Intercomparison of measurements of bulk snow density and water equivalent of snow cover with snow core samplers: Instrumental bias and variability induced by observers     

J. Ignacio López-Moreno  Leena Leppänen  Bartłomiej Luks  Ladislav Holko  Ghislain Picard  Alba Sanmiguel-Vallelado  Esteban Alonso-González  David C. Finger  Ali N. Arslan  Katalin Gillemot  Aynur Sensoy  Arda Sorman  M. Cansaran Ertaş  Steven R. Fassnacht  Charles Fierz  Christoph Marty 《水文研究》2020,34(14):3120-3133

Manually collected snow data are often considered as ground truth for many applications such as climatological or hydrological studies. However, there are many sources of uncertainty that are not quantified in detail. For the determination of water equivalent of snow cover (SWE), different snow core samplers and scales are used, but they are all based on the same measurement principle. We conducted two field campaigns with 9 samplers commonly used in observational measurements and research in Europe and northern America to better quantify uncertainties when measuring depth, density and SWE with core samplers. During the first campaign, as a first approach to distinguish snow variability measured at the plot and at the point scale, repeated measurements were taken along two 20 m long snow pits. The results revealed a much higher variability of SWE at the plot scale (resulting from both natural variability and instrumental bias) compared to repeated measurements at the same spot (resulting mostly from error induced by observers or very small scale variability of snow depth). The exceptionally homogeneous snowpack found in the second campaign permitted to almost neglect the natural variability of the snowpack properties and focus on the separation between instrumental bias and error induced by observers. Reported uncertainties refer to a shallow, homogeneous tundra-taiga snowpack less than 1 m deep (loose, mostly recrystallised snow and no wind impact). Under such measurement conditions, the uncertainty in bulk snow density estimation is about 5% for an individual instrument and is close to 10% among different instruments. Results confirmed that instrumental bias exceeded both the natural variability and the error induced by observers, even in the case when observers were not familiar with a given snow core sampler.  相似文献   

Combining climate with other influential factors for modelling the impact of climate change on species distribution     

Ana Luz M??rquez  Raimundo Real  Jes??s Olivero  Alba Estrada 《Climatic change》2011,108(1-2):135-157

We tested two approaches to forecast species distributions while balancing the impact of climate change against the inertia promoted by other influential factors that have been forecast as not changing. Given that mountain species are presumed to be more at risk due to climate warming, we selected an amphibian, a reptile, a bird, and a mammal species present in the Spanish mountains, to model their distributional response to climate change during this century. The climatic forecasts were made according to the general circulation models CGCM2 and ECHAM4 and to the A2 and B2 emission scenarios. We modelled the response of the species to spatial, topographic, human, and climatic variables separately. In our first approach, we compared each of these single-factor models using the Akaike Information Criterion, and produced a combined model weighting each factor (spatial, topographic, human, and climatic) according to Akaike weights. This procedure overestimated the best model, and the other factors were neglected in the combined model output. In our second approach, we produced a combined model using stepwise selection of the variables previously selected within each factor. In this way every factor was effectively represented in the combined explanatory model of the distributional response of the species to environmental conditions. This enabled the construction of models that combined climate with the other explanatory factors, to be later extrapolated to the future by replacing current climatic and human values with those expected from each emission and socio-economic scenario, while preserving spatial and topographic variables in the model.  相似文献   

Multiwavelength study of the nuclei of a volume-limited sample of galaxies – II. Optical, infrared and radio observations     

P. Lira  R. A. Johnson  A. Lawrence  R. Cid Fernandes 《Monthly notices of the Royal Astronomical Society》2007,382(4):1552-1590

We present optical and infrared broad-band images, radio maps, and optical spectroscopy for the nuclear region of a sample of nearby galaxies. The galaxies have been drawn from a complete volume-limited sample for which we have already presented X-ray imaging. We modelled the stellar component of the spectroscopic observations to determine the star formation history of our targets. Diagnostic diagrams were used to classify the emission-line spectra and determine the ionizing mechanism driving the nuclear regions. All those sources classified as active galactic nuclei present small Eddington ratios  (∼10⁻³–10⁻⁶)  , implying a very slow growth rate of their black holes. We finally investigate the relative numbers of active and normal nuclei as a function of host galaxy luminosity and find that the fraction of active galaxies slowly rises as a function of host absolute magnitude in the   M _B ∼−12  to −22 range.  相似文献   

A high resolution hindcast of the meteorological sea level component for Southern Europe: the GOS dataset     

Alba Cid  Sonia Castanedo  Ana J. Abascal  Melisa Menéndez  Raúl Medina 《Climate Dynamics》2014,43(7-8):2167-2184

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Paleolithic vs. Epipaleolithic fisheries in northern Iberia     

