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Item Evidence of anti-correlation between sporadic (Es) layers occurrence and solar activity observed at low latitudes over the Brazilian sector(Elsevier) Fontes Neto, Pedro Alves; Muella, Marcio Tadeu de Assis Honorato; Resende, Laysa Cristina Araújo; Fagundes, Paulo RobertoSporadic E-layers (Es) are thin and denser layers with high ionization observed at about 100–140 km altitude in the E region. Their formation is mainly associated with the tidal components of the diurnal and semidiurnal winds with the convergence of ions driven by the wind shear mechanism. This present work shows evidence of the relationship between the occurrence of Es layers and the solar activity at two observatories located in the Brazilian sector, the near-equatorial site of Palmas (PAL, 10.17 S; 48.33 W; dip lat. 7.31 ) and the low latitude station of Sa ̃o Jose ́ dos Campos (SJC, 23.18 S; 45.89 W; dip lat. 19.35 ). The analysis was performed from Decem- ber/2008 to November/2009 (a period of low solar activity) and from December/2013 to November/2014 (a period of high solar activity) using data collected from two digital ionosondes. Our results show an anti-correlation of the Es layer occurrence concerning the solar activity over both stations studied here. A more clearly observed anti-correlation at the SJC station can be attributed to a greater tidal amplitude at low latitudes. Other relevant aspects of the observations associated with the formation of the Es layers are highlighted and discussed.Item Effects of the terdiurnal tide on the sporadic E (Es) layer development at low latitudes over the Brazilian sector(European Geosciences Union) Fontes, Pedro Alves; Muella, Marcio Tadeu de Assis Honorato; Resende, Laysa Cristina Araújo; Andrioli, Vânia Fátima; Fagundes, Paulo Roberto; Pillat, Valdir Gil; Batista, Paulo Prado; Carrasco, Alexander JoseSporadic E (Es) layers are patches of high ionization observed at around 100–140 km height in the E region. Their formation at low latitudes is primarily associated with the diurnal and semidiurnal components of the tidal winds via the ion convergence driven by the wind shear mechanism. However, recent studies have shown the influence of other tidal modes, such as the terdiurnal tide. Therefore, this work investigates the effect of terdiurnal tide-like oscillations on the occurrence and formation of the Es layers observed over Palmas (10.17∘ S, 48.33∘ W; dip lat. −7.31∘), a low-latitude station in Brazil. The analysis was conducted from December 2008 to November 2009 by using data collected from CADI (Canadian Advanced Digital Ionosonde). Additionally, the E Region Ionospheric Model (MIRE) was used to simulate the terdiurnal tidal component in the Es layer development. The results show modulations of 8 h periods on the occurrence rates of the Es layers during all seasonal periods. In general, we see three well-defined peaks in a superimposed summation of the Es layer types per hour in summer and autumn. We also observed that the amplitude modulation of the terdiurnal tide on the Es occurrence rates minimizes in December in comparison to the other months of the summer season. Other relevant aspects of the observations, with complementary statistical and periodogram analysis, are highlighted and discussed.Item Effects of the Northern Hemisphere sudden stratospheric warmings on the Sporadic-E layers in the Brazilian sector(Elsevier) Fontes Neto, Pedro Alves; Muella, Marcio Tadeu de Assis Honorato ; Resende, Laysa Cristina Araújo; Jesus, Rodolfo de; Fagundes, Paulo Roberto; Batista, Paulo Prado; Pillat, Valdir Gil; Tardelli, Alexandre; Andrioli, Vania F.Tidal and Planetary Wave (PWs) amplitudes are strongly influenced by Sudden Stratospheric Warming (SSW) events. A nonlinear interaction between the tidal winds and planetary waves during the SSW may contribute to the intensification of sporadic-E (Es) layers in the lower thermosphere. This work investigated the relationship between SSW