F2 Peak Research Articles

Electron Density Profile Derived From Ionogram Using Ray Tracing Inversion Method

AbstractThe ionosonde is widely used for detecting electron density profiles below the F2 peak altitude. Extracting precise profiles from ionograms is crucial, as it serves as a significant data source for ionospheric studies and applications. In our study, we utilized the ray tracing profile inversion method (RTPI) to derive more realistic electron density profiles from the ionosonde observations. By comparing the electron density profiles inverted by RTPI method with and without geomagnetic field against the profiles observed by Incoherent Scatter Radar (ISR) plasma lines, we validated the high precision of the RTPI with magnetic field effect method. The results showed that the average height difference and average peak height difference between profiles inverted by RTPI and plasma line observations are less than 10 and 5 km, respectively. Additionally, we quantified the errors associated with the geomagnetic field effect. It would cause an ∼8–10 km overestimation in true height and a ∼10%–15% underestimation in electron density if the geomagnetic field effect is not considered. These errors induced by the magnetic field accumulate with the frequency of the radio waves. Moreover, we conducted a comparative analysis of simulated echo traces using profiles with different E‐layer shapes. It was demonstrated that the key parameters of the bottom structure have a significant impact on ionogram retrieval, while the E‐layer shape has negligible influence on inversion. Furthermore, we analyzed echo traces simulated using ray tracing with and without collision. The collision effect has weak effect on the delay of the radio waves.

Effect of The Density and Height of F2 layer on Ground-Based Observation of Jupiter's Radio Signal

The density and height of the ionospheric F2 layer affect the observation of Jupiter's radio signals. The study aims to determine an approximate observation threshold from the values of the F2 peak density and the height of the F2 peak. The Florida and Lamy stations in the USA were selected. Utilizing actual observation data of Jupiter's radio signals from the Radio JOVE Data Archive for the years 2014-2015. The Radio Jove Pro software was employed to predict radio emissions from Jupiter. Ionospheric data were sourced from the International Reference Ionosphere (IRI) website. The primary focus of this study is to examine the role of the ionosphere in blocking the radio signals emanating from Jupiter. It was found that 49% and 31% (for the Florida and Lamy stations, respectively) of the predicted radio emission events from Jupiter were not observed. The likelihood of observation is higher after sunset and depends on Jupiter's elevation above the horizon relative to the observer. The F2 peak density during nighttime and throughout the year ranged from approximately 1011 to 1012 m-3 at altitudes of about 260-360 km. 89% and 98% (for the Florida and Lamy stations, respectively) of the observations occurred when the F2 peak density was less than around 6×1011 m-3. In contrast, 80% and 56% (for the Florida and Lamy stations, respectively) of the cases of non-observation occurred when the F2 peak density was greater than approximately 6×1011 m-3. As for The height of the F2 peak (hmF2), 85% and 93% of the observations occurred when the hmF2 was greater than about 300 km for the Florida and Lamy stations, respectively. The probability of observation is significantly influenced by the relationship between the electron density and its corresponding altitude.

Effect of The Density and Height of F2 layer on Ground-Based Observation of Jupiter's Radio Signal

The density and height of the ionospheric F2 layer affect the observation of Jupiter's radio signals. The study aims to determine an approximate observation threshold from the values of the F2 peak density and the height of the F2 peak. The Florida and Lamy stations in the USA were selected. Utilizing actual observation data of Jupiter's radio signals from the Radio JOVE Data Archive for the years 2014-2015. The Radio Jove Pro software was employed to predict radio emissions from Jupiter. Ionospheric data were sourced from the International Reference Ionosphere (IRI) website. The primary focus of this study is to examine the role of the ionosphere in blocking the radio signals emanating from Jupiter. It was found that 49% and 31% (for the Florida and Lamy stations, respectively) of the predicted radio emission events from Jupiter were not observed. The likelihood of observation is higher after sunset and depends on Jupiter's elevation above the horizon relative to the observer. The F2 peak density during nighttime and throughout the year ranged from approximately 1011 to 1012 m-3 at altitudes of about 260-360 km. 89% and 98% (for the Florida and Lamy stations, respectively) of the observations occurred when the F2 peak density was less than around 6×1011 m-3. In contrast, 80% and 56% (for the Florida and Lamy stations, respectively) of the cases of non-observation occurred when the F2 peak density was greater than approximately 6×1011 m-3. As for The height of the F2 peak (hmF2), 85% and 93% of the observations occurred when the hmF2 was greater than about 300 km for the Florida and Lamy stations, respectively. The probability of observation is significantly influenced by the relationship between the electron density and its corresponding altitude.

