1,720,982 research outputs found
Extraction of characteristic constants in QCD with perturbative and nonperturbative methods
No full textThis work concerns two topics in QCD. Part I is devoted to the extraction of the strong coupling at lowenergy scales, where unphysical singularities make the RG-improved pQCD useless. In the present work, theoretical results on the meson spectrum based on a Bethe-Salpeter formalism adjusted for QCD have been exploited to extract experimental values for the QCD coupling below 1~GeV by comparison with the data. Results quantitatively confirm the recently developed Analytic Perturbation Theory approach to IR phenomena down to 200 MeV. Furthermore, below this scale the extracted values give a hint about the vanishing of the QCD coupling in agreement with results from lattice simulations.PartII investigates the nucleon spin structure, i.e. polarized pdfs.The possibility of inferring the gluon polarization from scaling violations has been studied by performing a NLO analysis in pQCD of world data from inclusive DIS. In addition, a phenomenological study of the open-charm photoproduction at COMPASS (CERN) has been performed.Results show that current DIS data only allow a better determination of the gluon first moment and leave the x-shape fairly undetermined. Pseudo-data analyses have revealed, on the other hand, that the open-charm approach is capable to strongly reduce the bias induced by the assumed functional form of input densities, and to pin down the x-shape of the gluon polarization
Improving estimation of missing values in daily precipitation series by a probability density function-preserving approach
No full textThis work presents a novel method for estimating missing values in daily precipitation series. It is aimed at identifying the event time location with good accuracy and reconstructing the correct amount of daily rainfall. In addition, the statistical properties of the time series, i.e. both probability distribution and long-term statistics, are preserved. The completion method is based on a two-step algorithm that uses information from a cluster of neighboring stations. First, wet and dry days are tagged, and subsequently, the full precipitation amount for wet-classified days is estimated by a modified multi-linear regression approach. This method avoids overestimation of the number of wet days and underestimation of intense precipitation events, which are typical side effects of common regression-based approaches
High-resolution analysis of daily precipitation trends in the central Alps over the last century
No full textIn this work we present a homogenized high-resolution data set composed of 200 daily precipitation series spanning the last 90 years, located over an area centred on the Trentino—South Tyrol region (central part of the European Alps), in a transition zone between the climates of the southern and northern slopes of the Alps. We analysed the trends of total precipitation (TP), wet days (WD) and average intensity (PI), as well as trends of the number of events and precipitation amounts belonging to 12 different daily intensity categories. For an easier understanding of geographical patterns, we set up a gridded data set in terms of anomalies, with a spatial resolution of 0.1°. All the statistics were analysed for trend over the entire period spanned by the data and on subperiods of variable length. On regional average, we found a weak decrease in TP (about 1%/decade with respect to the 1971–2000 mean) over the entire studied period (1922–2009), which was statistically significant only in spring. Gridded data show that the decrease is related to a reduction in the number of WD in the eastern part of the study area, and a decrement in PI in the western part, with orography playing a clear role in this differentiation. On a daily scale, trends of the strongest events present scarce spatial coherence and are only locally significant, however the results are highly dependent on the period analysed. Comparisons with previous low-resolution studies on the same area underline the importance of a high-resolution data set in characterizing spatial variability of climatic trends in precipitation
Eventi estremi e variabilità della temperatura in un clima che cambia
No full textIl cambiamento nella frequenza di eventi climatici estremi che si è osservato negli ultimi decenni in molte aree del nostro Pianeta è generalmente percepito come un segnale di profonde modificazioni della temperatura atmosferica superficiale, che riguardano non solo un innalzamento del valor medio. E’ infatti oggetto di intenso dibattito scientifico se eventi di natura eccezionale, quali le ondate di calore che hanno investito in modo drammatico l'Europa centro-occidentale nell'estate del 2003, siano determinati da condizioni climatiche più estreme, ovvero da un progressivo aumento della variabilità della temperatura.
Comprendere come la frequenza degli eventi estremi risponda ai cambiamenti delle condizioni climatiche è di cruciale importanza, sia per meglio interpretare i dati osservativi del passato sia per poter prevedere in modo più efficace il potenziale impatto dei cambiamenti climatici futuri. Questa complessa problematica è qui discussa in una nuova prospettiva, attraverso un approccio che consente di legare in modo rigoroso il verificarsi di eventi intensi ai cambiamenti nelle proprietà statistiche medie della temperatura
High-resolution analysis of 1 day extreme precipitation in Sicily
Full text linkSicily, a major Mediterranean island, has experienced several exceptional
precipitation episodes and floods during the last century, with serious
damage to human life and the environment. Long-term, rational planning of
urban development is indispensable to protect the population and to avoid
huge economic losses in the future. This requires a thorough knowledge of
the distributional features of extreme precipitation over the complex
territory of Sicily.
