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9th International Congress of the Brazilian Geophysical Society
- Conference date: 11 Sep 2005 - 14 Sep 2005
- Location: Salvador, Bahia, Brazil
- Published: 11 September 2005
421 - 440 of 462 results
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Very low frequency phase advances during solar X-ray flares
Authors Alessandra Abe Pacini, Jean-Pierre Raulin, Emília Correia and Pierre KaufmannVery Low Frequency (VLF) waves propagate in the Earth-ionosphere waveguide bounded by the base of the D-region and by the ground. VLF waves are very sensitive to the electron density profile in the D region, and they can propagate over long distances keeping a high stability for the observed phase and amplitude parameters. For these reasons VLF waves provide a useful diagnostic of the low ionosphere, in terms of its parameters β (conductivity sharpness) and H (reflection height). This study reports on Sudden Phase Anomalies (SPA) of VLF waves received at Atibaia (São Paulo, Brazil) and at Inubo (Japan), from several long distance (over 2800 kilometers) paths during solar flares. The time coverage of the data sample includes periods of high solar activity (January-March 1991 and October-December 1991) as well as epochs of reduced solar activity (January 1994 - July 1997). This report allows us to investigate the detect ability of X-ray producing ionization excess in the low ionosphere, and how this situation is modified along the solar cycle. The results are also discussed in terms of solar flare properties like intensity and spectrum. In particular during solar minimum, we were able to identify a lower X-ray flux level needed to account for a SPA (~ 5.10-7 and 4.10-8 Wm-2 in the 1-8 Ǻ and 0.5-4 Ǻ energy ranges respectively). We also confirm the importance of the X-ray spectral characteristics for the properties of the observed SPAs.
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EQUARS - Satélite Científico para Monitoramento da Atmosfera Equatorial
The objective of the EQUatorial Atmosphere Research Satellite (EQUARS), designed by, and presently under development, at INPE is the monitoring of the Earth’s equatorial low, middle, upper atmosphere and ionosphere. This work presents the project, design and development of the EQUARS onboard platform systems. Various aspects of the onboard subsystems, such as mechanical structure, thermal control, power supply, onboard computer, attitude control, data communication, and their importance to the mission accomplishment will be discussed.
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Relationships Between Intense Magnetic Storms Caused By Sheath Regions, CIRs and ICMEs
Authors A. de Lucas, E. Echer, W.D. Gonzalez, L.E.A. Vieira, L.F. Guarnieri, A. Dal Lago, M.R. da Silva and J.C. dos SantosIn this work we study comparatively intense magnetic storms (Dst < -100 nT) caused by Corotating Interaction Regions (CIRs), or by interplanetary coronal mass ejection (ICMEs), or by sheath regions. Our aim is to analyze their interplanetary characteristics (electric field Ey, Bs interplanetary magnetic field) and their energy coupling function, (e ), and the total energy input, (We ), to analyze the differences between events caused by different interplanetary structures. The geomagnetic data/indices are also employed to study the ring current dynamics and to search for the differences in the storm evolution in these events. The selected storms are 10 March 1998, 6 August 1998, 17 April 1999, 22 September 1999, 24 May 2000, and 6 de November 2000. The interplanetary data were obtained from ACE spacecraft’s Web page, and the geomagnetic data is from World Data Center for Geomagnetism - Kyoto (WDC-Kyoto) and from Space Physics Interactive Data Resource, on the NOAA’s web page.
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Um estudo sobre es ondas de choque no meio interplanetário
More LessO meio interplanetário, o espaço entre os planetas e o Sol, está permeado pelo vento solar que é a própria atmosfera solar se expandindo no espaço interplanetário. Esta atmosfera é composta por um plasma tênue magnetizado o qual favorece a ação das forças Coulombianas de longo alcance. Estas pela presença deste campo magnético, conseguem exercer seu papel que é o de transferência de momentum e informação às partículas provenientes do Sol. Qualquer mudança na atividade solar se reflete no meio interplanetário devido a transferência de informações. A agitação do Sol, conseqüência de sua constante atividade, é transmitida ao vento solar e freqüentemente produz Ondas de Choque. É possível, com o estudo das variações dos parâmetros interplanetários como: densidade, temperatura e velocidade do vento solar e intensidade do campo magnético interplanetário – CMI, identificar a presença desses choques e calcular sua velocidade, intensidade e direção. Neste trabalho utilizamos dados de plasma e CMI fornecidos pelo sistema de dados On-line da sonda ACE – Advanced Composition Explorer, para fazer um estudo acerca de ondas de choque, analisando os gráficos de dados destes eventos e classificando-os, segundo os perfis dos choques feitos por E. Echer et al. [2003], em choques frontais, rápidos e lentos; ou reversos, rápidos e lentos. Este estudo deteve-se ao período de 2002 – 2003, que corresponde ao declínio do
Ciclo Solar 23.