The effect of detoxification on acoustic features of Mandarin speech in male heroin users.

This study aims to investigate the effect of detoxification on acoustic features of Mandarin speech. Speech recordings were collected from 66 male abstinent heroin users with different durations of drug detoxification, specifically early abstinent users with a detoxification duration of less than 2 years, sustained abstinent users with 2 years of detoxification, and long-term abstinent users with a detoxification duration of more than 2 years. The results of the acoustic analyses showed that early abstinent users exhibited lower loudness, relative energies of F1, F2, and F3, higher H1-A3, and fewer loudness peaks per second, as well as a longer average duration of unvoiced segments, compared to the sustained and long-term abstinent users. The findings suggest that detoxification may lead to a rehabilitation process in the speech production of abstinent heroin users (e.g., less vocal hoarseness). This study not only provides valuable insights into the effect of detoxification on speech production but also provides a theoretical basis for the speech rehabilitation and detoxification treatment of heroin users.

Empirical Models of foF2 and hmF2 Reconstituted by Global Ionosonde and Reanalysis Data and COSMIC Observations

AbstractThe F2‐peak plasma frequency (foF2) and the height of the F2 peak (hmF2) are two of the most important parameters for any ionospheric model, as well as radio propagation studies and applications. In this study, we have developed empirical models to capture the most significant variations of foF2 and hmF2. The derived empirical models (referred to as the USTC models within this study) are specified through global ionosonde and reanalysis data based on the International Reference Ionosphere (IRI) Consultative Committee on International Radio (CCIR) method and Constellation Observindg System for Meteorology, Ionosphere, and Climate (COSMIC) observations based on the empirical orthogonal function analysis, respectively. The USTC models are validated against the IRI CCIR model prediction. The comparison results revealed that the empirical foF2 model performs better in capturing the foF2 variations than the IRI CCIR model, which can overcome the underestimation of the IRI CCIR model at low latitudes. Although the IRI CCIR model overestimation at middle latitudes is addressed by the empirical hmF2 model, the visible differences between the model predictions and ionosonde observations still exist at low latitudes, which could be attributed to the significant difference between COSMIC and ionosonde hmF2 measures.

One‐Dimensional Variational Ionospheric Retrieval Using Radio Occultation Bending Angles: 2. Validation

AbstractCulverwell et al. (2023, https://doi.org/10.1029/2023SW003572) described a new one‐dimensional variational (1D‐Var) retrieval approach for ionospheric GNSS radio occultation (GNSS‐RO) measurements. The approach maps a one‐dimensional ionospheric electron density profile, modeled with multiple “Vary‐Chap” layers, to bending angle space. This paper improves the computational performance of the 1D‐Var retrieval using an improved background model and validates the approach by comparing with the COSMIC‐2 profile retrievals, based on an Abel Transform inversion, and co‐located (within 200 km) ionosonde observations using all suitable data from 2020. A three or four layer Vary‐Chap in the 1D‐Var retrieval shows improved performance compared to COSMIC‐2 retrievals in terms of percentage error for the F2 peak parameters (NmF2 and hmF2). Furthermore, skill in retrieval (compared to COSMIC‐2 profiles) throughout the bottomside (∼90–300 km) has been demonstrated. With a single Vary‐Chap layer the performance is similar, but this improves by approximately 40% when using four‐layers.