events in the Northern Hemisphere and the Es layer occurrence at low latitudes in the Brazilian sector. We used data from digital ionosondes installed in the observatories of Araguatins (ARA, 5.65◦ S; 48.12◦ W; dip lat. − 5.44◦) and S ̃ao Jos ́e dos Campos (SJC, 23.18◦ S; 45.89◦ W; dip lat. − 21.37◦) to analyze the Es layers. Additionally, we used the temperature, zonal wind, and PWs data at high latitudes in the Northern Hemisphere during the major SSW event that occurred in February/2018 and during the events of Dec/2018–Jan/2019 and Dec/2020–Jan/2021. The results showed a maximum frequency peak of 20 MHz (~5 × 106 electrons.cm− 3) at ARA and SJC during these SSW events. The large values of ftEs, fbEs, and electronic densities were observed between 100 and 115 km height in the Esf/l type layers during daytime or nighttime periods. The results also showed that the number of large values of ftEs, fbEs, and electronic density of the Es layer was much higher in ARA than in SJC, in general. The wavelet power spectrum analyses of the ftEs and fbEs showed a periodicity of 2- days before and after the central day of the SSWs events at the station of ARA, with three prominent peaks in the 2018/2019 event. At the SJC station the quasi-2-day periodicity in the wavelet analyses of the ftEs was observed after the central day in all three SSW events, with a peak before the central day during the 2020/2021 event.Item New Findings of the Sporadic E (Es) Layer Development Around the Magnetic Equator During a High-Speed Solar (HSS) Wind Stream Event(Advancing Earth and Space Sciences) Resende, Laysa Cristina Araújo; Zhu, Y.; Denardini, Clezio Marcos; Batista, Inez Staciarini; Shi, Jiankui; Moro, Juliano; Chen, Sony Su; Santos, Fredson Conceição; Silva, Ligia Alves da; Andrioli, Vania Fatima; Muella, Marcio Tadeu de Assis Honorato; Fagundes, Paulo Roberto; Carrasco, Alexander Jose; Pillat, Valdir Gil; Wang, Chi; Liu, Z.The equatorial (Esq) and blanketing (Esb) sporadic (Es) layers occur due to the EquatorialElectrojet 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 context, we deeply investigated this EEJ influence expansion effect by analyzing the Esq layers in regions not so close to the magnetic equator during a high-speed solar wind stream event that occurred on May 05 and 06, 2018. To explain these atypical Esq layer occurrences, we considered the Es layer parameters obtained from digital ionosondes over the Brazilian regions, São Luís (dip: 9.5°), and Araguatins (dip: 10.5°). We use magnetometer data and a model named MIRE (E Region Ionospheric Model) to validate this mechanism. The results show that the eastward electric field of the Gradient Drift instability in the EEJ is effective during the magnetic storm main phase in the boundary equatorial magnetic sites, creating the Es q layers. Thus, the EEJ plasma irregularity superimposes the wind shear mechanism, changing the Es layer dynamics during disturbed periods over the magnetic equator boundary sites. Therefore, this work establishes new findings of the EEJ influence expansion dynamics in the Es layer formation over the Brazilian regions, which was considered in MIRE for the first time.Item Effects of planetary wave oscillation on E-sporadic (Es) layers during the rare Antarctic sudden stratospheric warming of 2019(Elsevier) Fontes, Pedro Alves; Muella, Marcio Tadeu de Assis Honorato; Resende, Laysa Cristina Araújo; Jesus, Rodolfo de; Fagundes, Paulo Roberto; Mitra, Gourav; Pillat, Valdir Gil; Batista, Paulo Prado; Buriti, Ricardo Arlen; Correia, Emília; Muka, Peter TaiwoThis study investigates the impact of the rare 2019 Antarctic Sudden Stratospheric Warming (SSW) event on the top frequency parameter (ftEs) of the sporadic E (Es) layers, using data from several ionosondes located at low and mid-latitudes across the Southern and Northern Hemispheres, including stations in the American, Oceanian, and Asian regions. The ionosonde data were also used to identify frequency anomalies in the Es layers during the