Ionospheric Irregularities Research Articles

Pressure-Gradient Current at High Latitude from Swarm Measurements

The pressure-gradient current is among the weaker ionospheric current systems arising from plasma pressure variations. It is also called diamagnetic current because it produces a magnetic field which is oriented oppositely to the ambient magnetic field, causing its reduction. The magnetic reduction can be revealed in measurements made by low-Earth orbiting satellites flying close to ionospheric plasma regions where rapid changes in density occur. Using geomagnetic field, plasma density and electron temperature measurements recorded on board ESA Swarm A satellite from April 2014 to March 2018, we reconstruct the flow patterns of the pressure-gradient current at high-latitude ionosphere in both hemispheres, and investigate their dependence on magnetic local time, geomagnetic activity, season and solar forcing drivers. Although being small in amplitude these currents appear to be a ubiquitous phenomenon at ionospheric high latitudes characterized by well defined flow patterns, which can cause artifacts in the main field models. Our findings can be used to correct magnetic field measurements for diamagnetic current effect, to improve modern magnetic field models, as well as to understand the impact of ionospheric irregularities on ionospheric dynamics at small-scale sizes of a few tens of kilometers.

African and American Equatorial Ionization Anomaly (EIA) Responses to 2013 SSW Event

AbstractThis study investigates the responses of the African and American Equatorial Ionization Anomaly (EIA) regions to 2013 Sudden Stratospheric Warming (SSW) event. The Total Electron Content (TEC) data obtained from chains of Global Positioning System receivers within ±40° geomagnetic latitudes in the African and American sectors were used to construct the EIA structures for both longitudinal sectors. The responses of the EIA structures, constructed from the TEC, ΔTEC, and ionospheric irregularities data to the 2013 SSW event were investigated. During the SSW peak phase, EIA structures in both longitudinal sectors responded significantly, with the pole‐ward flow of plasma from the equator to higher crests' locations (strengthening of the EIA). Furthermore, a clear asymmetry in plasma distribution in the northern and southern crests of the EIA was observed. Generally, for the entire data span, TEC enhancements and ionospheric irregularities occurrences during SSW were more in the American sector than the African sector. The geomagnetic activity of 17 January 2013 caused negative TEC response in the African sector and positive TEC response in the American sector. Moderate storm‐induced TEC enhancements were generally lower than SSW‐induced TEC enhancements. Furthermore, solar flux‐induced TEC of 10 January 2013 was lesser than the SSW‐induced TEC of 15–16 January 2013.

Solar and interplanetary events that drove two CIR-related geomagnetic storms of 1 June 2013 and 7 October 2015, and their ionospheric responses at the American and African equatorial ionization Anomaly regions

This study investigates the sequence of solar and interplanetary events that drove the 1 June 2013 and October 2015 geomagnetic storms and how the American (68°–78oE) and African (32°–42oE) Equatorial Ionization Anomaly (EIA) regions responded to them. We constructed the EIA structures by using Total Electron Content (TEC) and ionospheric irregularities derived from Global Navigation Satellite System (GNSS) receivers along with the study locations. We also analyzed disturbed time ionospheric electric field and model data alongside the GNSS data. The 1 June 2013 geomagnetic storm was driven by a combination of a weak CME and HSSs from solar coronal holes, while the 7 October 2015 storm was solely driven by HSSs. Storm-time hemispherical asymmetry in ionospheric TEC and irregularities distributions was consistently observed. Storm with minimum SYM-H value at day-side locations caused enhancement in plasma ionization and pole-ward movement of EIA crests, while storm with minimum SYM-H value at night-side locations caused reduction in plasma ionization and equator-ward movement of EIA crests. The phase of responses of the ionosphere to geomagnetic storms depends on the local time of storm’s onset and local time of the storm’s main phase minimum which also determine the orientation of Prompt Penetration Electric Field (PPEF). At storm’s onset time in the low latitude regions, the main storm-induced electric field is PPEF. Daytime eastward PPEF intensified plasma fountain to increase the EIA crests locations, while nighttime westward PPEF reversed plasma fountain to cause equator-ward collapse of the EIA crests. However, around the storm’s recovery phase, under southward turning of IMF Bz, depending on their orientations, PPEF and Disturbed Dynamo Electric Field (DDEF) collectively influenced low latitude ionosphere. Eastward PPEF at the Pre-Reversal Enhancement (PRE) time enhanced irregularities generation, while westward DDEF at PRE time inhibited irregularities generation. The season of storm’s occurrence is also a factor that dictates ionospheric response to a storm, for instance, the 7 October storm (SYM-H −124 nT) influenced the ionosphere more than the 1 June storm (SYM-H −137 nT). Both storms had long recovery phase. On pre-storm days, we observed stronger and well-developed EIA crests over the American sector than over the African sector.