Response of the mid-latitude ionosphere to the solar eclipse on 25 October 2022: Results of F2–layer vertical sounding

The results of observations of the critical frequency (foF2), ionospheric F2 peak electron density (NmF2) and peak height (hmF2) of the ionosphere over Kharkiv (Ukraine, 49.6° N, 36.3° E) during a partial solar eclipse (SE) on 25 October 2022 are presented. The data analysis showed a clear effect in the variations of foF2 (and, accordingly, NmF2): during the SE, foF2 decreased, and 5 min after the time of maximum eclipse, began to increase to its usual level. From the beginning of the SE, hmF2 decreased from 285 to 255 km, and then it began to grow with a maximum near the time of maximum obscuration. To study longitudinal effects and clarify contributions of different factors to the observed temporal variations of the ionospheric parameters, the results of observations of the ionosphere over Kharkiv were compared with the data obtained by the ionosonde in Pruhonice (Czech Republic, 50.0° N, 14.6° E). The NmF2 electron density decreased due to SE by the factor of 1.46 in Kharkiv, in contrast to 1.33 times in Pruhonice. Comparison of data in universal time (UT) showed a coincidence in the nature and time of fluctuations in both foF2 and hmF2 observed in Kharkiv and Pruhonice on 25 October. Variations in hmF2 caused by SE in Kharkiv and Pruhonice were identical. The SE was accompanied by a plasma flow from the plasmasphere to the ionosphere. The flux density change was about –2 × 1013 m–2s−1 and about 0 for Kharkiv and Pruhonice, respectively. The obtained value of the vertical velocity (tens of meters per second) for Kharkiv is the typical velocity for the mid-latitude F2 layer of the ionosphere. It was confirmed that in addition to typical SE effects, results of observations of the ionosphere over Kharkiv on October 25, 2022 had individual features.

Comparison of observed hmF2 and the IRI-2020 model for six stations in East Asia during the declining phase of the solar cycle 24

The height of the F2 peak electron density (hmF2) is a critical parameter in ionospheric electrodynamics and high-frequency wireless communication research. This study analyzed and compared data from six stations to validate the long-term predictive capabilities of three forecasting modes of the IRI-2020 for hmF2 in the East Asia region. Specifically, the three models of IRI-2020 for the hmF2 prediction are the BSE model proposed in 1955, the AMTB model presented in 2013, and the SHU model proposed in 2015. The experimental results indicate that the SHU model exhibits the most minor prediction error and the highest prediction accuracy for East Asia, demonstrating significant advantages over the other models (BSE and AMTB). Specifically, compared to the BSE model and the AMTB model, the SHU model reduces the mean absolute error by 2.66 km and 8.11 km, the root mean square error by 2.27 km and 8.62 km, and the relative root mean square error by 1.34 % and 3.84 %, respectively. The statistical results of the experimental also show that the predictive power of the AMTB model is more affected by solar activity than that of the BSE model and the SHU model. For the low-latitude region (SANYA), the BSE model exhibits the best predictive capability. In terms of season, the three models of IRI overestimated hmF2 in most cases.

Multi‐Instruments Observation of Ionospheric‐Thermospheric Dynamic Coupling Over Mohe (53.5°N, 122.3°E) During the April 2023 Geomagnetic Storm

AbstractThe state and variations of the Ionosphere‐Thermosphere (I‐T) system are strongly influenced by dynamical processes, with these effects being amplified during intense space environment disturbances such as geomagnetic storms, producing multi‐scale disturbance features in the I‐T system. The redistribution of energy and momentum through the dynamical processes is currently not well understood. Unfortunately, the dearth of thermospheric observations has yielded limited studies capable of monitoring and analyzing the I‐T dynamical coupling during storms using co‐located measurements. This work examines the responses of the I‐T system during the April 2023 geomagnetic storm based on high‐resolution continuous I‐T system observations at Mohe observatory, a middle latitude station. Both large‐scale features and short‐period oscillations were identified in multiple key parameters of the I‐T system. Similar disturbed patterns in thermospheric winds occurred during the main and recovery phases of the geomagnetic storm. However, the oscillation features in many parameters of the I‐T system are only observed during the main phase. The results of concurrent I‐T system observations unveil the oscillation features of thermospheric winds, temperatures, the ionospheric F2 peak height, electron density, and total electron content. These findings reveal the important influence of wind divergence on thermospheric temperature disturbances and its modulatory effect on ionospheric disturbances.

