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 Earth–ionosphere
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 H-component 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.
Review comment on Latitudinal variation of Pc3-Pc5 geomagnetic pulsation amplitude across the dip equator in central South America by Graziela Belmira Dias da Silva et al.
