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Spatial Characteristics of GNSS Fading and Scintillation in Low Latitudes
(Springer Nature) Santis, Victor Di; Moraes, Alison; Costa Emanoel; Sousasantos, Jonas; Silva, Paulo Renato Pereira; Souza, Ana Lucia Christovam de
Previous studies evaluated several characteristics of ionospheric fading events and amplitude scintillation. However, a detailed analysis on how the fading profiles and scintillation probabilities vary according to the dip latitude is still required. In this work, a statistical analysis of data from four ground-based scintillation monitors was performed to evaluate how the alpha coefficient (first parameter of the "alpha-mu" probability distribution model); the deepest fading occurrence; the number of fading events per minute; and the duration of fading events change according to the dip latitudes of the ionospheric pierce points (IPPs) of transionospheric propagation paths. The results reveal a nuanced spatial variation in amplitude scintillation, emphasizing an enhanced severity within the equatorial ionization anomaly (EIA) southern crest, resulting in a clear increase in the probability of severe fading events. An increasing trend in the alpha fading coefficient at more poleward dip latitudes was found, in comparison with results from equatorward locations, suggesting an asymmetry favoring more severe fading events within the former region. The average fading occurrences are significantly larger over the EIA peak region, especially for increasing scintillation levels. Complementary Cumulative Distribution Function (CCDF) curves demonstrate peak probabilities between dip latitudes from - 14.5 degrees to - 10.5 degrees for higher scintillation levels, also displaying an asymmetrical pattern around the EIA boundaries. This study provides important insights on the spatial dynamics of scintillation and fading profiles, enhancing the understanding of low-latitude ionospheric effects on global network satellite system (GNSS) signals.
Spatial Characteristics of GNSS Fading and Scintillation in Low Latitudes
(Springer Nature Link) Di Santis, Victor; Moraes, Alison; Costa, Emanoel; Sousasantos, Jonas; Silva, Paulo Renato Pereira; Souza, Ana Lucia Christovam de
Previous studies evaluated several characteristics of ionospheric fading events and amplitude scintillation. However, a detailed analysis on how the fading profiles and scintillation probabilities vary according to the dip latitude is still required. In this work, a statistical analysis of data from four ground-based scintillation monitors was performed to evaluate how the α coefficient (first parameter of the “α–μ” probability distribution model); the deepest fading occurrence; the number of fading events per minute; and the duration of fading events change according to the dip latitudes of the ionospheric pierce points (IPPs) of transionospheric propagation paths. The results reveal a nuanced spatial variation in amplitude scintillation, emphasizing an enhanced severity within the equatorial ionization anomaly (EIA) southern crest, resulting in a clear increase in the probability of severe fading events. An increasing trend in the α fading coefficient at more poleward dip latitudes was found, in comparison with results from equatorward locations, suggesting an asymmetry favoring more severe fading events within the former region. The average fad- ing occurrences are significantly larger over the EIA peak region, especially for increasing scintillation levels. Complementary Cumulative Distribution Function (CCDF) curves demonstrate peak probabilities between dip latitudes from − 14.5° to − 10.5° for higher scintillation levels, also displaying an asymmetrical pattern around the EIA boundaries. This study provides important insights on the spatial dynamics of scintillation and fading profiles, enhancing the understanding of low-latitude ionospheric effects on global network satellite system (GNSS) signals.
