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This work uses the Disturbance Ionosphere indeX (DIX) to evaluate the ionospheric responses to equatorial plasma bubble (EPB) events from 2013 to 2020 over the Brazilian equatorial and low latitudes. We have compared the DIX variations during EPBs to ionosonde and All-Sky Imager data, aiming to evaluate the physical characteristics of these events. Our results show that the DIX was able to detect EPB-related TEC disturbances in terms of their intensity and occurrence times. Thus, the EPB-related DIX responses agreed with the ionosphere behavior before, during, and after the studied cases. Finally, we found that the magnitude of those disturbances followed most of the trends of solar activity, meaning that the EPB-related total electron content variations tend to be higher (lower) in high (low) solar activity.

On September 6, 2017, the solar active region AR 2673 emitted two solar flares: the first at 08:57 UT (X2.2) and the second at 11:53 UT (X9.3); both were powerful enough to black-out high and low frequency radio waves (where UT is universal time). The X9.3 was the strongest solar flare event in the past decade. In this study, we took the advantage of these two extreme flare events to investigate corresponding effects on the ionosphere using multi-instrument observations from magnetometers, Global Positioning System – Total Electron content (GPS-TEC) receivers, ionosondes and Swarm satellites over a large geographical extent covering South American, African and European sectors. During the X2.2 flare, European and African sectors were sunlit and during X9.3 European, African, and South American sectors were sunlit and exposed to the solar flare radiation. During the X2.2 flare, there was an ionosonde blackout for a duration of about 45 min, while during the X9.3 flare this blackout lasted for 1 h and 30 min. The blackout are seen over a large global extent which demonstrates the severity of solar flare events in disrupting the radio communication. The horizontal component of Earth’s geomagnetic field has shown ripples and enhancements during these flare events. The ionospheric Vertical Total Electron Content (VTEC) showed a positive phase along with an intensification of the Equatorial Ionization Anomaly (EIA) over the South American and African sectors. The dynamical and physical processes associated with the TEC and EIA variabilities due to solar flare are discussed.

This work uses the Disturbance Ionosphere indeX (DIX) to evaluate the ionospheric responses to Equatorial Plasma Bubbles (EPBs) events from 2013 to 2020 over the Brazilian equatorial and low latitudes. We have compared the DIX variations during EPBs to ionosonde and All-Sky Imager data, aiming to evaluate the physical characteristics of these events. Our results show that the DIX was able to detect EPB-related TEC disturbances in terms of their intensity and occurrence times. Thus, the EPB-related DIX responses agreed with the ionosphere behavior before, during, and after the studied cases. Finally, we found that the magnitude of those disturbances followed most of the trend of solar activity, meaning that the EPB-related TEC variations tend to be higher (lower) in high (low) solar activity.

This work presents an analysis of the ionospheric responses to the solar eclipse that occurred on December 14, 2020, over the Brazilian sector. This event partially covers the south of Brazil, providing an excellent opportunity to study the modifications in the peculiarities that occur in this sector, as the Equatorial Ionization Anomaly (EIA). Therefore, we used the Digisonde data available in this period for two sites, Campo Grande (CG, 20.47° S, 54.60° W, dip ∼23° S) and Cachoeira Paulista (CXP, 22.70° S, 45.01° W, dip ∼35° S), assessing the E, and F regions, and Es layer behaviors. Additionally, a numerical model (MIRE, Portuguese acronym for E Region Ionospheric Model) is used to analyze the E layer dynamics modification around these times. The results show the F1 region disappearance and an apparent electronic density reduction in the E region during the solar eclipse. We also analyzed the total electron content (TEC) maps from the Global Navigation Satellite System (GNSS) that indicate a weakness in the EIA. On the other hand, we observe the rise of the Es layer electron density, which is related to the gravity waves strengthened during solar eclipse events. Finally, our results lead to a better understanding of the restructuring mechanisms in the ionosphere at low latitudes during the solar eclipse events, even though they only partially reached the studied regions.

F region vertical drifts (Vz) are the result of the interaction between ionospheric plasma with the zonal electric field and the Earth's magnetic field. Abrupt variations in Vz are strongly associated with the occurrence of plasma irregularities (spread F) during the nighttime periods. These irregularities are manifestations of space weather in the ionosphere's environment without necessarily requiring a solar burst. In this context, the Brazilian Space Weather Study and Monitoring Program (Embrace) of the National Institute for Space Research (INPE) has been developing different indexes to analyze these ionospheric irregularities in the Brazilian sector. Therefore, the main purpose of this work is to produce a new ionospheric scale based on the analysis of the ionospheric plasma drift velocity, named AV. It is based on the maximum value of Vz (Vzp), which in turn is calculated through its relationship with the virtual height parameter, h′F, measured by the Digisonde Portable Sounder (DPS-4D) installed in São Luís (2∘ S, 44∘ W; dip: −2.3∘). This index quantifies the time relationship between the Vz peak and the irregularity observed in the ionograms. Thus, in this study, we analyzed 7 years of data, between 2009 and 2015, divided by season in order to construct a standardized scale. The results show there is a delay of at least 15 min between the Vzp observation and the irregularity occurrence. Finally, we believe that this proposed index allows for evaluating the impacts of ionospheric phenomena in the space weather environment.

