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5th International Congress of the Brazilian Geophysical Society
- Conference date: 28 Sep 1997 - 03 Oct 1997
- Location: São Paulo, Brazil
- Published: 07 November 1997
321 - 340 of 416 results
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Ecofacies da Plataforma Continental Amazonica
Authors E. de Alencar Costa and A. FigueiredoO rio Amazonas apresenta uma vazăo que chega a atingir 350.000 m/s e fornece urn suprimento sedimentar de aproximadamente 1 bilhăo de toneladas por ano ŕ plataforma continental (MEADE et al., 1985). Com tamanha descarga sedimentar, o rio constrói urn delta submarino que estende-se até a plataforma externa (FIGUEIREDO et al., 1972). Esta regiăo sofre ainda a influęncia da corrente Norte Brasileira, que flui em direçăo NW; das grandes amplitudes de marés e fortes correntes associadas e dos ventos Alfsios de NE. A associaçăo de todos estes processos, promove uma distribuiçăo diferenciada de sedimentos e de tipos de eco ao longo da plataforma (fig. 1).
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About the Intensity of Strokes in Negative Lightning Flashes
Authors I.R.C.A. Pinto, O. Pinto Jr., J.H. Diniz and A.M. CarvalhoNegative cloud-to-ground lightning flashes were recorded by a lightning positioning and tracking system (LPATS) in the region of the Mount Agulhas Negras (altitude of 2787 m) in Brazil, during the winter and summer season of 1993. The dependence of the stroke peakcurrent on the order of the stroke, the flash multiplicity and the season was investigated. It was found that subsequent strokes tend to be less intense than first-order strokes and that first-order strokes tend to be more intense in multiple stroke flashes. It seems that the larger is the multiplicity, the higher is the intensity of the first-order stroke. The above results are more evident during the winter season. It was also found that the geometric mean of the first-order stroke peak-current increases in the winter season. The dependence of the results on the high altitude of the observation site was also investigated. Apparently, the high altitude of Mount Agulhas Negras has an effect on the lightning intensity during the summer season.
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An Evaluation of The Predicted Pulse-Type Thunderstorm Gusts Using Horizontal Divergence Field from Doppler Radar Data
Authors W.C. Maugeri Amorim, O. Massambani and I. ZawadzkiThe application of the cloud top penetrative downdraft mechanisms in combination to the Vertically Integrated Liquid water contents (VIL) and radar Echo Top heights (ET) as proposed by Stewart (1991), and in operational use as a "GUST Algorithm" at J. S. Marshall Weather Radar Observatory - Montreal, Canada, was evaluated using horizontal divergence field computed for the lowest antenna elevation (0.5 degree) from Doppler radar measurements. The study was based on a total of 25 events responsible for generating strong surface winds in the Montreal region as observed during the summers of 1994 to 1996. To compute the maximum vertical velocity (W) within the downdraft, the technique uses the estimated VIL and ET respectively related to the liquid water content and height parameters as theoreticaly proposed by Emanuel (1981). The horizontal divergence (S) was processed from differential Doppler velocity data using the "SHEAR Algorithm" also in operational use at the Radar Observatory. For all storms, Wand S were computed simultaneously in a 5 minute resolution corresponding the antenna elevation program cycle. A comparison between those two computed parameters (Wand S) resulted in an overall averaged correlation coefficient of 0.75 and an overall averaged time lag of 10 minutes. Vertical cross-sections from the Doppler radar data were used to determine that typically the level of horizontal divergences was about 1500 meters, corresponding to the height of the maximum vertical velocities. The application of a simple flux balance and mass continuity equations to the computed W for all cases, a distribution of expected heights was determined to be centered at 2000 meters level, indicating a fairly good agreement. The paper also presents a critical analysis of the assumptions built into the technique regarding the entrainment conditions at the cloud top level, as well as due to the effects of the quantitative estimation of the ET and VIL parameters from the radar reflectivity data. The results indicate that the technique can be used as a powerful nowcasting tool to potentially detect severe gust storms antecipating the presence of strong divergence field at the surface.