The Origin of Midlatitude Plasma Depletions Detected During the 12 February 2000 and 29 October 2003 Geomagnetic Storms

AbstractLarge amplitude plasma density irregularities have occasionally been detected at night in the midlatitudeFregion during geomagnetic storms. They are often interpreted in terms of equatorial plasma bubbles (EPBs) because midlatitude irregularities have the morphology of EPBs. This study assesses whether morphology can be a determining factor in ascribing the origin of such midlatitude ionospheric irregularities. We address this question by analyzing the observations of the First Republic of China satellite (ROCSAT‐1) and Defense Meteorological Satellite Program (DMSP)‐F14 and ‐F15 satellites during the geomagnetic storms on 12 February 2000 and 29 October 2003. On both days, ROCSAT‐1 detects plasma depletions at midlatitudes in broad longitude regions and DMSP satellites detect isolated severe plasma depletions whose widths and depths are much wider and deeper than those of typical EPBs. The distinguishing characteristics during the storms are the detection of midlatitude depletions only in the Southern Hemisphere and the occurrence of some of these depletions before 19 hr local time and at the longitudes where EPBs are absent in the equatorial region. These characteristics are not explained satisfactorily by the characteristics of EPBs. Considering the detection of some of the midlatitude depletions at the equatorward edge of ionospheric perturbations in midlatitudes, midlatitude depletions are likely ionospheric perturbations that originated from higher latitudes. Because midlatitude depletions can originate from different sources, the morphology alone is not a determining factor of their origin.

Lessons Learned from IDEASSat: Design, Testing, on Orbit Operations, and Anomaly Analysis of a First University CubeSat Intended for Ionospheric Science

Given the pervasive use of satellite and over the horizon wireless communication technology in modern society, ionospheric disturbances that can disrupt such services are a crucial consideration. Ionospheric irregularities, plasma bubbles and other phenomena can have a great impact on satellite navigation and communications, impacting other systems reliant on such technologies. The Ionospheric Dynamics and Attitude Subsystem Satellite (IDEASSat) was a 3U developed by National Central University (NCU) to measure irregularities in the ionosphere, as well as to establish spacecraft engineering and operations capacity at NCU. The onboard Compact Ionospheric Probe (CIP) could measure high-resolution plasma parameters, which can be used for identifying ionospheric irregularities that can cause scintillation in satellite navigation and communications signals. Part of the spacecraft sub-systems were independently designed and developed by students, who were also responsible for integration, testing, and operations. IDEASSat was successfully launched into low Earth orbit on 24 January 2021, and then began mission operations. The spacecraft successfully demonstrated three-axis attitude stabilization and control, tracking, telemetry and command (TT&C), as well as flight software and ground systems that could support autonomous operation. The spacecraft experienced a critical anomaly 22 days after launch, followed by a 1.5-month communications blackout. The spacecraft briefly recovered from the blackout for long enough to replay flight data, which allowed for the cause of the blackout to be determined as an inability of the electrical power subsystem reset circuit to recover from an ionizing radiation induced single event latch-up. Although the mission was not completed, flight data obtained during the mission will help to improve the designs of future spacecraft in development at NCU. This paper will introduce IDEASSat’s final flight model design and implementation, integration, testing, environmental verification, and failure analysis, and will review the performance of the spacecraft during on-orbit operations. The results and experiences encountered in implementation and operations of the IDEASSat mission are presented here as a reference for other university small satellite teams.