In the present work, we evaluate a new method for determining a non-perturbed Total Electron Content (TEC) reference to apply on a new version of the disturbance ionosphere index (DIX). This method is based on calculating a 3-hour moving average over the TEC obtained during a given reference day. We compared the proposed method with TEC values obtained from monthly medians and the International Reference Ionosphere (IRI) model to evaluate its performance. The results are presented and discussed in terms of a dispersion coefficient between each method and the averaged TEC from the five quietest days of each month of 2015, over three Brazilian sites. Finally, we calculated the DIX based on the proposed method and compared it with the original DIX values obtained during the St. Patrick’s Day magnetic storm (17-18 March 2015). Differences between the two approaches are discussed, and the results showed that the non-perturbed reference determination could highly influence the quality of the DIX calculation. Keywords: TEC, DIX, Ionospheric Indices, space weather. RESUMO. No presente trabalho, avaliamos um novo metodo para determinar um Conteudo Eletronico Total (TEC) de referencia para aplica-lo em uma nova versao do indice de perturbacao da ionosfera (DIX). Este metodo baseia-se no calculo de uma media movel de 3 horas sobre o TEC obtido durante um determinado dia de referencia. Comparamos o metodo proposto com os valores de TEC obtidos a partir de medianas mensais e do modelo IRI para avaliar o seu desempenho. Os resultados sao apresentados e discutidos em termos de um coeficiente de dispersao entre cada metodo e a media do TEC para os cinco dias mais calmos de cada mes de 2015, em tres localidades brasileiras. Finalmente, calculamos o DIX com base no metodo proposto e o comparamos com os valores de DIX originais obtidos durante a tempestade geomagnetica do dia de St. Patrick (17-18 de marco de 2015). As diferencas entre as duas abordagens sao discutidas, e os resultados mostram que a determinacao do TEC de referencia nao perturbado pode influenciar diretamente a qualidade do indice DIX. Palavras-chave: TEC, DIX, Indices Ionosfericos, clima espacial.

The ROTI index based on the variation of the TEC is used to detect and characterize the ionospheric irregularities. In the present work, we present a comparative study of five different methodologi...

Nighttime airglow images observed at the low-latitude site of Sao Joao do Cariri (7.4S, 36.5W) showed the presence of a medium-scale atmospheric gravity wave (AGW) associated with the...

In the present work, we propose and evaluate a new method for the determination of a non-perturbed Total Electron Content (TEC) reference to apply it on a new version of the disturbance ionosphere index (DIX). This method is based on the calculation of a 3-hour moving average over the TEC obtained during a given reference day (named 3hMAQd method). In this context, the reference day is supposed to represent a quiet pattern considering geomagnetic and ionospheric features. To evaluate its performance, we compared the proposed method with TEC values obtained from monthly medians and the International Reference Ionosphere (IRI) model. The results are presented and discussed in terms of a dispersion coefficient between each method and the averaged TEC from the five quietest days of each month of 2015, over three Brazilian sites. Finally, we calculated the new DIX based on our proposed method and compared it with the original DIX values obtained during the extreme space weather event of St. Patrick’s Day magnetic storm (17–18 March 2015). Differences between the two DIX approaches are discussed to show the improvements in new DIX due to the application of the proposed non-perturbed reference. Moreover, results showed that the quality of the DIX calculation can be highly influenced by the non-perturbed reference determination. In this regard, the 3-hour moving average (3hMAQd) method showed to be a quite appropriate technique for the new DIX calculation, besides the 3-hour window matches with ordinary magnetic indices resolution (e.g. Kp and Ksa).

During the solar cycle 24 there was a very intense geomagnetic storm due to the St. Patrick's day storm and the effects of this storm on ionosphere has become a topic of extensive space weather investigation. Up to now several aspects of the St. Patrick's ionospheric storm have been study such as the prompt penetration electric fields (PPEFs), TEC changes, electron density disturbances, plasma drift, O+ concentration modification, hemispherical asymmetry developments, equatorial ionization anomaly (EIA) modification, and ionospheric irregularities. Besides all these important studies, there are some essential aspects, which have not been addressed yet, related to the occurrence of multi-scale ionospheric irregularities. In this paper, we present and discuss the generation and suppression of multi-scale ionospheric irregularities, using the observations conducted in the Latin American Sector from 4 ionosondes, 20 dual frequency GPS stations, and JULIA radar observations during the month of March 2015, which includes the St. Patrick's day geomagnetic storm period. Suppression of large-small scales ionospheric irregularities has occurred during the main and second night of the recovery phases. However, during the first night of recovery phase there was post-midnight ionospheric irregularities.

