Navegando por Assunto "Ionosphere"

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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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    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 Roberto
    Sporadic 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.
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    Ionospheric GPS-TEC responses from equatorial region to the EIA crest in the South American sector under intense space weather conditions
    (Elsevier) Abreu, Alessandro José de; Correia, Emilia; Denardini, Clezio Marcos; Jesus, Rodolfo de; Venkatesh, Kavutarapu; Roberto, Marisa; Abalde, José Ricardo; Fagundes, Paulo Roberto; Bolzan, Maurício José Alves; Gende, Maurício Alfredo
    We present and discuss the ionospheric F-region observations from equator to the equatorial ionization anomaly (EIA) regions over the South American sector during an intense space weather event occurred between 27 and May 29, 2017. During this geomagnetic storm, the symmetric-H (SYM-H) reached a minimum of − 142 nT at ~0700 UT on May 28, 2017. For this investigation, we analyze the vertical total electron content (VTEC) observations from a chain of nearly 120 Global Positioning System (GPS) stations. Magnetometer measurements obtained at two stations in the low latitude regions are also presented. The observations do not indicate prompt penetration electric field (PPEF) effects in the VTEC variations. Magnetometer’s observations over Cuiaba ´ (CBA) and Cachoeira Paulista (CXP) in central west and south parts of Brazil, respectively, have shown a strong crosscorrelation with SYM-H in the period between 3 and 48 h. The results also show positive ionospheric storm phase during the recovery phase on May 28, 2017. Positive effect during the recovery phase of the geomagnetic storm is possibly associated with effects of disturbances winds. During the recovery phase, a strong intensification of the EIA took place, possibly related to an additional ionization effect. The VTEC values show differences between the west and east sectors. This indicates that the EIA crest is stronger in the east sector than in the west sector, possibly due to the combination of disturbance wind effects and geomagnetic field geometry where in the east sector the field lines are more inclined.