Assessment of Planetary-Boundary-Layer Schemes in the Weather Research and Forecasting Model Within and Above an Urban Canopy Layer

We tested several planetary-boundary-layer (PBL) schemes available in the Weather Research and Forecasting (WRF) model against measured wind speed and direction, temperature and turbulent kinetic energy (TKE) at three levels (5, 9, 25 m). The Urban Turbulence Project dataset, gathered from the outskirts of Turin, Italy and used for the comparison, provides measurements made by sonic anemometers for more than 1 year. In contrast to other similar studies, which have mainly focused on short-time periods, we considered 2 months of measurements (January and July) representing both the seasonal and the daily variabilities. To understand how the WRF-model PBL schemes perform in an urban environment, often characterized by low wind-speed conditions, we first compared six PBL schemes against observations taken by the highest anemometer located in the inertial sub-layer. The availability of the TKE measurements allows us to directly evaluate the performances of the model; results of the model evaluation are presented in terms of quantile versus quantile plots and statistical indices. Secondly, we considered WRF-model PBL schemes that can be coupled to the urban-surface exchange parametrizations and compared the simulation results with measurements from the two lower anemometers located inside the canopy layer. We find that the PBL schemes accounting for TKE are more accurate and the model representation of the roughness sub-layer improves when the urban model is coupled to each PBL scheme.     

Improved PPP performance in regional networks

It has been demonstrated that precise point positioning (PPP) is a powerful tool in geodetic and geodynamic applications. As is known, it provides solutions in the reference system of the satellite orbits. We focuses on the strategy to transform PPP solutions into the International Terrestrial Reference System (ITRS) by applying a set of local Helmert transformation parameters obtained from a regional network rather than using global parameters. In order to carry out this test, a regional network composed of 14 stations was analyzed using GIPSY-OASIS II software, over a period of 6 years. Two solutions differently aligned to the ITRS were compared in terms of accuracy, scattering, frequency content and local movements. One solution is aligned to IGb08 through the X-files provided by JPL, while the other is aligned to the European reference frame densification of IGb08 using customized regional X-files. Therefore, both are updated realizations of the ITRS. The test shows that a regional, instead of a global, alignment to the ITRS can significantly improve the repeatability of the solutions. A small improvement can also be found in terms of agreement with the regional densification of IGb08. The analysis of the signal content in the differently aligned time series allowed some differences to be found, in terms of both frequency and magnitude. These differences are mainly due to an evident common signal that is defined for the whole area and which is removed when using regional alignment. Finally, residual scattering was calculated after removing the modeled signals from each time series, which results in a scatter being significantly smaller for the regional solution than for the global solution. In order to obtain these results, the choice of the reference stations is a major question and therefore discussed in detail.     

Rainfall thresholds for the possible landslide occurrence in Sicily (Southern Italy) based on the automatic reconstruction of rainfall events

Review of the literature on the reconstruction of the rainfall responsible for slope failures reveals that criteria for the identification of rainfall events are lacking or somewhat subjective. To overcome this problem, we developed an algorithm for the objective and reproducible reconstruction of rainfall events and of rainfall conditions responsible for landslides. The algorithm consists of three distinct modules for (i) the reconstruction of distinct rainfall events, in terms of duration (D, in h) and cumulated event rainfall (E, in mm), (ii) the identification of multiple ED rainfall conditions responsible for the documented landslides, and (iii) the definition of critical rainfall thresholds for possible landslide occurrences. The algorithm uses pre-defined parameters to account for different seasonal and climatic settings. We applied the algorithm in Sicily, southern Italy, using rainfall measurements obtained from a network of 169 rain gauges, and information on 229 rainfall-induced landslides occurred between July 2002 and December 2012. The algorithm identified 29,270 rainfall events and reconstructed 472 ED rainfall conditions as possible triggers of the observed landslides. The algorithm exploited the multiple rainfall conditions to define objective and reproducible empirical rainfall thresholds for the possible initiation of landslide in Sicily. The calculated thresholds may be implemented in an operational early warning system for shallow landslide forecasting.     

Introducing dolomite seams: hybrid compaction–solution bands in dolomitic limestones

Bedding‐parallel dolomite seams occur in a clay‐poor carbonate succession of the Apennines. The seams are composed of a high concentration of dolomite crystals compared to the hosting dolomitic limestone. SEM images document microcracking, and in many cases even crushing and fragmentation, of dolomite crystals and accumulation of non‐carbonate insoluble material both along micro‐stylolites within the seams and around dolomite crystals of the seams. We interpret the seams as hybrid structures between pressure‐solution seams and compaction bands, which formed during burial. The euhedral dolomite crystals scattered in the micritic matrix represent the insoluble residue produced by the progressive dissolution of calcite. As calcite dissolution proceeds, the concentration of dolomite crystals increases, eventually resulting in a dolomite seam in which locally a dolomite crystal‐supported texture is attained. At this stage, the dolomite crystals within the seam start to collide, crush and fragment, so that the dolomite seam behaves like a compaction band.     