The geomagnetic field in the Brazilian sector is influenced by the South American Magnetic Anomaly (SAMA) that causes a decrease in the magnitude of the local geomagnetic field when compared to other regions in the world. Thus, the magnetometer network and data set of space weather over Brazil led by Embrace are important tools for promoting the understanding of geomagnetic fields over Brazil. In this sense, in this work we used the H component of geomagnetic fields obtained at different sites in South America in order to compare results from the phase coherence obtained from wavelet transform (WT). Results from comparison between Cachoeira Paulista (CXP) and Eusébio (EUS), and Cachoeira Paulista and São Luis (SLZ), indicated that there exist some phenomena that occur simultaneously in both locations, putting them in the same phase coherence. However, there are other phenomena putting both locations in a strong phase difference as observed between CXP and Rio Grande, Argentina (RGA). This study was done for a specific moderate geomagnetic storm that occurred in March 2003. The results are explained in terms of nonlinear interaction between physical phenomena acting in distinct geographic locations and at different times and scales. Keywords. Geomagnetism and paleomagnetism (time variations – diurnal to secular)

This work analysis the blanketing sporadic layers (Es b ) behavior over Sao Luis, Brazil (2° 31′ S, 44° 16′ W, dip: −4.80) which is classified as a transition region between equatorial and low-latitude. Hence, some peculiarities can appear as Es b occurrence instead of the common Es q , which is a non-blanketing irregularity layer. The analysis presented here was obtained using a modified version of a theoretical model for the E region (MIRE), which computes the densities of the metallic ions (Fe + and Mg + ) and the densities of the main molecular ions (NO + , O 2 + , N 2 + ) by solving the continuity and momentum equations for each one of them. In that model, the Es layer physics driven by both diurnal and semidiurnal tidal winds are taken into account and it was extended in height coverage by adding a novel neutral wind model derived from the all-sky meteor radar measurements. Thus, we provide more trustworthy results related to the Es layer formation in the equatorial region. We verified the contribution of each tidal wind component to the Es b layer formation in this equatorial region. Additionally, we compared the Es layer electron density computed by MIRE with the data obtained by using the blanketing frequency parameter ( fb Es) deduced from ionograms. The results show that the diurnal component of the tidal wind is more important in the Es b layer formation whereas the semidiurnal component has a little contribution in our simulations. Finally, it was verified that the modified MIRE presented here can be used to study the Es b layers occurrence over the equatorial region in the Brazilian sector.

We present the first simultaneous observation of mesopause sodium (Na) and potassium (K) layer by a lidar which has Na and K channel simultaneously at the South Hemisphere site, Sao Jose dos Campos (23.1°S, 45.9°W). Measurements reported here were conducted on two nights with 3.5 and 8 h of observations in November 2016. On 20 November 2016, sporadic layers in both Na and K layer occurred above 100 km, and the higher layers corresponded well with sporadic E (Es) layer. And the density of Na at 100–105 km is higher than that at main layer around 90 km, but K density around 100 km is at least 3 times smaller compared with the K density around 90 km for the similar period. On 21 November 2016, both sporadic layers occurred in main layer height with obvious descending variations with time, which seems like tidal induced. Notably, the peak K/Na ratio slowly increased with time. And Na layer and K layer showed different processes along with time with K density reaching its maximum 1 h later than that of Na. Correlations of Na/K density, Es, and winds were also discussed.

This work presents new results about sporadic E-layers (Es layers) using GPS (global positioning system) radio occultation (RO) measurements obtained from the FORMOSAT-3/COSMIC satellites and digisonde data. The RO profiles are used to study the Es layer occurrence as well as its intensity of the signal-to-noise ratio (SNR) of the 50 Hz GPS L1 signal. The methodology was applied to identify the Es layer on RO measurements over Cachoeira Paulista, a low-latitude station in the Brazilian region, in which the Es layer development is not driven tidal winds only as it is at middle latitudes. The coincident events were analyzed using the RO technique and ionosonde observations during the year 2014 to 2016. We used the electron density obtained using the blanketing frequency parameter (fbEs) and the Es layer height (h'Es) acquired from the ionograms to validate the satellite measurements. The comparative results show that the Es layer characteristics extracted from the RO measurements are in good agreement with the Es layer parameters from the digisonde. Keywords. Ionosphere (ionosphere–atmosphere interactions)

