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Rio de Janeiro, Brazil

Barbosa C.,Observatorio Nacional ON MCTI | Alves L.,National Institute for Space Research | Caraballo R.,University of the Republic of Uruguay | Hartmann G.A.,Observatorio Nacional ON MCTI | And 4 more authors.
Journal of Space Weather and Space Climate

Geomagnetically Induced Currents (GIC) are a space weather effect, which affects ground-based technological structures at all latitudes on the Earth's surface. GIC occurrence and amplitudes have been monitored in power grids located at high and middle latitudes since 1970s and 1980s, respectively. This monitoring provides information about the GIC intensity and the frequency of occurrence during geomagnetic storms. In this paper, we investigate GIC occurrence in a power network at low latitudes (in the central Brazilian region) during the solar cycles 23 and 24. Calculated and measured GIC data are compared for the most intense geomagnetic storms (i.e. -50 < Dst < -50 nT) of the solar cycle 24. The results obtained from this comparison show a good agreement. The success of the model employed for the calculation of GIC leads to the possibility of determining GIC for events during the solar cycle 23 as well. Calculated GIC in one transformer reached ca. 30 A during the "Halloween storm" in 2003 whilst most frequent intensities lie below 10 A. The normalized inverse cumulative frequency for GIC data was calculated for the solar cycle 23 in order to perform a statistical analysis. It was found that a q-exponential Tsallis distribution fits the calculated GIC frequency distribution for more than 99% of the data. This analysis provides an overview of the long-term GIC monitoring at low latitudes and suggests new insight into critical phenomena involved in the GIC generation. © 2015 C. Barbosa et al. Source

Solon F.F.,Observatorio Nacional ON MCTI | Gallardo L.A.,CICESE | Fontes S.L.,Observatorio Nacional ON MCTI
76th European Association of Geoscientists and Engineers Conference and Exhibition 2014: Experience the Energy - Incorporating SPE EUROPEC 2014

An attempt is made to locate fractured Archean basement underneath thick overburden sedimentary unit at São Francisco basin in Brazil. We applied a joint inversion methodology to verify if the method is able to produce estimated 2-D interpretation models that fit the observed data and are consistent with the prior geological knowledge. Also we aim to provide reliable information on the basement and sedimentary rocks in the São Francisco basin, central part of Brazil. This algorithm is based on the use of a structural constraint called cross-gradient which measures the structural similarity between different physical property distributions. Applications to the MT, gravity and magnetic anomalies data in São Francisco basin show the advantages of using structurally integrated physical property distributions obtained from joint inversion instead of separate inversion for geophysical interpretations. Beyond presenting similarity in structure, the physical property distributions are more geologically meaningful than the ones obtained from separate inversion. Source

Pimentel E.T.,Observatorio Nacional ON MCTI | Hamza V.M.,Observatorio Nacional ON MCTI
Hydrogeology Journal

Results of regional-scale geothermal studies are presented, providing new insights into the characteristics of deep groundwater flow systems in the Paleozoic sedimentary basins in the Amazon, Paraná and Parnaíba regions of Brazil. The study makes use mainly of bottom-hole temperature data sets for oil wells, the depths of which vary from 1,000 to 4,000m. The techniques employed in data analysis have allowed identification of non-linear features in vertical distributions of temperature, produced by deep groundwater flows in the study area. According to the results obtained, vertical velocities of subsurface flows are found to fall in the range 10-10 to 10-9 m/s, while the horizontal velocities are significantly higher, of the order 10-8 m/s. Identification of large-scale down flows has allowed inferences as to the existence of lateral movements of groundwater. The basins in the Amazon region are found to be characterized by widespread down flow of groundwater, implying the existence of distributed recharge systems operating on regional scales. There is a systematic decrease in horizontal velocities along the direction from west to east. This feature is considered indicative of gravity driven flows induced by episodes of uplift, since Miocene times, in the Andean region. © Springer-Verlag Berlin Heidelberg 2013. Source

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