Measuring rill erosion at plot scale by a drone‐based technology

The traditional direct method (i.e. metric ruler and rillmeter) of monitoring rill erosion at plot scale is time consuming and invasive because it modifies the surface of the rilled area. Measuring rill features using a drone‐based technology is considered a non‐invasive method allowing a fast field relief. In the experimental Sparacia area a survey by a quadricopter Microdrones md4‐200 was carried out, and this relief allowed the generation of a Digital Elevation Model (DEM), with a mesh size of 1 cm and a resolution elevation equal to 2 mm, for three plots (L, G and C) affected by rill erosion. At first for the experimental L plot, which is 44 m long, the rill features were surveyed by a ‘manual’ method which was carried out by drawing on the PC screen the rill paths obtained by a visual orthophoto interpretation. This manual method was not applicable for the plots in which rills of limited depth occurred and were not detectable. Then, for both L plot and the other experimental plots having a length ranging from 22 to 44 m, an ‘automatic’ extraction method of rills from DEM was applied. Using an appropriate calculation routine, a vector coverage of transects orthogonal to the main flow direction (i.e. the maximum slope steepness path) was generated. The intersection of each plot DEM with the transect coverage allowed to obtain both the cross sections and the main rill morphological features. For the L plot the comparison between the rill morphological features obtained by the two different methods (manual, automatic) was carried out. Finally, the length–volume relationship and a dimensionless relationship proposed in literature were tested for all studied experimental plots. Copyright © 2015 John Wiley & Sons, Ltd.     

From discrete to continuum modelling of boundary value problems in geomechanics: An integrated FEM-DEM approach

Double-scale numerical methods constitute an effective tool for simultaneously representing the complex nature of geomaterials and treating real-scale engineering problems such as a tunnel excavation or a pressuremetre at a reasonable numerical cost. This paper presents an approach coupling discrete elements (DEM) at the microscale with finite elements (FEM) at the macroscale. In this approach, a DEM-based numerical constitutive law is embedded into a standard FEM formulation. In this regard, an exhaustive discussion is presented on how a 2D/3D granular assembly can be used to generate, step by step along the overall computation process, a consistent Numerically Homogenised Law. The paper also focuses on some recent developments including a comprehensive discussion of the efficiency of Newton-like operators, the introduction of a regularisation technique at the macroscale by means of a second gradient framework, and the development of parallelisation techniques to alleviate the computational cost of the proposed approach. Some real-scale problems taking into account the material spatial variability are illustrated, proving the numerical efficiency of the proposed approach and the benefit of a particle-based strategy.     

Fractures and faults in volcanic rocks (Campi Flegrei,southern Italy): insight into volcano-tectonic processes

The present study was focused to analyze fractures and faults in the Campi Flegrei calderas presently hosting several volcanic edifices, such as lava domes, scoria, and tuff cones. A complex network of fractures and faults affects the volcanic rocks, mostly as planar with highly variable density. Frequently faults appearing as conjugate structures showing normal kinematics often associated with ductile deformation such as drag folds and deflexed layers, suggesting a syn-eruption deformation. However, the most of faults, mainly hosted along the caldera/crater rims, are very steep with dominant normal and secondary reverse movements. The fracture pattern indicates a slight prevalence of NE–SW and NW–SE directions, but N–S and E–W trends also occur. Fractures and faults found in rocks older than 15 ka (Neapolitan Yellow Tuff included), measured in western and eastern sectors of the study area, indicate a rotation of ca. 30° of the main directions among these two sectors. For the faults occurring along the caldera/crater rims, we suggest a kinematic evolution characterized by the reactivation of tensile fractures previously formed in response to both regional extension and locale resurgent dome. Finally, normal faults located in the central sector of caldera, between La Starza and Accademia localities, cutting the youngest volcanic deposits, indicate a constant NNE–SSW extension probably related to the caldera resurgence.     

Geoarchaeology of Pleistocene open-air sites in the Vila Nova da Barquinha-Santa Cita area (Lower Tejo River basin, central Portugal)

This paper aims to provide insight into human occupation and landscape change during the Pleistocene in a central area of the Lower Tejo basin (Portugal). Detailed geomorphological mapping, coupled with lithostratigraphy, sedimentology and luminescence dating, supports the identification of a complete terrace staircase sequence. It consists of six gravely terraces located below the culminant (Pliocene) basin unit. A chronological framework for the sedimentary sequences and associated human industries is proposed and correlated with marine oxygen isotope stages (MIS): T1 terrace, not dated; T2, not dated; T3, >300 ka; T4, ∼300-160 ka (MIS8, MIS7 and MIS6); T5, ∼136-75 ka (MIS5); T6, ∼62-30 ka (MIS3); colluvium and aeolian sands, ∼30-14 ka (MIS2); valley fill deposits, ∼14 ka to present (MIS1). The oldest artefacts were found at the base of the T4 terrace, with the local stratigraphic level dated to ≥175 ± 6 ka (Middle Pleistocene). The lithic assemblages collected from distinct stratigraphic levels (T4, T5 top, T6 terraces and colluvium) are characterized by the predominance of opportunistic technological choices, a feature that can be attributed partly to the preferential exploitation of the available raw material, dominated by local-sourced quartzites and quartz pebbles. The adaptation to local raw material (texture and volume), together with subsistence patterns and behaviours, could explain the rarity of Acheulian types (handaxes and cleavers) and picks in the T4 terraces of the Tejo tributaries; this is in contrast to the same terrace of the Tejo valley, in which these types are found. Interpretation of the environmental conditions (controlled by climate and glacio-eustatic sea-level changes) affecting the hunter-gatherer human groups is also presented.