We have analyzed low-latitude ionospheric current responses to two intense (X-class) solar flares that occurred on 13 May 2013 and 11 March 2015. Sudden intensifications, in response to solar flare radiation impulses, in the Sq and equatorial electrojet (EEJ) currents, as detected by magnetometers over equatorial and low-latitude sites in South America, are studied. In particular we show for the first time that a 5 to 8 min time delay is present in the peak effect in the EEJ, with respect that of Sq current outside the magnetic equator, in response to the flare radiation enhancement. The Sq current intensification peaks close to the flare X-ray peak, while the EEJ peak occurs 5 to 8 min later. We have used the Sheffield University Plasmasphere-Ionosphere Model at National Institute for Space Research (SUPIM-INPE) to simulate the E-region conductivity enhancement as caused by the flare enhanced solar extreme ultraviolet (EUV) and soft X-rays flux. We propose that the flare-induced enhancement in neutral wind occurring with a time delay (with respect to the flare radiation) could be responsible for a delayed zonal electric field disturbance driving the EEJ, in which the Cowling conductivity offers enhanced sensitivity to the driving zonal electric field. Keywords. Ionosphere (equatorial ionosphere)

In this work, we use a new version of the Disturbance Ionosphere Index (DIX) to evaluate ionospheric disturbances over the Brazilian region during two intense geomagnetic storms (22 June 2015 and St. Patrick's Day storm). The DIX values were obtained from the deviation of Total Electron Content (TEC) data acquired during the geomagnetically disturbed days in relation to a non-perturbed TEC reference to provide a single and dimensionless value of the ionospheric degree of perturbation during the magnetic events. Moreover, we used F-layer parameters (foF2 and h’F) measured by ionosondes to identify the ionospheric impacts of storm-time electric fields observed as perturbations in the DIX. Our results show that the geomagnetic storms caused large perturbations in the ionosphere as observed by increases/decreases in the TEC over different latitudinal sectors, which were also observed in the foF2, h’F, and DIX values. Therefore, the DIX has shown to be a useful parameter for observing the ionospheric impact under prompt penetration and disturbance dynamo electric field events, as well as to ionospheric disturbances related to the pre-storm period. Finally, from those observations, we found that the DIX resembles the ionosonde measurements, and that it is consistent with the physical processes that occurred during each phase of the geomagnetic storms.

In this paper, the effects of a minor sudden stratospheric warming (SSW) event of 2012 in the ionosphere over South American and African sectors have been studied using C/NOFS satellite data and GPS observations. Also, the magnetometer measurements obtained at two stations in the equatorial and low-latitude regions in the South American sector are presented. There were significant Vertical Total Electron Content (VTEC) depletions in the afternoon in both South American and African sectors during the 2012 minor SSW event. A novel feature of the present study is the reduction of the quasi 16-day oscillation (periods ranging from 11 to 20 days) in the daily averaged VTEC in the Brazilian and African sector during an SSW event. Also, the results for the Brazilian sector show an amplification of the ~2–6 day period in the daily averaged VTEC at equatorial and low-latitude regions, after the SSW temperature peak. This investigation shows that a minor SSW can affect the irregularities at ionospheric heights in the Brazilian and African sectors. Ground-based magnetometer measurements in the American sector shows strongly enhanced equatorial electrojet (EEJ) after the SSW temperature peak.

This study analyzes strong sporadic E layer (Es) formation in Boa Vista (BV, 2.8°N, 60.7°W, dip: 18°), a low‐latitude region in the Brazilian sector, which occurred far after the onset of a magnetic storm recovery phase. Such occurrences were observed during seven magnetic storms with available data for BV. Thus, the ionospheric behavior on days around the magnetic storm that occurred on 20 January 2016 was investigated to search for possible explanations. This analysis indicated that the probable mechanism acting during the Es layer strengthening is the zonal westward electric field caused by a disturbance dynamo. The same evidence was also observed in two other magnetic storms at the same location. Hence, a numerical model of the E region dynamics, called MIRE (Portuguese acronym for E Region Ionospheric Model), was used to confirm whether the disturbance dynamo could cause the Es layer intensification. The inputs for the model were the electric field deduced from the vertical drift and the wind components provided by GSWM‐00 model. The simulations indicate that the Es layer density is significantly enhanced when the zonal electric field is present compared to the reference scenario with only the winds. Therefore, it is concluded that the disturbance dynamo electric field is the likely cause of the strong Es layers in the analyzed cases. Finally, the combined results from the model and observational data seem to contribute significantly to advance our understanding of the role of the electric fields in the Es layer formation at low latitudes.

The formation of strong sporadic E-layers (Es) is frequently observed during the recovery phase of the magnetic storms over Boa Vista (BV, 2.8°N, 60.7°W), a low latitude region over the Bra...

The High-Intensity Long-Duration and Continuous AE Activities (HILDCAA) intervals are capable of causing a global disturbance in the terrestrial ionosphere. However, the ionospheric storms' behavior due to these geomagnetic activity forms is still not widely understood. In this study, we seek to comprise the HILDCAAs disturbance time effects in the Total Electron Content (TEC) values with respect to the quiet days' pattern analyzing local time and seasonal dependences, and the influences of the solar wind velocity to a sample of ten intervals occurred in 2015 and 2016 years. The main results showed that the hourly distribution of the disturbance TEC may vary substantially between one interval and another. Doing a comparative to geomagnetic storms, while the positive ionospheric storms are more pronounced in the winter, this season presents less geoeffectiveness or almost none to HILDCAA intervals. It was find an equinoctial anomaly, since the equinoxes represent more ionospheric TEC responses during HILDCAA intervals than the solstices. Regarding to the solar wind velocities, although HILDCAA intervals are associated to High Speed Streams, this association does not present a direct relation regards to TEC disturbances in low and equatorial latitudes.