event. Additionally, data from three meteor radars in South America were used to further analyze the impact of the SSW, focusing on key parameters such as tidal winds and Planetary Wave (PW) oscillations. The study found significant ftEs peaks exceeding 10 MHz, particularly at low-latitude stations, with values reaching up to 20 MHz. The presence of these atypical peaks in ftEs was related to PW activity, which intensified the electron densities in the Es layers. A wavelet analysis of the ftEs and neutral wind data revealed oscillations associated with PW and tidal interactions, with dominant periods of ∼2–8-days. These patterns were more pronounced in the Southern Hemisphere, indicating stronger PW-tide coupling compared to the Northern Hemisphere. In addition, this study shows that the non-linear interaction between the PW and the tides occurred globally, generating secondary oscillations of ∼2–8-days on the Es layer development for the three continents. These oscillations were observed in the zonal (U) and meridional (V) winds of the diurnal and semidiurnal tides (DT and ST) during the SSW event, demonstrating a coupling in the troposphere-stratosphere-lower atmosphere dynamics. The coupling between the stratosphere and lower thermosphere contributed to the observed anomalies, revealing the broader impacts of SSW events on Es layer behavior. This study provides an understanding of the impact of SSW on Es layers, using ionosonde data and wave oscillation analysis that could enhance data assimilation models for more accurate ionospheric prediction.Item Simultaneous occurrence of midlatitude plasma bubbles and LSTIDs during the 10 October 2024 geomagnetic storm(Elsevier) Picanço, Giorgio Arlan da Silva; Fagundes, Paulo Roberto; Moro, Juliano; Nogueira, Paulo Alexandre Bronzato; Muella, Marcio Tadeu de Assis Honorato; Nardini, Clezio Marcos de; Resende, Laysa Cristina Araújo; Silva, Lígia Alves da; Laranja, Sophia Rodrigues; Anoruo, Chukwuma Moses; Agyei-Yeboah, Ebenezer; Souza, Ana Lucia Christovam deIn this study, we present a multi-instrumental analysis of the extreme geomagnetic storm of October 10, 2024, focusing on the inter- action between Equatorial Plasma Bubbles (EPBs) and Large-Scale Traveling Ionospheric Disturbances (LSTIDs) over the American sector. Using Rate of Total Electron Content Index (ROTI), Total Electron Content (TEC), and Detrended Total Electron Content (DTEC) maps derived from Global Navigation Satellite System (GNSS) data, we investigated the ionospheric response to the geomag- netic storm. This analysis was complemented by far-ultraviolet airglow observations from the Global-scale Observations of the Limb and Disk (GOLD) mission, in situ electron density profiles from the Swarm satellite constellation, and ground-based ionosonde measure- ments. These multi-instrumental datasets revealed a sequence of coupled processes responsible for the generation, expansion, and mor- phological deformation of EPBs, extending well beyond their typical equatorial domain. Prompt Penetration Electric Fields (PPEFs), which led to an enhanced pre-reversal enhancement (PRE) over western South America, drove a substantial uplift of the ionospheric F-region, exceeding 700 km, and favored the development of large-scale EPBs. These structures manifested as a reversed-C-shaped plasma depletion band, confirmed by both ROTI and GOLD observations. Simultaneously, DTEC maps and keograms revealed the equatorward propagation of storm-time LSTIDs. A pronounced spatial and temporal overlap between EPB and LSTID signatures was observed at midlatitudes, especially across the western South American longitudinal sector. This interaction appears to have mod- ulated the outer structure of the EPBs, leading to asymmetric deformation and enhanced latitudinal expansion. Finally, our findings highlight the role of multiscale coupling between high-latitude and equatorial processes during geomagnetic storms and emphasize the need for integrated observations to fully characterize