Origin of the Multiple Metric Type II Radio Burst Structure Associated with the 2002 July 23 CME

We report on the analysis of a fast (>2,000 km/s) CME-driven shock event observed with the UVCS telescope operating aboard SoHO on 23 July 2002. The same shock was also detected in the metric band by several ground-based radiospectrographs. The peculiarity of this event is the presence in the radio spectra of two intense metric type II bursts features drifting at different rates, together with clear shock/related broadenings of the O VI doublet lines observed by UVCS that were found to be temporally associated with the above radio features. The nature of these multiple radio lanes in the metric band is still under debate. One possible explanation is that they are produced by multiple shock waves generated by different ejections or, alternatively, by the flare and the associated CME. Also, emission from the upstream and downstream shock regions can produce split bands. By adopting a plausible CME model, together with a detailed analysis of the white-light, UV, and radio data associated with this event, we are able to conclude that both the radio and the UV shock signatures were produced by a single shock wave surface generated by the expanding CME.     

Shoshonite and sub-alkaline magmas from an ultrapotassic volcano: Sr–Nd–Pb isotope data on the Roccamonfina volcanic rocks,Roman Magmatic Province,Southern Italy

The Roccamonfina volcano is characterised by two stages of volcanic activity that are separated by volcano-tectonic caldera collapses. Ultrapotassic leucite-bearing rocks are confined to the pre-caldera stage and display geochemical characteristics similar to those of other volcanoes in the Roman Province. After the major sector collapse of the volcano, occurred at ca. 400 ka, shoshonitic rocks erupted from cinder cones and domes both within the caldera and on the external flanks of the pre-caldera Roccamonfina volcano. On the basis of new trace element and Sr–Nd–Pb isotope data, we show that the Roccamonfina shoshonitic rocks are distinct from shoshonites of the Northern Roman Province, but are very similar to those of the Neapolitan volcanoes. The last phases of volcanic activity erupted sub-alkaline magmas as enclaves in trachytic domes, and as lavas within the Monte Santa Croce dome. Ultrapotassic rocks of the pre-caldera composite volcano are plagioclase-bearing leucitites characterised by high levels of incompatible trace elements with an orogenic signature having troughs at Ba, Ta, Nb, and Ti, and peaks at Cs, K, Th, U, and Pb. Initial values of ⁸⁷Sr/⁸⁶Sr range from 0.70926 to 0.70999, ¹⁴³Nd/¹⁴⁴Nd ranges from 0.51213 to 0.51217, while the lead isotope rations vary between 18.788–18.851 for ²⁰⁶Pb/²⁰⁴Pb, 15.685–15.701 for ²⁰⁷Pb/²⁰⁴Pb, and 39.048–39.076 for ²⁰⁸Pb/²⁰⁴Pb. Shoshonites show a similar pattern of trace element depletions and enrichments to the earlier ultrapotassic leucite-bearing rocks but have a larger degree of differentiation and lower concentrations of incompatible trace elements. On the other hand, shoshonitic rocks have Sr, Nd, and Pb isotopes consistently different than pre-caldera ultrapotassic leucite-bearing rocks. ⁸⁷Sr/⁸⁶Sr ranges from 0.70665 to 0.70745, ¹⁴³Nd/¹⁴⁴Nd ranges from 0.51234 to 0.51238, ²⁰⁶Pb/²⁰⁴Pb ranges from 18.924 to 19.153, ²⁰⁷Pb/²⁰⁴Pb ranges from 15.661 to 15.694, and ²⁰⁸Pb/²⁰⁴Pb ranges from 39.084 to 39.212. High-K calc-alkaline samples have intermediate isotopic values between ultrapotassic plagioclase leucitites and shoshonites, but the lowest levels of incompatible trace element contents. It is argued that ultrapotassic magmas were generated in a modified lithospheric mantle after crustal-derived metasomatism. Interaction between the metasomatic agent and lithospheric upper mantle produced a low-melting point metasomatised veined network. The partial melting of the veins alone produced pre-caldera leucite-bearing ultrapotassic magmas. It was possibly triggered by either post-collisional isotherms relaxation or increasing T°C due increasing heat flow through slab tears. Shoshonitic magmas were generated by further melting, at higher temperature, of the same metasomatic assemblage with addition 10–20% of OIB-like astenospheric mantle material. We suggest that addition of astenospheric upper mantle material from foreland mantle, flowing through slab tearing after collision was achieved. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Interpretation of combined infrared,submillimeter, and millimeter thermal flux data obtained during the Rosetta fly-by of Asteroid (21) Lutetia