F region vertical drifts (Vz) are the result of the interaction between the ionospheric plasma with the zonal electric field and the Earth's magnetic field. Abrupt variations in Vz are strongly associated with the occurrence of plasma irregularities (spread-F) during the nighttime periods. These irregularities are manifestations of the space weather in the ionosphere environment without necessarily require a solar burst. In this context, the Brazilian Space Weather Study and Monitoring Program (Embrace) of the National Institute for Space Research (INPE) has been developing different indexes to analyze these ionospheric irregularities in the Brazilian sector. Therefore, the main purpose of this work was to produce a new ionospheric scale based on the analysis of the ionospheric plasma drift velocity, named AV. It is based in the maximum value of Vz (Vzp), which in turn is calculated through its relationship with the virtual height parameter, h’F, measured by the Digisonde Portable Sounder (DPS-4D) installed in São Luís (2° S, 44° O, dip: −2,3°). This index quantifies the time relation between the Vz peak and the irregularity observed in the ionogramas. Thus, in this study, we analyzed 8 years of data, between 2009 and 2015, divided by season in order to construct a standardized scale. The results show there is a delay of at least 15 minutes between Vzp observation and the irregularity occurrence. Finally, we believe that this proposed index allow evaluating the impacts of ionospheric phenomena in the Space Weather environment recently.

In this work, we present the uncertainties of the empirical model developed to predict the solar quiet regular daily field variation (Sq) over the Brazilian sector called the Solar Quiet Reference Field (SQRF) model. The SQRF is based on the magnetic station records from the Embrace Magnetometer Network (Embrace MagNet) during the solar cycle 24. Although the prediction and the magnetic field records have a good agreement, we observe that each magnetic station shows a random error behavior, propagating small errors in the model. Also, some physical aspects, as tidal winds and ionospheric conductivity, may have influenced our predictions. Thus, these uncertainties in the Sq field can propagate errors and influence geomagnetic indices' calculation by erroneously scaling the geomagnetic disturbances. In this context, we introduce a new approach to derive a ‘real-time’ geomagnetic index based on the SQRF model for the Sq-H field over the South American sector. We analyze one geomagnetic storm event to show that the results have a good representation of the geomagnetic indices. Finally, this analysis yields a new approach to derive the geomagnetic index for space weather applications and studies that requires an Sq field prediction.

This work presents new results about simulations of blanketing sporadic E-layers, Esb, using a modified version of a theoretical model for the E region (MIRE) for a Brazilian region: Cachoeira Paulista, a low latitude station. MIRE computes the densities of the metallic ions (Fe+ and Mg+) and of the main molecular ions (NO+, O2+, N2+) by solving the continuity and momentum equations for each one of them. Additionally, this model includes the physics of Es layer development driven by tidal winds. In this study, we extend MIRE adding a novel neutral wind model derived from the all-sky meteor radar measurements, which provides more trustworthy results related to the Es layer formation in the Brazilian sector. Afterwards, this new model is validated comparing the computed electron density for the Es layer with the electron density obtained using the blanketing frequency parameter (fbEs) deduced from ionograms in the analyzed region. The results show that the values computed by the extended MIRE are in good agreement with the observational data for the Es layers formed by the wind shear mechanism. Therefore, the extended MIRE presented in this work is the only available model that allows simulating Esb layers with a much higher confidence level for the low-latitude in the Brazilian sector.

The effects of high-energy particle precipitation on mesospheric and stratospheric ozone have been investigated during the last decades. However, while these effects have been widely discussed for the auroral region, little is known about the role of the high-energy particle precipitation on the stratospheric composition and thermal structure in the tropical/subtropical region. Here we show that the spatial distribution of both the stratospheric ozone and temperature in the southern hemisphere matches the pattern of the Southern Hemisphere Magnetic Anomaly. We found that during the austral winter and spring, in the subtropical region (below 30°S), the reduction of the stratospheric ozone and temperature occurs systematically in the magnetic anomaly area. The differences between the temperatures inside the magnetic anomaly (60°W) and outside the anomaly (150°E) for 42.5°S from June to November are higher than 2 K. The maximum difference at this latitude is approximately 5.9 K and occurs in October during the austral spring.

