The International Radiation Symposium 2016

正1.Overview The 2016 International Radiation Symposium,a joint venture between the IRC(International Radiation Commission)and IAMAS(International Association of Meteorology and Atmospheric Sciences),took place at the University of Auckland from April 16th to 22nd.The wide scope of atmospheric radiation research was apparent,with focuses rang-     

Metal fluxes to the sediments of the northern Venice Lagoon

Eighteen short cores were analyzed for major and trace metals (Al, Fe, Ca, Mg, Mn, Si, K, Ti, Pb, Zn, Cu, Ni, Cr), ²¹⁰Pb, ¹³⁷Cs, and other sediment characteristics, so as to describe the chronology of pollution and calculate metal concentration factors and fluxes. Substantial evidence was found that trace metal profiles are influenced by anthropogenic sources and by changes in sediment composition. Only Zn presents concentrations (up to 13.1 μmol g⁻) and concentration factors (1.3 to 13.2) that can be attributed to heavy contamination. Pb, Cu and Ni, in this order, are less significant. The areal distribution of concentrations and inventories reflects the importance of direct sources, in particular the industrial area of Porto Marghera and the Dese river. The inventories of excess metals, above pre-industrial levels, were determined for each core and the three different parts of the study area, the amounts of Zn accumulated in sediments are 11.0 Mmol, 5.1 Mmol and 0.37 Mmol in the Campalto, S. Erasmo, and Palude di Cona areas, respectively. Ruxes were also calculated and compared with those suggested for the atmospheric delivery by Cochran et al. [(1995)b. Atmospheric fluxes of heavy metal contaminants to the Venice Lagoon, Rapp. Comm. Int. Mer Médit., 34, 136.], the atmospheric contribution is predominant or significant in many cases, especially at sites far from the major local inputs. Concentrations and fluxes show a significant increase in the anthropogenic metal supply starting from the second decade of this century, with maximum inputs in the period between the (1930)s and the (1970)s. At some stations a decrease in heavy metal contamination of surficial sediments was found and this could be ascribed to a reduced input of pollutants in recent years.     

Long-term growth and metropolitan spatial structures: an analysis of factors influencing urban patch size under different economic cycles

Urban forms are increasingly reflective of socio-economic change in metropolitan regions. The present study illustrates an original approach to identify latent mechanisms of urban growth through the analysis of metropolitan spatial structures and their proximate drivers of change. Urban transformations are evaluated here using built-up patches as the elementary analysis unit and background socio-economic attributes at four stages of the “city life cycle” (urbanization, suburbanization, dis-urbanization, re-urbanization). Regression models based on 13 indicators assessing urban patch area and shape, nearest neighbour urban patch area and shape, elevation, distance from 5 urban centres, 2 road infrastructures and sea coastline, were run with the aim to investigate direction and intensity of metropolitan growth in post-war Athens (1948–2012), a southern European city shifting from a compact mono-centric form towards discontinuous urban structures. Mono-centric configurations were characterized by linear dependence of urban patch size from the distance to central cities. Shifts toward scattered urban forms were associated with changes in the multivariate relationship between urban patch size and territorial drivers, pointing out the increased complexity of dispersed metropolitan structures. Our approach integrates economic and ecological visions of urban landscapes and contributes to understanding long-term mechanisms of metropolitan growth under dynamic spatial equilibriums. Investigating the multiple relationships between form and functions at the base of socio-economic transformations are relevant issues when identifying and profiling urbanization cycles.     

Anatexis and fluid regime of the deep continental crust: New clues from melt and fluid inclusions in metapelitic migmatites from Ivrea Zone (NW Italy)

