The eruption of the Hunga Tonga-Hunga Ha’apai volcano on 15 January 2022 dis- turbed the atmosphere at all altitudes. The NASA Ionospheric Connection Explorer (ICON) and ESA Swarm satellites were well placed to observe its impact on the ionospheric wind dynamo. After the lower atmospheric wave entered the dayside, Swarm A observed an eastward and then westward equatorial electrojet (EEJ) on two consecutive orbits, each with magnitudes exceeding the 99.9th percentile of typical variation.

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 Amer- ica 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 occur- rence characteristics near the southern crest of the Equatorial Ionization Anomaly in Argentina (Tucuma ́n, 26.8S, 65.2W; magnetic latitude 15.5S). We used ionosonde and Global Positioning System (GPS) data from November 2014 to December 2019 for different solar and geomagnetic conditions.

1 Mohe Observatory of Geophysics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, 2 Geophysics Center, National Earth System Science Data Center, Beijing, China, 3 Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, 4 Beijing National Observatory of Space Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, 5 College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China, 6 Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing, China, 7 Divisão de Aeronomia, Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Brazil

The equatorial (Esq) and blanketing (Esb) sporadic (Es) layers occur due to the Equatorial Electrojet Current (EEJ) plasma instabilities and tidal wind components, respectively. Both Esq and Esb layers can appear concurrently over some Brazilian equatorial regions due to the peculiar geomagnetic field configuration in this sector. Previous works indicate that the inclination angle limit for the Esq occurrence in ionograms is 7°. However, we found evidence that regions more distant can also experience such equatorial dynamics during disturbed periods.

In this research, we present data-driven forecasting of ionospheric total electron content (TEC) using the Long-Short Term Memory (LSTM) deep recurrent neural network method. The random forest machine learning method was used to perform a regression analysis and estimate the variable importance of the input parameters. The input data are obtained from satellite and ground based measurements characterizing the solar-terrestrial environment. We estimate the relative importance of 34 different parameters, including the solar flux, solar wind density, and speed the three components of interplanetary magnetic field, Lyman-alpha, the Kp, Dst, and Polar Cap (PC) indices. The TEC measurements are taken with 15-s cadence from an equatorial GPS station located at Bogota, Columbia (4.7110° N, 74.0721° W). The 2008–2017 data set, including the top five parameters estimated using the random forest, is used for training the machine learning models, and the 2018 data set is used for independent testing of the LSTM forecasting. The LSTM method as applied to forecast the TEC up to 5 h ahead, with 30-min cadence

CePIA, Departamento de Astronomía, Universidad de Concepción, Concepción, Chile. 2Departamento de Geofísica, Universidad de Concepción, Concepción, Chile. 3 Facultad de Educación y Ciencias Sociales, Universidad Adventista de Chile, Chillán, Chile. 4 Instituto Nacional de Pesquisas Espaciais, INPE, São José dos Campos, São Paulo, Brazil. 5Departamento de Física y Astronomía, Universidad de La Serena, La Serena, Chile. 6 Facultad de Ingeniería y Negocios, Universidad Adventista de Chile, Chillán, Chile. 7Centro Interuniversitario de Física de la Alta Atmósfera, Chile. 8 Laboratorio de Ionosfera, Atmosfera Neutra y Magnetosfera (LIANM), FACET, UNT, Argentina. 9 INFINOA, CONICET -UNT, Argentina. 10Departamento de Ciencias de la Computación, FACET, Universidad Nacional de Tucumán, Tucumán, Argentina. 1 Laboratorio de Telecomunicaciones, FACET, Universidad Nacional de Tucumán, Tucumán, Argentina. 12 Jicamarca Radio Observatory, Instituto Geofísi

This work presents, for the first time, the analysis of the occurrence of ionospheric irregularities during geomagnetic storms at Tucuma´n, Argentina, a low latitude station in the Southern American longitudinal sector (26.9
S, 294.6
E; magnetic latitude 15.5
S) near the southern crest of the equatorial ionization anomaly (EIA). Three geomagnetic storms occurred on May 27, 2017 (a month of low occurrence rates of spread-F), October 12, 2016 (a month of transition from low to high occurrence rates of spread-F) and November 7, 2017 (a month of high occurrence rates of spread-F) are analyzed using Global Positioning System (GPS) receivers and ionosondes. The rate of change of total electron content (TEC) Index (ROTI), GPS Ionospheric L-band scintillation, the virtual height of the F-layer bottom side (h’F) and the critical frequency of the F2 layer (foF2) are considered. Furthermore, each ionogram is manually examined for the presence of spread-F signatures.