Large-scale traveling ionospheric disturbances over central and eastern Europe during moderate magnetic storm period on 22–24 September 2020

We present the results of ground based remote sensing observations of large-scale traveling ionospheric disturbances (LSTIDs) occurring during the moderate magnetic storm evolution (22–24 September 2020) over central and eastern Europe. Three ionosondes located in Juliusruh, Pru˚honice and near Kharkiv, and the Kharkiv incoherent scatter radar were employed to study temporal and spatial LSTID signatures in ionospheric F2 peak density and height and electron density variations at the heights of 100–300 km. Two types of LSTIDs are detected, which are originated during enhancement in auroral activity (2 events) and local sunrise terminator passage (3 events) from the ionosonde data. The magnetic storm-related LSTIDs exhibit equatorward propagation with the horizontal phase velocities of 546 m/s and 576 m/s, similar dominant periods of 135–150 min and 165–180 min over all three sites and a longitudinal dependence in fractional (relative) amplitudes of electron density perturbation. The solar terminator induced LSTIDs demonstrate the variety in both relative amplitudes and dominant periods over different locations. They have a westward apparent horizontal phase velocities of 288–345 m/s, which are close to the solar terminator velocity at ionospheric heights. Employment of incoherent scatter data enabled the detection of additional LSTIDs over Ukraine with the periods in a broader range of 41–168 min, an establishment of phase and onset differences for the oscillations in the ionospheric F2 peak electron density and height.

3-D Ionospheric Electron Density Variations during the 2017 Great American Solar Eclipse: A Revisit

This paper studies the three-dimensional (3-D) ionospheric electron density variation over the continental US and adjacent regions during the August 2017 Great American Solar Eclipse event, using Millstone Hill incoherent scatter radar observations, ionosonde data, the Swarm satellite measurements, and a new TEC-based ionospheric data assimilation system (TIDAS). The TIDAS data assimilation system can reconstruct a 3-D electron density distribution over continental US and adjacent regions, with a spatial–temporal resolution of 1∘× 1∘ in latitude and longitude, 20 km in altitude, and 5 min in universal time. The combination of multi-instrumental observations and the high-resolution TIDAS data assimilation products can well represent the dynamic 3-D ionospheric electron density response to the solar eclipse, providing important altitude information and fine-scale details. Results show that the eclipse-induced ionospheric electron density depletion can exceed 50% around the F2-layer peak height between 200 and 300 km. The recovery of electron density following the maximum depletion exhibits an altitude-dependent feature, with lower altitudes exhibiting a faster recovery than the F2 peak region and above. The recovery feature was also characterized by a post-eclipse electron density enhancement of 15–30%, which is particularly prominent in the topside ionosphere at altitudes above 300 km.

Optimal Estimation Inversion of Ionospheric Electron Density from GNSS-POD Limb Measurements: Part II-Validation and Comparison Using NmF2 and hmF2

A growing number of SmallSat/CubeSat constellations with high-rate (50–100 Hz) global navigation satellite system radio occultations (GNSS-RO) as well as low-rate (1 Hz) precise orbit determination (GNSS-POD) limb-viewing capabilities provide unprecedented spatial and temporal sampling rates for ionospheric studies. In the F-region electron density (Ne) retrieval process, instead of the conventional onion-peeling (OP) inversion, an optimal estimation (OE) inversion technique was recently developed using total electron content measurements acquired by GNSS-POD link. The new technique is applied to data acquired from the COSMIC-1, COSMIC-2, and Spire constellations. Although both OE and OP techniques use the Abel weighting function in Ne inversion, OE significantly differs in its performance, especially in the lower F- and E-regions. In this work, we evaluate and compare newly derived data sets using F2 peak properties with other space-based and ground-based observations. We determine the F2 peak Ne (NmF2) and its altitude (hmF2), and compare them with the OP-retrieved values. Good agreement is observed between the two techniques for both NmF2 and hmF2. In addition, we also utilize autoscaled F2 peak measurements from a number of worldwide Digisonde stations (∼30). The diurnal sensitivity and latitudinal variability of the F2 peak between the two techniques are carefully studied at these locations. Good agreement is observed between OE-retrieved NmF2 and Digisonde-measured NmF2. However, significant differences appear between OE-retrieved hmF2 and Digisonde-measured hmF2. During the daytime, Digisonde-measured hmF2 remains ∼25–45 km below the OE-retrieved hmF2, especially at mid and high latitudes. We also incorporate F-region Ne measurements from two incoherent scatter radar observations at high latitudes, located in the North American (Millstone Hill) and European (EISCAT at Tromso) sectors. The radar measurements show good agreement with OE-retrieved values. Although there are several possible sources of error in the ionogram-derived Ne profiles, our further analysis on F1 and F2 layers indicates that the low Digisonde hmF2 is caused by the autoscaled method, which tends to detect a height systematically below the F2 peak when the F1 layer is present.

