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@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 = "24 jan. 2021"
}


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