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11.
Tiago Carrilho Biló Ilson Carlos Almeida da Silveira Wellington Ceccopieri Belo Belmiro Mendes de Castro Alberto Ricardo Piola 《Ocean Dynamics》2014,64(10):1431-1446
The Brazil Current (BC) is likely the least observed and investigated subtropical western boundary current in the world. This study proposes a simple and systematic methodology to estimate quasi-synoptic cross-sectional speeds of the BC within the Santos Basin (23° S–26° S) based on the dynamic method using several combinations of data: Conductivity, temperature, and depth (CTD), temperature profiles, CTD and vessel-mounted Acoustic Doppler Current Profiler (VMADCP), and temperature profiles and VMADCP. All of the geostrophic estimates agree well with lowered Acoustic Doppler Current Profiler (LADCP) velocity observations and yield volume transports of -5.56 ±1.31 and 2.50 ±1.01 Sv for the BC and the Intermediate Western Boundary Current (IWBC), respectively. The LADCP data revealed that the BC flows southwestward and is ～100 km wide, 500 m deep, and has a volume transport of approximately -5.75 ±1.53 Sv and a maximum speed of 0.59 m s?1. Underneath the BC, the IWBC flows northeastward and has a vertical extent of approximately 1,300 m, a width of ～60 km, a maximum velocity of ～0.22 m s?1, and a volume transport of 4.11 ± 2.01 Sv. Our analysis indicates that in the absence of the observed velocities, the isopycnal (σ 0) of 26.82 kg m?3 (～500 dbar) is an adequate level of no motion for use in geostrophic calculations. Additionally, a simple linear relationship between the temperature and the specific volume anomaly can be used for a reliable first estimate of the BC-IWBC system in temperature-only transects. 相似文献
12.
Alison de Oliveira Moraes Fabiano da Silveira Rodrigues Waldecir Jo?o Perrella Eurico Rodrigues de Paula 《Surveys in Geophysics》2012,33(5):1107-1131
Ionospheric scintillations are fluctuations in the phase and/or amplitude of trans-ionospheric radio signals caused by electron density irregularities in the ionosphere. A better understanding of the scintillation pattern is important to make a better assessment of GPS receiver performance, for instance. Additionally, scintillation can be used as a tool for remote sensing of ionospheric irregularities. Therefore, the study of ionospheric scintillation has both scientific as well as technological implications. In the past few years, there has been a significant advance in the methods for analysis of scintillation and in our understanding of the impact of scintillation on GPS receiver performance. In this work, we revisit some of the existing methods of analysis of scintillation, propose an alternative approach, and apply these techniques in a comprehensive study of the characteristics of amplitude scintillation. This comprehensive study made use of 32?days of high-rate (50?Hz) measurements made by a GPS-based scintillation monitor located in S?o José dos Campos, Brazil (23.2°S, 45.9°W, ?17.5° dip latitude) near the Equatorial Anomaly during high solar flux conditions. The variability of the decorrelation time (τ0) of scintillation patterns is presented as a function of scintillation severity index (S 4). We found that the values of τ0 tend to decrease with the increase of S 4, confirming the results of previous studies. In addition, we found that, at least for the measurements made during this campaign, averaged values of τ0 (for fixed S 4 index values) did not vary much as a function of local time. Our results also indicate a significant impact of τ0 in the GPS carrier loop performance for S 4?≥?0.7. An alternative way to compute the probability of cycle slip that takes into account the fading duration time is also presented. The results of this approach show a 38% probability of cycle slips during strong scintillation scenarios (S 4 close to 1 and τ0 near 0.2?s). Finally, we present results of an analysis of the individual amplitude fades observed in our set of measurements. This analysis suggests that users operating GPS receivers with C/N 0 thresholds around 30?dB-Hz and above can be affected significantly by low-latitude scintillation. 相似文献
13.
The aim of this study is to separate various fractions of phosphorus in surface sediments of the Amazon continental shelf and compare them with other areas of the Brazilian shelf. Surface sediments were collected from the river-mouth transect (RMT) and open-self transect (OST). The extraction techniques available in the literature have been used to separate the following forms: Fe-PO4, Al-PO4, Ca-PO4, and associated organic matter. The results indicate that the concentrations of phosphorus are uniform in the study area and may be compared with many other nonpolluted environments. Among the inorganic forms, Ca-PO4 is dominant in all the samples, and Fe-PO4 is present in lower concentrations. Al-PO4 is more significant on the Amazon continental shelf than other parts of the Brazilian coast and other coastal environments of the world. 相似文献
14.