Influence of geomagnetic disturbances on myocardial infarctions in women and men from Brazil
(SPRINGERNATURE) Rezende, Luiz Felipe Campos de; Paula, Eurico Rodrigues de; Muella, Marcio Tadeu de Assis Honorato; Dutra, Severino Luiz Guimaraes; Rosa, Reinaldo Roberto; Saldiva, Paulo Hilário Nascimento; Ometto, Jean Pierre Henry Balbaud
Background: Understanding the role of space weather, specifically Geomagnetic Disturbances (GMDs) caused by solar activity, on health outcomes is unclear. One emerging link includes the impact of space weather on myocardial infarctions (MI). In this study we examined the correlation between MI and GMDs in Brazil. Methods: We used a database from the public health in Brazil, focusing on the city of São José dos Campos (23 degrees 10 ' 44 '' S, 45 degrees 53 ' 13 '' W), located in the state of São Paulo, during the period of 1998-2005. We focused on admissions for MIs, which included a total of 871 men and 469 women. We categorized the MI data into three age groups: age 30 and younger, age 31-60, and age over 60. Additionally, we incorporated Planetary Index (Kp) data as an indicator of variations in the Earth's geomagnetic field resulting from solar disturbances, categorized as quiet, moderate, or disturbed days. In our analysis, we employed two methods: statistical counting and the unsupervised clustering known as K-Means, considering the attributes of age, sex, and geomagnetic condition. Results: Here we show that geomagnetic conditions have an impact on MI cases, particularly for women. The rate of relative frequency of MI cases during disturbed geomagnetic conditions is almost three times greater compared to quiet geomagnetic conditions. Using the unsupervised K-Means algorithm, the results indicate that the group associated with disturbed geomagnetic conditions has a higher incidence of MIs in women. Conclusions: Overall, our results provide evidence that women may exhibit a higher susceptibility to the effects of geomagnetic disturbances caused by solar activity on MI.
Preface: Ionospheric imaging: recent advances and future directions
(Elsevier) Muella, Marcio Tadeu de Assis Honorato; Prol, Fabricio dos Santos
Midnight Simultaneous Observations of Spread-F and Multiple F-Layer Stratifications During the 11-12 May 2024 Geomagnetic Superstorm
(Advancing Earth and Space Sciences) Fagundes, Paulo Roberto; Pillat, Valdir Gil; Anoruo, Chukwuma Moses; Picanço, Giorgio Arlan da Silva; Pezzopane, Michael; Habarulema, John Bosco; Kavutarapu, Venkatesh; Tardelli, Alexandre; Souza, Ana Lucia Christovam de; Vieira, Francisco
A geomagnetic superstorm occurred from May 10 to 12, 2024, producing significant spatial and temporal disturbances in the ionosphere. Ground‐based ionosonde and GPS‐TEC data enabled the identification, analysis, and possible interpretation of a unique event: the simultaneous occurrence of Spread‐F and multiple F‐layer stratifications during the local midnight hours of May 11. To the best of our knowledge, this is the first documented case of such a phenomenon occurring at local midnight. This study provides new insights into the dynamics of the equatorial and low‐latitude ionosphere under extreme geomagnetic conditions and highlights the critical role of coordinated, multi‐instrument observations in advancing our understanding of ionospheric electrodynamics.
Metallicity of active galactic nuclei from ultraviolet and optical emission lines - II. Revisiting the C43 metallicity calibration and its implications
(Oxford) Dors Junior, Oli Luiz; Oliveira, Celso Benedito de; Cardaci, Mónica Viviana; Hägele, Guillermo Federico; Armah, Mark; Riffel, Rogemar André; Vieira, Lucas Ramos; Almeida, Gleicy Caroline de; Morais, Istenio Nunes de; Santos, Pedro Camargo
In this study, a new semi-empirical calibration is proposed between ultraviolet emission lines (CIII]λ1909, CIVλ1549, HeII]λ1640) of type 2 active galactic nuclei (AGNs) and their metallicity (Z). This calibration is derived by comparing a large sample of 106 objects (data taken from the literature) located over a wide range of redshifts (0 􏰁 z 􏰁 4.0) with predictions from photoionization models that adopt a recent C/O–O/H relation derived via estimates using the Te method, which is considered the most reliable method. We found that the new calibration produces Z values in agreement (within an uncertainty of ±0.1 dex) with those from other calibrations and from estimates via the Te-method. We find also that AGN metallicities are already high at early epochs, with no evidence for monotonic evolution across the redshift range 0 􏰁 z 􏰁 12. Notably, the highest metallicities in our sample, reaching up to 4 Z⊙, are found in objects at 2 􏰁 z 􏰁 3. This redshift range coincides with the peak of the cosmic star formation rate history, suggesting a strong connection between the major epoch of star formation, black hole growth, and rapid metal enrichment in the host galaxies of AGNs. Furthermore, our analysis reveals no significant correlation between AGN metallicity and radio properties (radio spectral index or radio luminosity) or host galaxy stellar mass. The lack of a clear mass–metallicity relation, consistent with findings for local AGNs, suggests that the chemical evolution of the nuclear gas is decoupled from the global properties of the host galaxy.
