South American Sector Research Articles

The impact of the Hunga Tonga–Hunga Ha’apai volcanic eruption on the Peruvian atmosphere: from the sea surface to the ionosphere

The eruption of the Hunga Tonga Hunga Ha’apai volcano on 15 January 2022 significantly impacted the lower and upper atmosphere globally. Using multi-instrument observations, we described disturbances from the sea surface to the ionosphere associated with atmospheric waves generated by the volcanic eruption. Perturbations were detected in atmospheric pressure, horizontal magnetic field, equatorial electrojet (EEJ), ionospheric plasma drifts, total electron content (TEC), mesospheric and lower thermospheric (MLT) neutral winds, and ionospheric virtual height measured at low magnetic latitudes in the western South American sector (mainly in Peru). The eastward Lamb wave propagation was observed at the Jicamarca Radio Observatory on the day of the eruption at 13:50 UT and on its way back from the antipodal point (westward) on the next day at 07:05 UT. Perturbations in the horizontal component of the magnetic field (indicative of EEJ variations) were detected between 12:00 and 22:00 UT. During the same period, GNSS-TEC measurements of traveling ionospheric disturbances (TIDs) coincided approximately with the arrival time of Lamb and tsunami waves. On the other hand, a large westward variation of MLT winds occurred near 18:00 UT over Peru. However, MLT perturbations due to possible westward waves from the antipode have not been identified. In addition, daytime vertical plasma drifts showed an unusual downward behavior between 12:00 and 16:00 UT, followed by an upward enhancement between 16:00 and 19:00 UT. Untypical daytime eastward zonal plasma drifts were observed when westward drifts were expected. Variations in the EEJ are highly correlated with perturbations in the vertical plasma drift exhibiting a counter-equatorial electrojet (CEEJ) between 12:00 and 16:00 UT. These observations of plasma drifts and EEJ are, so far, the only ground-based radar measurements of these parameters in the western South American region after the eruption. We attributed the ion drift and EEJ perturbations to large-scale thermospheric wind variations produced by the eruption, which altered the dynamo electric field in the Hall and Pedersen regions. These types of multiple and simultaneous observations can contribute to advancing our understanding of the ionospheric processes associated with natural hazard events and the interaction with lower atmospheric layers.Graphical

Variability of the equatorial ionization anomaly over the South American sector: Effects of electric field and effective meridional wind

Vertical Total Electron Content (VTEC) Maps over the South American Continent were utilized to investigate the temporal and longitudinal climatology of Equatorial Ionization Anomaly (EIA) using more than 350 Global Navigation Satellite Systems (GNSS) receivers. At a temporal resolution of 10 min, the EIA motions, morphologies, and evolutions were mapped using VTEC keogram along magnetic meridians lines. Between 2014 and 2019, characteristics of the EIA were studied at two different South American magnetic meridians (i.e., 3.36° E and 7.58° E) separated by ∼555 km at an altitude of 300 km. The aim of this study is to examine the EIA’s variability, monthly variations and occurrences at evenly spaced longitudinal sectors. The effects of effective meridional winds component and E × B drift velocity on the daytime asymmetry of EIA anomalies were studied using a physics-based numerical model, Sheffield University Plasmasphere-Ionosphere model at Instituto Nacional de Pesquisas Espaciais (SUPIM-INPE). We found that the EIA parameters such as strength, shape, intensity, and latitudinal positions are affected by the eastward electric field and effective meridional wind. The monthly variations in the EIA over two magnetic meridian sectors demonstrate a semiannual variation. The EIA crests were more symmetric in equinox than in solstice seasons. The asymmetries of the EIA observed during the December solstice are more intense than during the June solstice, whereas September equinox is less symmetric than March equinox seasons. Moreover, this study indicates that the vertical drift and the meridional neutral wind plays a very significant role in the development of the EIA asymmetry by transporting the plasma up the field lines. There was a notable contraction of the EIA southern hemispheric (SH) crests from the December solstice to the June solstice. Meanwhile, the EIA crest positions in the northern hemisphere (NH) expand from the December solstice to the June solstice. According to our observations, the March equinox season had the most EIA occurrences, which were then followed by the September equinox, the December and June solstices. The intensities of the EIA crests also considerably decreased with solar descending phases. Through modeling, this work provides the scientific community with new insights into the evolution/development of EIA and their latitudinal asymmetry, as well as the role of E × B drift and thermospheric neutral wind in assessing the statistical analysis of EIA variability using the largest VTEC database over the South American sector.

