Navegando por Autor "Fontes, Pedro Alves"

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    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 Taiwo
    This 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.
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    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 Jose
    Sporadic 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.