Dynamic range and dose linearity of the radiophotoluminescence intensity in lithium fluoride crystals irradiated with 2.3 and 26 MeV protons

Irradiation of lithium fluoride with protons causes the formation of electronic defects, known as colour centres, in the crystal lattice. Two stable defects among them, the F2 and F3+ aggregate ones, under blue light simultaneous excitation show broad photoluminescence in the red and green visible spectral ranges, respectively, their peculiar characteristics being well known for applications in optically-pumped tuneable lasers, broad-band miniaturized light-emitting photonic devices and passive radiation imaging detectors. Recently, exploitation of their radiophotoluminescence has been successfully proposed for proton-beam advanced diagnostics and dosimetry, even at low dose values typical of radiotherapy. In the present study, lithium fluoride crystals were irradiated with 2.3 MeV protons in the dose range from ∼104 to ∼107 Gy and their dynamic range, that is the capability of detecting the widest possible range of radiophotoluminescence intensity emitted by the colour centres, was found to be 114 dB at the F2 peak emission wavelength of 675 nm under continuous-wave laser excitation at 445 nm. Moreover, after including in the analysis a set of lithium fluoride crystals irradiated with 26.1 MeV protons in the dose range from 0.5 to 48 Gy at a much lower dose-rate, it was found that the radiophotoluminescence intensity of the F2 colour centres shows a linear dependence with dose from 0.5 to ∼2 × 105 Gy.

Are There One or More Geophysical Coupling Mechanisms before Earthquakes? The Case Study of Lushan (China) 2013

Several possible lithosphere–atmosphere–ionosphere coupling mechanisms before earthquake occurrence are presented in the literature. They are described by several models with different interaction channels (e.g., electromagnetic, mechanics, chemical, thermal), sometimes in conflict with each other. In this paper, we search for anomalies six months before the Lushan (China) 2013 earthquake in the three geo-layers looking for a possible view of the couplings and testing if one or another is more reliable to describe the observations. The Lushan earthquake occurred in China’s Sichuan province on 20 April 2013, with a magnitude of Mw = 6.7. Despite the moderate magnitude of the event, it caused concern because its source was localized on the southwest side of the same fault that produced the catastrophic Wenchuan event in 2008. This paper applies a geophysical multi-layer approach to search for possible pre-earthquake anomalies in the lithosphere, atmosphere, and ionosphere. In detail, six main increases in the accumulated seismic stress were depicted. Anomalous geomagnetic pulsations were recorded in the Chengdu observatory, sometimes following the increased stress. Atmosphere status and composition were found to be anomalous in several periods before the earthquake, and, spatially, the anomalies seem to appear firstly far from the upcoming earthquakes and later approaching the Longmenshan fault where the Lushan earthquakes nucleated. The Formosat-3 data identified interesting anomalies in the altitude or electron content of the ionospheric F2 peak in correspondence with seismic and atmospheric anomalies 130 days before the earthquake. In addition, the total electron content showed high anomalous values from 12 to 6 days before the earthquake. We compared the anomalies and tried to explain their correspondences in different geo-layers by the lithosphere–atmosphere–ionosphere coupling models. In particular, we identified three possible couplings with different mechanisms: a first, about 130 days before the earthquake, with a fast (order of one day) propagation delay; a second, about 40 days before the earthquake occurrence, with a propagation delay of few days and a third from 2.5 weeks until one week before the event. Such evidence suggests that the geo-layers could interact with different channels (pure electromagnetic or a chain of physical-chemical processes) with specific propagation delays. Such results support the understanding of the preparation for medium and large earthquakes globally, which is necessary (although not sufficient) knowledge in order to mitigate their impact on human life.

