Long‐term morphological impacts of the opening of a new inlet on a multiple inlet system     

A. Pacheco  Ó. Ferreira  J. J. Williams 《地球表面变化过程与地形》2011,36(13):1726-1735

In this study, the artificial opening of a new tidal inlet in an existing multiple inlet system is shown to significantly modify the adjacent nearshore and backbarrier morphology, as well as both updrift and downdrift shorelines. The study focuses on the dominant Faro‐Olhão and Armona inlets in the Ria Formosa barrier island system of southern Portugal. The equilibrium state and future evolution of the system are inferred using a range of morphological and hydrodynamic indicators, including the evolution of the inlet cross‐section, changes in tidal prism, and changes in the dimensions (length and area) of barrier islands. The results reveal how the morphology of an interconnected two‐inlet bay system and the adjacent coastlines has evolved following the artificial opening and stabilization of Faro‐Olhão inlet since 1929. A clear relationship between barrier island size, inlet cross‐section/width, and tidal prism is demonstrated. Decadal time‐scale changes in the tidal prism of the two interconnected inlets are shown to be the main mechanism responsible for morphological change, and have resulted in the remobilization of ebb‐tidal delta sediments deposited during previous hydraulic configurations. These changes, in turn, have contributed to a narrowing of Armona inlet and an increase in the size of Culatra Island. The work highlights the importance of ebb‐tidal deltas both as sand reservoirs and as conduits through which sand exchange between estuaries or lagoons and the open coast is regulated. It also shows the pivotal role of ebb‐tidal deltas in trapping longshore‐transported sediment and releasing it again during periods of increased wave activity. The findings have implications regarding the accurate assessment of the stability of multiple inlet systems. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Assessing the control exerted by soil mineralogy in the fixation of potentially harmful elements in the urban soils of Lisbon,Portugal     

C. Costa  A. P. Reis  E. Ferreira da Silva  F. Rocha  C. Patinha  A. C. Dias  C. Sequeira  D. Terroso 《Environmental Earth Sciences》2012,65(4):1133-1145

The main purposes of this study are the textural, chemical and mineralogical characterization of the urban soils of Lisbon and the identification of probable relations between the several soil properties. The results are used to infer which soil properties control the superficial dispersion of potential harmful elements to human health. Soil sampling was carried out in 51 selected sites all through the city, under the criterion that such sites should be spaces usually frequented by children. The concentrations of 42 elements in the >2 mm soil size fraction were determined at a commercial laboratory in Canada (ActLabs, LTD), by ICP-MS/ICP-OES after an acid digestion with aqua regia. The soil mineralogy was determined by X-ray diffraction in the <2 and <62 μm size fractions. The results indicate that the urban soils have mainly a sandy texture and a main mineralogical assemblage of quartz, K-feldspar, plagioclase and calcite. In terms of clay minerals, smectite, illite and kaolinite are the main clays in the soil. Smectite and illite show a dichotomy in their distribution, with the smectites prevailing in the soils of the volcanic complex of Lisbon, which are classified as being residual, and illite prevailing in the remaining soils, which are considered mainly as man-made soils. Smectite seems to exert an important role in the fixation of Ni and Cr. The results of the geochemical study show that Ni and Cr have concentrations above the soil guideline value established to the UK and pose a probable risk to human health.  相似文献   

Sediment transport measurements with tracers in very low‐energy beaches     

A. R. Carrasco  Ó. Ferreira  A. Matias  P. Freire  X. Bertin  J. A. Dias 《地球表面变化过程与地形》2013,38(6):561-569

This study investigates sediment transport at a very low‐energy backbarrier beach in southern Portugal, from a spring‐to‐neap tide period, during fair‐weather conditions. Rates and directions of transport were determined based on the application of fluorescent tracer techniques. Wind and currents were collected locally, whereas the dominant small and short‐period wind waves were characterized using a morphodynamic modelling system coupling a circulation model, a spectral wave model, and a bottom evolution model, well validated over the study area. For the recorded conditions sediment transport was small and ebb oriented, with daily transport rates below 0.02 m³ day^‐1. Tidal currents (mainly ebb velocities) were found to be the main causative forcing controlling sediment displacements. Transport rates were higher during spring tides, tending towards very small values at neap tides. Results herein reported points towards the distinction between tracer advection and tracer dispersion in this type of environment. Transport by advection was low as a consequence of the prevailing hydrodynamic conditions (H_s < 0.1 m, and max. current velocity of 0.5 m s^‐1) and the tracer adjustment to the transport layer, whereas dispersion was relatively high (few metres per day). Tracer techniques allowed distinguishing the broad picture of transport, but revealed the need for refinement in this type of environments (bi‐directional forcing by ebb and flood cycles). Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Self-Collimated Jets, Accretion Discs and Young Stars     

Jonathan Ferreira 《Astrophysics and Space Science》2003,287(1-4):15-20

This paper is focused on the huge dynamical importance of the mass load in magnetized jet models. I will first review some `naive' questions (Why should jets be magnetized? What is the jet driving source?), then show why the jet mass load is so important and why numerical simulations are unable yet to deal with jet formation. I will afterwards briefly describe some results of the only accretion disc model addressing explicitely this question and present a possible star-disc magnetospheric interaction giving rise to time-dependent outbursts.  相似文献   

Multiple methods for estimating the bispectrum of the cosmic microwave background with application to the MAXIMA data     