Seismic-Atmospheric Ionospheric Disturbances (SAIDs) can be generated by seismic activity. Earth displacement due to earthquakes (EQ) causes effects on the atmosphere up to 300 km in height, as a result of the coupling of the Lithosphere Atmosphere Ionosphere interfaces. For the moderate EQ (Mw=6.3) using GPS receiver data, we detect the SAIDs that are associated with gravity waves with velocities 0.22 and 0.16 km/s. For EQ (Mw=7.1) using magnetometer networks, we detect SAIDs in the form of geomagnetic disturbances that have propagation velocities greater than the velocity of the primary and secondary waves recorded by seismographs, and due to the very high velocities, these disturbances may be associated mainly to the shear or oblique Alfvén waves.

: Comparison With Total Electron Content Estimations and the Modeled Maximum Electron Concentration and Its Height

Total electron content (TEC) values measured with several arrays of dual‐frequency GPS receivers operating continuously and simultaneously at equatorial and low latitudes are used to construct regional maps of TEC over South and Central America and the Caribbean region. This extended database comprises TEC values collected by 126 stations that operated in South America in 2008, 181 stations in 2009, and 324 stations in 2010. The latter year includes GPS stations in Central America and the Caribbean region, extending the TEC coverage from the southern tip of South America to the northern boundary of Mexico (~30°N latitude). The TEC maps contain high (0.5° × 0.5°) spatial resolution and good (30 min) temporal resolution. The most prominent feature of these maps is the day‐to‐day variability that is observed during all seasons and under quiet and active magnetic conditions. Single station plots display TEC variations with time scales of few hours and the appearance of TEC enhancements near‐midnight that can be accounted for by electric fields associated with disturbed magnetic conditions and the reverse fountain effect, respectively. To assess the TEC dependencies upon season, solar flux, magnetic activity, and local time over South and Central America, two statistical procedures were employed. First, we constructed monthly averages of TEC values along three field lines that intersect the magnetic equator at 70°, 60°, and 50°W longitudes that show a complex pattern of variability and symmetry/asymmetry of the equatorial anomaly depending on the season, the longitude, and the solar flux

Ionospheric irregularities can severely degrade radio communication and navigation sys- tems. Geomagnetic storms may afect 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 diferent regions of the world, and in particular in the equatorial ioni- zation anomaly (EIA) where irregularities are usually more intense. This study analyses the efect of geomagnetic storms on ionospheric irregularities. We examined the occur- rence 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 diferent solar sources, between 2015 and 2018.

Esta dissertação visa investigar Distúrbios Ionosféricos Sismogênicos Propagantes, do inglês "Seismic T riggered T ravelling Ionospheric Disturbances"(SAIDs) sobre a América do Sul, a partir de dados geomagnéticos e ionosféricos. Este assunto é relativamente novo no contexto desse continente, que frequentemente hospeda ati- vidades sísmicas. O objetivo deste trabalho é aplicar as ferramentas de análise nos dados obtidos com vários instrumentos e suas interpretações, que podem num futuro próximo, facilitar a previsão de terremotos e tsunamis. Desta forma serão abordados os seguintes tópicos: (1) Aplicação das ferramentas Transformada de Hilbert-Huang (HHT) e Transformada W avelet Contínua (CWT), para detectar propagação de ondas nas séries temporais; (2) Análise dos dados de Conteúdo Eletrônico Total (do inglês T otal Electron Content - TEC), do campo geomagnético e de sismogra- mas utilizando para isso receptores GNSS (Global N avigation Satellite System), magnetômetros e sismômetros, respectivamente; (3) Interpretação das característi- cas observadas dos SAIDs, baseado no mecanismo que envolve as ondas sísmicas, atmosféricas e ionosféricas.

An ionogram is a graph of the time that a vertically transmitted wave takes to return to the earth as a function of frequency. Time is typically represented as virtual height, which is the time divided by the speed of light. The ionogram is shaped by making a trace of this height against the frequency of the transmitted wave. Along with the echoes of the ionosphere, iono- grams usually contain a large amount of noise and interference of different nature that must be removed in order to extract useful information. In the present work we propose a method based on convolutional neural networks to extract ionospheric echoes from digital ionograms. Extraction using the CNN model is compared with extraction using machine learning techniques. From the extracted traces, ionospheric parameters can be determined and electron density profile can be derived.