Made available in DSpace on 2019-10-04T12:34:23Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-12-01 CONACyT Posgrado en Ciencias de la Tierra, UNAM Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) CONACYT CONACYT-AEM DGAPA-PAPIIT Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) DGAPA-PAPIIT project NSF National Science Foundation NASA-ROSES UNAM-PAPIIT The present work is the first of a two-part weather study of the ionospheric Total Electron Content (TEC), based on data collected by four ground-based Global Navigation Satellite System networks that cover the whole Latin America from the Patagonia to the north of Mexico. From the best of our knowledge, the maps presented here are the first TEC maps obtained using ground-based data that covers the entire Latin America region, which represent an advance to the space weather monitoring and forecasting of the ionosphere. This work provides a qualitative and quantitative daytime analysis of the ionospheric TEC variation, which encompasses: (a) the response of TEC to the solar flux at midday; (b) the seasonal variation of TEC in different latitudinal ranges; and (c) the North-South asymmetry of TEC over Latin America. The response to the solar flux is based on day-to-day TEC variations during two periods of different solar activity conditions: 2011 (ascending phase) and 2014 (maximum). The approximations of meridional wind component derived from Horizontal Wind Model-14 model and h(m)F(2) obtained from International Reference Ionosphere model were used. Equinoctial asymmetries with an opposite configuration in high and moderate solar activity were identified in the TEC variation. For 2011, it was related to the solar flux change. However, in 2014, according to the h(m)F(2) variation, the influence of neutral wind becomes dominant. Among the results, we highlight an absence of winter anomaly in the Northern Hemisphere in 2014 and a stronger annual anomaly for latitudes under -20 degrees. Univ Autonoma Nuevo Leon, Fac Ciencias Fis Matemat, LANCE, Monterrey, Mexico Inst Nacl Pesquisas Espaciais, Sao Jose Dos Campos, Brazil Univ Nacl Autonoma Mexico, Inst Geofis, Unidad Michoacan, LANCE, Morelia, Michoacan, Mexico Inst Fed Educ Ciencia & Tecnol Sao Paulo, Jacarei, Brazil MIT, Haystack Observ, Westford, MA 01886 USA Univ Nacl Autonoma Mexico, Unidad Morelia, Escuela Nacl Estudios Super, Morelia, Michoacan, Mexico Univ Nacl Autonoma Mexico, Inst Geofis, Unidad Michoacan, CONACyT, Morelia, Michoacan, Mexico Univ Estadual Paulista, Dept Cartog, Presidente Prudente, Brazil Univ Estadual Paulista, Dept Cartog, Presidente Prudente, Brazil CNPq: 303643/2017-0 CONACYT: LN 293598 CONACYT: PN 2015-173 CONACYT: 220981 CONACYT: 253760 CONACYT: 256012 CONACYT: 2017-01-5955 CONACYT: 253691 CONACYT-AEM: 2017-01-292684 DGAPA-PAPIIT: IN106916 DGAPA-PAPIIT: IN104213 DGAPA-PAPIIT: IN109315-3 DGAPA-PAPIIT: IN104818-3 FAPESP: 2014/11198-9 CAPES: 1622967 DGAPA-PAPIIT project: IN101718 NSF: AGS-1242204 National Science Foundation: EAR-1338091 NASA-ROSES: NNX12AQ08G UNAM-PAPIIT: IA107116 UNAM-PAPIIT: IN118119

We have being studying the zonal and vertical E region electric field components inferred from the Doppler shifts of type 2 echoes (gradient drift irregularities) detected with the 50 MHz backscatter coherent radar set at Sao Luis, Brazil (SLZ, 2.3°S, 44.2°W) during the solar cycle 24. In this report we present the dependence of the vertical and zonal components of this electric field with the solar activity, based on the solar flux F10.7. For this study we consider the geomagnetically quiet days only (Kp ≤ 3+). A magnetic field-aligned-integrated conductivity model was developed for proving the conductivities, using the IRI-2007, the MISIS-2000, and the IGRF-11 models as input parameters for ionosphere, neutral atmosphere, and Earth magnetic field, respectively. The ion-neutron collision frequencies of all the species are combined through the momentum transfer collision frequency equation. The mean zonal component of the electric field, which normally ranged from 0.19 to 0.35 mV/m between the 8 and 18 h (LT) in the Brazilian sector, show a small dependency with the solar activity. Whereas the mean vertical component of the electric field, which normally ranges from 4.65 to 10.12 mV/m, highlights the more pronounced dependency of the solar flux.