Ionized gas outflows and shock-heated emission in the highly inclined active galaxy CGCG 012-070
(Royal Astronomical Society) Vieira, Lucas Ramos; Riffel, Rogemar André; Riffel, Rogério; Dors Junior, Oli Luiz; Bianchin, Marina; Storchi-Bergmann, Thaisa
Active galactic nuclei (AGNs) exhibit excess mid-infrared H2 emission compared to star-forming galaxies, likely driven by outflows and shocks inferred from integrated spectra. We present optical IFU (integral field unit) observations of the central 2 kpc of the AGN host CGCG 012-070, selected for its pronounced H2 emission excess, to map stellar and gas kinematics. The stellar velocity field is well described by a rotating disc with a line of nodes at 103◦ ± 4◦, with the north-west side approaching and the southeast side receding. Gas kinematics, traced by strong emission lines, show two components: a narrow one (σ 􏰁 200 km s−1 ) in the disc plane following stellar motions, and a broad (σ 􏰂 300 km s−1 ) associated with outflows within the inner ∼1 kpc. Disc gas emission is mainly driven by AGN photoionization, while the outflow also includes shock-heated gas, as indicated by flux ratio diagnostics. The outflows are radiatively driven, with a mass-outflow rate of (0.067 ± 0.026) M⊙ yr−1 and a kinetic coupling efficiency of 0.07 per cent, potentially redistributing gas and contributing to maintenance-mode feedback in CGCG 012-070. Our results provide further evidence that the warm H2 emission excess in nearby AGN is associated with shocks produced by outflows. Observations of other gas phases, such as cold molecular gas, are necessary to gain a more comprehensive understanding of the impact of the outflows on the host galaxy.
Effects of X2.8-class solar flare on the ionosphere occurred during the recovery phase of a geomagnetic storm over South American and Antarctic sectors
(Elsevier) Abreu, Alessandro José de; Correia, Emilia; Venkatesh, Kavutarapu; Pignalberi, Alessio; Pezzopane, Michael; Pillat, Valdir Gil; Fagundes, Paulo Roberto; Gende, Mauricio Alfredo; Jesus, Rodolfo de
In this investigation, we present and discuss the effects of an X2.8-class solar flare occurred on 14 December 2023 on the ionospheric F region and on the geomagnetic field over South American and Antarctic sectors. This flare coincides with the recovery phase of a geomag- netic storm. To this end, we rely on vertical total electron content (VTEC) observations from nearly 250 Global Positioning System (GPS) receiver stations over South American and Antarctic sectors, complemented by in-situ electron density observations from Swarm satellites, magnetometer measurements, and ionospheric sounding observations from ionosondes. The magnetic observations show a large increase in the variations of the horizontal component (DH) of the geomagnetic field and equatorial electrojet (EEJ) currents at all stations, syn- chronized with the increase in X-rays flux, indicating solar flare effects or magnetic crochet on the Earth’s geomagnetic field. VTEC shows how the impact of the solar flare on the ionosphere is enhanced from east to west of South America in the equatorial and low-latitudes. VTEC from a specific GPS satellite-receiver also shows great effects at mid-latitudes. Results are confirmed and further elaborated through Swarm in-situ observations. In addition, an asymmetry is observed in the equatorial ionization anomaly (EIA), in which the eastern South American sector shows an intensified EIA compared to the western sector. Ionospheric sounding observations by ionosondes show total fade out in the echo traces of the ionograms, characterizing blackouts in the radio signals from equatorial to low-latitudes. Overall, our results show that an X-class solar flare occurring near the limb of the solar disk is capable of producing effects on the Earth’s ionosphere with similar or even stronger intensities than flares occurring at the center of the solar disk.
