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Item 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 RobertoSporadic 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.Item 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 HonoratoScintillations 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.Item Advantages and disadvantages of VTEC, ROTI and airglow images in studying equatorial plasma bubbles(Elsevier) Souza, Ana Lucia Christovam de; Prol, Fabricio dos Santos; Muella, Marcio Tadeu de Assis Honorato; Picanço, Giorgio Arlan da Silva; Camargo, Paulo de Oliveira; Monico, João Francisco GaleraEquatorial plasma bubbles (EPBs) are large-scale plasma depletion structures, observed near the geomagnetic equator and in low- latitude regions after sunset. Several instruments have been employed to study EPBs, such as ionosondes, in situ satellites, coherent and incoherent scatter radars, airglow imagers, GNSS radio occultation, and GNSS ground-based stations. Among these instruments, Total Electron Content (TEC) and Rate of TEC change Index (ROTI) data derived by GNSS measurements are presenting as outstand- ing data sources to study the climatology of EPBs. In this study, we evaluate the reliability of TEC and ROTI index for mapping iono- spheric plasma bubble structures in comparison to airglow images, demonstrating the performance of each technique and highlighting their respective advantages and disadvantages. The results demonstrate that TEC and ROTI time series are effective to identify plasma bubble occurrence in terms of temporal profiles, horizontal maps, and keograms for EPB velocity estimation. In terms of ionospheric temporal profiles, all techniques presented a good correspondence, TEC data may present direct characteristics of plasma bubbles, i.e., the intensity of the electron density depletions, while ROTI values are more suitable to present the occurrence, or not, of plasma bubbles. TEC maps showed advantages in mapping the horizontal distributions of EPBs, specially at the equatorial regions where ROTI failed to detect disturbances. Velocity estimates based on keograms from airglow data averaged 111 m/s, while TEC and ROTI index averaged 106 m/s and 107 m/s, respectively. Overall, TEC data presented better estimates of velocities due to the geometric and physical information, while ROTI offers statistical insights that often mask the natural propagation of EPBs.