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10th International Congress of the Brazilian Geophysical Society
- Conference date: 19 Nov 2007 - 23 Nov 2007
- Location: Rio de Janeiro, Brazil
- Published: 19 November 2007
421 - 440 of 484 results
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Estudo da Variação do Ângulo de Inclinação Magnética em São Luís (MA): Modelo IGRF vs Magnetômetro
Authors P.D.S.C. Almeida, C.M. Denardini, L.C.A. Resende and H.C. AveiroIn the present paper we show some new results related to a comparative study on variation of the dip angle at São
Luís (2º31´ S, 44º16´ W), on the equatorial region, calculated from magnetometers data and from IGRF simulations. We have investigated the secular variation of the Earth magnetic field using both magnetometers and
IGRF method. The altitudinal dependence of the dip equator location was investigated from IGRF simulations alone. Short time scale (less then a day) magnetic variations of the dip angle were also investigated from magnetometers measurements using a spectral analysis. Among the conclusion, we have obtained an evidence of a coupling processes between the neutral atmosphere (thought the Sq system) and its effects on the induced magnetic field at the ground level. The analysis have reveled a significance order for the atmospheric tides. The diurnal, semidiurnal and terdiurnal tides driven by solar heating appeared to dominate. And the semidiurnal, diurnal and terdiurnal lunar gravitational tides appeared next in strength.
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Estudo de ondas de gravidade atmosférica observadas em flutuações na taxa de emissão e na temperatura da aeroluminescência do O2 e do OH
The response of airglow emission layers in the upper mesosphere and lower thermosphere (MLT) region against passages of the gravity waves was studied using the Krassovsky h parameter, which is a ratio between the emission rate and temperature variations. For this study we used the data of groundbased O2(0,1) and OH(6,2) band airglow measurements carried out at Rikubetsu, Japan, from March 2004 to August 2005. The temperatures are obtained from their rotational line intensity distributions. A total of 280 nights of observation was used in this analysis.
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Counter Electrojet – Can meteoric dust in the lower E-region be responsible for it?
Authors P. Muralikrishna and V.H. KulkarniDust particles of meteoric origin in the lower E-region can affect the conductivity parameters by varying the effective collision frequency and by causing electron bite outs through the capture of ambient electrons. A significant fraction of the dust particles may capture free electrons from the ambient medium and get charged negatively. This can result in reduction in the number density of free electrons especially below the electrojet. This can once alter the vertical profile of the east-west Hall current and under favorable conditions, can even account for the reversal of the electrojet currents.
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In situ observation of propagating waves associated with developing plasma bubbles
More LessSpectral analysis of the fluctuations in electron density and electric field observed in situ by rocket-borne plasma probes indicated the presence of propagating waves in the nighttime F-region over a large height range. The electron temperatures estimated from the LP data showed abnormally high values in the base of the F-region during the upleg of the rocket and practically normal values in the same height region during the downleg. A brief study of the characteristic features of the spectra of electron density and electric field fluctuations and the associated electron temperature variations are presented and discussed here.
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Airglow observations in the region of South Atlantic magnetic anomaly
Since 2001, the formation of plasma bubbles observed by ionospheric airglow OI 630.0 nm and OI 577.0 nm emissions have been registered at Southern Space Observatory, located at São Martinho da Serra, RS, south of Brazil (29° S, 53° W). A photometer to monitor the zenith intensity and an all-sky imager to observe the spatial variation of the emissions were used. The observed zenith intensities showed strong seasonal variation, maxima in the equinox season (March-April and September-October) and minima in solstice (June-July and December- January). The Ol 630.0 intensity depletions caused by formation of the plasma bubble along the magnetic field line were detected by the imager. The depletions were observed more frequently in the period from September to March during the summer season in Southern Hemisphere.
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Estudos Estatísticos de ocorrência das bolhas ionosféricas sobre a região equatorial brasileira durante 2000-2005
This work presents a statistical study of the frequency of occurrence of large-scale ionospheric plasma depletions,
or bubbles over the Brazilian region. This study was based on data gathered by an OI 630 nm imager deployed at São João do Cariri (PB, latitude -7,23°, longitude -36,31°, dip -20.35º). The ionospheric p lasma bubbles are known to interfere in the trans-ionospheric telecommunications over the Brazilian territory. The data were obtained from September 2000 to November 2005. The data processing IDL computer program used here was developed at the Aeronomy Division of the Brazilian institute of Space Research (INPE). This software allows one to process the airglow image. The main dynamical and morphological characteristics of the plasma bubble phenomenon are the following: (a) they are aligned along the geomagnetic field lines, (b) they are generated after sunset (c) they expand upwards and drift (move) eastwards (d) they are known as large-scale irregularities because they extend for hundreds up to thousand kilometers along the field lines (e) inside the bubbles the depletion may attain 99% of plasma rarefaction. This work focus their zonal (east-west) motion and their frequency of occurrence as a function of the geomagnetic Kp and Dst indexes. The statistical study presented is of help to better understand the dynamics of the ionospheric plasma over the Brazilian region.
