Navegando por Autor "Correia, Emília"

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    Climatology of ionospheric amplitude scintillation on GNSS signals at south American sector during solar cycle 24
    (Elsevier) Macho, Eduardo Perez; Correia, Emília; Spogli, Luca; Muella, Marcio Tadeu de Assis Honorato
    Scintillations are caused by ionospheric irregularities and can affect the propagation of trans-ionospheric radio signals. One way to understand and predict the impact of such irregularities on Global Navigation Satellite System (GNSS) signals is through the spatial/temporal characterization of the scintillation’s climatology during different phases of a solar cycle covering different latitudes and longitudes. This characterization is performed using amplitude scintillation index S4, during the full solar cycle 24, in the South American (SA) sector. The investigation considers the diurnal, daily, and seasonal variation of S4 index for climatological purpose, and the goal of this study is to investigate the scintillations covering a large spatial scale during the full solar cycle 24. The characterization shows a latitudinal asymmetry, whereas at the south, the scintillations were more frequent and their peak was more distant from the magnetic equator, which can be attributed by the South Atlantic Magnetic Anomaly (SAMA), and/or by the transequatorial meridional neutral winds. It also shows a longitudinal asymmetry, where the scintillations at the eastern sector occurred between November and February, while at the western sector, they occurred during the months of October, November, February and March, which can be attributed to the difference between the magnetic and geographic equators. The occurrence of scintillations during two distinct geomagnetic storms with similar storm time in the SA sector is also presented.
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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.