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.

3‐D Regional Imaging of Ionosphere Over Africa Through Assimilating Satellite and Ground‐Based Data

AbstractIn this study, the first high‐resolution regional ionospheric model over Africa and adjacent areas (−40–40°N latitude, 30°W–60°E longitude, and 80–1,400 km in altitude) is constructed by assimilating ground‐based slant total electron content (STEC) from 40 GPS (Global Positioning System) receiver stations and space‐based NmF2 (ionospheric F2 peak density) data from C2 (Constellation Observing System for Meteorology, Ionosphere, and Climate‐2) into the International Reference Ionosphere (IRI‐2016) model. An Ionospheric Data Assimilation Four‐Dimensional (IDA4D) technique was used to estimate electron densities as high as 1.5° 3° in latitude and longitude, 10 km in altitude in the E and F regions, and 15 min in universal time. Two experiments were run for the following data sets: (a) GPS‐STECs only and (b) GPS‐STECs and NmF2s from C2 during geomagnetically quiet (6–11 May 2021) and storm periods (12–14 May 2021). The IDA4D assimilation results are validated using independent C2 control group, ionosonde, and JASON‐3 observations. Results for the storm period show that experiment 2 reduces the average root‐mean‐square error (RMSE) of NmF2, foF2, and VTEC by 34%, 31%, and 34%, respectively, and increases the associated correlations by 10%, 14%, and 2% over IRI, respectively. Using IDA4D, we observed enhancement of the northern crest equatorial ionization anomaly in the late evening that was caused by upward and northward plasma transport.

Statistical validation of ionospheric electron density profiles retrievals from GOES geosynchronous satellites

In this paper, we discuss a novel retrieval of ionospheric electron density profiles using the Radio Occultation (RO) technique applied to measurements captured by the Global Positioning System (GPS) receivers onboard two Geostationary Operational Environmental Satellites (GOES). The GOES satellites operate at ~35,800 km altitude and are primarily weather satellites that operationally contribute continuous remote-sensing data for real-time weather forecasting, as well as near-Earth environment monitoring and Sun observations. The GPS receivers onboard GOES-16 and GOES-17 satellites can track GPS signals propagated through the Earth’s atmosphere, and although the receivers are primarily designed for navigation and station-keeping maneuvers, these GPS measurements that traverse the Earth’s atmosphere can be used to retrieve the ionospheric electron density profiles. This process poses a range of technical challenges. GOES RO links are different from the traditional low Earth orbit (LEO) RO geometry since the receiver is located in an orbit that is higher in altitude than the GPS constellation of transmitters. Additionally, the GPS receivers onboard GOES satellites provide only single-frequency GPS L1 observations and have clocks much less stable than those typically used for RO measurements. The geographical distribution of the retrieved GEO-based RO profiles was found to be uniquely constrained and repeatable based on the relative geostationary fixed positions in the Earth-Centered Earth Fixed reference frame with respect to the GPS constellation orbiting at lower altitude, and significantly different from the coverage patterns of LEO-based RO missions. We demonstrate the successful application of the proposed RO profiling technique with a statistically significant set of GPS observations from GOES-16 and GOES-17 satellites over several years of data collection. This enabled us to retrieve more than 10,000 ionospheric electron density profiles with a maximum altitude of up to 1000–2000 km, much higher than any existing LEO-based RO mission. We demonstrate good performance of GEO-based RO measurements for properly specifying the vertical distribution of ionospheric plasma density by comparing the profiles dataset from the GOES RO experiment with independent reference observations – ground-based ionosondes and LEO-based RO missions, as well as model simulation results provided by the empirical International Reference Ionosphere model. Over multiple years of observations, statistical analysis of discrepancies between the ionospheric F2 layer peak parameters (peak density and height) derived from geosynchronous GOES observations and reference measurements was conducted. This analysis reveals a very good agreement between GOES RO electron density profiles and independent types of measurements in both the F2 peak and the profile shape.