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GPS scintillations, TEC and zonal plasma drifts observed during the COPEX 2002 campaign: Preliminary results
Radio signal amplitude scintillations at the Global Positioning System (GPS) L1 frequency (1.575 GHz) and the ionospheric irregularity zonal velocities were measured simultaneously at three sites during the Conjugate Point Equatorial Experiment (COPEX)
campaign conducted in Brazil from October 1 to December 10, 2002. These observations used two GPS receivers at each site spaced geomagnetically in the eastwest direction and the three observation sites were located along a same magnetic meridian, one at the magnetic equator, Cachimbo (9.5º S, 54.8º W, dip angle: -3.9º), one at the northern conjugate point, Boa Vista (2.8º N, 60.7º W, dip angle: 22.5º) and one at the southern conjugate point, Campo Grande (20.5º S, 54.7º W, dip angle: -22.5º). The data collected in the COPEX campaign occurred during high scintillation activity months which are associated to periods of high occurrence of ionospheric plasma depletions, also known as plasma bubbles. The average decimetric solar radio flux for this period of increased solar activity was about 156. Only magnetically quiet days with åKp £ 24 were selected for this study. Simultaneous dual-frequency GPS receivers measurements revealed total electron content (TEC) decreases, which are bubble signatures, during the observed strong amplitude scintillations. In this paper we will present some preliminary investigations of latitudinal variations and dynamics of scintillations, TEC and ionospheric zonal plasma drifts over magnetic conjugate points.
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Upper atmosphere phenomena in Brazilian geomagnetic anomaly region and its surrounding area
Authors Kazuo Makita, Masanori Nishino, Tatuo Torii, Recardo Monreal, Albert Foppiano and J. SchuchIn order to examine the effect of high energy particle precipitation in Brazilian geomagnetic anomaly region, we examined optical phenomena obtained at Brazil and Japan. During large magnetic storm, airglow phenomena with multiple bands structure were observed at Brazil, however, remarkable airglow phenomena was not recognized at Okinawa. We also examined atmospheric electric field, cosmic ray and 38.2MHz emission during this magnetic storm period. Electric field enhancements were continuously observed for more than 27 hours during the recovery phase of magnetic storm and a good relationship was seen between electric field and 38.2MHz variations. However cosmic ray enhancement was not recognized during this period. On the other hand, we installed imaging riometer at SSO, Brazil
and recently Punta Arenas and Concepcion, Chile. At the present, we did not obtained simultaneous data at these 3 points. So, we shows the preliminary results of imaging riometer observations.
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Study of the gravity wave propagation direction observed by airglow imaging in the South American sector
Airglow all sky imaging observation has been carried out in three different locations in the south America, at Cachoeira Paulista (22.7 S, 45.0 W) in 1999, São João do Cariri (7.5 S, 36.5 W) in 2001 and Boa Vista (2.8 N, 60.7 W) in 2002. Comparing the atmospheric gravity wave characteristics retrieved from the image data for the three different sites and including a previous work at Alcantara (2.3 S, 44.5 W) carried out by Taylor et al. (1997), we found that there is a preferential propagation direction, from the Continent to Atlantic Ocean. Possible source of the wave generation is discussed.