Magnetic Field and Electron Density Scaling Properties in the Equatorial Plasma Bubbles

The ionospheric plasma density irregularities are known to play a role in the propagation of electromagnetic signals and to be one of the most important sources of disturbance for the Global Navigation Satellite System, being responsible for degradation and, sometimes, interruptions of the signals received by the system. In the equatorial ionospheric F region, these plasma density irregularities, known as plasma bubbles, find the suitable conditions for their development during post-sunset hours. In recent years, important features of plasma bubbles such as their dependence on latitude, longitude, and solar and geomagnetic activities have been inferred indirectly using their magnetic signatures. Here, we study the scaling properties of both the electron density and the magnetic field inside the plasma bubbles using measurements on board the Swarm A satellite from 1 April 2014 to 31 January 2016. We show that the spectral features of plasma irregularities cannot be directly inferred from their magnetic signatures. A relation more complex than the linear one is necessary to properly describe the role played by the evolution of plasma bubbles with local time and by the development of turbulent phenomena.

Development of the Storm‐Induced Ionospheric Irregularities at Equatorial and Middle Latitudes During the 25–26 August 2018 Geomagnetic Storm

AbstractCan geomagnetic storms during low solar activity trigger formation of extreme equatorial plasma bubbles (EPBs) that affect low and midlatitudes? We analyzed the ionospheric response to the 25–26 August 2018 geomagnetic storm and revealed formation of intense ionospheric plasma irregularities over broad latitudinal ranges from equatorial toward middle latitudes in the American and Pacific sectors. Storm‐induced penetration electric fields created favorable conditions for strong fountain effect uplifted the equatorial ionosphere, enhancement of the equatorial ionization anomaly (EIA), and postsunset EPBs generation. We found two patterns of equatorial ionospheric irregularities expansion toward low and middle latitudes: (a) storm‐induced EPBs developed over a large latitudinal extent between widely spread EIA crests, (b) narrow channel of the ionospheric irregularities stretched away from the EPB location toward the auroral zone in the northwestward direction. The EPBs latitudinal extent largely exceeded climatological‐based expectations for solar minimum conditions; EPBs reached atypically high latitudes (20°–25° magnetic latitude [MLAT]) in the Pacific Ocean sector. The poleward‐streaming plasma density depletions were registered along the western coast of North America. The ionospheric irregularities transported in the northwestward direction toward midlatitudes reaching as high as 40°–45° MLAT. The passage of these ionospheric irregularities coincided with the spread‐F conditions recorded at a midlatitude ionosonde (42° MLAT)—rather atypical phenomenon for midlatitudes. It is suggested that enhanced westward drifts associated with prompt penetration and Sub Auroral Polarization Stream electric fields can support the northwestward plasma transportation.

Investigating the impact of the latitudinal velocity profile on nonlinear gradient drift instability development in the subauroral ionosphere

Subauroral polarization streams (SAPS) are regions in the subauroral ionosphere with lower plasma density and large westward flow driven by a poleward electric field. Density irregularities have been observed in the SAPS region; these irregularities can negatively impact radio signals by causing phase and amplitude fluctuations. Previous work identified the gradient drift instability (GDI) as a generation mechanism of such ionospheric irregularities in SAPS and investigated the impact of the velocity profile on the GDI development. The turbulence spectra of the GDI are important to understand as they can provide insight into spatial scales associated with the turbulent evolution that may impact radio propagation. We hypothesize that the background electric field, through the neutral wind, and the nature of the velocity shear have an impact on the power laws from the turbulence spectra. A 2D fluid model is used to investigate the turbulence spectra of GDI in SAPS with a fixed background density profile and different latitudinal velocity profiles. Data from Super Dual Auroral Radar Network (SuperDARN) radar and Global Positioning System (GPS) provide the background ionospheric conditions. The neutral wind direction is chosen to be in the equatorward direction, which is in line with typical observations; however, this can be used to modify the electric field to consider new possibilities in the SAPS region. The angle of the electric field is manifested through the combination of the background velocity profile ( drift) and the neutral wind. The turbulence spectra of cases with no velocity profile and with different neutral wind directions are analyzed. The impact of velocity shear is studied by translating the velocity shear location relative to the density gradient. Numerical spectral analysis results are presented and compared to recent experimental observations. Results of spectral slopes of GDI simulations with no background velocity ( drift) were found to be and for the normalized density and the perturbed electric potential, respectively. Spectral slopes for simulations with different velocity shear locations were found to follow power laws of and for the normalized density and perturbed electric potential (inside SAPS region), respectively.

