Effects of the number of stations and time resolution on derivation     

Odim Mendes  Jr.  Aracy Mendes da Costa  Fernando Celso Perin Bertoni 《Journal of Atmospheric and Solar》2006,68(18):2127-2137

For at least 30 years now it has been well known that the Dst index can be modelled using the solar wind as input. Since then, many attempts have been made to improve the predictability of Dst using different approaches. These attempts are useful, for instance, to understand which features of the solar wind–magnetosphere interactions are most important in producing magnetospheric activity and how the Dst index would improve the space weather forecast. The Dst index is by far the most reliable and simple indication that a magnetic storm is in progress. In this work, the effect of using more than four magnetic stations and shorter time intervals than the hourly averages used in Sugiura's procedures is evaluated. The discussion is based on the results presented by Burton in 1975 and Feldstein in 1984 considering 4 or 12 magnetic stations and time averages of 2.5 min for a magnetic disturbed period that occurred from February 7–28, 1967, including two geomagnetic storms. The analysis has shown that the global representation of a magnetic storm by the standard Dst (Sugiura) is well preserved either using 4, 6, 12 magnetic stations or using 1 h, 2.5 min 1 min averages. A brief review of the current understanding of Dst has been included to support the discussions. The analysis performed has shown that a more refined Dst index (time and number of stations>4) would be useful to investigate the intrinsic processes and the different current systems involved in the ring current development during magnetic storms; the standard Dst, as it is conceived, is quite adequate to monitor geomagnetic storms and identify their overall features; concerning the magnetic stations normally considered, the inclusion of higher magnetic latitude stations (>35) may underestimate the observed Dst.  相似文献   

Erratum to: Mission design,operation and exploitation of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission     

Rune?FloberghagenEmail author  Michael?Fehringer  Daniel?Lamarre  Danilo?Muzi  Bj?rn?Frommknecht  Christoph?Steiger  Juan?Pi?eiro  Andrea?da?Costa 《Journal of Geodesy》2012,86(3):241-241

  相似文献   

Downward longwave radiation estimates for clear and all-sky conditions in the Sertãozinho region of São Paulo, Brazil     

Nadiane Smaha Kruk  Íria Fernades Vendrame  Humberto Ribeiro da Rocha  Sin Chan Chou  Osvaldo Cabral 《Theoretical and Applied Climatology》2010,99(1-2):115-123

The accurate estimate of the surface longwave fluxes contribution is important for the calculation of the surface radiation budget, which in turn controls all the components of the surface energy budget, such as evaporation and the sensible heat fluxes. This study evaluates the performance of the various downward longwave radiation parameterizations for clear and all-sky days applied to the Sertãozinho region in São Paulo, Brazil. Equations have been adjusted to the observations of longwave radiation. The adjusted equations were evaluated for every hour throughout the day and the results showed good fits for most of the day, except near dawn and sunset, followed by nighttime. The seasonal variation was studied by comparing the dry period against the rainy period in the dataset. The least square linear regressions resulted in coefficients equal to the coefficients found for the complete period, both in the dry period and in the rainy period. It is expected that the best fit equation to the observed data for this site be used to produce estimates in other regions of the State of São Paulo, where such information is not available.  相似文献   

Rainfall trends in the Brazilian Amazon Basin in the past eight decades     

Prakki Satyamurty  Aline Anderson de Castro  Julio Tota  Lucia Eliane da Silva Gularte  Antonio Ocimar Manzi 《Theoretical and Applied Climatology》2010,99(1-2):139-148

Rainfall series at 18 stations along the major rivers of the Brazilian Amazon Basin, having data since 1920s or 1930s, are analyzed to verify if there are appreciable long-term trends. Annual, rainy-season, and dry-season rainfalls are individually analyzed for each station and for the region as a whole. Some stations showed positive trends and some negative trends. The trends in the annual rainfall are significant at only six stations, five of which reporting increasing trends (Barcelos, Belem, Manaus, Rio Branco, and Soure stations) and just one (Itaituba station) reporting decreasing trend. The climatological values of rainfall before and after 1970 show significant differences at six stations (Barcelos, Belem, Benjamin Constant, Iaurete, Itaituba, and Soure). The region as a whole shows an insignificant and weak downward trend; therefore, we cannot affirm that the rainfall in the Brazilian Amazon basin is experiencing a significant change, except at a few individual stations. Subregions with upward and downward trends are interspersed in space from the far eastern Amazon to western Amazon. Most of the seasonal trends follow the annual trends, thus, indicating a certain consistency in the datasets and analysis.  相似文献   

Future change of climate in South America in the late twenty-first century: intercomparison of scenarios from three regional climate models   总被引：2，自引：1，他引：1  

Jose A. Marengo  Tercio Ambrizzi  Rosmeri P. da Rocha  Lincoln M. Alves  Santiago V. Cuadra  Maria C. Valverde  Roger R. Torres  Daniel C. Santos  Simone E. T. Ferraz 《Climate Dynamics》2010,35(6):1073-1097