M. A. Allison C. A. Nittrouer L. E. C. Faria Jr. O. M. Silveira A. C. Mendes 《Geo-Marine Letters》1996,16(1):36-40
Modern and Holocene muddy strata were studied along the shoreline adjacent to the Amazon river mouth using sedimentological, radiochemical, physical, and seismic methods. The present paper is a synthesis of the results, collected during the AmasSeds project, that is used to outline a regional shoreline sediment budget. Erosion of relict Amazon muds in southern Amapa supplies 106 tons yr–1 to the Amazon advective mud stream. Local rivers are sediment-poor (total suspended discharge ~ 1 × 106 tons yr–1), but form depositional sandflats on the shoreface downdrift of the river mouths. Mudflat accumulation in northern Amapa sequesters 106–107 tons yr–1 by tidal-flat aggradation, alongshore mudcape accretion, and sediment trapping by mangroves. The processes temporarily store 1.5 × 108 tons of Amazon mud in January–June. 相似文献
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16.
Geslaine Rafaela Lemos Gonçalves Luana Ferraz da Silveira Palomares Aline Nonato Sousa Gilson Stanski Gustavo Sancinetti Rogerio Caetano da Costa Antonio Leão Castilho 《Marine Ecology》2020,41(4):e12606
The Brazilian coast is home to two species of Majoid crabs: Libinia ferreirae and Libinia spinosa, with similar habits, as they live in symbiosis with the jellyfish Lychnorhiza lucerna during their juvenile stage and dwell on the bottom of the ocean near the coast when adults. This study investigated the spatial and temporal distribution of L. ferreirae and L. spinosa during different ontogenic phases on the south and south-eastern coast of Brazil, between latitudes 22º and 27ºS. Our results showed that both species have different distributions during their development in the three studied regions. Libinia ferreirae were more abundant associated with jellyfish, and L. spinosa were more abundant in the free-living phase. Environmental factors, especially temperature and salinity, for associated and free-living crabs, respectively, are the main factors that need to be supported for the establishment of these specimens. We were able to identify that the presence or absence of hosts (given the ecological interactions between the species) is determinant in finding the associated crabs. Geographical variations (morphology of the regions, marine currents and the strength of the tide) are linked directly to the movement of the jellyfish hosts to the coast, influencing the abundance of L. fereirae and L. spinosa populations and affecting their distribution patterns. We can infer that both species are connected with other populations because of the association with the jellyfish, crabs could be passively transported along the south and south-eastern coast of Brazil, maintaining the connection between metapopulations. 相似文献
17.
Carlos Augusto Ramos e Silva Pablo Bezerra Dávalos Leonel da Silveira Lobo Sternberg Flavo Elano Soares de Souza Maria Helena Constantino Spyrides Paulo Sérgio Lucio 《Estuarine, Coastal and Shelf Science》2010
We evaluated the physical–chemical properties and nutrient concentrations in two shrimp ponds under conventional management, intensive (I-P) and semi-intensive (SI-P), and one under organic management (O-P), three days after loading and before stoking. The mean’s total alkalinity concentrations were 2.26 ± 0.04 mM, 2.28 ± 0.01 mM and 2.59 ± 0.01 mM, respectively for I-P, SI-P and O-P. Bicarbonate and carbonate accounted for 62% and 37% in I-P, 64% and 36% in SI-P and 83–17% in O-P, respectively. Aragonite and calcite were oversaturated around Ω = 5. Mean total phosphate (TP) concentrations were 441.37 ± 92.06 μg/L, 449 ± 48 μg/L and 473.64 ± 84.17 μg/L, under I-P SI-P and O-P management respectively. Following this sequence, NO3− concentration was 2.98 ± 0.7 μg/L, 1.16 ± 0.16 μg/L and 0.32 ± 0.12 μg/L, under I-P, SI-P and O-P management respectively. Thus, the data suggest that different management of farm organic waste leads to different chemical water quality. 相似文献
18.