Evaluating sustainable efficiency: A study on transportation systems in South America using data envelopment analysis

The transport sector is pivotal in fostering economic growth and environmental sustainability. Extensive research has scrutinized various transportation modes individually, yet a holistic assessment encompassing all modes while considering CO2 emissions needs to be more conspicuously present. Our study employs Data Envelopment Analysis (DEA) to evaluate the efficacy of transportation policies in South American nations in the context of United Nations-established sustainable development goals. Our overarching objective is to classify the sustainability status of South American countries' transport sectors and to establish benchmark models rooted in the six dimensions of sustainability. Methodologically, our analysis integrates operational transportation metrics, Gross Domestic Product per capita, Human Development Index, and CO2 emissions from transportation systems. Additionally, we draw comparative insights by juxtaposing South American countries against the G8 and BRICS nations. The rigorous application of DEA coupled with bootstrap validation fortifies the reliability of our findings. Our results bring to light these findings, positioning South American countries closer to their developed counterparts. Notably, the sustainable development models of Chile and Uruguay emerge as prominent exemplars. This study underscores the pressing demand for holistic and integrated development strategies to attain more sustainable outcomes across South American nations in a faster way. In conclusion, our research fills a conspicuous void in the extant literature by furnishing a comprehensive evaluation of transportation policy performance in South America. Based on a robust methodology, this empirical evidence offers valuable insights for policymakers striving to advance sustainable regional development.

Variations of Inter‐Hemispheric Field‐Aligned Currents: Observations From Ground Geomagnetic Measurements

AbstractThe east–west component of the geomagnetic field (Y‐component) at the Trivandrum (TRD) station, an equatorial site, is used to investigate the characteristics of Inter‐Hemispheric Field‐Aligned Currents (IHFACs) in the Indian sector during solar cycles 21 and 22. The observations reveal an annual variation of IHFAC in the dawn/noon sector with positive/negative peaks around northern summer. Furthermore, it is noted that IHFAC amplitudes are modulated by solar activity, superimposed with seasonal effects, with consistently higher amplitudes during the northern summer months. The dusk‐time IHFAC also shows a pattern modulated by seasons and solar cycles, with negative peaks around northern summer only during the low solar active years. The seasonal pattern of IHFAC shows a similar trend from April to September, where dawn/noon IHFAC is south/north directed, and for the remaining months, both are northward directed. The dusk‐side IHFAC is mostly south‐directed irrespective of the season. Moreover, it is demonstrated that the seasonal pattern of dawn and noon‐time IHFAC amplitudes show a strong to moderate correlation with amplitudes of Sq asymmetries between two hemispheres, but dusk‐time IHFAC does not follow this trend. The IHFAC directions at TRD follow the Fukushima model for May to September during the dawn‐noon sector for 70%–95% of the days and less than 50% of the days for remaining months. The noon‐dusk sector shows Fukushima model‐type polarity for ∼60% of days in June–July and less than 50% for remaining months. The global analysis of IHFAC, using monthly averages of hourly values from eight observatories spanning Asia, Africa, and America, reveals spatial differences in amplitude and directions. The directions of noon‐time IHFAC in the Indian‐East Asian and East‐African sectors follow similar trends, and the amplitude variations of noon‐time IHFAC can be explained by DE‐3 tidal effects. The IHFAC from the South American and West African sectors show intense southward and northward currents compared to other sites, indicating the influence of the South Atlantic Anomaly (SAA).