In this study, we perform a detailed investigation of observed 1 day
precipitation extremes and their frequency distribution, based on a dense
data set of high-quality, homogenized station records in 1921–2005. We
estimate very high quantiles (return levels) corresponding to 10-, 50- and
100-year return periods, as predicted by a generalized extreme value
distribution. Return level estimates are produced on a regular
high-resolution grid (30 arcsec) using a variant of regional frequency
analysis combined with regression techniques. Results clearly reflect the
complexity of this region, and show the high vulnerability of its eastern
and northeastern parts as those prone to the most intense and potentially
damaging events
Sicily monthly high resolution solar radiation climatologies and comparison with future projections
No full textWe developed a methodology to estimate solar radiation climatologies starting from a network of global radiation and/or sunshine duration records and a digital elevation model and applied it to a data set of 41 Sicilian global radiation records covering the 2002-2011.
All records were subjected to quality and homogeneity control. Moreover, the monthly record were subjected to a procedure aiming at estimate missing data.
The first step of the methodology consists in calculating global radiation monthly normals for all station sites or estimating them from sunshine duration normals, when global radiation data are not available.
The second step consists in estimating, the bias due to shading and adjusting the normal values in order to make them representative of un-shaded sites.
The third step consists in interpolating shading-bias-adjusted global radiation normals onto a 30 arc-resolution regular grid. This global radiation normals are then decomposed into the direct and diffuse components. Atmospheric turbidity is then evaluated over the same grid by means of the direct component obtained from shading-bias-adjusted global radiation.
The last steps consists in calculating direct, diffuse and reflected components of global radiation for any grid-cell, taking into account its slope and aspect and considering shading from the cell itself and from the neighboring cells. Knowing the direct, diffuse and reflected components, the global radiation can easily calculated by their sum.
This procedure will be presented and the resulting climatologies will be compared with those obtained from future projections (ENSEMBLES RCMs) with the objective to compare modelled and observed radiation climatologies
Increasingly warm summers in the Euro–Mediterranean zone : mean temperatures and extremes
No full textThe recent increase in European temperatures led to a strong enhancement in the occurrence of extremely warm events, with relevant consequences for environment and everyday life. Here, we investigate the evolution of very intense warm and cold events in a south-western European zone during 1961–2007 at a seasonal level. Special attention is given to summertime when warming is the most pronounced. Using a previously developed theoretical model, we discuss how the average properties and long-term trends observed in probability density functions of daily temperatures can explain changes in the frequency of severe, isolated events. In this perspective, the recent intensification of extremely warm events, especially experienced by the Mediterranean zone, is proved to be well consistent with a pure shift of seasonal mean temperatures. On the other hand, any change in the second and higher distributional moments of daily temperatures is ruled out by the data, whereas the average values of these properties, that is, variability and asymmetry, do play a role by shaping the temporal behavior of very intense events
Evolution of extreme temperatures in a warming climate
No full textThe ongoing increase in extremely warm temperature events across large areas of the globe is generally thought to be a signature of a more extreme climate. However, it is still unclear whether global warming is accompanied by changes in statistical properties beyond the mean, such as an increasing temperature variability. Here we shed light on this issue by uncovering the way probabilities of extremes are being influenced by temperature evolution. Focusing on Europe, we show how the behavior of warm and cold extremes can be determined to a high accuracy by statistically modeling daily temperatures and their changes. Detailed comparison with observations over the past decades puts forward the dominant role of the mean in explaining exceptionally hot events, and rules out contributions from potential changes in second and higher moments
High‐resolution temperature climatology for Italy: interpolation method intercomparison
No full textHigh-resolution monthly temperature climatologies for Italy are presented. They are based on a dense and quality-controlled observational dataset which includes 1484 stations and on three distinct approaches: multi-linear regression with local improvements (MLRLI), an enhanced version of the model recently used for the Greater Alpine Region, regression kriging (RK), widely used in literature and, lastly, local weighted linear regression (LWLR) of temperature versus elevation, which may be considered more suitable for the complex orography characterizing the Italian territory. Dataset and methods used both to check the station records and to get the 1961-1990 normals used for the climatologies are discussed. Advantages and shortcomings of the three approaches are investigated and the results are compared. All three approaches lead to quite reasonable models of station temperature normals, with lowest errors in spring and autumn and highest errors in winter. The LWLR approach shows slightly better performances than the other two, with monthly leave-one-out estimated root mean square errors ranging from 0.74°C (April and May) to 1.03°C (December). Further evidence in its favour is the greater reliability of local approach in modelling the behaviour of the temperature-elevation relationship in Italy's complex territory. The comparison of the different climatologies is a very effective tool to understand the robustness of each approach. Moreover, the first two methods (MLRLI and RK) turn out to be important to tune the third one (LWLR), as they help not only to understand the relationship between temperature normals and some important physiographical variables (MLRLI) but also to study the decrease of station normals covariance with distance (RK). © 2013 The Authors. International Journal of Climatology published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society
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