@InProceedings{SilvaAlvePadi:2017:ExAmCh,
author = "Silva, Graziela Belmira Dias da and Alves, Livia Ribeiro and
Padilha, Ant{\^o}nio Lopes",
affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto
Nacional de Pesquisas Espaciais (INPE)} and {Instituto Nacional de
Pesquisas Espaciais (INPE)}",
title = "Experimental amplitude characterization of Pc3 and Pc5 pulsations
at the brazilian equatorial region",
booktitle = "Proceedings...",
year = "2017",
organization = "AGU Fall Meeting",
abstract = "Daytime equatorial electrojet currents (EEJ) are known to amplify
geomagnetic variations on the ground in the equatorial region,
with the possible exception of Pc3 pulsations for which there are
reports of both amplification and damping in the pulsation
amplitude near the magnetic equator. To clarify the EEJ effects on
ground continuous pulsations (Pc) in the Brazilian equatorial
region, we statistically analyzed the amplitude structure of Pc3
(10 45 s) and Pc5 (150 600 s) pulsations recorded preferably
during quiet days at multiple equatorial to low latitude stations
(L = 1.00 1.12) nearly aligned along the 10° magnetic meridian. It
was observed that diurnal Pc5s were amplified at all stations of
the equatorial region, but mainly at those closest to the dip
equator (latitudes less than 2°), whereas diurnal Pc3s were
preferentially damped at equatorial stations, especially at one
station under the dip equator. We interpret these differences as
associated with different mechanisms of pulsation generation and
transmission, and to the increase of Cowling conductivity in the
diurnal equatorial ionosphere. Daytime Pc5s are transmitted
horizontally in the TM0 mode from polar latitudes and amplified in
the equatorial region by the higher ionospheric conductivity. On
the other hand, daytime Pc3s are preferably upstream waves
generated by ion-cyclotron instability on the bow shock, which
propagate as compressional waves along the equatorial plane of the
magnetosphere and are damped by the high conductivity of the
equatorial ionosphere before reaching the ground. Our data also
show significant sunrise terminator effects in Pc3 pulsations at
the stations closest to the dip equator. However, on contrary to
reported at other longitudes, in the Brazilian equatorial region
the sunrise effect increases the H-to-D (north-south to east-west)
amplitude ratio. We suggest that these significant differences
could be arising from the markedly different magnetic declination
angles between the Brazilian sector and the regions of the other
studies. In our case, the H-component amplification can be
explained by enhancements of the zonal (eastward) electric field
near the magnetic equator driven by F region neutral winds (the F
region dynamo) shortly after sunrise.",
conference-location = "New Orleans",
conference-year = "11-15 Dec.",
language = "en",
targetfile = "silva_experimental.pdf",
urlaccessdate = "11 maio 2024"
}