the dynamics of storm-induced ionospheric disturbances.Item Study of height-spread sporadic-E layers observed in the South American Magnetic Anomaly(Frontiers) Moro, Juliano; Xu, Jiyao; Bageston, Jose Valentin; Silva, Ligia Alves da; Resende, Laysa Cristina Araújo; Nardin, Clezio Marcos de; Andrioli, Vania Fatima; Santos, Angela Machado; Picanco, Giorgio Arlan da Silva; Li, Hui; Zhengkuan, Liu; Wang, Chi; Schuch, Nelson JorgeSpread echoes from the E-region observed in ionograms obtained at high latitudes are generally classified as auroral sporadic-E (Esa) layers. These layers have also been detected in nighttime ionograms collected at some ionospheric stations in the South American Magnetic Anomaly (SAMA) region in Brazil during the recovery phases of geomagnetic storms. However, similar echoes have also been observed in the SAMA during geomagnetically quiet periods or daytime, which are not caused by energetic particle precipitation. Therefore, investigating the occurrence of these spread echoes over a longer period, rather than focusing solely on case studies, has become important. Thus, this study aims to analyze the occurrences of spread echoes from the E-region, referred to here for the first time as “Height-Spread Es (HSEs) layers.” The analysis is based on Digisonde data obtained at the Santa Maria station (29.7° S, 53.8° W, ∼22.000 nT) in Brazil over 1 year (2019/2020). The study initially presents examples of these traces on ionograms and then examines their occurrence rates over several time intervals (hours, months, seasons). Among other findings, the statistical analysis reveals that the occurrence rate of HSEs layers is 9.8% during the analyzed period. The HSEs layers appeared predominantly at night and under geomagnetically quiet conditions. Most HSEs layers lasted between 1 h and 3 h 30 min, with a peak incidence during November, December, and January. Finally, the study discusses the most likely mechanisms responsible for HSEs layer formation, considering the geomagnetic conditions and time of their detection on ionograms.Item Characteristics of slant sporadic-E layers observed at low-latitudes(Elsevier) Muka, Peter Taiwo; Muella, Marcio Tadeu de Assis Honorato; Santos, Fredson Conceição; Resende, Laysa Cristina Araújo; Fagundes, Paulo Roberto; Ogunmola, Olufemi Louis; Fontes Neto, Pedro Alves; Pillat, Valdir Gil; Cesar, Mariah; Jesus, Rodolfo deThis study investigates the occurrence, characteristics, and formation mechanisms of slant sporadic-E layers (Ess). The Ess-type layers observed at the Brazilian low-latitude stations of Jata ́ı (17.9°S, 51.7°W) and Sa ̃o Jose ́ dos Campos (23.2°S, 45.8°W), are analyzed using ionosonde data recorded for four months (April, June, September, and December) of 2016. Parameters such as top frequency (ftEs), blanketing frequency (fbEs), and virtual height (h’Es) were scaled from ionograms to characterize the slant (Ess) traces. The results show that Ess-type layers predominantly occur at night, forming between 95 and 120 km altitudes, with monthly and local variations. Model simulations using meteor radar-derived winds revealed that strong and stable zonal wind shear are associated with increased Ess-type layer activity. In addition, wavelet spectral analyses of ftEs and fbEs showed that tidal periodicities (diurnal, semidiurnal, terdiurnal, and quarterdiurnal) and their interactions with gravity waves seem to play fundamental roles in the formation of Ess-type layers. A com- parison of DF (ftEs-fbEs) during Ess-type events confirmed the presence of strong plasma density gradients, supporting the hypothesis that the slanted traces in ionograms result mostly from oblique reflections in inhomogeneous Es layer structures. However, the appearance of slant Es traces may in some cases be related to an actual tilt of the layer. Other relevant aspects of the observations associated with the possible physical mechanisms behind the formation of Ess-type layers at low latitudes are highlighted and discussed.