M. G. Santos  A. Heavens  A. Balbi  J. Borrill  P. G. Ferreira  S. Hanany  A. H. Jaffe  A. T. Lee  B. Rabii  P. L. Richards  G. F. Smoot  R. Stompor  C. D. Winant  J. H. P. Wu 《Monthly notices of the Royal Astronomical Society》2003,341(2):623-643

We describe different methods for estimating the bispectrum of cosmic microwave background data. In particular, we construct a minimum-variance estimator for the flat-sky limit and compare results with previously studied frequentist methods. Application to the MAXIMA data set shows consistency with primordial Gaussianity. Weak quadratic non-Gaussianity is characterized by a tunable parameter   f _NL  , corresponding to non-Gaussianity at a level of  ∼10⁻⁵ f _NL  (the ratio of non-Gaussian to Gaussian terms), and we find limits of   f _NL= 1500 ± 950  for the minimum-variance estimator and   f _NL= 2700 ± 1650  for the usual frequentist estimator. These are the tightest limits on primordial non-Gaussianity, which include the full effects of the radiation transfer function.  相似文献   

Definition of geochemical patterns on the soil of Paul de Arzila using correspondence analysis     

C. Patinha  E. Correia  E. Ferreira da Silva  A. Simes  P. Reis  F. Morgado  E. Cardoso Fonseca 《Journal of Geochemical Exploration》2008,98(1-2):34

The aim of this study is to define geochemical and geological patterns, not only inside of Paul de Arzila natural reserve but in the surrounding area. The Correspondence Analysis was used as a discriminate technique to separate previously identified groups, in this case three types of soils (cambisols + luvisols + fluvisols). The purpose was to identify the main chemical association representative for the local types of soils. The results allow us to separate the chemical elements that are related to natural sources from the anthropogenic sources.  相似文献   

Moisture and heat budgets of the south American monsoon system: climatological aspects     

Samia?R.?GarciaEmail author  Mary?T.?Kayano  Alan?J.?P.?Calheiros  Rita?Valéria?Andreoli  Rodrigo?Augusto?Ferreira?de?Souza 《Theoretical and Applied Climatology》2017,130(1-2):233-247

The climatology of the moisture and heat budget equation terms for subareas within the South American Monsoon System (SAMS) region is investigated for the 1958–2014 period considering the distinct phases of the Pacific Decadal Oscillation (PDO). These budget equations are applied to the data from the National Centers for Environmental Prediction (NCEP) Reanalysis project. Sources or sinks of moisture and heat are equation residues, referred to as residue and diabatic terms, respectively. Analyses are done for the Central Amazon Basin (CAM) and Western-Central Brazil (WCB) for three distinct periods, 1958–1976, 1977–1995, and 1996–2014, that correspond to the cold, warm, and undefined PDO phases. The differences among the PDO phases for each term are discussed. The CAM region acts dominantly as a moisture sink and heat source in all months during the three phases. On the other hand, in the WCB region, the monsoon characteristics are better defined, with a moisture sink (source) and a heat source (sink) during the wet (dry) season. The main result of the present analysis is the persistence of SAMS intensification signs in both CAM and WCB areas up to the last analyzed period (1996–2014), which is consistent with intense flooding in the Amazon Basin in 2008/2009, 2012, and 2014.  相似文献   

Trends in marine climate change research in the Nordic region since the first IPCC report     

M. W. Pedersen  A. Kokkalis  H. Bardarson  S. Bonanomi  W. J. Boonstra  W. E. Butler  F. K. Diekert  N. Fouzai  M. Holma  R. E. Holt  K. Ø. Kvile  E. Nieminen  K. M. Ottosen  A. Richter  L. A. Rogers  G. Romagnoni  M. Snickars  A. Törnroos  B. Weigel  J. D. Whittington  P. Woods  J. Yletyinen  A. S. A. Ferreira 《Climatic change》2016,134(1-2):147-161

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Spatiotemporal variability of methane over the Amazon from satellite observations     

Igor Oliveira Ribeiro  Rodrigo Augusto Ferreira de Souza  Rita Valéria Andreoli  Mary Toshie Kayano  Patrícia dos Santos Costa 《大气科学进展》2016,33(7):852-864

The spatiotemporal variability of the greenhouse gas methane(CH_4) in the atmosphere over the Amazon is studied using data from the space-borne measurements of the Atmospheric Infrared Sounder on board NASA's AQUA satellite for the period 2003–12. The results show a pronounced variability of this gas over the Amazon Basin lowlands region, where wetland areas occur. CH_4 has a well-defined seasonal behavior, with a progressive increase of its concentration during the dry season, followed by a decrease during the wet season. Concerning this variability, the present study indicates the important role of ENSO in modulating the variability of CH_4 emissions over the northern Amazon, where this association seems to be mostly linked to changes in flooded areas in response to ENSO-related precipitation changes. In this region, a CH_4 decrease(increase) is due to the El Nino-related(La Ni ?na-related) dryness(wetness). On the other hand, an increase(decrease) in the biomass burning over the southeastern Amazon during very dry(wet) years explains the increase(decrease) in CH_4 emissions in this region. The present analysis identifies the two main areas of the Amazon, its northern and southeastern sectors, with remarkable interannual variations of CH_4. This result might be useful for future monitoring of the variations in the concentration of CH_4, the second-most important greenhouse gas, in this area.  相似文献   

Effects of climate change on the distribution of indigenous species in oceanic islands (Azores)     

Maria Teresa Ferreira  Pedro Cardoso  Paulo A.V. Borges  Rosalina Gabriel  Eduardo Brito de Azevedo  Francisco Reis  Miguel B. Araújo  Rui Bento Elias 《Climatic change》2016,138(3-4):603-615

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