3‐D Ionospheric Imaging Over the South American Region With a New TEC‐Based Ionospheric Data Assimilation System (TIDAS‐SA)

AbstractThis study has developed a new TEC‐based ionospheric data assimilation system for 3‐D regional ionospheric imaging over the South American sector (TIDAS‐SA) (45°S–15°N, 35°–85°W, and 100–800 km). The TIDAS‐SA data assimilation system utilizes a hybrid Ensemble‐Variational approach to incorporate a diverse set of ionospheric data sources, including dense ground‐based Global Navigation Satellite System (GNSS) line‐of‐sight Total Electron Content (TEC) data, radio occultation data from the Constellation Observing System for Meteorology, Ionosphere, and Climate‐2 (COSMIC‐2), and altimeter TEC data from the JASON‐3 satellite. TIDAS‐SA can produce a reanalyzed three‐dimensional (3‐D) electron density spatial variation with a high time cadence, yielding spatial‐temporal resolution of 1° (latitude) × 1° (longitude) × 20 km (altitude) × 5 min. This allows us to reconstruct and study the 3‐D ionospheric morphology with multi‐scale structures. The performance of the data assimilation system is validated against independent ionosonde and in situ measurements through an experiment for a strong geomagnetic storm event on 03–04 November 2021. The results demonstrate that TIDAS‐SA can provide detailed and altitude‐resolved information that accurately characterizes the storm‐time ionospheric disturbances in vertical and horizontal domains over the equatorial and low‐latitude regions of South America.

Ground and Space-based response of the ionosphere during the geomagnetic storm of 02–06 November 2021 over the low-latitudes across different longitudes

The strong geomagnetic storm of class G3 that occurred on 03 November 2021 (Dst min = −118 nT, Kp = 8) was the first of this class recorded during the ascending phase of solar cycle 25. In this study, we examined the response of the ionosphere during the geomagnetic storm period from 02–06 November 2021 using the Total Electron Content (TEC) observations from a chain of Global Navigation Satellite System (GNSS) receiver stations in five longitudinal sectors i.e, Asian, East-African, West-African, South-American, and Pacific-west sectors, in the low-latitudes and space-based Swarm satellite electron density, Ne and TEC measurements. The Rate of Change of TEC Index (ROTI) was derived from the ground and space based TEC measurements to examine the occurrence of ionospheric irregularities. The Rate of change of electron density index (RODI) was also derived from Swarm Ne measurements to identify the occurrence of ionospheric irregularities at Swarm altitudes. A positive ionospheric storm effect was observed in all the longitudinal sectors considered in this study. A clear hemispherical asymmetry, with higher VTEC in the northern hemisphere was observed. The determining factors for ionospheric responses to this storm are; local time of the storm’s onset, local time of storm’s minimum SYM-H, and changes in thermospheric O/N2 ratio. These geomagnetic storm effects were discussed in terms of the Prompt Penetration Electric Field (PPEF) storm induced wind lifting effect and Disturbance Dynamo Electric Field (DDEF). The geomagnetic storm inhibited the occurrence of ionospheric irregularities in all the sectors, during the main phase, except for three IGS receiver stations in South American sector. Overall, a longitudinal dependence of the enhancement/inhibition of ionospheric irregularities was observed. The generation of post-sunset irregularities was attributed to the local time occurrence of maximum ring current, PPEF and DDEF.

Abnormal Sub‐Auroral Ion Drifts (ASAID) Developed in the Postmidnight (1–4) Magnetic Local Time Sector in 2013