Regional climate change projections for the last half of the twenty-first century have been produced for South America, as part of the CREAS (Cenarios REgionalizados de Clima Futuro da America do Sul) regional project. Three regional climate models RCMs (Eta CCS, RegCM3 and HadRM3P) were nested within the HadAM3P global model. The simulations cover a 30-year period representing present climate (1961–1990) and projections for the IPCC A2 high emission scenario for 2071–2100. The focus was on the changes in the mean circulation and surface variables, in particular, surface air temperature and precipitation. There is a consistent pattern of changes in circulation, rainfall and temperatures as depicted by the three models. The HadRM3P shows intensification and a more southward position of the subtropical Pacific high, while a pattern of intensification/weakening during summer/winter is projected by the Eta CCS/RegCM3. There is a tendency for a weakening of the subtropical westerly jet from the Eta CCS and HadRM3P, consistent with other studies. There are indications that regions such of Northeast Brazil and central-eastern and southern Amazonia may experience rainfall deficiency in the future, while the Northwest coast of Peru-Ecuador and northern Argentina may experience rainfall excesses in a warmer future, and these changes may vary with the seasons. The three models show warming in the A2 scenario stronger in the tropical region, especially in the 5°N–15°S band, both in summer and especially in winter, reaching up to 6–8°C warmer than in the present. In southern South America, the warming in summer varies between 2 and 4°C and in winter between 3 and 5°C in the same region from the 3 models. These changes are consistent with changes in low level circulation from the models, and they are comparable with changes in rainfall and temperature extremes reported elsewhere. In summary, some aspects of projected future climate change are quite robust across this set of model runs for some regions, as the Northwest coast of Peru-Ecuador, northern Argentina, Eastern Amazonia and Northeast Brazil, whereas for other regions they are less robust as in Pantanal region of West Central and southeastern Brazil.  相似文献   

Is the meander growth in the Brazil Current system off Southeast Brazil due to baroclinic instability?     

I.C.A. da Silveira  J.A.M. Lima  A.C.K. Schmidt  W. Ceccopieri  A. Sartori  C.P.F. Franscisco  R.F.C. Fontes 《Dynamics of Atmospheres and Oceans》2008,45(3-4):187

Temporally-growing frontal meandering and occasional eddy-shedding is observed in the Brazil Current (BC) as it flows adjacent to the Brazilian Coast. No study of the dynamics of this phenomenon has been conducted to date in the region between 22° S and 25°S. Within this latitude range, the flow over the intermediate continental slope is marked by a current inversion at a depth that is associated with the Intermediate Western Boundary Current (IWBC). A time series analysis of 10-current-meter mooring data was used to describe a mean vertical profile for the BC-IWBC jet and a typical meander vertical structure. The latter was obtained by an empirical orthogonal function (EOF) analysis that showed a single mode explaining 82% of the total variance. This mode structure decayed sharply with depth, revealing that the meandering is much more vigorous within the BC domain than it is in the IWBC region. As the spectral analysis of the mode amplitude time series revealed no significant periods, we searched for dominant wavelengths. This search was done via a spatial EOF analysis on 51 thermal front patterns derived from digitized AVHRR images. Four modes were statistically significant at the 95% confidence level. Modes 3 and 4, which together explained 18% of the total variance, are associated with 266 and 338-km vorticity waves, respectively. With this new information derived from the data, the [Johns, W.E., 1988. One-dimensional baroclinically unstable waves on the Gulf Stream potential vorticity gradient near Cape Hatteras. Dyn. Atmos. Oceans 11, 323–350] one-dimensional quasi-geostrophic model was applied to the interpolated mean BC-IWBC jet. The results indicated that the BC system is indeed baroclinically unstable and that the wavelengths depicted in the thermal front analysis are associated with the most unstable waves produced by the model. Growth rates were about 0.06 (0.05) days⁻¹for the 266-km (338-km) wave. Moreover, phase speeds for these waves were low compared to the surface BC velocity and may account for remarks in the literature about growing standing or stationary meanders off southeast Brazil. The theoretical vertical structure modes associated with these waves resembled very closely to the one obtained for the current-meter mooring EOF analysis. We interpret this agreement as a confirmation that baroclinic instability is an important mechanism in meander growth in the BC system.  相似文献   

The impact of dust on the scaling properties of galaxy clusters     

Antonio C. da Silva  rea Catalano  Ludovic Montier  Etienne Pointecouteau  Joseph Lanoux  Martin Giard 《Monthly notices of the Royal Astronomical Society》2009,396(2):849-859