Ionospheric Variability over the Brazilian Equatorial Region during the Minima Solar Cycles 1996 and 2009: Comparison between Observational Data and the IRI Model

The behavior of the Brazilian equatorial ionosphere during the solar minimum periods, 1996 and 2009, which cover the solar cycles 22/23 and 23/24, respectively, is investigated. For this, the F2 layer critical frequency (foF2) and peak height (hmF2) registered by a Digisonde operated at São Luis (2.33° S; 44° W) are carefully analyzed. The results show that the seasonal mean values of the foF2 and the hmF2 in the equinoxes and winter during 2009 were lower than in 1996. In the summer, an anomalous response to solar variability was observed. In this case, the hmF2 in 2009 is higher than in 1996 during a specific daytime interval. Besides that, it was verified that the prereversal enhancement of the zonal electric field (PRE) during the equinoxes in 2009 occurred a few minutes earlier than in 1996. Additionally, a Fast Fourier Transform (FFT) analysis was used to investigate the impacts of solar atmospheric tides (amplitude, diurnal, semidiurnal, and terdiurnal modes) on foF2 and hmF2 parameters with respect to its seasonality. Significant differences were observed between their values during the two minima, mainly in the amplitude of hmF2, which was higher in 1996 than in 2009 for all days analyzed. Moreover, the seasonality in the diurnal and semidiurnal modes for both periods presented an annual variability, while the terdiurnal mode exhibited annual and semiannual components. The results are compared with the International Reference Ionosphere (IRI) model, and the main differences between the observation and the model results are discussed in this work.

Driver of the Positive Ionospheric Storm over the South American Sector during 4 November 2021 Geomagnetic Storm

During geomagnetic storms, ionospheric storms can be driven by several mechanisms. Observations performed using ground- and space-based instruments were used to reveal the driver of the positive ionospheric storm over the South American sector during the 4 November 2021 geomagnetic storm. The positive storm appeared from 10:30 UT to 18:00 UT and covered the region from 40°S to 20°N. The maximum magnitudes of TEC (Total Electron Content) enhancement and relative TEC enhancement were about 20 TECU and 100%, respectively. Defense Meteorological Satellite Program (DMSP) also observed a significant electron density increase over South America and the eastern Pacific Ocean. In the meantime, about 50% ∑O/N2 enhancement was observed by the Global-scale Observations of the Limb and Disk (GOLD) satellite at low latitudes. Ionosonde observations (AS00Q and CAJ2M) registered an ~80 km uplift in F2 peak height (HmF2) and a prominent F2 peak electron density (NmF2) increase ~3 h after the uplift. A prominent enhancement in the cross-polar cap potential (CPCP) in the southern hemisphere was also observed by Super Dual Auroral Radar Network (SuperDARN) one hour earlier than the HmF2 uplift. Measurements of the Ionospheric Connection Explorer satellite (ICON) showed that the outward E×B drift was enhanced significantly and that the horizontal ion drift was poleward. According to the ICON ion drift observations, the HmF2 uplift was caused by an electric field rather than equatorward neutral wind. We propose that the enhanced eastward electric field dominated the positive ionospheric storm and that the thermospheric composition variation may have also contributed.

Characterization and Climatological Modeling of Equatorial Ionization Anomaly (EIA) Crest Position

AbstractThe Equatorial Ionization Anomaly (EIA) is characterized by strong ionospheric gradients that complicate ionospheric modeling and mitigation of ionospheric impact on Global Navigation Satellite System applications. In this study, the variation of EIA crest locations as a function of longitude and solar radio flux index F10.7 has been derived and modeled. Seven years (2013–2019) of ionospheric NmF2 and in‐situ ion density data from Constellation Observing System for Meteorology Ionosphere and Climate and Swarm‐A satellites have been used. We find that the distance between the northern and southern crest of EIA grows slightly with increase of solar flux. The position of the crests of EIA follows a wave number 4 structure with peak values at around −130°, 0°, and 100°E. At the altitude of Swarm‐A (∼460 km), the equatorial crests are found closer to the geomagnetic dip equator than they are at the peak density height hmF2 (∼310 km) which may be due to the spatial variations of geomagnetic field strength. Accordingly, two Crest Position climatological Models have been developed, one for the F2 Peak height (CPM_F2P) and the other one for Swarm‐A height (CPM_SAH).