Spread-F characteristics over Tucumán near the southern anomaly crest in South America during the descending phase of solar cycle 24

Ionospheric F-region irregularities can acutely affect navigation and communication systems. To develop predictive capabilities on their occurrence, it is key to understand their variabilities in a wide range of time scales. Previous studies at low latitudes in South America have been performed mostly in the eastern region. However, there are still few reports on the spread-F over Argentina owing to a lack of ionosonde data. This work presents the analysis of the spread-F (range spread-F and frequency spread-F) and plasma bubble occurrence characteristics near the southern crest of the Equatorial Ionization Anomaly in Argentina (Tucumán, 26.8°S, 65.2°W; magnetic latitude 15.5°S). We used ionosonde and Global Positioning System (GPS) data from November 2014 to December 2019 for different solar and geomagnetic conditions. The data show that spread-F and plasma bubble occurrence rates peak in local summer and are minimum in equinox and winter, respectively. There is a negative correlation between each type of spread-F and solar activity, whereas the opposite happens for plasma bubbles. Geomagnetic activity suppresses the generation of spread-F in equinox and summer and enhances it in winter. Plasma bubble occurrence is higher during disturbed days than during quiet days, but under medium solar activity, summer months register more plasma bubbles in quiet conditions. Range spread-F observed in winter under low solar activity is not associated with plasma bubbles originated at the magnetic equator. These results contribute to the knowledge necessary to improve the prediction of the spatial and temporal distribution of the night-time ionospheric irregularities.

Simultaneous Observations of a Sporadic E Layer by Digisonde and SuperDARN HF Radars at Zhongshan, Antarctica

AbstractSporadic E (Es) layers could be composed of metallic ions and formed, modified, or transported by the action of convective electric fields in the high latitude ionosphere. In this paper, by utilizing simultaneous observations from Digisonde and Super Dual Auroral Radar Network (SuperDARN) HF radars at Zhongshan Station (ZHS, 69.4°S, 76.4°E), Antarctica, a thin Es layer, which initially formed in the lower F region and descended into the lower E region, with wavelike structures, was recorded by Digisonde on 14 November 2019. The Es layer‐related concurrent ionospheric irregularities were also detected by the SuperDARN ZHS HF radar. By using a global‐scale 2‐D convection map, combined with images from the Special Sensor Ultraviolet Spectrographic Imager instruments onboard Defense Meteorological Satellite Program (DMSP) spacecraft, it is proposed that the flow shears associated with the duskside convective circulation are responsible for the evolution of the Es layer. Moreover, using the HF radar elevation angle data to measure the scatter height, it is strongly suggested that the Es layer was elongated with convection circulation. The electrodynamic processes responsible for the formation and evolution of the Es layer are discussed.