L. Matias N. A. Dias I. Morais D. Vales F. Carrilho J. Madeira J. L. Gaspar L. Senos A. B. Silveira 《Journal of Seismology》2007,11(3):275-298
The Faial earthquake (M
L 5.8) that occurred on the 9th of July, 1998, in the Azores region (north Atlantic), caused nine casualties and severe destruction
affecting more than 5,000 people. The main shock was located at sea, 10 km NE of the Faial Island, and triggered a seismic
sequence that lasted for several weeks and was characterized by an unusual high p-value of 1.40 for the modified Omori law. We present here the results of a joint inversion of hypocenters and 1D velocity
model performed on the data collected by the permanent network complemented with a temporary network installed shortly after
the occurrence of the main event. The 1D velocity model shows a heterogeneous upper crust, testified by the observed differences
in site effects at the stations, while the middle crust from ∼2.5 to 8 km in depth is quite homogeneous. The Moho is located
at a depth of about 12–13 km and the Vp/Vs ratio is found to be around 1.78. The events at depth are mainly concentrated in
the middle-lower crust (8–12 km), while their spatial distribution shows a main cluster, visible after relocation, SSE trending.
This direction of elongation is consistent with one of the fault planes (N151°E) of the centroid moment tensor (CMT) solution
for the main shock. The same plane is the preferred main shock fault plane inferred after a Coulomb failure function analysis
on the aftershock distribution. The main event relocation points to a focal depth shallower than 5 km. The aftershocks pattern
shows that several fault systems were reactivated by the stress perturbation induced by the main shock. Besides the two main
tectonic directions, trending WNW–ESE and NNW–SSE, observed in the tectonics of Faial, Pico, and S. Jorge, there is also evidence
of a new tectonic direction trending WSW–ENE. 相似文献
19.
L. Calado I.C.A. da Silveira A. Gangopadhyay B.M. de Castro 《Continental Shelf Research》2010,30(10-11):1181-1188
The regional ocean off southeast Brazil (20°S–28°S) is known as a current-eddy-upwelling region. The proximity of the Brazil Current to the coast in the Cape São Tomé vicinities, as well as of its quasi-stationary unstable meanders, suggests the possibility of background eddy-induced upwelling. Such phenomenon can intensify the prevalent coastal upwelling due to wind and topographic effects. In this paper, with the help of a numerical simulation, we provide evidence that eddy-induced upwelling in the absence of wind is possible in this region. The simulation was conducted with a regional configuration of the 3-D Princeton Ocean Model initialized by a feature-based implementation of the Brazil Current and Cape Frio eddy, blended with climatology. 相似文献
20.
Effects of afforestation on groundwater recharge and water budgets in the western region of Uruguay 
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下载免费PDF全文 Uruguay has stimulated the development of its forest sector since the promulgation of Forest Law N° 15 939 in December of 1987. Nevertheless, the substitution of natural grasslands with forest plantations for industrial use has raised concerns regarding hydrological processes of groundwater recharge and water consumption involving evapotranspiration. The purpose of this study is to assess the effects of this substitution approach on water resources. Input data were collected from two small experimental watersheds of roughly 100–200 hectares located in western Uruguay. The watersheds are characterized by Eucalyptus Globulus ssp. Maidenni and natural grasslands for cattle use. Total rainfall, stream discharge, rainfall redistribution, soil water content and groundwater level data were collected. Groundwater recharge was estimated from water table fluctuations and from groundwater contributions to base flows. Seasonal and annual water budgets were computed from October of 2006 to September of 2014 to evaluate changes in the hydrological processes. The data show a decrease in annual specific discharge of roughly 17% for mean hydrological years and no conclusive effects on annual groundwater recharge in the forested watershed relative to the reference pasture watershed. Reduced annual specific discharge is equivalent to the mean annual interception. The computed actual annual evapotranspiration is consistent with international catchment measurements. Reduction rates vary seasonally and according to accumulated rainfall and its temporary distribution. The degree of specific discharge decline is particularly high for drier autumns and winters (32 to 28%) when the corresponding rainfall varies from 275 to 400 mm. These results are of relevance for water resources management efforts, as water uses downstream can be affected. These findings, based on a study period dominated by anomalous wet springs and summers and by dry autumns and winters, oppose earlier results based on 34 years of rainfall and discharge data drawn from Uruguayan large basins. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献