Navegando por Assunto "Solar activity"

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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 disturbances over the American and African sectors due to the 2019 major Sudden Stratospheric Warming (SSW 2019), under low solar activity conditions
    (Elsevier) Vieira, Francisco; Fagundes, Paulo Roberto; Pillat, Valdir Gil; Agyei-Yeboah, Ebenezer; Venkatesh, Kavutarapu; Arcanjo, Mateus de Oliveira
    Sudden Stratospheric Warming (SSW) is one of the most spectacular atmospheric large-scale phenomena, which takes place at high latitudes during winter months and is more frequent in the Arctic region than in the Antarctic region. SSWs can change the vertical, latitudinal, and longitudinal distributions of the neutral atmosphere and its dynamics, which in turn affects the ionospheric electrodynamic processes. Simultaneous inferred VTEC from GPS networks over the American and African sectors are used to investigate the ionospheric response due to the SSW 2019 from DOY 356 to DOY 20 (December 22, 2018–January 20, 2019). This study investigates the VTEC and EIA diurnal and day-to-day responses in the American and African sectors during the SSW. It is noted that the VTEC decreased on most of the days at several latitude regions. However, it is also noted that the VTEC increased on some days and in some latitude regions, particularly during the SSW temperature peak. The EIA exhibits significant changes in its shape, intensity, and symmetry during the SSW. This study using simultaneous observations over American and African sectors covering a large geographical extent demonstrates the similarities and differences in ionospheric response to the SSW 2019 event over different regions.
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    Morphological Features of Ionospheric Scintillations During High Solar Activity Using GPS Observations Over the South American Sector
    (Advancing Earth and Space Sciences) Jesus, Rodolfo de; Batista, Inez Staciarini; Takahashi, Hisao; Barros, Diego; Figueiredo, Cosme Alexandre Oliveira Barros; Abreu, Alessandro José de; Jonah, Olusegun Folarin; Fagundes, Paulo Roberto; Venkatesh, Karnam
    The main objective of this study is to investigate the ionospheric irregularities observed by Global Positioning System‐total electron content (GPS‐TEC) receivers during the high solar activity years of 2013 and 2014 at different stations in the equatorial and low‐latitude regions in the South American sector. The ionospheric parameters used in this investigation are the TEC, the rate of change of the TEC index (ROTI), and the amplitude scintillation index (S4). In the South American sector, the ROTI and S4 indices showed that the ionospheric irregularities have an annual variation with maximum occurrence from September to April, between 20:00 LT and 02:00 LT, and no occurrence from May to August. Also, strong phase fluctuations (ROTI >1) are observed over South America at 19 LT in October and November. Morlet wavelet analysis of ROTI and S4 showed that planetary wave‐scale periods ranging from 2 to 8 days are predominant during September–March at 20–02 LT in South America. In addition, using a keogram it was possible to evaluate the distance between adjacent ionospheric plasma depletions, and this result is presented and discussed. The longitudinal distances between adjacent bubbles vary around ~600–1000 km, which is larger than values reported in most previous studies.