Signatures of Equatorial Plasma Bubbles and Ionospheric Scintillations from Magnetometer and GNSS Observations in the Indian Longitudes during the Space Weather Events of Early September 2017

Scintillation due to ionospheric plasma irregularities remains a challenging task for the space science community as it can severely threaten the dynamic systems relying on space-based navigation services. In the present paper, we probe the ionospheric current and plasma irregularity characteristics from a latitudinal arrangement of magnetometers and Global Navigation Satellite System (GNSS) stations from the equator to the far low latitude location over the Indian longitudes, during the severe space weather events of 6–10 September 2017 that are associated with the strongest and consecutive solar flares in the 24th solar cycle. The night-time influence of partial ring current signatures in ASYH and the daytime influence of the disturbances in the ionospheric E region electric currents (Diono) are highlighted during the event. The total electron content (TEC) from the latitudinal GNSS observables indicate a perturbed equatorial ionization anomaly (EIA) condition on 7 September, due to a sequence of M-class solar flares and associated prompt penetration electric fields (PPEFs), whereas the suppressed EIA on 8 September with an inverted equatorial electrojet (EEJ) suggests the driving disturbance dynamo electric current (Ddyn) corresponding to disturbance dynamo electric fields (DDEFs) penetration in the E region and additional contributions from the plausible storm-time compositional changes (O/N2) in the F-region. The concurrent analysis of the Diono and EEJ strengths help in identifying the pre-reversal effect (PRE) condition to seed the development of equatorial plasma bubbles (EPBs) during the local evening sector on the storm day. The severity of ionospheric irregularities at different latitudes is revealed from the occurrence rate of the rate of change of TEC index (ROTI) variations. Further, the investigations of the hourly maximum absolute error (MAE) and root mean square error (RMSE) of ROTI from the reference quiet days’ levels and the timestamps of ROTI peak magnitudes substantiate the severity, latitudinal time lag in the peak of irregularity, and poleward expansion of EPBs and associated scintillations. The key findings from this study strengthen the understanding of evolution and the drifting characteristics of plasma irregularities over the Indian low latitudes.

Assessing the Kinematic GPS Positioning Performance Under the Effect of Strong Ionospheric Disturbance Over China and Adjacent Areas During the Magnetic Storm

AbstractThe geomagnetic storm caused numerous disturbances of the ionosphere, particularly, plasma irregularities, which can affect the accuracy of Global Positioning System (GPS) positioning. This study quantifies the impacts of the ionospheric disturbance on GPS precise point positioning (PPP) solutions during extreme space weather events by taking advantage of 260 GPS stations in China. The results show that the average positioning error in China increased significantly during the ionospheric disturbance on 08 Sep 2017. By comparing the kinematic GPS‐PPP (3‐D) error distribution map and the ROTI index map, it is found that the ionospheric irregularities are one of the main reasons for degrading the GPS positioning accuracy. The statistical analysis results show that when the ionospheric scintillation index S4 is greater than 0.4, the average kinematic GPS‐PPP error calculated by the station is higher than 0.8 m.

Multifractal characteristics of the low latitude equatorial ionospheric E–F valley region irregularities

Ionospheric irregularities of the E–F valley region are relatively less explored with in situ experiments enabling to capture local fine structures. Here, we present the multifractal analysis of electron density fluctuations in the E–F valley region, obtained from a rocket experiment performed at equatorial low latitude station, Alcântara, Brazil to explore scaling structures in the plasma irregularities. The multifractal spectrum is validated with a analytical model that mimics the energy distribution in a turbulent cascade using probabilistic weights. We report the nature of the E–F valley region irregularities to be multifractal, asymmetric, intermittent and non–homogeneous. The multifractal measures show transition of the influence from smaller to larger fluctuations as the rocket approaches the F layer base, consolidating earlier observations. By identifying the nature of the irregularities, we explore the possible cause for a wide variation reported in the spectral indices. Our analysis demonstrates the usability of the multifractal approach in studying the nonlinear fluctuations observed from the E-F valley region in situ data.