AbstractWe investigate the Abnormal Sub‐Auroral Ion Drifts (ASAID) developed in the postmidnight (1–4) magnetic local time sector in 2013. Shown by the Defense Meteorological Satellite Program F15 horizontal ion velocity measurements, we specified 21 antisunward (eastward) ASAID flow channels (FCs) based on their respective underlying polar convections. Overall, the polar convection formed a two‐cell pattern with its convection axis tilted in the morning‐evening direction because of the underlying BY < 0 conditions. Its dawn cell intruded into the duskside from the dawnside where the eastward ASAID flows were streaming antisunward, opposite to the dawn cell sunward convection flows. Mostly, the ASAID FC appeared in the coinciding ring‐current–related ionospheric trough and flow‐stagnation–related main ionospheric trough in the South American sector because of the favorable conditions created by the South Atlantic Magnetic Anomaly promoting also the development of Stable Auroral Red (SAR) arc. Rarely observed, the ASAID FC was associated with the SAR arc detected over Rothera. Detected in the Mid Pacific longitude sector, a pair of northern‐southern ASAID FCs demonstrated northern‐southern conjugacy. With correlated observations, demonstrating magnetosphere‐ionosphere conjugacy, the inward (earthward) ASAID electric (E) field could also be investigated. These reveal the ASAID E field's fast‐time development by short‐circuiting when the hot‐ring‐current—cold‐plasmasphere interface developed and became impacted by finite Larmor radius effects because of the earthward intrusion of hot ring current protons. The ASAID E field's inner‐magnetosphere environment was characterized by the hot zone where heating was generated by low‐frequency waves and auroral kilometric radiations.

Stepping Into an Equatorial Plasma Bubble With a Swarm Overfly

AbstractESA's Swarm constellation entered in a “overfly” configuration in the period between September and October 2021, when the longitudinal distance between the lower pair and the upper satellite was at its minimum since the launch of the spacecrafts. In addition, the local time of the nighttime tracks was favorable to detect and study the morphology of post‐sunset equatorial plasma bubbles (EPBs). In this study, we focus on the Swarm overfly occurring between 00:41 UT and 00:59 UT on 30 September 2021, which covered one of the most densely instrumented regions for the study of the ionospheric irregularities embedded in the EPBs: the South American sector. By exploiting the use of ground‐based receivers of Global Navigation Satellite System (GNSS) signals in combination with the Swarm plasma density measurements, we study the irregularities in the EPB formed at ∼60°W and investigate the different scales of the irregularities and the cascading processes along the magnetic flux tubes. We also highlight how diffusion along the magnetic field lines occurs simultaneously with the plasma uplift, contributing then to the correct interpretation of the EPB evolution and decay process. The precious overfly conditions also allow the introduction of ionosphere‐related quantities, evaluated across the tracks at satellite altitudes enlarging the possibilities given by the same quantities already available along the tracks. Such opportunity envisages the possibility to proxy the impact of EPBs on GNSS signals with Low‐Earth Orbit satellite data provided by future missions specifically dedicated to the characterization of the near‐Earth environment and ionospheric studies.

Tree-ring δ18Ocellulose variations in two Nothofagus species record large-scaleclimatic signals in the South American sector of the Southern Ocean

In recent decades, southernmost South America (50–56° S) has experienced marked climate change (regional warming, decreased precipitation, reduced snow cover, and increased frequency of heat waves) related to variations in atmospheric circulation over varied timescales. In this paper, we develop oxygen isotopes from tree-ring cellulose (δ18OTRC) as a proxy for climate and atmospheric circulation in order to extend the regional meteorological record to deeper time intervals. Our work focuses on Nothofagus forests in two areas: (i) deciduous N. pumilio forest in the steppe transition zone near Punta Arenas and (ii) humid evergreen N. betuloides forest in the Navarino Island region. To investigate the potential for reconstructing palaeoclimate, δ18OTRC variations were correlated with local climate parameters as well as regional (Amundsen Sea Low, ASL) and hemispheric (Antarctic Oscillation, AAO) atmospheric circulation modes for the last 60 years. N. betuloides δ18OTRC variations show an overall positive trend, indicating isotopic enrichment over the study period, whereas no trend is recorded for the N. pumilio record. The strongest relationships with climate, together with the widest spatial representativeness, occur in the N. betuloides chronology during the growing season (spring to austral summer) and extend spatially from mid to high latitudes. In contrast, the sensitivity of the records is limited to summer months, and spatial correlations are much more limited. In addition, the N. betuloides record shows greater potential for reconstructing local climate features such as soil water (r = − 0.76), wind speed (r = 0.69), and precipitation (r = − 0.66), as well as regional (ASL, r = − 0.80) and hemispheric (AAO, r = 0.77) patterns of extratropical atmospheric circulation. Overall, we conclude that the N. betuloides record represents the most valuable tree-ring climate proxy for southernmost South America over past centuries.

