joint estimator containing causality constraints is developed in the minimum mean-squared error sense, and further extended to the case of nonlinear measurement model via iterative optimization. A target tracking example with four resolvable propagation modes illustrates the effectiveness of the proposed estimation scheme.

Height Dependency of Solar Eclipse Effects: The Ionospheric Perspective

AbstractA reliable interpretation of solar eclipse effects on the geospace environment, and on the ionosphere in particular, necessitates a careful consideration of the so‐called eclipse geometry. A solar eclipse is a relatively rare astronomical phenomenon, which geometry is rather complex, specific for each event, and fast changing in time. The standard, most popular way to look at the eclipse geometry is via the two‐dimensional representation (map) of the solar obscuration on the Earth's surface, in which the path of eclipse totality is drawn together with isolines of the gradually‐decreasing eclipse magnitude farther away from this path. Such “surface maps” are widely used to readily explain some of the solar eclipse effects including, for example, the well‐known decrease in total ionization (due to the substantial decrease in solar irradiation), usually presented by the popular and easy to understand ionospheric characteristic of total electron content (TEC). However, many other effects, especially those taking place at higher altitudes, cannot be explained in this fashion. Instead, a more detailed description of the umbra (and penumbra), would be required. This paper addresses the issue of eclipse geometry effects on various ionospheric observations carried out during the total solar eclipse of 21 August 2017. In particular, GPS‐based TEC measurements were analyzed and eclipse effects on the ionosphere are interpreted with respect to the actual eclipse geometry at ionospheric heights. Whenever possible, a comparison was made with results from other eclipse events.

Statistics of ionospheric responses to Southeast Asia’s typhoons during 2006–2018 using the rate of change in the TEC index

When the ionosphere is strongly disturbed, the performances of satellite navigation and positioning systems as well as various radio communication systems are reduced due to the electronic density gradient and ionospheric irregularities. However, the characteristics and coupling mechanism of ionospheric disturbances caused by meteorological activities in the lower atmosphere are still unclear. Therefore, as one of the most severe surface weather changes, it is of great practical significance to study the influence of typhoons on the ionosphere. In this paper, the ionospheric irregularities during 20 typhoons landing in Taiwan, Guangdong Province and the Philippines during the quiet solar and geomagnetic activities from 2006 to 2018 were analyzed by using the rate of change in the total electron content (ROTI). Through a statistical analysis of 20 typhoons, it was found that there are ionospheric irregularities during 15 typhoons. There was a certain correlation between ionospheric disturbances and the typhoons. Both typhoons MANGKHUT and HAIMA landed in Guangdong Province, but ROTI > 0.5 TEC·min-1 was detected only when typhoon HAIMA made landfall in Guangdong. This phenomenon can be explained by the influence of terrain on the acoustic gravity waves. The HAIMA typhoon passed through Lianhua Mountain (altitude: 1336 m). When the typhoon landed in higher terrain, due to the resistance effect of the high terrain, the high rate of decline in the air creates an ideal condition for the development of the acoustic gravity waves. During the impact of the typhoon, the acoustic gravity waves can spread to the ionosphere height and have an impact on the ionosphere.

Far Ultraviolet Remote Sensing of the Nighttime Ionosphere Using the OI 130.4‐nm Emission

AbstractRoutine monitoring and forecasting of the ionosphere is becoming imperative for our society due to the rapid increase of our reliance on space‐based technologies. In the last two decades, satellite remote sensing of the OI 135.6‐nm airglow emission has been used as a primary means for inferring the nighttime ionosphere on a global scale. By contrast, the OI 130.4‐nm emission, another prominent airglow feature, has long been suggested to be possibly useful for ionospheric remote sensing but has rarely been studied in the literature, partially due to the complexity of the radiative transfer effects involved in the interpretation of this emission. In this study, we explore the use of OI 130.4‐nm emission for nighttime ionospheric remote sensing by analyzing the data observed by the Global Ultraviolet Imager (GUVI) aboard NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission using a newly developed radiative transfer model. We demonstrate through data analysis and theoretical investigations that limb observations of the OI 130.4‐nm emission can be used to complement the OI 135.6‐nm emission for a better characterization of the spatial variation of nighttime ionosphere and that nadir observations of the OI 130.4‐nm emission can be used to estimate the total electron content (TEC) and the peak density (NmF2) in smoothly varying ionospheric regions more accurately than the OI 135.6‐nm emission. We further propose techniques for estimating the ionospheric peak height (hmF2) using nadir observations of the two emissions. Our results can provide useful information for future ionospheric remote sensing missions.

On the Accuracy of Ray-Theory Methods to Determine the Altitudes of Intracloud Electric Discharges and Ionospheric Reflections: Application to Narrow Bipolar Events.

Narrow bipolar events (NBEs) (also called narrow bipolar pulses [NBPs] or compact intracloud discharges [CIDs]) are energetic intracloud discharges characterized by narrow bipolar electromagnetic waveforms identified from ground‐based very low frequency (VLF)/low‐frequency (LF) observations. The simplified ray‐theory method proposed by Smith et al. (1999, https://doi.org/10.1029/1998JD200045; 2004, https://doi.org/10.1029/2002RS002790) is widely used to infer the altitude of intracloud lightning and the effective (or virtual) reflection height of the ionosphere from VLF/LF signals. However, due to the large amount of high‐frequency components in NBEs, the propagation effect of the electromagnetic fields for NBEs at large distance depends nontrivially on the geometry and the effective conductivity of the Earth‐ionosphere waveguide (EIWG). In this study, we investigate the propagation of NBEs by using a full‐wave Finite‐Difference Time‐Domain (FDTD) approach. The simulated results are compared with ground‐based measurements at different distances in Southern China, and we assess the accuracy of the simplified ray‐theory method in estimating the altitude of the NBE source and the effective reflection height of the ionosphere. It is noted that the evaluated NBE altitudes have a slight difference of about ±1 km when compared with the full‐wave FDTD results, while the evaluated ionospheric reflection heights are found to be bigger than those obtained from FDTD model by about 5 km.

Advanced Machine Learning Optimized by The Genetic Algorithm in Ionospheric Models Using Long-Term Multi-Instrument Observations

The ionospheric delay is of paramount importance to radio communication, satellite navigation and positioning. It is necessary to predict high-accuracy ionospheric peak parameters for single frequency receivers. In this study, the state-of-the-art artificial neural network (ANN) technique optimized by the genetic algorithm is used to develop global ionospheric models for predicting foF2 and hmF2. The models are based on long-term multiple measurements including ionospheric peak frequency model (GIPFM) and global ionospheric peak height model (GIPHM). Predictions of the GIPFM and GIPHM are compared with the International Reference Ionosphere (IRI) model in 2009 and 2013 respectively. This comparison shows that the root-mean-square errors (RMSEs) of GIPFM are 0.82 MHz and 0.71 MHz in 2013 and 2009, respectively. This result is about 20%–35% lower than that of IRI. Additionally, the corresponding hmF2 median errors of GIPHM are 20% to 30% smaller than that of IRI. Furthermore, the ANN models present a good capability to capture the global or regional ionospheric spatial-temporal characteristics, e.g., the equatorial ionization anomaly and Weddell Sea anomaly. The study shows that the ANN-based model has a better agreement to reference value than the IRI model, not only along the Greenwich meridian, but also on a global scale. The approach proposed in this study has the potential to be a new three-dimensional electron density model combined with the inclusion of the upcoming Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC-2) data.