Measurement of Aspect Angle of Field-Aligned Plasma Irregularities in Mid-Latitude E Region Using VHF Atmospheric Radar Imaging and Interferometry Techniques

Multireceiver and multifrequency radar imaging were carried out with the 46.5 MHz MU radar in Japan (34.85°N and 136.10°E) to examine the aspect sensitivity of field-aligned plasma irregularities (FAIs) in the mid-latitude ionosphere E region. A radar beam was directed to geographic north and at 51° zenith angle, which was normal to the geomagnetic field line around 100 km height. Nineteen receivers and five carrier frequencies were used for radar imaging to retrieve the power distribution in the radar volume, and then the aspect angle along the geomagnetic field line was calculated according to the angular power distribution. Retrieval algorithms such as Fourier, Capon, and norm-constrained Capon (NC-Capon) were employed, in which the NC-Capon was applied to FAIs for the first time and found to be more suitable for the present study. The aspect angles estimated by the NC-Capon ranged between 0.1° and 0.4° mostly, and averaged around 0.2°, which were the same order to the previous measurements with radar interferometry (RI), made for equatorial electrojet irregularities and the lower mid-latitude sporadic E region. For comparison, RI-estimated aspect angles were also investigated and found to be close to that of NC-Capon, but distributed over a wider extent of angles.

Study of the Ionospheric Scintillation Radio Propagation Characteristics with Cosmic Observations

The ionosphere has important influences on trans-ionosphere radio propagation. When signals pass through ionospheric irregularities, their amplitude and phase are often attenuated and distorted. In this work, the statistical features of scintillation observed by the Global Navigation Satellite System (GNSS) and low earth orbit (LEO) satellites are investigated with Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) data in solar cycle 24. The amplitude scintillation propagation channel is fitted by the Nakagami-m, α-μ and κ-μ models. The performance is evaluated in terms of root mean square error (RMSE), kurtosis and information entropy. The results reveal that the α-μ model achieves the best performance in all considered scintillation intensities, while the Nakagami-m model achieves better performance under severe scintillation in the GNSS-LEO propagation channels.

Ionospheric irregularities during disturbed geomagnetic conditions over Argentinian EIA region

Ionospheric irregularities can severely degrade radio communication and navigation systems. Geomagnetic storms may affect the generation of these irregularities in a way that is not yet fully understood. To improve the forecasting of this phenomenon, we need to study the ionosphere in different regions of the world, and in particular in the equatorial ionization anomaly (EIA) where irregularities are usually more intense. This study analyses the effect of geomagnetic storms on ionospheric irregularities. We examined the occurrence of irregularities at the southern crest of the EIA in Argentina (Tucumán, 26.9°S, 294.6°E, dip latitude 15.5°S) during three intense and one moderate geomagnetic storm of different solar sources, between 2015 and 2018. We used data from an ionosonde, a Global Positioning System receiver and magnetometers. Ionogram spread-F, the F-layer bottom side (h'F), the critical frequency of the F2-layer (foF2), the rate of TEC index and the S4 scintillation index were analysed. The data show irregularities were present as range spread-F and moderate TEC fluctuations in one storm: 27 May 2017 (a coronal mass ejection CME-driven storm occurred on local winter), and were absent in the other events. We suggest that eastward disturbance dynamo electric field and over-shielding prompt penetration electric fields may create favourable conditions for developing these irregularities, whereas westward storm time electric fields might inhibit the growth of irregularities during the other storms considered. During co-rotating interaction region CIR-driven storms, the westward disturbance dynamo electric field may be associated with the non-occurrence of irregularities.

The implications of ionospheric disturbances for precise GNSS positioning in Greenland

Ionospheric irregularities impair Global Navigation Satellite System (GNSS) signals and, in turn, affect the performance of GNSS positioning. Such effects are especially evident at low and high latitudes, which are currently gaining the attention of research and industry sectors. This study evaluates the impact of ionospheric irregularities on GNSS positioning in Greenland. We assess the performance of positioning methods that meet the demands of a wide range of users. In particular, we address the needs of the users of mass-market single-frequency receivers and those who require a solution of high precision provided by geodetic dual-frequency receivers. We take advantage of the datasets collected during three ionospheric storms: the St. Patrick’s Day storm of March 17, 2015, the storm on June 22, 2015, and another on August 25–26, 2018. We discover a significant impact of the ionospheric disturbances on the ambiguity resolution performance and the accuracy of the float solution in Real Time Kinematics (RTK) positioning. Next, assessing the single-frequency ionosphere-free Precise Point Positioning (PPP), we demonstrate that the model is generally unaffected by ionospheric disturbances. Hence, the model is predestined for the application by the users of single-frequency receivers in the areas of frequent ionospheric disturbances. Finally, based on the observation analyses, we reveal that phase signals on the L2 frequency band are more prone to cycle slips induced by ionospheric irregularities than those transmitted on the L1. Such signal properties explain a noticeable decline in the dual-frequency RTK performance during the ionospherically disturbed period and merely no effect for the single-frequency ionosphere-free PPP model.