Erratum: Ionospheric response modeling under eclipse conditions: Evaluation of 14 December 2020, total solar eclipse prediction over the South American sector

Ionospheric response modeling under eclipse conditions: Evaluation of 14 December 2020, total solar eclipse prediction over the South American sector. by Bravo MA, Molina MG, Martínez-Ledesma M, de Haro Barbás B, Urra B, Elías A, Souza J, Villalobos C, Namour JH, Ovalle E, Venchiarutti JV, Blunier S, Valdés-Abreu JC, Guillermo E, Rojo E, de Pasquale L, Carrasco E, Leiva R, Castillo Rivera C, Foppiano A, Milla M, Muñoz PR, Stepanova M, Valdivia JA andCabrera M (2022). Front. Astron. Space Sci. 9:1021910. doi: 10.3389/fspas.2022.1021910 Due to a production error, the words "us a" were erroneously changed to "United States of America".A correction has been made to the section 3 Results, "3.4 ISR of Jicamarca", first paragraph, page 9. The corrected sentence is as follows:"However, the general ionospheric trends are well represented in this figure, allowing us a direct comparison to the predicted values (bottom row)."The publisher apologizes for this mistake.The original version of this article has been updated.

GOLD Mission's Observation About the Geomagnetic Storm Effects on the Nighttime Equatorial Ionization Anomaly (EIA) and Equatorial Plasma Bubbles (EPB) During a Solar Minimum Equinox

AbstractThe nighttime ionospheric response to a geomagnetic storm that occurred on 23–29 September 2020 is investigated over the South American, Atlantic, and West African longitude sectors using NASA's Global‐scale Observations of the Limb and Disk measurements. On 27 September the solar wind conditions were favorable for prompt penetration electric fields to influence the equatorial ionosphere over extended longitudes. The equatorial ionization anomaly (EIA) crests were shifted 8°–10° poleward compared to the quiet time monthly mean across ∼65°–35°W during the main phase. Ionosonde hmF2 (peak electron density height) measurements from Fortaleza (GG: 3.9°S and 38.4°W) indicated a stronger prereversal enhancement this evening than other nights. As a result, equatorial plasma bubbles (EPB) occurred at these longitudes on this evening. This is the first simultaneous investigation of EIA morphology and EPB occurrence rate over an extended longitude range from geostationary orbit during a geomagnetic storm.

The 14 December 2020 Total Solar Eclipse Effects on Geomagnetic Field Variations and Plasma Density Over South America

AbstractWe discuss the effects in the geomagnetic field variations and ionospheric plasma density modifications caused by the Total Solar Eclipse that occurred on 14 December 2020 over the South American sector. We used ground‐based magnetometer data and the Total Electron Content maps derived from the Global Navigation Satellite System to evaluate these changes. The results show that the geomagnetic field daily variation weakens between the first and last solar eclipse penumbra contact. Additionally, we observed a significant reduction of about 52.33 nT on the Equatorial Electrojet strength at Jicamarca (11.95°S, 76.88°W), where the solar obscuration reached 16.67% approximately. This behavior indicates that the solar eclipse in the equatorial region has possibly affected electric conductivities, altering the E region dynamo electric field. Consequently, it weakens the equatorial plasma fountain, affecting the Equatorial Ionization Anomaly development. Additionally, the ionospheric dynamics variations over Jicamarca during the solar eclipse event are analyzed using ionosonde data. We observe that the solar eclipse also caused a modification in the sporadic E layer and F region dynamics, indicating possible evidence of the gravity wave occurrence. Therefore, the results found here provide a better understanding of how the solar eclipse passage in the equatorial region affects the electron density in the low‐latitude regions.

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.