We investigate the inclusions hosted in peritectic garnet from metapelitic migmatites of the Kinzigite Formation (Ivrea Zone, NW Italy) to evaluate the starting composition of the anatectic melt and fluid regime during anatexis throughout the upper amphibolite facies, transition, and granulite facies zones. Inclusions have negative crystal shapes, sizes from 2 to 10 μm and are regularly distributed in the core of the garnet. Microstructural and micro‐Raman investigations indicate the presence of two types of inclusions: crystallized silicate melt inclusions (i.e., nanogranitoids, NI), and fluid inclusions (FI). Microstructural evidence suggests that FI and NI coexist in the same cluster and are primary (i.e., were trapped simultaneously during garnet growth). FI have similar compositions in the three zones and comprise variable proportions of CO₂, CH₄, and N₂, commonly with siderite, pyrophyllite, and kaolinite, suggesting a COHN composition of the trapped fluid. The mineral assemblage in the NI contains K‐feldspar, plagioclase, quartz, biotite, muscovite, chlorite, graphite and, rarely, calcite. Polymorphs such as kumdykolite, cristobalite, tridymite, and less commonly kokchetavite, were also found. Rehomogenized NI from the different zones show that all the melts are leucogranitic but have slightly different compositions. In samples from the upper amphibolite facies, melts are less mafic (FeO + MgO = 2.0–3.4 wt%), contain 860–1700 ppm CO₂ and reach the highest H₂O contents (6.5–10 wt%). In the transition zone melts have intermediate H₂O (4.8–8.5 wt%), CO₂ (457–1534 ppm) and maficity (FeO + MgO = 2.3–3.9 wt%). In contrast, melts at granulite facies reach highest CaO, FeO + MgO (3.2–4.7 wt%), and CO₂ (up to 2,400 ppm), with H₂O contents comparable (5.4–8.3 wt%) to the other two zones. Our results represent the first clear evidence for carbonic fluid‐present melting in the Ivrea Zone. Anatexis of metapelites occurred through muscovite and biotite breakdown melting in the presence of a COH fluid, in a situation of fluid–melt immiscibility. The fluid is assumed to have been internally derived, produced initially by devolatilization of hydrous silicates in the graphitic protolith, then as a result of oxidation of carbon by consumption of Fe³⁺‐bearing biotite during melting. Variations in the compositions of the melts are interpreted to result from higher T of melting. The H₂O contents of the melts throughout the three zones are higher than usually assumed for initial H₂O contents of anatectic melts. The CO₂ contents are highest at granulite facies, and show that carbon‐contents of crustal magmas are not negligible at high T. The activity of H₂O of the fluid dissolved in granitic melts decreases with increasing metamorphic grade. Carbonic fluid‐present melting of the deep continental crust represents, together with hydrate‐breakdown melting reactions, an important process in the origin of crustal anatectic granitoids.     

Dynamics of snow ablation in a small Alpine catchment observed by repeated terrestrial laser scans

The spatio‐temporal distribution of snow in a catchment during ablation reflects changes in the total amount of snow water equivalent and is thus a key parameter for the estimation of melt water run‐off. This study explores possible rules behind the spatial variability of snow depth during the ablation season in a small Alpine catchment with complex topography. The snow depth observations are based on more than 160 000 terrestrial laser scanner data points with a spatial resolution of 1 m, which were obtained from 11 scanning campaigns of two consecutive ablation seasons. The analysis suggests that for estimating cumulative snow melt dynamics from the catchment investigated, assessing the initial snow distribution prior to the melt season is more important than addressing spatial differences in the melt behaviour. Snow volume and snow‐covered area could be predicted well using a conceptual melt model assuming spatially uniform melt rates. However, accurate results were only obtained if the model was initialized with a pre‐melt snow distribution that reflected measured mean and standard deviation. Using stratified melt rates on the other hand did not improve the model results. At least for sites with similar meteorological and topographical conditions, the model approach presented here comprises an efficient way to estimate snow depletion dynamics, especially if persistent snow accumulation pattern between years facilitate the characterization of the initial snow distribution prior to the melt. Copyright © 2011 John Wiley & Sons, Ltd.     

Detection of Miocene saucer‐shaped sills (offshore Senegal) via integrated interpretation of seismic,magnetic and gravity data

The Atlantic margin offshore Senegal has been explored by seismic reflection and GRAV‐MAG surveys. High‐amplitude, laterally transgressive seismic reflectors are found to coincide with gravimetric and magnetic highs. Once seismic data are integrated with potential fields modelling, these reflectors can be safely interpreted as saucer‐shaped igneous sills, up to some hundreds of metres thick, some km wide. The occurrence of hydrothermal vent complexes and forced folds in the stratigraphic sequence above the sills constrain the intrusion age to the Miocene. Field observations and in‐situ magnetic susceptibility measurements of Oligocene–Miocene and Quaternary igneous rocks emplaced in coastal Senegal support this interpretation.     