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Cloud-to-Ground Lightning Flash Characteritics in Meteorogical Conditions
Authors R.B.B. Gin, O. Pinto Jr., I.R.C.A. Pinto and O. Mendes Jr.About 200,000 lightning flashes recorded in the summer season of 1993 in the state of Minas Gerais, Brazil, were analysed in terms of the predominant meteorological condition in the synoptic scale. The results indicate that most lightning characteristics are independent on the synoptical conditions. However, the mean intensity of first-order strokes in both negative and positive lightning flashes were found to be lower in flashes associated with isolated thunderstorms than in flashes associated with cold front or tropical convection.
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Estimativas de Precipitaçăo Através da Freqüęncia de Raios Nuvem-Solo, em Belém
Altas freqüęncias de ocorręncias de raios e elevadas razőes de precipitaçăo, estăo principalmente associadas com as nuvens cumulonimbos, na troposfera. As relaçőes entre a eletrificaçăo dessas nuvens e a razăo de crescimento de seus hidrometeoros, bem como, a ocorręncia de uma rajada ou jorro de chuva por 4 a 6 minutos observado na superfície, após a ocorręncia de raio nas proximidades do observador, tem sido objeto de diversos relatos e estudos. Entretanto, as relaçőes de causa e efeito, nas condiçőes microfísicas que prevalecem no interior das cumulonimbos, permanecem sem explicaçăo satisfatória.
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Cloud-to Ground Lightning Flash Characteristics in Southeastern Brazil in the Winter Season
Authors R.M.L. Rocha, I.R.C.A. Pinto and O. Pinto Jr.The lightning flash characteristics in the southeastern region of Brazil were obtained in the winter season of 1993 through a lightning positioning and tracking system (LPATS). The preliminary data are presented in terms of polarity, multiplicity, and peak current of the first-order stroke. The results are compared with similar data obtained in the same region in the summer season.
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Estrutura Tridimensional da Linha de Instabilidade da Amazônia
Authors J.C. Paiva Cohen and M.A. Faus da Silva DiasAs Linhas de Instabilidade (LI) formam-se ao longo da costa norte-nordeste da América do SuI, desde a Guiana até o estado do Maranhăo, sendo que algumas destas linhas de cumulonimbus propagam-se para o interior da Bacia Arnazônica e outras dissipam-se próximo a costa atlântica. Tanto as linhas de cumulonimbus que se propagam, quanta as que năo se propagam associam-se ŕ circulaçăo de brisa marítima junto ŕ costa (Kousky, 1980). O objetivo deste trabalho é avaliar a estrutura tridimensional de uma LI através de experimentos numéricos, validando esses resultados através dos dados coletados na rede de estaçőes automáticas instaladas durante o experimento ABLE 2B (Amazon Boundary Layer).
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Severe Weather Systems for Southeast Brazil, 1989-1994
Authors J.C. Conforte, V. Brahmananda Rao and M.A.F. Silva DiasA brief climatology of severe weather systems is made for the period 1989-1994. It is found that the number of severe weather systems is highest in austral spring and lowest in winter.
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Direct Lightning Current Measurements in Southeastern Brazil I. Current Waveform
Authors M. Lacerda, O. Pinto Jr., I.R.C.A. Pinto, J.H. Diniz and A.M. CarvalhoThis paper shows for the first time in the scientific literature data of 22 natural negative cloud to ground lightning discharges in South America captured by a 60 m metalic tower between 1985 and 1994. The technique for obtaining the data is briefly described. We show current waveform for several return strokes with resolution of 1 us, 0.5 us and 0.2 us.The average current waveform shows some differences when compared with data from Switzerland tower.
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Direct Lightning Current Measurements in southeastern Brazil II: Correlations
Authors M. Lacerda, O. Pinto Jr., I.J.H. Diniz, A.M. Carvalho and R.C.A. PintoThis paper shows data associated with 50 subsequent return stroke of 22 natural negative descendent Jightining discharges in Brazil captured by a 60 m metalic tower, between 1985 and 1994. It is investigated the possible correlations among the time to peak value of derivative current, time to peak current, the peak value of the electric current, and the peak value of the derivative current.We discuss some physical consequences relating to them. We suggest that there may be a non-linear correlation between the time to peak occurence and the magnitude of these parameters.