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Possible role of parallel dynamics in the generation of 150-km echoes in the equatorial ionosphere
Authors E. Alam Kherani, Eurico R.de Paula, M. Mathews and J.H. SobralIn this paper, we discuss the generation mechanism of 150-km echoes in the ionosphere. The presence of these echoes has been known for past two decades. However, their generation mechanism is not yet completely understood. We discuss the role of collisional interchange instability (CII) to generate these echoes in the 140-180 km altitude region of equatorial ionosphere. Based on our recent statistcis of these echoes from the Sao Luis radar, the parallel dynamics is included in the estimation of linear growth rate of CII. The study indicates that under certain range of ionospheric parameters, the linear growth rate of CII can overcome the damping rate and could possibly excite the irregular echoes in the 140-180 km altitude region.
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Simultaneous observation of ionospheric plasma bubble and mesospheric gravity wave activities during CAWSES 2005 SpreadFEx Campaign
Authors H. Takahashi, P.D. Pautet, J. Fechine, M.A. Abdu, I.S. Batista, E. Paula, J.H.A. Sobral, D. Gobbi, D. Arruda, P.P. Batista and F.S. SabbaDuring the SpreadFEx campaign from September 22 to November 8, 2005, two airglow CCD imagers, located at near Brasilia (14.8S, 47.6W, Mag. 10S) and at Cariri (7.4S, 36.5W, Mag. 9S) were operated simultaneously and measured the equatorial ionospheric bubble structures and their time evolution by monitoring the OI 6300 emission. From the 10 nights of coincident data, we observed that on some nights the bubbles was formed at the west of
Cariri, but not seen from the Brasilia site. This suggests that the bubble formation and development started near the Cariri observation site. Identification of a longitudinal zone where the SpF is seeding is very important in order to find the mechanism of formation. The present paper will discuss SpF seeding mechanisms and possible contribution of the mesospheric gravity wave activity.
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Efeitos da Alteração nas Taxas de Colisões no Modelo de Condutividade Ionosférica para a Região E Brasileira
Authors E.P.A. Olivio and C.M. DenardiniIn the present paper we show some new results related to the evolution in the set of equations used to calculate the electron-neutron and ion-neutron collision rates in the Field Aligned Integrated Conductivity Model developed for the Brazilian Equatorial E-Region and its implications on the Hall and Pedersen conductivities and Hall-to-
Pedersen conductivities ratio. The results are shown in a comparative way between the current version and its old
version, and have reveled an increase of the region of high Hall-to-Pedersen conductivities ratio.
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Recent developments in research on noctilucent clouds - why are we still interested ?
More LessThe middle atmosphere is a complex and important region. It contains a wealth of important geophysical phenomena, e.g., the Earth's coldest environment - the mesopause; the airglow layers and the meteoric metal layers. Planetary, tidal and gravity wave activities play a vital role in controlling the structure and driving the overall global circulation of the region. The gravity wave driven large-scale circulation governs the region’s thermal balance and therefore the summer mesopause region at high latitudes is the coldest place on the Earth in spite of the fact that it is continuously illuminated by the Sun. In this very dry part of the atmosphere, at an altitude of about 83 km ice clouds are formed and persist during the entire summer period. These clouds are created in a delicate interplay of microphysical processes and large-scale transport that is not yet completely understood. Because of their sensitivity to atmospheric conditions, NLC are an important test for our understanding of middle atmospheric interactions and are now also regarded as a possibly important way for detecting and understanding climate change. A review of recent developments and results will be given.
