@Article{GonzalezGonz:2013:LoVaGe,
author = "Gonzalez, Alicia Luisa Clua de and Gonzalez, Walter Demetrio",
affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto
Nacional de Pesquisas Espaciais (INPE)}",
title = "Local-time variations of geomagnetic disturbances during intense
geomagnetic storms and possible association with their
interplanetary causes",
journal = "Advances in Space Research",
year = "2013",
volume = "51",
number = "10",
pages = "1924--1933",
keywords = "geomagnetic disturbance, geomagnetic fields, geomagnetic indices,
intense geomagnetic storms, mid-latitude station, relative
intensity, solar-terrestrial relations, temporal evolution, solar
energy, storms, geomagnetism.",
abstract = "In the present paper the local-time variations in the disturbance
of the geomagnetic-field horizontal component (H) for eight
intense geomagnetic storms that occurred during the descending
phase of solar cycle 23 have been analyzed. The study was based on
the plot of contour lines of the H-depletion intensity in the
plane local time versus universal time (LT-UT maps) with the
objective of observing how the morphology and evolution of the
ring current is mapped into the surface of the Earth in presence
of intense geomagnetic storms. The criterion for the selection of
the events was a peak Dst below about-200 nT. The values of the
horizontal geomagnetic field were obtained from six mid-latitude
stations, with 1 min resolution, and the disturbances were
computed by a process similar to that for obtaining the Sym-H
geomagnetic index. By means of a cubic spline, the results were
interpolated to all longitudes with 6 min in LT spacement. The
observed contour maps show, as expected, that the region of
largest depletion in H are situated around dusk, as a consequence
of the formation of a partial ring current, mainly located in the
noon-dusk-midnight hemisphere. However, H disturbances are also
observed around midnight and, to a less extend, at the noon-dawn
sector. In order to detect a prevalent pattern for the behavior of
the geomagnetic-disturbance distribution, a statistical analysis
was done by means of occurrence histograms, for different levels
of the relative intensity of the storm as a function of local
time. The relative intensity for each event was defined as a
parameter varying between 0 and 1, with 0 (1) corresponding to the
maximum (minimum) horizontal field disturbance during that
particular event. Although this analysis does not show the
temporal evolution of the disturbance, it confirms the above
conclusions about its LT distribution. When only the main phases
of the storms are considered in the statistics, the basic
differences are the dawn peak is lightly shifted towards noon and
that the noon-dawn contribution becomes larger. The observed
distributions were tentatively associated with the corresponding
interplanetary causes of the events. Since among the eight
considered storms four are associated to magnetic cloud with a
shock interplanetary structure (sMC) and three to sheath regions
followed by a magnetic cloud (SH/MC), the statistical study was
also performed for the two subsets of storms separately. For the
first group (sMC) the LT distribution looks very similar to that
of the whole set of storms. On the other hand, it was observed
that for the last group (SH/MC) the peak around midnight was not
present. This result might be a consequence that these type of
storms are probably not associated to the presence of substorms.",
doi = "10.1016/j.asr.2012.10.029",
url = "http://dx.doi.org/10.1016/j.asr.2012.10.029",
issn = "0273-1177",
label = "scopus",
language = "en",
targetfile = "1-s2.0-S0273117712006801-main.pdf",
urlaccessdate = "15 jun. 2024"
}