Ionospheric response modeling under eclipse conditions: Evaluation of 14 December 2020, total solar eclipse prediction over the South American sector

In this work, we evaluate the SUPIM-INPE model prediction of the 14 December 2020, total solar eclipse over the South American continent. We compare the predictions with data from multiple instruments for monitoring the ionosphere and with different obscuration percentages (i.e., Jicamarca, 12.0°S, 76.8°W, 17%; Tucumán 26.9°S, 65.4° W, 49%; Chillán 36.6°S, 72.0°W; and Bahía Blanca, 38.7°S, 62.3°W, reach 95% obscuration) due to the eclipse. The analysis is done under total eclipse conditions and non-total eclipse conditions. Results obtained suggest that the model was able to reproduce with high accuracy both the daily variation and the eclipse impacts of E and F1 layers in the majority of the stations evaluated (except in Jicamarca station). The comparison at the F2 layer indicates small differences (<7.8%) between the predictions and observations at all stations during the eclipse periods. Additionally, statistical metrics reinforce the conclusion of a good performance of the model. Predicted and calibrated Total Electron Content (TEC, using 3 different techniques) are also compared. Results show that, although none of the selected TEC calibration methods have a good agreement with the SUPIM-INPE prediction, they exhibit similar trends in most of the cases. We also analyze data from the Jicamarca Incoherent Scatter Radar (ISR), and Swarm-A and GOLD missions. The electron temperature changes observed in ISR and Swarm-A are underestimated by the prediction. Also, important changes in the O/N2 ratio due to the eclipse, have been observed with GOLD mission data. Thus, future versions of the SUPIM-INPE model for eclipse conditions should consider effects on thermospheric winds and changes in composition, specifically in the O/N2 ratio.

Validation of equatorial electrojet derived from Swarm observations using ground based magnetometers

This paper presents the analysis of the Equatorial electrojet (EEJS) and Counter equatorial electrojet (CEJS) at quiet times (Kp⩽3) deduced from the absolute scalar magnetometers (ASM) of the Swarm satellites. The EEJS and CEJS were compared with their corresponding values, EEJG and CEJG respectively, from ground magnetometers in the South American, West African, and Asian sectors during the years 2014–2018. The results show that EEJS highly correlated with EEJG, over South American, West African and Asian sectors with correlation coefficients of 0.91, 0.77 and 0.92 respectively. CEJS with CEJG also showed a reasonably good correlation of 0.78, 0.98 and 0.83 over South American, West African and Asian sectors respectively. For the first time, the Swarm observations of CEJ and EEJ are validated against CEJ and EEJ from ground magnetometers, over South America, West Africa and Asia. Both the occurrence rates of CEJS and CEJG show similar diurnal and seasonal trends, with the highest occurrence rates in the morning (7:00–9:00 LT) and evening (15:00–19:00 LT) times and the lowest occurrence rates around noon (11:00 to 12:00 LT) time. The seasonal occurrence rates of CEJS and CEJG were high in the solstice months and the lowest rates were during equinox months for all the sectors. The longitudinal variability of CEJS and CEJG show highest occurrence rates in the West African sector and the lowest occurrence rates in the Asian sector. This longitudinal variability of CEJS and CEJG occurrence rates were attributed to the effect of the non-migrating tides, migrating tides and stationary planetary waves. The annual occurrence rates of CEJS and CEJG seemed anti-correlated with F10.7.

Occurrence Rates of SuperDARN Ground Scatter Echoes and Electron Density in the Ionosphere

AbstractGround scatter (GS) echoes in Super Dual Auroral Radar Network (SuperDARN) observations have been always expected to occur under high‐enough electron density in the ionosphere providing sufficient bending of high frequency radio wave paths toward the ground. In this study, we provide direct evidence statistically supporting this notion by comparing the GS occurrence rate for the Rankin Inlet SuperDARN radar and the F region peak electron density measured at Resolute Bay by the Canadian Advanced Digital Ionosonde and incoherent scatter radars RISR‐N/C. We show that the occurrence rate increases with roughly linearly up to about and the trend saturates at larger . One expected consequence of this relationship is correlation in seasonal and solar cycle variations of the GS echo occurrence rate and . GS occurrence rates for a number of SuperDARN radars at middle latitudes, in the auroral zone and in the polar cap are considered separately for daytime and nighttime. The data indicate that the daytime occurrence rates are maximized in winter and nighttime occurrence rates are maximized in summer for middle latitude and auroral zone radars in the Northern Hemisphere, consistent with the winter anomaly (WA) phenomenon. The effect is most evident in the North American and Japanese sectors, and the quality of WA signatures deteriorates in the European and, especially, in the Australian sectors. The effect does not exist in the South American sector and in the polar caps of both hemispheres.