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Spectral features of F-region plasma irregularities as observed by rocket- borne electron density probes from Brazil
Authors P. Muralikrishna and L.P. Vieira and M.A. AbduThe height variation of the ionospheric electron density was measured with rocket-borne electron density probes from Alcantara (2.31oS; 35.2oW) in Brazil. A Black Brant X sounding rocket was launched on 14-th October 1994 at 1955hrs (LT) to investigate the phenomenon of high-altitude equatorial spread-F events. Ground equipments were operated during the campaign to ensure that the rocket was launched under conditions favorable for the generation of plasma bubbles in the F-region. The electron density was measured by three different types of probes. A High Frequency Capacitance probe (HFC) gave density data with low height resolution, while a conventional Langmuir Probe (LP) and a Plasma Frequency Probe (PFP) measured the electron density and the spatial fluctuations in it. The k-spectra of the plasma irregularities were obtained by the spectral analysis of the electron density fluctuation data. An important feature observed was the continuous presence of plasma irregularities of a large range of vertical scale sizes in the altitude range of 340km to 817km. The electron number density varied considerably in these spatial structures, for example a decrease by a factor of 2.6 in a vertical extension of 1km near the altitude of 497km. Near 535km altitude the electron density increased by a factor of 1.8 within a height range of 2.7km. Density structures of vertical scale sizes in the range of hundreds of meters also were observed superposed on the large scale structures. During the rocket upleg two height regions of intense irregularities were observed, one between 366 and 480km and the other between 684 and 812km. The Langmuir Probe (LP) could make measurements of irregularities of vertical scale sizes more than 8m in these height ranges, while the Plasma Frequency Probe, could make measurements of irregularities of vertical scale sizes as small as 0.5m. Spectral features of these irregularities as observed by the two plasma probes at different height regions are presented and discussed here.
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Equatorial F-region irregularities generated by the Rayleigh-Taylor instability mechanism – rocket observations from Brazil
Authors P. Muralikrishna and L.P. VieiraSeveral sounding rockets carrying plasma diagnostic experiments were launched from the Brazilian rocket launching stations in Natal (5.9°S, 35.2°W Geog. Lat.) and Alcantara (2.31°S, 44.4°W Geog. Lat.). Langmuir Probes (LP) were used to measure the height profiles of electron density and electron temperature and High Frequency Capacitance (HFC) probes were used to measure electron density. The LP’s were also used to measure the amplitude of electron density fluctuations ranging in scale size from a few meters to several kilometers. A detailed study of the characteristic features of large scale electron density irregularities observed by rocket-borne electron density probes under different ionospheric conditions is presented here. The main objective of these studies is the identification of these irregularities from the point of view of the dynamic and eletrodynamic processes responsible for their generation. The existing theories of the Rayleigh Taylor Instability mechanism are adapted for conditions of the geomagnetic equatorial ionosphere over Brazil. Appropriately modified equations are used to estimate the minimum expected wavelength of the irregularities, the minimum growth time of irregularities, and the wavelength of irregularities corresponding to the minimum growth time. Through these parameters it is possible to discuss about the importance of the RTI mechanism for the ionosphere. The observed characteristics of the irregularities during four rocket launches are compared with the theoretically expected characteristics. These results confirm the operation of a cascade process that is responsible for the generation of a wide spectrum of irregularities. The cascade process is initiated by conditions favourable for the operation of Gradient Drift Instability (GDI) mechanism, though the growth times expected from theories do not always match with the observations. The large scale irregularities are first generated probably by the RTI mechanism that creates conditions favourable for the operation of the GDI mechanism. From the k-spectra of irregularities it is possible to obtain the spectral index n corresponding to the height chosen. In most of the cases the estimated spectral indices agree well with those published in the literature for the cases of irregularities generated by the GDI mechanism.
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Temporal dynamics and chaotic intermittency in nonlinear wave-wave interactions in space plasmas
Authors Rodrigo A. Miranda, Abraham C.-L. Chian and Erico L. RempelA nonlinear model of three-wave interactions and its temporal evolution is studied. First, we revise the techniques used to obtain the model. Starting from the MHD equations, we found an electrostatic expression for the Zakharov equations, which in the static approximation yield to the Nonlinear Schrödinger equation. The model is finally obtained using a three traveling wave truncation consisting in one linearly unstable pump wave and two linearly damped daughter waves. Then we proceed with the nonlinear dynamics analysis by constructing a bifurcation diagram, where we found a period-3 window. Examples of intermittency driven by temporal chaos present in the time series are shown. Some reviews of in-situ experiments and observations related to wave-wave interactions, and the relevance of the studied model are discussed.