Vertical dynamics of disc galaxies in modified Newtonian dynamics

We investigate the possibility of discriminating between modified Newtonian dynamics (MOND) and Newtonian gravity with dark matter, by studying the vertical dynamics of disc galaxies. We consider models with the same circular velocity in the equatorial plane (purely baryonic discs in MOND and the same discs in Newtonian gravity embedded in spherical dark matter haloes), and we construct their intrinsic and projected kinematical fields by solving the Jeans equations under the assumption of a two-integral distribution function. We find that the vertical velocity dispersion of deep MOND discs can be much larger than in the equivalent spherical Newtonian models. However, in the more realistic case of high surface density discs, this effect is significantly reduced, casting doubt on the possibility of discriminating between MOND and Newtonian gravity with dark matter by using current observations.     

Correction to: Rip current hazard assessment on a sandy beach in Liguria,NW Mediterranean

Natural Hazards - The article was published showing the first two author names in the wrong order.     

Controls on the morphology of braided rivers and braid bars: An empirical characterization of numerical models

Braided rivers exhibit highly variable morphologies, morphodynamic behaviours and resulting depositional records. To evaluate relationships between characteristics of braided-river channel belts and river depth, water discharge and streambed gradient, 39 numerical modelling experiments were conducted with the software Delft3D to simulate braided-river evolution under a broad range of boundary conditions. Data from model outputs were integrated with observations from 63 natural braided rivers differing with respect to river depth and streambed gradient. The modelled rivers each underwent similar evolutions, yet each culminated in markedly different final river morphologies, dependent on discharge and riverbed gradient. The rivers underwent evolutionary stages of: (i) formation of transverse unit bars with limited relief from an initially featureless bed; (ii) channel development around bars and in some cases dissecting transverse unit bars; (iii) formation of relatively simpler compound bars; and (iv) amalgamation of these simpler compound bars into more complex compound bars. Quantitative relationships relating to braided-river channel-belt morphology and organization are established, and the following results are noted: (i) bar elongation (length-to-width ratio) is correlated positively with riverbed gradient; (ii) bar height and area are correlated positively with discharge, and negatively with riverbed gradient; (iii) the river depth is the main predictor of mean braid-bar area; and (iv) the degree of braiding is primarily associated with river width-to-depth ratio and riverbed gradient. Results arising from this research improve our understanding of controls on the morphology and architectures of braided fluvial channel belts; they provide a novel empirical characterization that can be applied for predicting channel depth, bar morphology, streambed gradient, and degree of braiding of modern fluvial systems and of the formative rivers of ancient preserved successions.     

相似集合预报方法在北京区域地面气温和风速预报中的应用

相似集合是近年来提出的一种基于相似理论、大数据挖掘和集合预报思路的统计释用方法。文中首先介绍了相似集合的基本原理,并应用该方法对北京快速更新循环数值预报系统（BJ-RUC）v3.0预报地面要素开展了订正释用试验。结果表明,相似集合订正后,在0—36 h预报时段内,10 m风速的均方根误差降低44%,2 m气温的均方根误差降低22%,均方根误差均显著减小。对比测站预报误差的水平分布,相似集合方法的应用对于提升非城区站点的10 m风速预报、复杂地形区域的2 m气温预报具有更为明显的效果。相同预报因子的相似集合和支持向量机方法对模式10 m风速和2 m气温预报均具有显著且相似的订正效果,但相似集合方法具有计算资源需求较少、不需要大量人工干预的优势。相似集合方法形成的集合较好地模拟了模式平均误差的增长情况,集合离散度与集合平均均方根误差表现出理想的统计一致性,即相似集合方法在形成确定性预报的同时,还能够提供预报要素的不确定性或概率信息。因此,相似集合方法在模式预报订正及释用方面具有广阔的应用前景。