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Publications

Publications by CRAS

2014

Opportunistic Usage of Maritime VHF Band—Deployment Challenges for a New Regulatory Framework

Authors
Bolas, E; Carvalho, NBd; Vieira, JN; Oliveira, PMd;

Publication
Wireless Engineering and Technology

Abstract

2014

Witnessing North Atlantic westerlies variability from ships' logbooks (1685-2008)

Authors
Barriopedro, D; Gallego, D; Carmen Alvarez Castro, MC; Garcia Herrera, R; Wheeler, D; Pena Ortiz, C; Barbosa, SM;

Publication
CLIMATE DYNAMICS

Abstract
A monthly index based on the persistence of the westerly winds over the English Chanel is constructed for 1685-2008 using daily data from ships' logbooks and comprehensive marine meteorological datasets. The so-called Westerly Index (WI) provides the longest instrumental record of atmospheric circulation currently available. Anomalous WI values are associated with spatially coherent climatic signals in temperature and precipitation over large areas of Europe, which are stronger for precipitation than for temperature and in winter and summer than in transitional seasons. Overall, the WI series accord with the known European climatic history, and reveal that the frequency of the westerlies in the eastern Atlantic during the twentieth century and the Late Maunder Minimum was not exceptional in the context of the last three centuries. It is shown that the WI provides additional and complementary information to the North Atlantic Oscillation (NAO) indices. The analysis of WI series during the industrial era indicates an overall good agreement with the winter and high-summer NAO, with the exception of several multidecadal periods of weakened correlation. These decoupled periods between the frequency and the intensity of the zonal flow are interpreted on the basis of several sources of non-stationarity affecting the centres of the variability of the North Atlantic and their teleconnections. Comparisons with NAO reconstructions and long instrumental indices extending back to the seventeenth century suggest that similar situations have occurred in the past, which call for caution when reconstructing the past atmospheric circulation from climatic proxies. The robustness and extension of its climatic signal, the length of the series and its instrumental nature make the WI an excellent benchmark for proxy calibration in Europe and Greenland.

2014

Changes in extreme sea-levels in the Baltic Sea

Authors
Ribeiro, A; Barbosa, SM; Scotto, MG; Donner, RV;

Publication
TELLUS SERIES A-DYNAMIC METEOROLOGY AND OCEANOGRAPHY

Abstract
In a climate change context, changes in extreme sea-levels rather than changes in the mean are of particular interest from the coastal protection point of view. In this work, extreme sea-levels in the Baltic Sea are investigated based on daily tide gauge records for the period 1916-2005 using the annual block maxima approach. Extreme events are analysed based on the generalised extreme value distribution considering both stationary and time-varying models. The likelihood ratio test is applied to select between stationary and non-stationary models for the maxima and return values are estimated from the final model. As an independent and complementary approach, quantile regression is applied for comparison with the results from the extreme value approach. The rates of change in the uppermost quantiles are in general consistent and most pronounced for the northernmost stations.

2014

Selective feeding by Anodonta cygnea (Linnaeus, 1771): The effects of seasonal changes and nutritional demands

Authors
Lopes Lima, M; Lima, P; Hinzmann, M; Rocha, A; Machado, J;

Publication
LIMNOLOGICA

Abstract
Many animal species, during their life cycles, can select specific food elements that meet the special and unique metabolic needs of crucial stages such as growth, gonad maturation or larvae production and brooding. The objective of this study was to analyze the seasonal phytoplankton composition in the stomach contents of the freshwater mussel Anodonta cygnea in order to determine whether it was capable of selecting food seasonally and which were its preferences. Specimens and water samples were collected monthly from Barrinha de Mira lagoon in the northwest of Portugal during one year. From the microalgae composition found in the water and stomach content samples, Chlorophyta presented a clear predominance, followed by Cryptophyta and Bacillariophyta in water samples, and Bacillariophyta and Cyanobacteria in stomach contents. Although mussels ingested algae in a pattern very similar to its abundance in the natural habitat, in some periods specific groups were preferred even if they were present in very low concentrations in the environment. Thus, these animals are capable of selecting food by its specific characteristics and this selectivity may be associated with its physiological cycle, mainly with the reproductive cycle. Namely, the large relative abundance (ratio stomach/environment) peak of blue green algae that co-occur with gamete development covering two other smaller peaks: one of Bacillariophyta that co-occurs with gametogenesis restart and the other of Chlorophyta at the end. In addition, a significant peak of Cryptophyta co-occurs with growth and glochidia brooding periods.

2014

Rock strength assessment and structural features analysis on rocky coasts

Authors
Pires, A; Chamine, HI; Perez Alberti, A; Gomes, A; Rocha, F;

Publication
ROCK ENGINEERING AND ROCK MECHANICS: STRUCTURES IN AND ON ROCK MASSES

Abstract
This work addresses the rock matrix strength comparative analysis on rocky coasts. A coastal geoengineering integrated system for rocky coast assessment was proposed and applied in two fissured granitic key-sites in NW Iberia (NW Portugal, and Galicia). The main stages of the study comprise six steps: (i) high-resolution aerial imagery survey; (ii) visual inspection and systematic monitoring; (iii) applied field datasheet; (iv) in situ evaluation; (v) scanline survey; (vi) coastal geosciences engineering GIS based mapping. The Schmidt Hammer and Equotip tester were applied to measure the rebound and hardness, respectively, in rocky platforms, geoforms and coastal boulders. Moreover a detailed description of discontinuities and a geologic-geotechnical evaluation in the rocky platforms was performed. The current rock project is of great interest especially to highly dynamic coastal areas. This approach evolving geomorphic processes, geoengineering issues and geomechanical testing assessment contributes to support coastal management/planning.

2014

Coastal Geo-Engineering Techniques for the Assessment of Rock Armour Structures

Authors
Pires, A; Chamine, HI; Piqueiro, F; Rocha, F;

Publication
MARINE GEORESOURCES & GEOTECHNOLOGY

Abstract
This work deals with the problem of assessing armourstone structures focusing on strengthening the combination of geo-marine techniques and geotechnical properties. The research has two main purposes: (i) to establish an integrative coastal geo-engineering approach for better assessment of the hydraulic structures; and (ii) to draw attention to the importance of quarry evaluation in order to improve armourstone quality and durability. Several studies have demonstrated the relevance of a holistic approach to coastal design issues. The suggested approach couples GIS-based mapping with geo-engineering techniques assessment along five pilot sectors of the Espinho coastal system in Northwestern Portugal. This investigation allowed us to propose zoning a coastal structure according to its degree of deterioration, geomechanical properties and geomaterial status. Replacement of the primary armour layer in only selected sections or components of the structure will reduce the cost of maintenance, repair and reinforcement work. All the gathered data about the preservation status of the armour layer and the quarry inventory have been compiled in a powerful GIS geo-database. The paper argues for the wider use of combination of coastal geo-engineering and GIS analysis in planning the monitoring and/or maintenance of marine works using armourstone.

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