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Submissões Recentes
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.