The European Space Agency’s Rosetta spacecraft is the first Solar System mission to include instrumentation capable of measuring planetary thermal fluxes at both near-IR (VIRTIS) and submillimeter–millimeter (smm–mm, MIRO) wavelengths. Its primary mission is a 1 year reconnaissance of Comet 67P/Churyumov–Gerasimenko beginning in 2014. During a 2010 close fly-by of Asteroid 21 Lutetia, the VIRTIS and MIRO instruments provided complementary data that have been analyzed to produce a consistent model of Lutetia’s surface layer thermal and electrical properties, including a physical model of self-heating. VIRTIS dayside measurements provided highly resolved 1 K accuracy surface temperatures that required a low thermal inertia, I < 30 J/(K m² s^0.5). MIRO smm and mm measurements of polar night thermal fluxes produced constraints on Lutetia’s subsurface thermal properties to depths comparable to the seasonal thermal wave, yielding a model of I < 20 J/(K m² s^0.5) in the upper few centimeters, increasing with depth in a manner very similar to that of Earth’s Moon. Subsequent MIRO-based model predictions of the dayside surface temperatures reveal negative offsets of ～5–30 K from the higher VIRTIS-measurements. By adding surface roughness in the form of 50% fractional coverage of hemispherical mini-craters to the MIRO-based thermal model, sufficient self-heating is produced to largely remove the offsets relative to the VIRTIS measurements and also reproduce the thermal limb brightening features (relative to a smooth surface model) seen by VIRTIS. The Lutetia physical property constraints provided by the VIRTIS and MIRO data sets demonstrate the unique diagnostic capabilities of combined infrared and submillimeter/millimeter thermal flux measurements.     

PFS/MEX observations of the condensing CO2 south polar cap of Mars

The condensing CO₂ south polar cap of Mars and the mechanisms of the CO₂ ice accumulation have been studied through the analysis of spectra acquired by the Planetary Fourier Spectrometer (PFS) during the first two years of ESA's Mars Express (MEX) mission. This dataset spans more than half a martian year, from Ls∼330° to Ls∼194°, and includes the southern fall season which is found to be extremely important for the study of the residual south polar cap asymmetry. The cap expands symmetrically and with constant speed during the fall season. The maximum extension occurs sometime in the 80°-90° Ls range, when the cap edges are as low as −40° latitude. Inside Hellas and Argyre basins, frost can be stable at lower latitudes due to the higher pressure values, causing the seasonal cap to be asymmetric. Within the seasonal range considered in this paper, the cap edge recession rate is approximately half the rate at which the cap edge expanded. The longitudinal asymmetries reduce during the cap retreat, and disappear around Ls∼145°. Two different mechanisms are responsible for CO₂ ice accumulation during the fall season, especially in the 50°-70° Ls range. Here, CO₂ condensation in the atmosphere, and thus precipitation, is allowed exclusively in the western hemisphere, and particularly in the longitudinal corridor of the perennial cap. In the eastern hemisphere, the cap consists mainly of CO₂ frost deposits, as a consequence of direct vapor deposition. The differences in the nature of the surface ice deposits are the main cause for the residual south polar cap asymmetry. Results from selected PFS orbits have also been compared with the results provided by the martian general circulation model (GCM) of the Laboratoire de Météorologie dynamique (LMD) in Paris, with the aim of putting the observations in the context of the global circulation. This first attempt of cross-validation between PFS measurements and the LMD GCM on the one hand confirms the interpretation of the observations, and on the other hand shows that the climate modeling during the southern polar night on Mars is extremely sensitive to the dynamical forcing.     

Changes in the rainfall–streamflow regimes related to climate change in a small catchment in Northern Italy

Theoretical and Applied Climatology - Climate change has become an important issue for scientific community, for its numerous impacts, especially on agriculture and environment. To shed light on...     