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Modelo para Cálculo da Coluna Total de Ozônio usando Dados do Espectroradiômetro do Observatório Espacial do Sul
The ozone total column has been obtained through UV Radiation detectors as Radiometers and Spectroradiometers. It was used as an alternative method for stations which does not have expensive equipments to measure ozone like Brewer Spectrophotometers. The aim of this work is to find a mathematic model using the relation between UVB/UVA radiations ratio measured by Spectroradiometer MS 701 and effective ozone measured by Brewer Spectrophotometer MKIII #167. Both equipments are installed at Southern Space Observatory, at southern Brazil. The period selected for this analysis was the year of 2003 and only clean sky days were used. The mathematic model found was an exponential function with a correlation coefficient about 0.85. The effective ozone data obtained by Spectroradiometer were fitted with the model found and compared with the Brewer and TOMS ozone total column. The average difference between the model results and Brewer ozone total column was 0.7% and between the model and TOMS ozone data was 3.1%. It verifies the efficiency of the method used and a good approximation of the model.
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Atividade de Ondas de Gravidade na Estratosfera Terrestre Inferida Através da Técnica de Rádio Ocultação de GPS
More LessNeste trabalho são apresentados alguns resultados da atividade de ondas de gravidade na estratosfera sobre a América Latina, inferida através da técnica de rádio ocultação de GPS. Os dados utilizados foram obtidos pelo satélite Challenging Minisatellite Payload (GPSCHAMP). Também serão apresentados, a teoria e a metodologia empregada no cálculo da atividade das ondas de gravidade.
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A Técnica de Rádio Ocultação de GPS como Ferramenta para o Estudo da Atmosfera Terrestre
Authors Cristiano Max Wrasse, Hisao Takahashi and Joaquim FechineNeste trabalho será descrita a técnica de rádio ocultação de GPS e as suas potencialidades para o estudo da atmosfera terrestre, bem como as diversas áreas da ciência em que esta técnica vem sendo empregada.
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A Conductivity Model for the Brazilian Equatorial E-Region
More LessIn this paper we present field-line-integrated local ionospheric conductivity model for the Brazilian equatorial region. It was developed aiming to calculate the E-region electric fields that drive the 3-meter plasma irregularity of the equatorial electrojet. This model was based on the neutral atmosphere and electron densities, on the ion composition, and on E-region critical frequency foE measured by digisonde. Due to the large magnetic declination angle in the Brazilian sector we approximate the geomagnetic field model with a dipole which is not located at the centre of the Earth. We have also considered the eccentric dipole having an inclination of 20° with respect to the Earth rotation axis. The local conductivities resulting from our model are compared to the local conductivities obtained from the conductivity model of the Kyoto University.
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Ozone Hole Depletion over Brazilian Antarctic Station in the spring 2003/2004
More LessWe present measurements of ozone and UV-B radiation made in Brazilian Antarctic Station on King George Island (62.1°S; 58.4°W), during 2003/2004 spring. A field campaign was organized to measured the ozone using a ground based Brewer spectrophotometer, filter photometers, and the vertical profile was obtained on several days using balloon-borne ECC ozonesondes. During this period the UV-B radiation were also measured daily with the Brewer spectrophotometer. 13 successful ozone soundings were obtained during September and October 2003 and 6 ozone soundings were launched during October of 2004. The comparison between 2003 and 2004 these soundings showed severe depletion of stratospheric ozone, mostly in the lower stratosphere, which reached a maximum on October 06 2003, with 60% the reduction on ozone concentration and 2004 the maximum depletion was on October 14, with reduction of the 40%. During 2003 the total ozone content varied considerably: between 121 Dobson Units (DU) on October 06 and 391.6 DU for November 03 and the occurrence the minimum total ozone was the 35 days showing 16 consecutive days. During 2004 the ozone depletion was present 22 days with 11 consecutive days.
The comparison of the total ozone content measured by the ozonesondes with the total ozone Brewer spectrophotometer that operates from the ground has also been used during the campaign, giving a percentage difference of 3.9 + 2.4%.
In terms of the UV-B index, higher values were seen during 2003: on two occasions the Index passed the level of 9; which is larger than values observed on any campaign at the site. During the end of September and the beginning of October the index running mean reached 6, while during the 2004 equivalent period the higher value was about 6.8 and the running mean reached 3.3.
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Comparative study of the ionospheric characteristics of two low latitude Brazilian stations
Authors F. Bertoni, W. Lima, P. Fagundes, F. Becker-Guedes and Y. SahaiWe present, in this paper, a comparative study of ionospheric parameters obtained by two digital ionosondes located at the Brazilian stations of Palmas (10.17°S, 48.20°W) and São José dos Campos (23.21°S, 45.86°W), during periods of geomagnetically quiet days of the equinoctial months of September, October and November 2003. It is suggested that some of the differences between the ionosphere behaviors over those locations to be related to seasonality and some to geographic and geomagnetic configurations.
