@Article{SilvaPadiAlve:2020:LaVaPc,
               author = "Silva, Graziela Belmira Dias da and Padilha, Antonio Lopes and 
                         Alves, Livia Ribeiro",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)}",
                title = "Latitudinal variation of Pc3–Pc5 geomagnetic pulsation amplitude 
                         across the dip equator in central South America",
              journal = "Annales Geophysicae",
                 year = "2020",
               volume = "38",
               number = "1",
                pages = "35--49",
                month = "Jan.",
             abstract = "In order to clarify the equatorial electrojet effects on ground 
                         magnetic pulsations in central South America, we statistically 
                         analyzed the amplitude structure of Pc3 and Pc5 pulsations 
                         recorded during days considered quiet to moderately disturbed at 
                         multiple equatorial stations nearly aligned along the 10\◦ 
                         magnetic meridian. It was observed that Pc3 amplitudes are 
                         attenuated around noon at the dip equator for periods shorter than 
                         \∼ 35 s. It is proposed that daytime Pc3s are related to 
                         MHD (magnetohydrodynamic) compressional wave vertically incident 
                         on the ionosphere, with the screening effect induced by enhanced 
                         conductivity in the dip equator causing wave attenuation. Daytime 
                         Pc5s showed amplitude enhancement at all equatorial stations, 
                         which can be explained by the model of waves excited at higher 
                         latitudes and propagating equatorward in an Earthionosphere 
                         waveguide. However, a slight depression in Pc5 amplitude compared 
                         to neighboring equatorial stations and a phase lag in relation to 
                         an off-equatorial station were detected at the dip equator. This 
                         wave amplitude depression in the Pc5 frequency band cannot be 
                         explained by the ionospheric waveguide model alone, and we propose 
                         that an alternative propagation model that allows ULF 
                         (ultra-low-frequency) waves to penetrate directly from the 
                         magnetosphere to low latitudes could be operating simultaneously 
                         to produce these features at the dip equator. Significant effects 
                         of the sunrise terminator on Pc3 pulsations were also observed at 
                         the stations closest to the dip equator. Contrary to what is 
                         reported at other longitudes, in central South America the sunrise 
                         effect decreases the D/H amplitude ratio. We suggest that these 
                         differences may arise from the unique characteristics of this 
                         sector, with a strong longitudinal variation in the magnetic 
                         declination and precipitation of energetic particles due to the 
                         presence of the South Atlantic Magnetic Anomaly (SAMA). The 
                         Hcomponent amplification can be explained by enhancements of the 
                         zonal electric field near the magnetic equator driven by F-region 
                         neutral winds and waves in the fast-mode of propagation during 
                         sunrise.",
                  doi = "10.5194/angeo-38-35-2020",
                  url = "http://dx.doi.org/10.5194/angeo-38-35-2020",
                 issn = "0992-7689",
             language = "en",
           targetfile = "silva_latitudinal.pdf",
        urlaccessdate = "27 abr. 2024"
}