Spectral energy distribution analysis of the supersoft X-ray source CAL 87: Multiwavelength constraints
(Elsevier) Stecchini, Paulo Eduardo Freire; Jablonski, Francisco; Diaz, Marcos Perez; Oliveira, Alexandre Soares de; D’Amico, Flavio; Palivanas, Natália
We analyse the spectral energy distribution (SED) of the eclipsing supersoft X-ray source CAL 87 covering wavelengths from X-rays to the near-infrared. Our study incorporates 26 data points across ultraviolet to near-infrared, sourced from published literature, unpublished data, and new observations. In addition, archival XMM-Newton spectra were used to represent the X-ray emission. Care was taken to use out-of-eclipse flux measurements when the irradiated side of the companion faces the observer. The SED model includes contributions from a central source, a reprocessed accretion disk, and an irradiated companion star atmosphere, resulting in a good match to the observed fluxes. The revised and new parameters for the disk and the central source align with previous studies and match expectations for such systems. The temperature of the irradiated side of the companion star was estimated based on its B-V colour during the secondary eclipse. This work highlights the importance of broad wavelength coverage for understanding the properties of supersoft X-ray sources.
Cosmic fertilization? Implantation of astrobiologically relevant cosmic rays in molecular clouds
(Elsevier) Pilling, Sergio; Pazianotto, Maurício Tizziani
This study investigates the implantation of astrobiologically relevant elements (e.g., carbon (C), oxygen (O), nitrogen (N), sulfur (S) and phosphorus (P)) into molecular clouds induced by cosmic rays. Using the Monte Carlo toolkit Geant4, we simulated the interaction of incoming high-energy protons and alpha particles with a mo- lecular clump characterized by a centrally concentrated density profile and a mass of approximately 30 M⊙. The results reveal a spatial gradient in implantation rates, with the highest rates occurring in the central regions due to increased target densities and reduced projectile energy. Protons (p) dominate the implantation process across all regions, followed by O, C, N, S, and P, with element-specific implantation efficiencies varying with distance from the clump center. This research identified regions inside the molecular cloud with distinct domains of atomic implantation enrichment with implications for astrobiology. The region at ∼1 AU exhibits the interesting atom implantation enrichment of the studied atoms, making it particularly significant for the formation of complex organic molecules. The findings highlight the importance of cosmic ray interactions in selectively enriching specific regions of molecular clouds with astrobiologically essential elements.
Characterization of the chemical evolution of CH4 ices under processing by cosmic ray analogues with the PROCODA code – I. Effective reaction rate coefficients and chemical equilibrium phase
(Royal Astronomical Society) Gerasimenko, Svitlana; Carvalho, Geanderson Araújo; Zanatto, Fernanda; Santana, Fernanda Kelly de; Pilling, Sergio
Methane (CH4⁠), the simplest alkane, is a fundamental component of astrophysical ices, particularly in the outer Solar system and the interstellar medium. Understanding its chemical evolution under energetic particle irradiation is essential for modelling these environments. In this work, we investigate the chemical evolution of pure methane ice subjected to high-energy ion irradiation until chemical equilibrium is reached. We employ the procoda code to simulate the time-dependent evolution of molecular abundances and to determine effective reaction rate coefficients. The simulations are constrained using experimental data from a previous study, in which pure CH4 ice at 16 K was irradiated, providing the necessary input parameters for the model. Our reaction network comprises 1857 chemical reactions involving 36 molecular species, both observed and unobserved by Fourier-transform infrared spectroscopy during the experiment. The best-fitting model satisfies multiple criteria: a low for observed species, a desorption yield consistent with experimental estimates, similar trends in abundance evolution for observed and unobserved species, and overall mass conservation. At chemical equilibrium, the most abundant species predicted by the model are H2 (38.0 per cent), CH4 (20.8 per cent), H (17.0 per cent), and CH3CH2CH3 (16.9 per cent). The total desorption yield is calculated as molecules/ion, and the effective destruction cross-section of CH4 is cm. The reaction rate coefficients and equilibrium abundances derived from this study provide valuable inputs for astrochemical models, enhancing our understanding of CH4 processing in interstellar ices under cosmic ray irradiation.
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 de
This 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.