The equatorial electrojet (EEJ) is a narrow band of current flowing eastward at the ionospheric E region altitudes along the dayside dip equator. Mutually perpendicular electric and magnetic fields over the equator results in the formation of equatorial ionization anomaly (EIA), which in turn generates large electron density variabilities. Simultaneous study on the characteristics of EEJ and EIA is necessary to understand the role of EEJ on the EIA variabilities. This is helpful for the improved estimation of total electron content (TEC) and range delays required for satellite-based communication and navigation applications. Present study reports simultaneous variations of EEJ and GPS-TEC over Indian and Brazilian sectors to understand the role of EEJ on the day-to-day characteristics of the EIA. Magnetometer measurements during the low solar activity year 2004 are used to derive the EEJ values over the two different sectors. The characteristics of EIA are studied using two different chains of GPS receivers along the common meridian of 77°E (India) and 45°W (Brazil). The diurnal, seasonal, and day-to-day variations of EEJ and TEC are described simultaneously. Variations of EIA during different seasons are presented along with the variations of the EEJ in the two hemispheres. The role of EEJ variations on the characteristic features of the EIA such as the strength and temporal extent of the EIA crest has also been reported. Further, the time delay between the occurrences of the day maximum EEJ and the well-developed EIA is studied and corresponding results are presented in this paper.

Equatorial ionosphere plasma bubbles over the South American continent were successfully observed by mapping the total electron content (TECMAP) using data provided by ground-based GNSS receiver networks. The TECMAP could cover almost all of the continent within ~4000 km distance in longitude and latitude, monitoring TEC variability continuously with a time resolution of 10 min. Simultaneous observations of OI 630 nm all-sky image at Cachoeira Paulista (22.7°S, 45.0°W) and Cariri (7.4°S, 36.5°W) were used to compare the bubble structures. The spatial resolution of the TECMAP varied from 50 km to 1000 km, depending on the density of the observation sites. On the other hand, optical imaging has a spatial resolution better than 15 km, depicting the fine structure of the bubbles but covering a limited area (~1600 km diameter). TECMAP has an advantage in its spatial coverage and the continuous monitoring (day and night) form. The initial phase of plasma depletion in the post-sunset equatorial ionization anomaly (PS-EIA) trough region, followed by development of plasma bubbles in the crest region, could be monitored in a progressive way over the magnetic equator. In December 2013 to January 2014, periodically spaced bubble structures were frequently observed. The longitudinal spacing between the bubbles was around 600–800 km depending on the day. The periodic form of plasma bubbles may suggest a seeding process related to the solar terminator passage in the ionosphere.

There is a growing appreciation that the environmental conditions that we call space weather impact the technological infrastructure that powers the coupled economies around the world. With that comes the need to better shield society against space weather by improving forecasts, environmental specifications, and infrastructure design. [...] advanced understanding of space weather requires a coordinated international approach to effectively provide awareness of the processes within the Sun-Earth system through observation-driven models. This roadmap prioritizes the scientific focus areas and research infrastructure that are needed to significantly advance our understanding of space weather of all intensities and of its implications for society. Advancement of the existing system observatory through the addition of small to moderate state-of-the-art capabilities designed to fill observational gaps will enable significant advances. Such a strategy requires urgent action: key instrumentation needs to be sustained, and action needs to be taken before core capabilities are lost in the aging ensemble. We recommend advances through priority focus (1) on observation-based modeling throughout the Sun-Earth system, (2) on forecasts more than 12 hrs ahead of the magnetic structure of incoming coronal mass ejections, (3) on understanding the geospace response to variable solar-wind stresses that lead to intense geomagnetically-induced currents and ionospheric and radiation storms, and (4) on developing a comprehensive specification of space climate, including the characterization of extreme space storms to guide resilient and robust engineering of technological infrastructures. The roadmap clusters its implementation recommendations by formulating three action pathways, and outlines needed instrumentation and research programs and infrastructure for each of these. [...], In press for Advances of Space Research: an international roadmap on the science of space weather, commissioned by COSPAR and ILWS (63 pages and 4 figures)

The present work is the first of a two-part paper on the Embrace Magnetometer Network. In this part, we present the new Embrace Magnetometer Network (Embrace MagNet) in South America, which is originally planned to cover most of the eastern portion of the Southern America longitudinal sector by installing and operating fluxgate magnetometer stations. We discuss the purpose and scientific goals of the network, associated with aeronomy and space weather. We provide details on the instrumentation, location of the sensors, sensitivity matching process, gain matching process, and magnetometer installation. In addition, we present and discuss details about the data storage, near-real time display, and availability., Facultad de Ciencias Astronómicas y Geofísicas

The present work is the second of a two-part paper on the Embrace Magnetometer Network. In this part, we provide some of the first scientific findings that we have already achieved with this network. We identified the diurnal and the seasonal natural variations of the H component. We provided the precise determination of sudden storm commencements and sudden impulse. We showed that the ΔH amplitudes derived from the Embrace MagNet during intense magnetic storm are in very good agreement with the Dst index. We showed that it is possible to investigate the effects on the solar quiet ionospheric current systems as a response to the X-class solar flares occurring during daytime under magnetically quiet conditions., Facultad de Ciencias Astronómicas y Geofísicas