Instantaneous amplitude of low-latitude ionospheric irregularities probed by ROCSAT-1, DEMETER, and FORMOSAT-7/COSMIC-2

The occurrence probability of plasma irregularities has long been used to quantify that of ionospheric scintillations. We use the Hilbert-Huang transform to examine the occurrence probability and the instantaneous total amplitude of plasma irregularities in the low-latitude nighttime ionosphere observed by the low-inclination satellites, ROCSAT-1 during 1999–2004 and FORMOSAT-7/COSMIC-2 (F7C2) in 2020, as well as a high-inclination satellite, DEMETER, during 2006–2010. Generally, the longitudinal distribution of the occurrence probability is similar to that of the total amplitude, except that the probability of ion density irregularity observed by F7C2 and DEMETER yields nonphysical anomalous enhancements over the South American sector during May–August of 2007–2010 and 2020, respectively. S4 scintillations observed by F7C2 show that the anomalous enhancement results from the low ambient density in calculating the occurrence probability during the low solar activity year of 2020. We suggest the instantaneous total amplitude as a better indicator for describing ionospheric plasma irregularities.

Climatology of ionospheric amplitude scintillation on GNSS signals at south American sector during solar cycle 24

Scintillations are caused by ionospheric irregularities and can affect the propagation of trans-ionospheric radio signals. One way to understand and predict the impact of such irregularities on Global Navigation Satellite System (GNSS) signals is through the spatial/temporal characterization of the scintillation's climatology during different phases of a solar cycle covering different latitudes and longitudes. This characterization is performed using amplitude scintillation index S4, during the full solar cycle 24, in the South American (SA) sector. The investigation considers the diurnal, daily, and seasonal variation of S4 index for climatological purpose, and the goal of this study is to investigate the scintillations covering a large spatial scale during the full solar cycle 24. The characterization shows a latitudinal asymmetry, whereas at the south, the scintillations were more frequent and their peak was more distant from the magnetic equator, which can be attributed by the South Atlantic Magnetic Anomaly (SAMA), and/or by the transequatorial meridional neutral winds. It also shows a longitudinal asymmetry, where the scintillations at the eastern sector occurred between November and February, while at the western sector, they occurred during the months of October, November, February and March, which can be attributed to the difference between the magnetic and geographic equators. The occurrence of scintillations during two distinct geomagnetic storms with similar storm time in the SA sector is also presented.

Ionospheric response to the 26 August 2018 geomagnetic storm along 280° E and 316° E in the South American sector

This paper studies the response of the ionospheric parameters critical frequency (foF2), their height (hmF2), and Total Electron Content (TEC) at mid, low, and near-equatorial latitudes of the South American sector during the intense geomagnetic storm of 26 August 2018.

Effects of the 12 May 2021 Geomagnetic Storm on Georeferencing Precision

In this work, we present the positioning error analysis of the 12 May 2021 moderate geomagnetic storm. The storm happened during spring in the northern hemisphere (fall in the south). We selected 868 GNSS stations around the globe to study the ionospheric and the apparent position variations. We compared the day of the storm with the three previous days. The analysis shows the global impact of the storm. In the quiet days, 93% of the stations had 3D errors less than 10 cm, while during the storm, only 41% kept this level of accuracy. The higher impact was over the Up component. Although the stations have algorithms to correct ionospheric disturbances, the inaccuracies lasted for nine hours. The most severe effects on the positioning errors were noticed in the South American sector. More than 60% of the perturbed stations were located in this region. We also studied the effects produced by two other similar geomagnetic storms that occurred on 27 March 2017 and on 5 August 2019. The comparison of the storms shows that the effects on position inaccuracies are not directly deductible neither from the characteristics of geomagnetic storms nor from enhancement and/or variations of the ionospheric plasma.