Advantages and disadvantages of VTEC, ROTI and airglow images in studying equatorial plasma bubbles
(Elsevier) Souza, Ana Lucia Christovam de; Prol, Fabricio dos Santos; Muella, Marcio Tadeu de Assis Honorato; Picanço, Giorgio Arlan da Silva; Camargo, Paulo de Oliveira; Monico, João Francisco Galera
Equatorial plasma bubbles (EPBs) are large-scale plasma depletion structures, observed near the geomagnetic equator and in low- latitude regions after sunset. Several instruments have been employed to study EPBs, such as ionosondes, in situ satellites, coherent and incoherent scatter radars, airglow imagers, GNSS radio occultation, and GNSS ground-based stations. Among these instruments, Total Electron Content (TEC) and Rate of TEC change Index (ROTI) data derived by GNSS measurements are presenting as outstand- ing data sources to study the climatology of EPBs. In this study, we evaluate the reliability of TEC and ROTI index for mapping iono- spheric plasma bubble structures in comparison to airglow images, demonstrating the performance of each technique and highlighting their respective advantages and disadvantages. The results demonstrate that TEC and ROTI time series are effective to identify plasma bubble occurrence in terms of temporal profiles, horizontal maps, and keograms for EPB velocity estimation. In terms of ionospheric temporal profiles, all techniques presented a good correspondence, TEC data may present direct characteristics of plasma bubbles, i.e., the intensity of the electron density depletions, while ROTI values are more suitable to present the occurrence, or not, of plasma bubbles. TEC maps showed advantages in mapping the horizontal distributions of EPBs, specially at the equatorial regions where ROTI failed to detect disturbances. Velocity estimates based on keograms from airglow data averaged 111 m/s, while TEC and ROTI index averaged 106 m/s and 107 m/s, respectively. Overall, TEC data presented better estimates of velocities due to the geometric and physical information, while ROTI offers statistical insights that often mask the natural propagation of EPBs.
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 Jorge
Spread 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.
Observation and simulation studies of ionospheric F-region in the South American and Antarctic sectors in the intense geomagnetic storm of August 2018
(Elsevier) Abreu, Alessandro José de; Correia, Emilia; Jonah, Olusegun Folarin; Venkatesh, Kavutarapu; Thomas, Evan G.; Jesus, Rodolfo F. de; Roberto, Marisa; Abalde, José Ricardo; Fagundes, Paulo Roberto
In this investigation, we present and discuss the ionospheric F region observations in the equatorial, low-, mid-, and near high-latitude regions in the South American and Antarctic sectors during the intense geomagnetic storm that occurred on 25–27 August 2018. The geomagnetic storm reached a minimum Dst of − 175 nT at ~0700 UT on 26 August. We present the variations of vertical total electron content (VTEC) from a chain of almost 200 GPS stations, covering the South American and Antarctic sectors. A comparison with model simulations from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM) is realized. The results ob- tained show that during the main phase of the storm, a southward Bz component of the interplanetary magnetic field (IMF) and an eastward prompt penetration electric field (PPEF) can be observed, but they had no significant impact on the ionospheric plasma. A long recovery phase a predominance of positive phase is observed during daytime. The observations show the effects of an unusual case of multiple PPEF, occurred on 26 August, and effects of thermospheric winds disturbances, occurred on 27 August, resulting in increased VTEC values on both days. The TIE-GCM model reproduces the VTEC increases during the main and recovery phases from mid- latitudes to the equatorial region, but it underestimates the observed values near high-latitudes.
Momentum flux characteristics of vertically propagating gravity waves
(European Geosciences Union) Nyassor, Prosper Kwamla; Wrasse, Cristiano Max; Paulino, Igo; Yigit, Erdal; Tsali-Brown, Vera Yesutor; Buriti, Ricardo Arlen; Figueiredo, Cosme Alexandre Oliveira Barros; Giongo, Gabriel Augusto; Egito, Fabio; Adebayo, Oluwasegun Micheal; Takahashi, Hisao; Gobbi, Delano
Momentum flux and propagation dynamics of two vertically propagating atmospheric gravity waves (GWs) are studied using observations at São João do Cariri (7.40° S, 36.31° W), Brazil, from co-located pho- tometer, all-sky imager, and meteor radar instruments. Time series of the atomic oxygen green line (OI 557.7 nm), molecular oxygen (O2 (0–1)), sodium D-line (NaD), and hydroxyl (OH (6–2)) airglow intensity variations mea- sured by the photometer were used to investigate the vertical characteristics and vertical phase progression of the GWs with similar (± 10 % of the error margin) or nearly the same (± 5 % of the error margin) period across these emission layers. The horizontal parameters of the same GWs were determined from the OH airglow im- ages, whereas the intrinsic parameters of the horizontal and vertical components of the GWs were estimated with the aid of the observed winds. Using the phase of the GWs at each emission layer, the characteristics of the phase progression exhibited near-vertical propagation under a duct background propagation condition. This indicates that the duct contributes significantly to the observed near-vertical phase propagation. The GW mo- mentum flux and potential energy were estimated using the rotational temperatures of OH and O2, revealing that the time series of momentum fluxes and potential energies are higher in the O2 emission band than in the OH band, indicating a transfer of momentum and energy across OH to the O2 altitude. These results reveal the effect of a duct on vertically propagating GWs and the associated momentum flux and potential energy transfer from the lower to the upper altitudes in the mesosphere.