The present study investigates the ionospheric F region response in the Brazilian sector due to sudden stratospheric warming (SSW) events of 2014. The data used for this work are obtained from GPS receivers and magnetometer measurements during day of year (DOY) 01 to 120, 2014 at different stations in the equatorial and low-latitude regions in the Brazilian sector. In addition, the data obtained from Communication/Navigation Outage Forecasting System satellites during DOY 01 to 75 of 2014 are used. The main novelty of this research is that, during the 2014 SSW events, daytime vertical total electron content (VTEC) shows a strong increase on the order of about 23% and 11% over the equatorial and low-latitude regions, respectively. We also observed that the nighttime VTEC (SSW days) is increased by 8% and 33% over equatorial and low-latitude regions, respectively. The magnetometer measurements show a strong counterelectrojet during the SSW days. The results show an amplification of the 0.5 day and ~2–16 day periods in the VTEC and equatorial electrojet during the SSWs. The occurrences of ionospheric irregularities during the SSW events are around 84% and 53% in the equatorial and low-latitude regions, respectively, which is less frequent when compared with those during the pre-SSW periods.

The total electron content (TEC) in the equatorial and low-latitude ionosphere over Brazil was monitored in two dimensions by using 2011 data from the ground-based global navigation satellite system (GNSS) receiver network operated by the Brazilian Institute for Geography and Statistics. It was possible to monitor the spatial and temporal variations in TEC over Brazil continuously during both day and night with a temporal interval of 10 min and a spatial resolution of about 400 km. The daytime equatorial ionization anomaly (EIA) and post-sunset plasma enhancement (PS-EIA) were monitored over an area corresponding to a longitudinal extension of 4000 km in South America. Considerable day-to-day variation was observed in EIA and PS-EIA. A large latitudinal and longitudinal gradient of TEC indicated a significant ionospheric range error in application of the GNSS positioning system. Large-scale plasma bubbles after sunset were also mapped over a wide range. Depletions with longitudinally separated by more than 800 km were observed. They were extended by more than 2000 km along the magnetic field lines and drifted eastward. It is expected that 2-dimensional TEC mapping can serve as a useful tool for diagnosing ionospheric weather, such as temporal and spatial variation in the equatorial plasma trough and crest, and particularly for monitoring the dynamics of plasma bubbles.

Using global magnetohydrodynamic (MHD) simulations, we investigate the role played by a complex solar structure composed of a corotating interaction region (CIR) followed by solar wind Alfvénic fluctuations on the magnetosphere’s nightside, equatorial electric field oscillations in the ultra-low-frequency range. A series of numerical experiments are performed employing synthetic solar wind inputs resembling those of a real CIR+Alfvénic fluctuation event that reached Earth’s magnetosphere on 2003 April 20. The following is found: (i) Radial electric field component fluctuations are excited via magnetopause boundary motions driven either by solar wind density variations characteristic of CIRs or by solar wind Alfvénic fluctuations with a given oscillation period. (ii) Azimuthal electric field component fluctuations nearer to Earth, that is, at radial distances R less than about 5R E ( Earth radius), are apparently not related to either of the two types of sinusoidal solar wind Alfvénic fluctuations used in this study featuring monochromatic frequencies of 0.833 mHz (20-minute period) and 1.666 mHz (10-minute period). Instead, these innermost azimuthal component fluctuations show enhanced activity when inner magnetosphere convection increases as a result of a southward turning of the interplanetary magnetic field component B z . (iii) Lastly, outermost (R ≳ 7 R E) azimuthal electric field oscillations weakly respond to monochromatic solar wind Alfvénic fluctuations by showing power spectral density peaks at both driving frequencies, but only near the flanks of the magnetopause, thus suggesting that such oscillations are being excited also owing to magnetopause boundary motions driven by solar wind Alfvénic fluctuations.

[1] Recent observations of the low-latitude ionospheric electron density revealed a four-peaked longitudinal structure in the equatorial ionization anomaly when plotted at a constant-local-time frame. It was proposed that neutral wind-driven E region dynamo electric fields due to nonmigrating tidal modes are responsible for this pattern. We examine the four-peaked structure in the observed topside ion density and its manifestation as longitudinal structures in total electron content (TEC) over South America. The strong longitudinal variation in TEC characterized by larger value over Brazilian eastern longitude sector as compared to that over the Peruvian western longitude is modeled using the Sheffield University plasmasphere-ionosphere model (SUPIM) aiming to identify the control factors responsible for the longitude variation. We found that the SUPIM runs using as input the existing standard models of vertical drift, and thermospheric winds do not explain the TEC longitudinal structure. Realistic values of these control parameters were generated based on the strong vertical drift longitudinal variation as determined from magnetometer and Digisonde data and appropriately adjusted winds (horizontal wind model). These realistic vertical drifts together with the modified thermospheric wind, when used as input to the SUPIM, are found to satisfactorily explain the longitudinal differences in the TEC and topside ion density (Ni) over South America. The study shows that the TEC in the whole latitude distribution is larger over the east coast than over the west coast of South America and that the vertical drift and thermospheirc winds control the longitudinal four wave structure in the TEC and Ni.