Statistical Characteristics of Mid‐Latitude Ionospheric Irregularities at Geomagnetic Quiet Time: Observations From the Jiamusi and Hokkaido East SuperDARN HF Radars

AbstractNewly built Jiamusi (JME) radar and Hokkaido East (HOK) radar data reveal statistical features of the mid‐latitude ionospheric irregularities during quiet times. In this paper, the distribution features and seasonal variations of the scattering occurrence rate and convection velocity of the ionospheric, F‐region irregularities between 45°N and 60°N magnetic latitude (MLAT) during geomagnetic quiet times are studied by using one‐year observation data from the JME radar and HOK radar. The results show that the scattering occurrence rate is strongest in summer and weakest in winter in this region, and the highest value always appears on the dusk side, especially in summer and the equinox. Line‐of‐sight (LOS) velocity also shows significant seasonal variation. It is stronger in winter and the equinox than in summer, which is in good agreement with previously reported observations from six midlatitude Super Dual Auroral Radar Network radars in the North American sector. An interesting new finding is that on the night side, LOS velocity decreases first and then increases as the MLAT increases from 45°N to 56°N, particularly in summer and the equinox. This implies that there is a velocity reversal region during the geomagnetic quiet time in regard to night side, mid‐latitude, ionospheric convection.

Variability of the Critical Frequency foF2 during Minimum and Maximum Phases of Solar Cycles 20 and 21: A Comparative Study between American and African Equatorial Regions

The present work is a comparative study between the foF2 variabilities for two equatorial regions (Ouagadougou: lat. 12°21'N; long. 1°30'E, dip. 1.43° in Africa and Huancayo: Lat. 12°S; Long. 75°12'W in America) during solar cycles 20 and 21 minima and maxima phases under geomagnetic extreme conditions (quiet and disturb). Profiles from these two stations are very similar for all the seasons over the solar cycles. However, measured data from Huancayo station are higher than those from Ouagadougou station during winter with a reverse phenomenon for summer. The investigations suggest that the gap between foF2 values and the reverse phenomenon observed for the two stations may be explained by their hemispheric location (Huancayo in south hemisphere and Ouagadougou in North one). Longitudinal irregularities in ionosphere may also contribute to that little difference observed during the time interval of our investigation.

Mapping of S4 Over the Arabian Peninsula During Solar Minimum

In this letter, we study the temporal and spatial variability of ionospheric irregularities by generating high-resolution maps of the observed amplitude scintillation index (S4) using data from a multi-constellation and multi-frequency GNSS receiver. The study is located in the Arabian Peninsula region, which falls under the northern crest of the equatorial ionization anomaly (EIA). Even though the study was conducted during a solar minimum period, considerable pre-sunset scintillation occurrences have been observed between 15-17 local time, particularly during the winter solstices. While most scintillation occurrences have been observed at low elevation (20 to 25 degrees), a considerable number of scintillation causing ionospheric irregularities have been observed towards the north, east, and southeast of the receiver location, for elevation ranging from 40 to 60 degrees. Out of all the GNSS constellations with medium-earth-orbit (MEO) satellites, GPS was the most impacted by amplitude scintillation, while BeiDou and Galileo satellites were the least affected. It is anticipated that the patches of ionospheric irregularities reported in this work will be further enhanced as solar activity increases in the coming years. Therefore, this work can serve as a reference for future studies during periods of increased geomagnetic activity.