We investigate the effect of dust on the scaling properties of galaxy clusters based on hydrodynamic N -body simulations of structure formation. We have simulated five dust models plus radiative cooling and adiabatic models using the same initial conditions for all runs. The numerical implementation of dust was based on the analytical computations of Montier & Giard. We set up dust simulations to cover different combinations of dust parameters that make evident the effects of size and abundance of dust grains. Comparing our radiative plus dust cooling runs with a purely radiative cooling simulation, we find that dust has an impact on cluster scaling relations. It mainly affects the normalization of the scalings (and their evolution), whereas it introduces no significant differences in their slopes. The strength of the effect critically depends on the dust abundance and grain size parameters as well as on the cluster scaling. Indeed, cooling due to dust is effective in the cluster regime and has a stronger effect on the 'baryon driven' statistical properties of clusters such as   L _X– M , Y – M , S – M   scaling relations. Major differences, relative to the radiative cooling model, are as high as 25 per cent for the   L _X– M   normalization, and about 10 per cent for the Y – M and S – M normalizations at redshift zero. On the other hand, we find that dust has almost no impact on the 'dark matter driven'   T _mw– M   scaling relation. The effects are found to be dependent in equal parts on both dust abundances and grain size distributions for the scalings investigated in this paper. Higher dust abundances and smaller grain sizes cause larger departures from the radiative cooling (i.e. with no dust) model.  相似文献   

Variations in stratigraphic and reservoir properties adjacent to the Mid-Paleocene sequence boundary, Campo section, Pyrenees, Spain     

A.-C. da Silva  C. Loisy  A. Cerepi  R. Toullec  E. Kiefer  L. Humbert  P. Razin 《Sedimentary Geology》2009,219(1-4):237-251

The Paleocene of the Campo section, Spain has different sedimentological characteristics above and below the Mid-Paleocene Unconformity. Beneath the unconformity sediments are dominated by evaporitic carbonates and collapse breccias. Above it they are characterized by continental detrital beds alternating with paleosols. Different subaerial features are observed and correspond to different porosity values, pore–throat sizes and micrite morphologies. Unexposed or intertidal facies have low porosity, low throat–pore size (mesoporosity) and well preserved rhombic crystals. Intermediate exposed facies (paleosols) possess medium porosity, medium pore–throat size (microporosity) and mainly micro-rhombic crystals. Finally, the facies corresponding to high exposure intensity and to evaporitic original facies presents high porosity, permeability, large pore–throat size and rounded micritic crystals. These observations show that the emersion phase caused important dissolution, especially when associated with an easily dissolved original lithofacies.  相似文献   

Isolation,biodegradation ability and molecular detection of hydrocarbon degrading bacteria in petroleum samples from a Brazilian offshore basin     

Suzan Pantaroto de Vasconcellos  Elaine Crespim  Georgiana Feitosa da Cruz  Diego Barbosa Senatore  Karen Christina Marques Simioni  Eugênio Vaz dos Santos Neto  Anita Jocelyne Marsaioli  Valéria Maia de Oliveira 《Organic Geochemistry》2009,40(5):574-588

The detection of microorganisms with potential for biodeterioration and biodegradation in petroleum fields is of great relevance, since these organisms may be related to a decrease in petroleum quality in the reservoirs or damage in the production facilities. In this sense, petroleum formation water and oil samples were collected from the Campos Basin, Brazil, with the aim of isolating microorganisms and evaluating their ability to degrade distinct classes of hydrocarbon biomarkers (9,10-dihydrophenanthrene, phytane, nonadecanoic acid and 5α-cholestane). Twenty eight bacterial isolates were recovered and identified by sequencing their 16S rRNA genes. Biodegradation assays revealed that bacterial metabolism of hydrocarbons occurred through reactions based on oxidation, carbon–carbon bond cleavage and generation of new bonds or by the physical incorporation of hydrocarbons into microbial cell walls. Based on the biodegradation results, selective PCR-based systems were developed for direct detection in petroleum samples of bacterial groups of interest, namely Bacillus spp., Micrococcus spp., Achromobacter xylosoxidans, Dietzia spp. and Bacillus pumilus. Primer sets targeting 16S rRNA genes were designed and their specificity was confirmed in silico (i.e. computational analysis) and in PCR reactions using DNA from reference strains as positive and negative controls. Total DNA from oil was purified and the amplification tests revealed the presence of the target bacteria in the samples, unraveling a significant potential for petroleum deterioration in the reservoirs sampled, once proper conditions are present for hydrocarbon degradation. The application of molecular methods for rapid detection of specific microorganisms in environmental samples would be valuable as a supporting tool for the evaluation of oil quality in production reservoirs.  相似文献   

Water Availability of Sub-Basins with Restrictions on Use under Climate Change Scenarios in Brazil     

Redivo  Polyana Comino  Sanches  Luciana  de Carvalho Alves  Marcelo  Barbosa da Silva  Jhonatan 《Water Resources》2021,48(6):905-913

Water Resources - The Queima Pé Stream Basin (QPSB) and Ararão River Basin (ARB) in central Brazil have had recurrent problems with water scarcity. This may get worse under anthropogenic...  相似文献