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Direct Lightning Current Measurements i
Authors M. Lacerda, O. Pinto Jr., I.R.C.A. Pinto, J.H. Diniz and A.M. CarvalhoIn this paper it is analyzed 13 M-component of 11 subsequent return stroke (of order three or higer) of natural negative cloud. to ground lightning captured by a 60 m metallic tower of Cemig Research Lightning Station (CLRS) in Brazil. The CLRS .has registered Mcomponents in times less then 1.2 millisecond arter the preceding return stroke. The M-components are more. intense than those recordered in triggered lightning flashes and occur during periods of higher continuing current level The half peak Width was found to be shorter than those obtained in triggered lightning flashes.
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Basement Reactivation, Rifting and Sedimentary Basin Development on the Continental Shelf and Margin of NW Europe: Evidence from BIRPS Deep Seismic Reflection Profiling
By R. EnglandDeep seismic reflection and refraction profiling provides the most direct method of imaging basement structures and the relationship between basement structure and basin development. The technique has been successfully used to discriminate between pure and simple shear mechanisms of sedimentary basin formation, by providing the fundamental geometrical relationships between basement faults and the distribution of syn- and post-rift sedimentary sequences. It is the only technique available capable of uniquely characterising the thickness and properties of the continental basement, and therefore provides constraints for thermo-mechanical modelling of the lithosphere. Since 1984 BIRPS has acquired an extensive grid of deep seismic reflection profiles over the United Kingdom and Ireland continental shelf and continental margin. These data can now be used to synthesize the basement structure of the continental shelf of NW Europe and determine its effects on both intracontinental rifts, such as the North Sea, and on passive margin development in the NE Atlantic.
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A Intrusăo da Extensăo da Corrente das Malvinas na Costa do Rio de Janeiro, Brasil, Vista Através do Sensoriamento Remoto e Dados Biológicos in situ
Authors J.L. Stech, M.R. Stevenson, D. Dias-Brito and M. KampelAtravés de imagens do sensor Advanced Very High Resolution Radiometer (AVHRR) instalados a bordo dos satélites da série National Oceanic and Atmospheric Administration (NOAA) e possível obter mapas diários da Temperatura da Superfície do Mar (TSM) para grandes regiőes oceânicas. Stech et al. (1996) observaram, através destes mapas, importantes feiçőes oceanográficas, no Oceano Atlântico SuI. Dentre estas se destacam, o fenômeno da ressurgęncia na costa SE do Brasil e vórtices de mesoescala na Corrente do Brasil (CB). Sirnilarmente, Kampel (1993) estudou a variaçăo da confluęncia das Correntes do Brasil e Malvinas e a penetraçăo para norte, ao longo da costa brasileira, do ramo costeiro da extensăo da Corrente das Malvinas.
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Dispositivo de Proteçăo Szillard: Resultado de 55 Vistorias
Em 1989, a Comissăo Nacional de Energia Nuclear (CNEN), orgăo responsável pela orientaçăo, planejamento, supervisăo e fiscalizaçăo do comércio de materiais radioativos em território brasileiro, proibiu, através da Res. n04 de 19/4/89 (publicada no D.O. em 9/5/89), a "concessăo de autorizaçăo para utilizaçăo de material radioativo em pára-raios", por ferir o princípio da justificativa, fundamento da filosofia intemacional de radioproteçăo, que está ligada ao ganho da sociedade com essa aplicaçăo de material radioativo. "Considerando a necessidade de dar destino adequado ao material radioativo dos pára-raios desativados", foi também resolvido que "o material radioativo remanescente dos pára-raios desativados deve ser imediatamente recolhido a CNEN" (CNEN 1989), 0 que deveria se dar quando da manutencao dos mesmos.