The zonal electric field and the meridional neutral wind are the principal drivers that define the geometry and characteristics of the equatorial ionization anomaly (EIA). Here we present the response of the EIA to the variability of the zonal electric field based on measurements of the equatorial electrojet (EEJ) currents and trans-equatorial neutral winds for the generation and control of the asymmetries of the EIA crests of total electron content (TEC) in the western side of the South American continent. The EEJ strengths are determined using a pair of magnetometers. The 24-hr trans-equatorial neutral wind profile is measured using the Second-Generation, Optimized, Fabry-Perot Doppler Imager (SOFDI) located near the geomagnetic equator. The EIA is evaluated using TEC data measured by Global Positioning System (GPS) receivers from the Low-Latitude Ionospheric Sensor Network and several other networks in South America. A physics-based numerical model, Low-Latitude Ionospheric Sector, and SOFDI data are used to study the effects of daytime meridional neutral winds on the consequent evolution of an asymmetry in equatorial TEC anomalies during the afternoon and onward for the first time. We find that the configuration parameters such as strength, shape, amplitude, and latitudinal width of the EIAs are affected by the eastward electric field associated with the EEJ under undisturbed conditions. The asymmetries of EIA crests are observed more frequently during solstices and the September equinox than in the March equinox season. Importantly, this study indicates that the meridional neutral wind plays a very significant role in the development of the EIA asymmetry by transporting the plasma up the field lines. This result suggests that a precise observation of the latitudinal TEC profile at low latitudes can be used to derive the meridional wind

We have used total electron content (TEC) values from low, middle, and high latitudes recorded over the American continent and density and ion temperature measured in situ by the DMSP-F15 and F17 satellites during the geomagnetic storms of 3–4 August 2010 and 5–6 August 2011 to study the formation and dynamics of plasma density enhancements that developed during these two storms. Common to both storms are the timing of the main phase that extends between 20 and 24 UT and their seasonality with both storms occurring near the end of theNorthern Hemisphere summer solstice. During both storms, TEC data show incipient equatorial anomalies lacking a poleward expansion beyond 20° magnetic latitude. Two large-scale TEC enhancements were observed at middle latitudes showing a complicated pattern of structuring and merging. The first TEC enhancement corresponds to a storm-enhanced density (SED) seen between 21 and 01 UT on the following day. The second TEC enhancement was observed over Central America, located equatorward of the SED and apparently moving northward. However, careful analysis of the TEC values indicates that this second TEC enhancement is not transported from lower latitudes through a superfountain effect. Instead, the enhanced plasma has a local origin and is driven by a southward directed meridional wind that moves plasma up the tilted magnetic field lines. DMSP flights passing over the second TEC enhancement show a reduction of the ion temperature, confirming an adiabatic expansion of the plasma as it moves up the field lines. It is concluded that the midlatitude TEC enhancements do not arise from a low-latitude ionospheric fountain effect

t The zonal electric field and the meridional neutral wind are the principal drivers that define the geometry and characteristics of the equatorial ionization anomaly (EIA). Here we present the response of the EIA to the variability of the zonal electric field based on measurements of the equatorial electrojet (EEJ) currents and trans-equatorial neutral winds for the generation and control of the asymmetries of the EIA crests of total electron content (TEC) in the western side of the South American continent. The EEJ strengths are determined using a pair of magnetometers. The 24-hr trans-equatorial neutral wind profile is measured using the Second-Generation, Optimized, Fabry-Perot Doppler Imager (SOFDI) located near the geomagnetic equator. The EIA is evaluated using TEC data measured by Global Positioning System (GPS) receivers from the Low-Latitude Ionospheric Sensor Network and several other networks in South America. A physics-based numerical model, Low-Latitude Ionospheric Sector, and SOFDI data are used to study the effects of daytime meridional neutral winds on the consequent evolution of an asymmetry in equatorial TEC anomalies during the afternoon and onward for the first time. We find that the configuration parameters such as strength, shape, amplitude, and latitudinal width of the EIAs are affected by the eastward electric field associated with the EEJ under undisturbed conditions. The asymmetries of EIA crests are observed more frequently during solstices and the September equinox than in the March equinox season. Importantly, this study indicates that the meridional neutral wind plays a very significant role in the development of the EIA asymmetry by transporting the plasma up the field lines. This result suggests that a precise observation of the latitudinal TEC profile at low latitudes can be used to derive the meridional wind