Molecular Evolution of H2O:O2 Ices at Different Temperatures in Simulated Space Environments. I. Chemical Kinetics and Equilibrium
(IOP science) Silva, Josiane Ribeiro Campos; Queiroz, Letícia Marques de Souza Vetrano de; Ferrão, Luiz Fernando de Araújo; Pilling, Sergio
We computationally investigated the chemical evolution of H2O:O2 ices (6:1 ratio) under irradiation by cosmic- ray analogs (0.8MeV H+) at 9, 50, and 100K to understand the implications the chemical evolution of O2-containing ices in space, such as the surface of the Moon, comets, outer solar system bodies such Europa and Enceladus, as well as Kuiper Belt objects, and cold regions of the interstellar medium (ISM). Using experimental data and the PROCODA code with 200 reactions coupled equations involving 12 species, we calculated physicochemical parameters such as effective rate coefficients (ERCs), chemical abundances, and desorption. Six species were observed experimentally (H2O, O2, HO2, H2O2, O3, and HO3), while six were predicted but not observed in the experiments (H, H2, H3, O, OH, and H3O). Our findings highlight the influence of temperature on chemical equilibria and desorption yields, with certain reaction rates diminishing at 50 K. Among the results were the lists with the ERCs, and the reaction branching ratio obtained by best-fit models can be employed in astrochemical models. Curiously, we observe that the average ERCs for bimolecular collisions decrease by half as the ice temperature increases, varying from 5.8e-25 to 2.9e-25 cm3 molecules−1 s−1 for the ices studied. These results enhance our understanding of the physical chemistry of astrophysical ices under ionizing radiation, providing valuable data for astrochemical models that assess the effects of cosmic radiation on the composition and stability of icy bodies in the solar system and denser and colder regions of the ISM.
Metallicity of active galactic nuclei from ultraviolet and optical emission lines: I. Carbon abundance dependence
(Royal Astronomical Society) Dors Junior, Oli Luiz; Oliveira Junior, Celso Benedito de; Cardaci, Mónica Viviana; Hagele, Guillermo Federico; Morais, Istenio Nunes de; Ji, Xihan; Riffel, Rogemar André; Riffel, Rogério; Mezcua, Mar; Almeida, Gleicy Caroline de; Santos, Pedro Camargo; Mellos, Maitê Silvana de Zorzi de
Metallicity (Z) estimates based on ultraviolet (UV) emission lines from the narrow-line regions of active galactic nuclei (AGNs) have been found to differ from those derived from optical lines. However, the origin of this discrepancy (ZR) remains poorly understood. To investigate the source of ZR, we compiled from the literature the fluxes of narrow near- UV [1000 < λ(Å) < 2000] and optical [3000 < λ(Å) < 7000] emission-line measurements for a sample of 11 AGNs (nine at z < 0.4 and two at z ∼ 2.4). Metallicity values for our sample were derived using a semi-empirical calibration based on the C43 = log[(C IVλ1549 + C III]λ1909)/He IIλ1640] emission-line ratio and compared with those obtained via direct measurement of the electron temperature (Te-method) and via calibrations based on optical emission lines. The source of the discrepancy was investigated in terms of the ionization parameter (U), electron density (Ne), and carbon abundance (C/H). We found a weak correlation between ZR, U, and Ne. However, a moderate correlation was observed between ZR and direct estimates of C/H, suggesting that the previously assumed (C/O)–Z relations in photoionization models used to derive UV carbon-line calibrations may not be valid for AGNs. By combining a large set of abundance estimates for local star-forming regions with those of our AGN sample, we derived a new (C/O)–Z relation. Comparisons between the results of photoionization models that assume this new abundance relation and the UV observational data of our sample produce Z values derived from the C43 index that are consistent with those obtained using the Te-method.
