The tidal and wind induced hydrodynamics of the composite system Adriatic Sea/Lagoon of Venice

A shallow water hydrostatic 2D hydrodynamic numerical model, based on the boundary conforming coordinate system, was used to simulate aspects of both general and small scale oceanic features occurring in the composite system constituted by the Adriatic Sea and the Lagoon of Venice (Italy), under the influence of tide and realistic atmospheric forcing. Due to a specific technique for the treatment of movable lateral boundaries, the model is able to simulate efficiently dry up and flooding processes within the lagoon. Firstly, a model calibration was performed by comparing the results of the model, forced using tides and ECMWF atmospheric pressure and wind fields, with observations collected for a set of 33 mareographic stations uniformly distributed in the Adriatic Sea and in the Lagoon of Venice. A second numerical experiment was then carried out by considering only the tidal forcing. Through a comparison between the results obtained in the two experiments it was possible to assess the reliability of the estimated parameter through the composite forcing. Model results were then verified by comparing simulated amplitude and phase of each tidal constituent as well as tidal velocities simulated at the inlets of the lagoon and in the Northern Adriatic Sea with the corresponding observed values. The model accurately reproduces the observed harmonics: mean amplitude differences rarely exceed 1 cm, while phase errors are commonly confined below 15°. Semidiurnal and diurnal currents were correctly reproduced in the northern basin and a good agreement was obtained with measurements carried out at the lagoon inlets. On this basis, the outcomes of the hydrodynamic model were analyzed in order to investigate: (i) small-scale coastal circulation features observed at the interface between the adjoining basins, which consist often of vortical dipoles connected with the tidal flow of Adriatic water entering and leaving the Lagoon of Venice and with along-shore current fields connected with specific wind patterns; (ii) residual oscillations, which are often connected to meteorological forcing over the basin. In particular, it emerges that small-scale vortical features generated near the lagoon inlet can be efficiently transported toward the open sea, thus contributing to the water exchange between the two marine regions, and a realistic representation of observed residual oscillations in the area would require a very detailed knowledge of atmospheric as well as remote oceanic forcing.     

Microzonation of Potenza (Southern Italy) in terms of spectral intensity ratio using joint analysis of earthquakes and ambient noise

A temporary seismic network composed of 11 stations was installed in the city of Potenza (Southern Italy) to record local and regional seismicity within the context of a national project funded by the Italian Department of Civil Protection (DPC). Some stations were moved after a certain time in order to increase the number of measurement points, leading to a total of 14 sites within the city by the end of the experiment. Recordings from 26 local earthquakes (M_l 2.2−3.8 ) were analyzed to compute the site responses at the 14 sites by applying both reference and non-reference site techniques. Furthermore, the Spectral Intensity (SI) for each local earthquake, as well as their ratios with respect to the values obtained at a reference site, were also calculated. In addition, a field survey of 233 single station noise measurements within the city was carried out to increase the information available at localities different from the 14 monitoring sites. By using the results of the correlation analysis between the horizontal-to-vertical spectral ratios computed from noise recordings (NHV) at the 14 selected sites and those derived by the single station noise measurements within the town as a proxy, the spectral intensity correction factors for site amplification obtained from earthquake analysis were extended to the entire city area. This procedure allowed us to provide a microzonation map of the urban area that can be directly used when calculating risk scenarios for civil defence purposes. The amplification factors estimated following this approach show values increasing along the main valley toward east where the detrital and alluvial complexes reach their maximum thickness.     

Wavy Vertical Motions in the ABL Observed by Sodar

Some characteristics of wavelike motions in the atmospheric boundary layer observed by sodar are considered. In an experiment carried out in February 1993 in Milan, Italy, Doppler sodar measurements were accompanied by in situ measurements of temperature and wind velocity vertical profiles using a tethered balloon up to 600 m. The oscillations of elevated wavy layers containing intense thermal turbulence, usually associated with temperature-inversion zones, were studied by using correlation and spectral analysis methods. The statistics of the occurrence of wavelike and temperature-inversion events are presented. The height distributions of Brunt–Vaisala frequency and wind shear and their correlation within elevated inversion layers were determined, with a strong correlation observed between the drift rate of the wavy layers and the vertical velocity measured by Doppler sodar inside these layers. Spectral analysis showed similarities regarding their frequency characteristics. The phase speed and propagation direction of waves were estimated from the time delay of the signals at three antennae to provide estimates of wavelength. Moreover, wavelengths were estimated from the intrinsic frequency obtained from sodar measurements of the Doppler vertical velocity and oscillations of wavy turbulent layers. The two wavelength estimates are in good agreement.     

Redox Potential and Seasonal Porewater Biogeochemistry of Three Mountain Wetlands in Southeastern Kentucky, USA

Redox potentials (Eh) were monitored bimonthly and porewater chemistry was analyzed seasonally at three slightly-acidic, high-elevation Kentucky wetlands that differed in hydrology, parent materials, and vegetation. At all sites, Eh values were below 300 mV, which indicated that reducing conditions persisted within the upper 90 cm and fluctuated mainly within the range of iron and sulfate reduction. Significant relationships of Eh values with depth were observed only at the Martins Fork wetland, where precipitation was the primary water source. The strongest and most stable reducing conditions, observed at the Kentenia site, reflected consistently high water levels, which were sustained by ground water. The third wetland (Four Level) was distinguished by irregular Eh fluctuations coinciding with strong seasonal ground-water upwelling. Although Fe³⁺ and SO₄ ²⁻ were the primary terminal electron acceptors in all wetlands, porewater chemistry also varied significantly by season and soil depth in response to piezometric water level fluctuations. Additional factors that influenced porewater chemistry included: (1) the presence of limestone parent materials that affected porewater pH, Ca²⁺, and Mg²⁺; and (2) the prevalence of sphagnum moss or graminoid species that influenced dissolved organic carbon, CO₂, and CH₄. Results from this study indicated the diverse range and importance of multiple factors in controlling biogeochemical processes and properties in small, high-elevation Appalachian wetlands.     

Fluid geochemistry of the Mondragone hydrothermal systems (southern Italy): water and gas compositions vs. geostructural setting

International Journal of Earth Sciences - The geochemistry of natural thermal fluids discharging in the Mondragone Plain has been investigated. Thermal spring emergences are located along the...