@Article{EspinosaSarmientoPadiAlve:2019:CaStLo,
author = "Espinosa Sarmiento, Karen Viviana 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 = "Effects of ionospheric conductivity and ground conductance on
geomagnetically induced currents during geomagnetic storms: case
studies at low-latitude and Equatorial regions",
journal = "Space Weather",
year = "2019",
volume = "17",
number = "2",
pages = "252--268",
month = "Feb.",
abstract = "Geomagnetic field variations recorded by fluxgate magnetometers
are used to evaluate geomagnetically induced currents (GICs) under
the equatorial electrojet (EEJ) and South Atlantic Magnetic
Anomaly (SAMA) during two geomagnetic storms in March and June
2015. Geomagnetic stations with information about the underground
electrical conductivity structure and that can be approximated by
unidimensional (1-D) models for calculation of the geoelectric
field are selected. GICs levels are estimated using a realistic
local power grid model located in the central region of Brazil,
artificially moved to the sites where the geomagnetic measurements
are available. GIC magnitudes are not large during the storms, and
a maximum amplitude of 3.8 A was estimated at an equatorial
station positioned over high resistivity underground during the
main phase of the June storm. Effects of the ionospheric currents
over the measurement sites and of the conductivity distribution
beneath these sites are also evaluated. It is observed that both
(EEJ) and (SAMA) increase the GICs amplitudes, with the greatest
effects associated with daytime (EEJ) currents. A cutoff frequency
was identified for both the (EEJ) and (SAMA) so that signals with
frequencies lower than 2 mHz (periods longer than 500 s) are not
amplified by the ionospheric currents. In relation to the
underlying conductivity structure, GIC magnitude is affected by
variation of the surface impedance and the sampling rate of the
geomagnetic field. In our case, differences in amplitude of the
surface impedance at the Nyquist frequency control the relative
effects of the ground conductance between the stations.",
doi = "10.1029/2018SW002094",
url = "http://dx.doi.org/10.1029/2018SW002094",
issn = "1542-7390",
language = "en",
targetfile = "Espinosa_et_al-2019-Space_Weather.pdf",
urlaccessdate = "02 maio 2024"
}