Influence of Climate and Solar Variability on Growth Rings of Araucaria angustifolia in Três Barras National Forest (Brazil)
(MDPI) Muraja, Daniela Oliveira Silva; Klausner, Virginia; Prestes, Alan; Silva, Aline Conceicao da; Lemes, Cecilia Leite
This research applies continuous wavelet analysis and seasonal correlation anal- ysis to tree-ring data from Três Barras National Forest (FLONA Três Barras), revealing diverse influences on growth, including climate, solar activity, and external factors. The methodology involved tree-ring collection and subsequent wavelet and seasonal analy- ses to unveil the non-stationary characteristics of and multifaceted influences on growth. Key findings include the subtle effects of El Niño events on tree-ring development, the sensitivity of Araucaria angustifolia to temperature changes, the significant influence of precipitation during drought periods, and the intricate relationship between tree growth and solar cycles. The El Niño–Southern Oscillation (ENSO) emerges as a primary climatic driver during specific intervals, with external factors (precipitation, temperature, and solar cycle–solar irradiance) influencing tree response between 1936 and 1989. Additionally, the seasonal correlation analysis highlighted the importance of sub-annual climate variability, capturing specific intervals, such as a 3-month season ending in March of the previous year, that significantly impacted tree-ring growth. The study underscores the importance of protecting the endangered Araucaria angustifolia for climatic studies and local commu- nities. Historically, in Brazil, Araucaria angustifolia seeds played a vital role in sustaining indigenous populations, which in turn helped to disperse and propagate forests, creating anthropogenic landscapes that highlight the interconnected relationship between humans and the preservation of these forests.
Global ionospheric response to a G2 and a G3 geomagnetic storms of November 4 and 5 2023
(Elsevier) Agyei-Yeboah, Ebenezer; Fagundes, Paulo Roberto; Tardelli, Alexandre; Pillat, Valdir Gil; Vieira, Francisco; Bolzan, Mauricio José Alvez
Two successive geomagnetic storms of G2 and G3 intensities were observed on November 4, 2023, and November 5, 2023. The results presented in this study investigated the impacts of two geomagnetic storms during the main phases at equatorial, low-latitude, and EIA and beyond over west/east American, west/east African/European, and west/east Asian longitudinal sectors. This study was carried out using 30 GPS receivers, 30 magnetometers, and three ionosondes (East Brazilian sector). Positive storm effects were observed during the main phases of both the G2 (storm1) and G3 (storm2) storms, however the magnitude of the positive storm effects was greater during the G3 main phase than during the G2 main phase. The American sectors recorded the highest VTEC variations. Negative storm effects were mostly observed over the Asian sectors. Minimal changes in VTEC were observed in the Asian sectors during both main phases, except over DAEJ. The American sectors exhibited the strongest positive storm responses, followed by the African and Asian sectors, with VTEC enhancements being more pronounced during the G3 storm’s main phase compared G2 storm. Positive ionospheric effects extended to higher latitudes during the main phase of G3 storm especially in the American sectors, likely due to eastward prompt pen- etration electric fields (PPEF) uplifting the F-region to altitudes where lower recombination rates lead to VTEC enhancement. This PPEF effect varied with longitude and storm intensity, resulting in significant positive ionospheric responses in the American sector, par- ticularly during the G3 storm. Variations in the thermospheric O/N2 ratio further influenced the VTEC changes across all sectors. The EIA exhibited notable disturbances, particularly in the American sector. By contrast, EIA crest features were less distinct in the African sector, highlighting the longitudinal dependencies of PPEF effects on the EIA structure. The EIA features were more pronounced during the main phase of the first storm, whereas during the second, the crests appeared to merge into one structure extending beyond the typical crest regions. The foF2 obtained from ionogram also increased during the main phases in the American sector with no significant h’F variations. The DH showed marked depressions, particularly in the American and African sectors, with the G3 storm producing stronger DH depressions than the G2 storm. Similar longitudinal and latitudinal DH variations were observed across both events, with substantial decreases in DH over specific stations, such as ABG and JAI, in the West Asian sector.

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