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Determinação do Fluxo de Momentum das Ondas de Gravidade Através de Imagens das Emissões da Hidroxila e da Banda Atmosférica do Oxigênio
Authors Delano Gobbi, Fabio Augusto Vargas and Hisao TakahashiThe calculation of gravity waves momentum fluxes and their forcing on the atmosphere mean state, using airglow image observation, depends critically on the amplitude of the brightness fluctuations and the amplitude of the major gas kinetic temperature fluctuations. In this report, a numerical model was developed by introducing a transfer function, a relation between the radiance and temperature perturbations. The model includes atmospheric viscosity effects and a realistic photochemistry for OH and O2 emissions. The present model was applied for calculating the gravity wave momentum fluxes from the OH NIR and O2 (A) all-sky imaging observation at Cachoeira Paulista (23o S, 45o W) and São João do Cariri (7.4° S, 36.6° W). The observed amplitudes flutuations of OH and O2 airglow brightness range from 3 − 15% and 1 − 8%, respectively; the infered momentum fluxes were 2 − 10 m2 s-2 and 1 − 15 m2 s-2, respectively, mostly due to high frequency gravity waves.
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Gravity Wave Fluxes in the Mesopause Region
Authors Alan Z. Liu and Chester S. GardnerLidar observations of wind and temperature profiles between 85 and 100 km, conducted at the Starfire Optical
Range, NM, Maui, HI are used to characterize the seasonal variations of gravity wave fluxes and their
relationships to gravity wave activity in this region. At SOR, the gravity wave variance and heat flux all exhibit
strong semi-annual oscillations with maxima during the summer and winter and minima during the spring and fall.
At Maui, annual variation is dominant. The heat flux is also related to the stability of the background atmosphere.
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Observations of the 16-day wave in the equatorial meteor winds and TIMED/SABER temperatures
Horizontal wind measurements obtained from São João do Cariri-PB (7.4° S, 36.5° W), Brazil, associated with equatorial MLT temperature data acquired by the TIMED/SABER satellite, have been used to investigate the presence of planetary-scale oscillations. The data were obtained from January to December, 2005, which were subjected to the spectral analysis and the results revealed the quasisimultaneous presence of distinct power spectrum with peaks associated with low-frequency oscillations. In this time, our focus is the range period from 12 to 20 days, whose activities were revealed mainly during time-intervals from day 120 to day 250. The characteristics observed suggest that the perturbations were due to presence of 16-day planetary waves. From satellite data, was possible identified a westward propagating 16-day wave with zonal wave number 1.
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Software para análise de tempestades produtoras de sprites
Authors V.T. Rampinelli, F.T. São Sabbas and P.D. PautetEste trabalho apresenta a metodologia utilizada no desenvolvimento de um software para o estudo de sprites onde se investiga a inter-relação desses fenômenos com temperaturas específicas do topo das nuvens de tempestades que os geram e com a ocorrência de relâmpagos. O objetivo é a criação de uma ferramenta que permita tratar especificamente a América do Sul.
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Space storms are roaring through the solar system: why do we earthlings care?
More LessIn this review, I will primarily describe the several chains of actions originating in our parent star, the Sun, that affect Earth, with particular attention to the solar phenomena and the subsequent effects in interplanetary space. Once a disturbance has reached the outer boundaries of the Earth system, a whole new series of processes (only briefly addressed here) will be triggered that are controlled by the Earth’s magnetic field, its ionosphere and atmosphere.
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Some infrared imagery characteristics of a prolific TLE producing MCS over Argentina observed from Brazil
Authors F.T. São Sabbas, P.D. Pautet, O. Pinto, V.T. Rampinelli, M.J. Taylor, M. Bailey, J. Thomas, R.H. Holzworth, N. Solorzano, S. Cummer and N.J. SchuchA total of 445 Transient Luminous Events, TLEs, were observed above a Mesoscale Convective System, MCS ,over Argentina on the night of 22-23 February, 2006, during the third sprite campaign ever conduced in Brazil. We investigated the temporal-spatial evolution of the cloudtop temperature of the MCS based on satellite infrared imagery and their relationship with cloud-to-ground lightning and TLE activity. We used the same methodology São Sabbas and Sentman [2003] applied to a US sprite producing MCS and compared the results. The temperature of the cloud cover, ~ -52o C, was ~ 10 o C higher than of the US MCS, and most of the lightning tended to occur at the borders of the convective cores instead of occurring at the cores themselves. Another difference was that while the US MCS produced sprites only in the back region, the Argentina system produced sprites/TLEs both in the back and front regions. The sprites occurred above regions with ~ -40o C in the beginning of the observations and with ~ -58o C at the end. This also differs from the US case study, in which all sprites happened above regions with ~ -70o C and ~ -64o C. The main similarity was that in the growth phase the lightning occurrence rate increased in association with regions with decreasing cloudtop temperatures (~ -50o C to ~ -58o C ), until a maximum rate was reached in association with minimum temperatures, however in the US MCS the temperatures involved were lower (~ -64o C to ~ -70o C).