Seismic design of floor–wall joints of multi-storey CLT buildings to comply with regularity in elevation

The effects of irregularity in elevation of cross-laminated timber buildings have not been fully analysed in literature to provide useful information for the design. In this work, a number of building configurations, regular or irregular in elevation, characterized by a different arrangement per storey of the floor–wall joints have been analysed by means of non-linear dynamic analyses. Comparative results in terms of ratio between the behaviour q-factor of the investigated irregular configurations and that of reference regular ones, show that less dissipative capacity can be expected if the building is irregular due to a disequilibrium among storeys between the actual and the required strength provided by the floor–wall joints. A correlation method to estimate the behaviour q-factor for perfectly regular cross-laminated timber buildings is here presented and extended to in-elevation irregular ones. A new empirical formulation to assess the reliable corrective factor accounting for the irregularity in elevation of cross-laminated timber buildings, according to Eurocode 8 provisions, is also proposed. A final discussion about the implications of in-elevation irregularity on the building design is reported.     

Deep tunnel fronts in cohesive soils under undrained conditions: a displacement-based approach for the design of fibreglass reinforcements

The fronts of tunnels excavated under particularly difficult ground conditions by employing conventional tunnelling methods are commonly supported: the stabilization is usually achieved either by improving the mechanical properties of the soil (injections, jet grouting, soil freezing, etc.) or by introducing linear inclusions. This last technique, consisting in the introduction of pipes (usually made of fibreglass reinforced polymers) in the front, is particularly popular since it is very simple to adapt the reinforcement geometry, length and number to the different conditions encountered during the excavation. The design of this reinforcement technique is nowadays based on very simplified approaches: on either empirical formula or the limit equilibrium method. In a previous paper, the authors numerically studied the mechanical response of unreinforced fronts in cohesive soils and defined a non-dimensional front characteristic curve. In this paper, the authors intend to take into consideration the role of reinforcements by following the same approach. A procedure allowing the definition of the reinforced non-dimensional front characteristic curve, once the reinforcement pattern is assigned, is introduced. The practical use of this curve is described.

     

A semi-empirical approach to model pressure dependence of elastic moduli in granular media accounting for variations of coordination-number and Poisson-ratio

The effective medium theory based on the Hertz–Mindlin contact law is the most popular theory to relate dynamic elastic moduli (or elastic velocities) and confining pressure in dry granular media. However, many experimental results proved that the effective medium theory predicts pressure trends lower than experimental ones and over-predicts the shear modulus. To mitigate these mispredictions, several evolutions of the effective medium theory have been presented in the literature. Among these, the model named modified grain contact theory is an empirical approach in which three parametric curves are included in the effective medium theory model. Fitting the parameters of these curves permits to adjust the pressure trends of the Poisson ratio and the bulk modulus. In this paper, we present two variations of the modified grain contact theory model. First, we propose a minor modification in the fitting function for the porosity dependence of the calibration parameters that accounts for non-linearity in the vicinity of the critical porosity. Second, we propose a major modification that reduces the three-step modified grain contact theory model to a two-step model, by skipping the calibration parameter–porosity fit in the model and directly modelling the calibration parameter–pressure relation. In addition to an increased simplicity (the fitting parameters are reduced from 10 to 6), avoiding the porosity fit permits us to apply the model to laboratory data that are not provided with accurate porosity measurements. For this second model, we also estimate the uncertainty of the fitting parameters and the elastic velocities. We tested this model on dry core measurements from literature and we verified that it returns elastic velocity trends as good as the original modified grain contact theory model with a reduced number of fitting parameters. Possible developments of the new model to add predictive power are also discussed.     

Long-term model of planimetric and bathymetric evolution of a tidal lagoon

This model is based on the concept of transport concentration, defined as the time-averaged concentration in a given location of a lagoon, which determines the long-term net transport of sediments as the sum of a dispersive and an advective flux. Dispersive net flux of sediments is due to the alternate components of the tidal flow, while the advective net flux of sediments is due to the residual (Eulerian) component of the tidal, fluvial and littoral flow and possibly to the asymmetry between flow and ebb tide.