An analysis of the occurrence of equatorial plasma bubbles (EPBs) around the world during the 2015 St. Patrick’s Day geomagnetic storm is presented. A network of 12 Global Positioning System receivers spanning from South America to Southeast Asia was used, in addition to colocated VHF receivers at three stations and four nearby ionosondes. The suppression of postsunset EPBs was observed across most longitudes over 2 days. The EPB observations were compared to calculations of the linear Rayleigh-Taylor growth rate using coupled thermosphere-ionosphere modeling, which successfully modeled the transition of favorable EPB growth from postsunset to postmidnight hours during the storm. The mechanisms behind the growth of postmidnight EPBs during this storm were investigated. While the latter stages of postmidnight EPB growth were found to be dominated by disturbance dynamo effects, the initial stages of postmidnight EPB growth close to local midnight were found to be controlled by the higher altitudes of the plasma (i.e., the gravity term). Modeling and observations revealed that during the storm the ionospheric plasma was redistributed to higher altitudes in the low-latitude region, which made the plasma more susceptible to Rayleigh-Taylor growth prior to the dominance of the disturbance dynamo in the eventual generation of postmidnight EPBs.other networks that operate in South and Central America were used to study the characteristics and origin of traveling ionospheric disturbances (TID) in these regions. The TEC perturbations associated with these TIDs show a high degree of spatial coherence over distances>1000km allowing us to use measurements from receivers spaced by hundreds of km to calculate the TIDs’ travel velocities, propagation direction, and scale size. We first applied the TID analysis to TEC measurements corresponding to 4 July 2011. This processing method is then used to study the characteristics of TIDs for 20 and 21 August 2011, a period when a tropical storm was active in the Caribbean region. A pronounced increase in TID activity was observed in South and Central America at 16 UT on 20 August 2011 lasting until the end of 21 August 2011. The TID velocities show a very variable pattern that depends upon their local time and location. Counter‐streaming TIDs were observed over the western part of South America on 21 August 2011. Regional maps of tropospheric temperature brightness, measured by the GOES‐12 satellite, are used to identify and follow the development of the tropical storm (TS) Irene and several deep convective plumes. TIDs were observed propagating away from TS Irene.

Data from the Low‐Latitude Ionospheric Sensor Network are used to examine ionospheric electrodynamics during quiet, low solar conditions from September to November 2009. The ground‐based magnetometers and the Jicamarca Vertical Incidence Pulsed Ionospheric Radar ionosonde in the Peruvian Sector are used to identify the neutral winds and plasma drifts that control the large‐scale plasma structure of the ionosphere. It is observed that the solar‐ and lunar‐driven semidiurnal tides have a significant influence on the background electrodynamics during this period of extreme solar minimum. The lunar tidal influence of the ionosphere electrodynamics is a large component of the variation of the vertical drift during the geophysically quiet study period. A significant portion, though not all, of the variation through the lunar month can be attributed to the lunar semidiurnal tide.

GPS-TEC data were observed at the same local time at two equatorial stations on both longitudes: Lagos (6.52◦ N, 3.4◦ E, 3.04◦ S magnetic latitude), Nigeria; and Pucallpa (8.38◦ S, 74.57◦ W, 4.25◦ N magnetic latitude), Peru during the minimum (2009, 2010) and ascending (2011) phases of solar cycle 24. These data were grouped into daily, seasonal and solar activity sets. The day-to-day variations in vertical TEC (VTEC) recorded the maximum during 14:00– 16:00 LT and minimum during 04:00–06:00 LT at both longitudes. Seasonally, during solar minimum, maximum VTEC values were observed during March equinox and minimum during solstices. However, during the ascending phase of the solar activity, the maximum values were recorded during the December solstice and minimum during the June solstice. VTEC also increased with solar activity at both longitudes. On longitude by longitude comparison, the African GPS station generally recorded higher VTEC values than the American GPS station. Furthermore, harmonic analysis technique was used to extract the annual and semi-annual components of the amplitudes of the TEC series at both stations. The semi-annual variations dominated the TEC series over the African equatorial station, while the annual variations dominated those over the American equatorial station. The GPS-TEC-derived averages for non-storm days were compared with the corresponding values derived by the IRI-2007 with the NeQuick topside option