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Observações simultâneas da emissão do OI 630 nm da Aeroluminescência Noturna através de Fotômetros nos Observatórios Espaciais de São Martinho da Serra (OES) e Cachoeira Paulista (CP)
Este trabalho visa estudar o comportamento das “Bolhas de Plasma” na Ionosfera observando a emissão da Aeroluminescência do oxigênio OI 630 nm em dois sítios observacionais na mesma Latitude Geomagnética, um em São Martinho da Serra, RS (29°S, 53°W, -33° dip latitude), e o outro em Cachoeira Paulista, SP (22.7°S, 45°W, -34° dip latitude). Foram realizadas as medidas simultâneas das variações temporais da intensidade de emissão OI 630 nm no período de janeiro de 2000 a fevereiro de 2005. Para o
presente trabalho foram escolhidas quatro noites quando com ocorrência de “Bolhas de Plasma” nos dois locais. Observou-se nos eventos uma assimetria em relação ao número de “Bolhas” e simetria em relação à intensidade da emissão medida. A análise estatística sobre a ocorrência das “Bolhas” está sendo desenvolvida.
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Modelo Empírico para determinação do Índice UV, obtido com dados do Radiômetro e do Biômetro para o Observatório Espacial do Sul
The Ultraviolet Index was created to advise the population about the solar exposure risk. It can be obtained through biologically active radiation detectors or UV detectors able to measure the irradiance for each wavelength. A network of UV – B Radiometers were installed in cities as: São Martinho da Serra – Brazil, Punta Arenas – Chile, Concepcion – Argentina and Rio Grande – Brazil, through a cooperation between the Tokushoku and Rikkyo Universities, in Japan, the Federal University of Santa Maria and the Southern Regional Space Research Center of the National Institute for Space Research, in Brazil. These equipments measure the accumulated UV Radiation in the spectral range from 280 to 315 nm, which does not permit the radiation be weighed with the Erythema Action Spectrum (Mckinlay-Diffey). The aim of this work is to calculate a model which infers the Ultraviolet Index by UV – B Radiometer MS 210 W data using a Biometer 501 A as reference. The equipments used in this analysis are installed at Southern Space Observatory SSO/CRSPE/INPE – MCT, in São Martinho da Serra, RS – Brazil. The period selected for this analysis was the months of June and November of 2003. Two functions were obtained comparing the Biometer and Radiometer data, one for each month. The models obtained made possible the calculus of the Ultraviolet Index. The correlation coefficients obtained by the models are 0.95 for June and 0.96 for November.
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Ventos Mesosféricos no Sul do Brasil
The Radar System of Meteoric Trails - "All-Sky Interferometric Meteor Radar - SKiYMET", makes it possible the study of Mesosphere in the South of Brazil, in the geographical center of Rio Grande do Sul. Of all theexistent techniques to study the winds in the middle atmosphere, only the ones that use radars and, meteoric radars specially, allows the continuous study in long periods, making possible the evaluation of the diurnal and seasonal variations on winds. The radar technique is based on the determination of average speed of the neutral winds, through the radial speed of the meteoric trails. When penetrating in the atmosphere in high speed, the cosmic particles suffer ablation and produce long ionized columns, which are moved by neutral winds. The movement of these particles produces a Doppler displacement in the sign reflected by the meteoric trail. From this displacement, the radial speed of the meteor can be determined, and together with other information, the position, the speed and direction of the wind also can
be determined.
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Estudo da estrutura vertical da emissão OI 630,0 nm na camada F na região tropical brasileira
Authors C.M.N. Cândido, P. R. Fagundes, J. R. Abalde, V. G. Pillat, D. Gobbi and H. TakahashiIn this paper we present the optical study using the OI 630,0 nm all-sky imaging observations, which occurs in the bottom side of the F layer, between 250 and 300 km altitude. This study is based on the simultaneous observations of the emission OI 630,0 nm which are performed by two similar all-sky imaging systems, based on CCD system set up at two separate sites, Brazópolis, MG (22,53S; 45,57W; Dip Latitude 17,47S) and Cachoeira Paulista, SP (22,7S; 45,0W; Dip Latitude 17,95 S) and São José dos Campos, SP (23,21S; 45,86W; Dip Latitude 17,61S). Applying the triangulation method we analyze two simultaneous images obtained at pair of stations and we derive the altitude of the emission layer.
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