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Recurrence through time of fluid escapes features: relationship with sedimentary cycles and tectonic activity (Niger Delta)
Authors Tania Marsset, Bruno Marsset, Pierre Vagner, Laure Simplet, Michel Voisset, Eric Cauquil and Didier DrapeauThis work was done within the framework of a joint research project (Neris, 2002-2005) between IFREMER and TOTAL. The study area is the distal part of the Niger Delta off Nigeria. The main objective is to address the spatio-temporal distribution of fluid escape features (volcanic mud flows and carbonate pavements among others) and to highlight their relationship with sedimentary and tectonic environments. A two step approach including TOTAL’s 3D exploration “short offset” reprocessed seismic and IFREMER near bottom geophysics (a new developed deep-towed Chirp) was used as well as sedimentological and geochemical analyses from gravity cores (Marsset et al., 2004; Marsset et al., submitted a and b).
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Avulsion phenomenon: process and consequences on fan evolution. A new perspective from the Zaire (Congo) Turbidite System (ZaiAngo Project, Ifremer/Total)
Authors Laurence Droz, Tania Marsset, Bernard Dennielou, Nathalie Babonneau, Bruno Savoye and Martine BezGeological and geophysical data acquisitions by Ifremer and Total since 1992 (Guiness cruises, 1992-1993, and ZaiAngo cruises, 1998-2000) on the Zaire (Congo) turbidite system revealed a well-organized Quaternary architecture governed by avulsion processes (Savoye et al., 2000; Droz et al., 2003). Active avulsion process throughout the Quaternary resulted in more than 76 channel/levee systems, grouped into 3 individual fans (Northern, Southern and Axial Fan from the oldest to the youngest). In the objective to contribute to a sharper understanding of the avulsion phenomenon and to be finally able to anticipate the sediment distribution in the turbidite systems, we focused part of our research efforts on the avulsion phenomenon that governs the architecture of fans and therefore the sediment partitioning. Two main aspects of this process will be addressed in this presentation: (1) the detailed architecture and evolution of a bifurcation point in the Axial Fan (called A21/22, from the initial channel A21 to the new channel A22) and (2) the spatial and temporal evolution of the bifurcation points at the scale of the whole fan.
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Sediment Transfer Mechanisms from the Coastal Zone/Shelf to the Slope/Basin during the Last 400,000 yrs: a case study for the north-central shelf of Bahia state
More LessThe continental shelf of the São Francisco craton is the narrowest in Brazil. Average widths average 5 to 25 km. The shelf break is located at a 45m depth. As a result in the last 400,000 yrs, the continental shelf was entirely exposed to subaerial conditions during 85% of the time with the rivers emptying directly into the upper slope and therefore delivering sediment directly to the deeper portions of the basin. Erosional retreat of the knickpoint resulted favored widespread erosion and incision on the shelf area and adjacent continent, delivering extra sediment loads to the slope/basin areas. The retreat of the knick points have actually given origin to smaller sub-drainage basins embedded in the larger drainage basins directly influencing the morphology of the coastal zone. During the very short highstand periods, such as the last 6,000 yrs, siliciclastics sedimentation was restricted to inner shelf and did not extend beyond the 15-20m isobaths. In the two study areas investigated it has been possibly to located the exact point where the major rivers emptied in the upper slope. The sediment transfer model presented herein is very different from those valid for classically studied areas such as the Gulf of Mexico, where the shelf break is located in much greater depths. In these areas exposure of the shelf break, and therefore incision, occurred only in very limited time intervals, during the last 400,000 yrs. Our model has possibly limited applications to the Cretaceous and Early Tertiary, because of the absence of high frequency high amplitude sea-level oscillations during those periods.
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Uso do coeficiente de reflexão dos sedimentos superficiais extraído com o perfilador de sub-fundo na confecção de mapa de fácies sedimentar do fundo marinho
The reconnaissance of the sedimentary cover on the continental shelf has academic (study the origin of sediments) and economic (installation of engineering structures) implications. There are direct and indirect methods to collect seabed sediment data. Dredging gives direct information of the collected sediments while high frequency seismic profiling registers the reflection coefficients of the sediments, allowing to infer its texture. The integration of direct and indirect methods permits to better construct submarine bottom sedimentary facies maps. Direct methods are used to identify the types of sediments and the indirect methods increase the precision of the spatial limits within different sediment types.
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