TEC values measured by GPS receivers that belong to the low‐latitude ionosphere sensor network (LISN) and several other networks that operate in South and Central America were used to study the characteristics and origin of traveling ionospheric disturbances (TID) in these regions. The TEC perturbations associated with these TIDs show a high degree of spatial coherence over distances>1000km allowing us to use measurements from receivers spaced by hundreds of km to calculate the TIDs’ travel velocities, propagation direction, and scale size. We first applied the TID analysis to TEC measurements corresponding to 4 July 2011. This processing method is then used to study the characteristics of TIDs for 20 and 21 August 2011, a period when a tropical storm was active in the Caribbean region. A pronounced increase in TID activity was observed in South and Central America at 16 UT on 20 August 2011 lasting until the end of 21 August 2011. The TID velocities show a very variable pattern that depends upon their local time and location. Counter‐streaming TIDs were observed over the western part of South America on 21 August 2011. Regional maps of tropospheric temperature brightness, measured by the GOES‐12 satellite, are used to identify and follow the development of the tropical storm (TS) Irene and several deep convective plumes. TIDs were observed propagating away from TS Irene.

The Low-Latitude Ionospheric Sensor Network (LISN) is a distributed observatory designed to nowcast the state and dynamics of the low-latitude ionosphere and to develop forecasts of the electric fields, densities, and equatorial spread F over the South American continent. The LISN observatory consists of three different types of instruments: GPS receivers, fluxgate magnetometers, and vertical incidence pulsed ionospheric radar (VIPIR) ionosondes. This report provides a succinct summary of recent observations obtained using the LISN GPS receivers and complemented with measurements from other instruments and GPS receivers that operate in South America. More specifically, the following are shown here: (1) observations of total electron content (TEC) enhancements that occur near local midnight, (2) maps of TEC perturbations associated with the passage of traveling ionospheric disturbances over South America, and (3) statistics of TEC depletions for 2 years of low solar activity. Near-midnight TEC enhancements consist of sudden increases in TEC that occur after sunset at low latitudes on 30% of the days. These TEC enhancements last for several hours and can have amplitudes between 1 and 50 TEC units. On 11–12 March 2011 the largest TEC enhancement was observed in South America at times when the Jicamarca incoherent scatter radar operated and observed peak densities above 106 el/cc at 300 km altitude. It is suggested that a combination of zonal electric fields and meridional neutral winds are able to redistribute the plasma along the field lines and create regions of enhanced TEC. Maps of TEC perturbations associated with the passage of gravity waves (GWs) over South America have been used to measure the phase velocity and direction of propagation of GWs. The large number of GPS receivers over South America has allowed us to record bubble events for every day during 2008 and 2009. It was found that the number of TEC depletion detections varies with a periodicity of 28 days. It is mentioned how these new observations and the installation of the last four VIPIR ionosondes will lead to new discoveries in the near future

This paper presents for the first time regional plots of total electron content (TEC) depletions derived from GPS observations over the South American continent with a coverage of over 45° longitude (i.e., 35°W to 80°W). We introduce a new numerical algorithm that has been developed to automatically detect TEC bite‐outs that are produced by the transit of equatorial plasma bubbles. This algorithm was applied to TEC values measured by the Low Latitude Ionospheric Sensor Network (LISN) and by receivers that belong to 3 other networks that exist in South America. The general characteristics of the TEC depletions are provided along with their temporal length, local time distribution and depletion depth. The regional day‐to‐day and seasonal variability of the TEC depletions are also presented for 2008, a year of low solar activity. The regional day‐to‐day variability of TEC depletions is highly dynamic, but their seasonal distributions follow the longitudinal characteristics of plasma bubbles presented by other authors. During the equinoxes, TEC depletions are mainly observed on the west coast of South America, and during the December solstice they mostly occur on the east side of the continent. However, in all seasons, we observe days when depletions extend all over the continent. We place these new results in the context of theories of plasma bubble seeding.

We investigate the effects of penetration electric fields, meridional thermospheric neutral winds, and composition perturbation zones (CPZs) on the distribution of low-latitude plasma during the 7–11 November 2004 geomagnetic superstorm. The impact on low-latitude plasma was assessed using total electron content (TEC) measurements from a latitudinally distributed array of ground-based GPS receivers in South America. Jicamarca Radio Observatory incoherent scatter radar measurements of vertical E  B drift are used in combination with the Low-Latitude IONospheric Sector (LLIONS) model to examine how penetration electric fields and meridional neutral winds shape low-latitude TEC. It is found that superfountain conditions pertain between 1900 and 2100 UT on 9 November, creating enhanced equatorial ionization anomaly (EIA) crests at 7201 geomagnetic latitude. Large-amplitude and/or long-duration changes in the electric field were found to produce significant changes in EIA plasma density and latitudinal location, with a delay time of 2–2.5 h