Pablo Turrero  Alba Ardura  Eva García-Vázquez 《Quaternary Research》2014

A comparison of Paleolithic and Epipaleolithic fisheries in NW Iberia shows an overall high trophic level of catch. Freshwater fisheries (and thus their impacts) are ca. 8000 yr older than marine fisheries and have suffered virtually no changes in the region except for the increase in numbers, being focused on two families (Salmonidae, and Anguillidae to a very minor extent). Marine fisheries in the Paleolithic likely had a low impact but rapidly increased in importance, raising the average trophic level of the catch, the number of affected taxa and the proportion of marine to freshwater fisheries with time.  相似文献   

Assessing the applicability of OpenStreetMap data to assist the validation of land use/land cover maps     

Cidália C. Fonte  Nuno Martinho 《International journal of geographical information science》2017,31(12):2382-2400

The validation of land use/land cover (LULC) maps is usually performed using a reference database consisting of a sample of points or regions to which the ‘real’ class is assigned. This assignment is usually performed by specialists using photointerpretation (PI) of high-resolution imagery and/or field visits, which are time consuming and expensive processes. The aim of this article is to assess if the data available in the collaborative project OpenStreetMap (OSM) may be used as a source of data to assist the creation of these reference databases, reducing the time spent and costs associated with their generation. For this aim, two case studies were used, where the validation of the Global Monitoring for Environment and Security Urban Atlas (UA) was performed. The used methodology requires the harmonization of the data available in OSM with the UA nomenclature, and the subsequent creation of a LULC map from the OSM data. This map was then compared to UA to assess the similarity of the regions mapped in both. To test the usefulness of OSM data to assess the accuracy of UA, a sample of points was created and two reference databases generated, one assigning the data extracted automatically from OSM to the points where these data were available, and PI for the remaining points, and the other using only PI. The accuracy assessment of UA for the two case studies was then made building confusion matrixes and computing accuracy indicators. The results showed that for the two study areas, only low percentages of points had to be photo interpreted in the first reference database (respectively, 12% and 2% for the two study areas), decreasing the work load considerably. The results obtained with both reference databases are comparable for level 1 classes. For level 2 classes, worse results were obtained for some classes, showing that the OSM data used are not enough to create reliable reference data.  相似文献   

Multi-hazard assessment in Europe under climate change   总被引：2，自引：0，他引：2  

Giovanni Forzieri  Luc Feyen  Simone Russo  Michalis Vousdoukas  Lorenzo Alfieri  Stephen Outten  Mirco Migliavacca  Alessandra Bianchi  Rodrigo Rojas  Alba Cid 《Climatic change》2016,137(1-2):105-119

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Regularization and linearization of the equations of motion in central force-fields     

R. Cid  S. Ferrer  A. Elipe 《Celestial Mechanics and Dynamical Astronomy》1983,31(1):73-80

Within the framework of linear and regular celestial mechanics, a wide class of central force field problems are considered. We take as potential function a polynomial whose variable is the reciprocal of the distance from the origin, and, as regularizing function the square root of a certain reciprocal polynomial, related to the potential function. The relations between the coefficients of both functions, in order to arrive to linear equations, are given. In particular, the case of a quintic polynomial is analyzed, and an application is made to artificial earth satellites considering harmonicsJ ₂,J ₃,J ₄.  相似文献   

Diffusive-Shock-Accelerated Interplanetary Ions At Several Energies During the Solar Cycle 21 Maximum     

Rodríguez-Pacheco  J.  Sequeiros  J.  Del Peral  L.  Bronchalo  E.  Cid  C. 《Solar physics》1998,181(1):185-200

The most intense energetic particle (mainly proton) events in the energy range 36–1600 keV, during the years of maximum activity of solar cycle 21 (1978 to 1982), have been studied with regard to their spectra, temporal profiles, source location at the Sun, interplanetary plasma parameters and interplanetary magnetic field topology. In all the events, the particles were accelerated by the 'Diffusive Shock' acceleration mechanism, because all the events were 'long-duration events', shock-associated, and their spectra fitted to a power-law energetic particle spectrum dJ/dE E^-\gamma with the exponent values ranging from 1.25 up to 1.94, with a mean value of 1.60 ± 0.06. We also show that the spectral indexes are related to the shock properties by a linear expression. The solar sources were located on a wide longitudinal belt extending from 50^ W up to 73^ E. Neither the spectral indexes nor the shock parameters present any dependence on the source location at the Sun. Finally, only one event showed the complete set of properties that characterize the presence of a magnetic cloud associated with the event.  相似文献   

About the problem of motion of n gyrostats: I. The first integrals     

R. Cid  A. Vigueras 《Celestial Mechanics and Dynamical Astronomy》1985,36(2):155-162

In this paper, the problem of the motion of n gyrostats in a central field, with relative momenta _k ^r (k=1, 2, ..., n) functions of the time, is considered.In these conditions, the existence of the linear and angular momentum integrals is established.Moreover, a sufficient condition for the existence of the Jacobi's Integral is given. This study generalizes the results given by Duboshin for n rigid bodies.  相似文献