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Lightning Characteristics Associated with Altitude and Ground Conductivity
Authors M.A.S.S. Gomes, O. Pinto Jr., I.R.C.A. Pinto, J.H. Diniz, A.M. Carvalho, A.L. Padilha and I. VitorelloAbout 160,000 strokes recorded in the state of Minas Gerais in the summer season of 1993 were analysed in terms of the dependence of the peak-current stroke intensity and stroke density on altitude and ground conductivity. Preliminary results will be presented and discussed in the context of measurements made in other countries.
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Recent Trends in Stratospheric Ozone: Implications of Anthropogenic, Volcanic and Solar Cycle Perturbations
By S. ChandraSatellite instruments since early 1970 have provided an almost a continuous record of column ozone and ozone profiles on a near global basis. The quality and long term stability of these measurements are now well characterized to make realistic assessments of long term changes in stratospheric ozone associated with anthropogenic chlorine and bromine emissions, solar cycle ultraviolet flux variations and the major volcanic eruptions of El Chichon and Mt. Pinatubo. In this review I will present an overview of ozone changes derived from satellite data and their implications for future changes based on two dimensional photochemical models.
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Estimando Dimensőes Fractais de Relâmpagos
Authors A.L. Martins Jorge and M. Basílio de MatosDiversos objetos naturais apresentam características geométricas que tornam difícil a atribuiçăo de uma dimensăo inteira bem definida a eles. Um exemplo săo as linhas costeiras: definir sua extensăo e uma tarefa que exige a escolba de uma esc ala arbitrária. Quanto menor a escala mais "enseadas" e "pontas" aparecem, num processo que no limite levaria a urn comprimento infinito. Outros objetos típicos săo nuvens, árvores, rios, etc. Nesses casos podemos dizer que a melhor definiçăo de dimensăo é aquela que inclui valores fracionários, e chamamos a esses objetos de fractais.
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Observations of High Densities and Rates of Positive Flashes in Summertime Thunderstorms in Brazil
Authors R.B.B. Gin, O. Pinto Jr., I.R.C.A. Pinto and O. Mendes Jr.Observations of summertime thunderstorms in Brazil in 1993 indicate periods with the predominance of positive cloud-to-ground lightning flashes. The periods present high density (average value of 0.66/km2h.) and high hourly rate (average value of 478/h) of positive flashes. In most cases, they occurred at or near the beginning of the storm's cloud-to-ground lightning activity and had duration of about 2.Sh.
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Stratospheric Balloon Measurements of Sferics in Brazil
Authors M.M.F. Saba, O. Pinto Jr., I.R.C.A. Pinto, R.B.B. Gin and O. Mendes Jr.Measurements of sferics were obtained during two balloon flights launched from Cachoeira Paulista, Brazil, on 26 January 1994 and 23 March 1995 carrying double-probe electric field detectors. The results are discussed in terms of the polarity of the associated lightning flashes and the relationship between the sferic amplitude and the sferic decay time constant. Sferic signatures of one negative flash and two large positive flashes in the quasi-DC and VLF electric field data, obtained in 1995, are presented. From the data obtained in 1994 associated with negatives flashes, a linear relationship between the amplitude and the decay time constant of sferics was found.
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Stratospheric Electric-Field Measurements Before and After Lightning Events
Authors M.M.F. Saba, O. Pinto Jr., I.R.C.A. Pinto, R.B.B. Gin and O. Mendes Jr.Stratospheric vertical electric-field measurements associated with an isolated thunderstorm were obtained during a balloon flight launched in Cachoeira Paulista, Brazil, on 23 March 1995. The behavior of the vertical electric-field before and after large cloud-toground positive lightning flashes is discussed and attributed to the existence of static and transient shielding layers around the thunderstorm. The data just after the flashes can be explained by assuming a static shielding layer around the thunderstorm correspondent to a decrease in the conductivity inside the cloud by a factor of three or more. The data before the first lightning flash can be explained by assuming a transient shielding layer just above the top of the thunderstorm, produced by the near breakdown field inside the cloud.
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