@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 = "28 abr. 2024"
}