Update of the search for Gamma Ray Bursts with ARGO-YBJ in scaler mode

We report an update of the search for emission from Gamma Ray Bursts (GRBs) in the energy range 1−100 GeV in coincidence with the prompt emission detected by satellites, using the large field of view (about 2 sr) air shower detector ARGO-YBJ, appropriate to monitor unpredictable and short duration events like GRBs. The search has been carried out using the single particle technique in time coincidence with satellite detections both for single events and by stacking GRBs in time and phase. Between December 2004 and April 2011, 131 GRBs detected by different satellites occurred in the ARGO-YBJ field of view (zenith angle within 45 degrees). For 110 of these we searched for a high energy counterpart in the ARGO-YBJ data, finding no statistically significant signal. The resulting fluence upper limits between 1 and 100 GeV reach values as low as 10^(−5) erg/cm2, and in one case (GRB090902B) can be compared with observations by the LAT instrument on the Fermi satellite

Feasibility of Tsunami Early Warning Systems for small volcanic islands

Abstract. This paper investigates the feasibility of Tsunami Early Warning Systems for small volcanic islands focusing on warning of waves generated by landslides at the coast of the island itself. The critical concern is if there is enough time to spread the alarm once the system has recognized that a tsunami has been generated. We use the results of a large scale physical model experiment in order to estimate the time that tsunamis take to travel around the island inundating the coast. We discuss how and where it is convenient to place instruments for the measurement of the waves

Improvement in workability of terminals placed along the inner side of port vertical breakwaters by means of recurved parapet walls

The function of main port breakwaters is to protect harbour basins from incoming waves and currents. In the event that a maritime terminal is placed on the inner side of a main breakwater, it is extremely important to limit waves overtopping the structure, because the overtopping flows may be very dangerous for the safety of the operations taking place in the terminal. Very often during storms if the overtopping discharges are severe, the terminal is temporarily closed, reducing its average annual workability accordingly. Wave overtopping is normally limited by using high parapet walls (crownwalls) which are not well considered from an environmental point of view due to their visual impact. A good solution to reduce wave overtopping limiting the increasing of the crownwalls height, is to use recurved parapet walls. The paper presents a new formula for recurved walls which can be used to estimate the overtopping flow rates reduction compared to normal vertical parapets. The formula has been obtained for vertical breakwaters by using numerical computations. The recurved parapet has the shape of a circumference sector, characterized by a radius and an opening angle. The numerical computations were performed applying OpenFOAM® which solves the 3D RANS equations for multiphase flows (air and water). The results show the high hydraulic efficiency of recurved walls in reducing overtopping rates compared to traditional vertical parapets

Numerical and Physical Modeling of Ponte Liscione (Guardialfiera, Molise) Dam Spillways and Stilling Basin

Issues such as the design or reauditing of dams due to the occurrence of extreme events caused by climatic change are mandatory to address to ensure the safety of territories. These topics may be tackled numerically with Computational Fluid Dynamics and experimentally with physical models. This paper describes the 1:60 Froude-scaled numerical model of the Liscione (Guardialfiera, Molise, Italy) dam spillway and the downstream stilling basin. The k-omega SST turbulence model was chosen to close the Reynolds-averaged Navier-Stokes equations (RANS) implemented in the commercial software Ansys Fluent(R). The computation domain was discretized using a grid with hexagonal meshes. Experimental data for model validation were gathered from the 1:60 scale physical model of the Liscione dam spillways and the downstream riverbed of the Biferno river built at the Laboratory of Hydraulic and Maritime Constructions of the Sapienza University of Rome. The model was scaled according to the Froude number and fully developed turbulent flow conditions were reproduced at the model scale (Re > 10,000). From the analysis of the results of both the physical and the numerical models, it is clear that the stilling basin is undersized and therefore insufficient to manage the energy content of the fluid output to the river, with a significant impact on the erodible downstream river bottom in terms of scour depths. Furthermore, the numerical model showed that a less vigorous jet-like flow is obtained by removing one of the sills the dam is supplied with

Lidar in Space Technology Experiment correlative measurements by lidar in Potenza, southern Italy.

An intensive lidar measurement campaign was carried out in Potenza (40°36′N-15°44′E, 820 m above sea level (asl)) in conjunction with the Lidar in Space Technology Experiment (LITE) mission and primarily aimed at the validation of LITE stratospheric aerosol measurements. Potenza lidar measurements in coincidence with all five nighttime overpasses near southern Italy (September 11, 12, 17, and 18, 1994) are compared with simultaneous LITE data. Potenza lidar data appear to be highly correlated with LITE data both at 355 and 532 nm. Potenza lidar versus LITE measurements of the aerosol-scattering ratio show a correlation coefficient of 0.72–0.81 at 355 nm and 0.88–0.93 at 532 nm, with an average calibration coefficient of 0.92 ± 0.19 at 355 nm and 1.02 ± 0.07 at 532 nm. Comparisons are also made in terms of the average Angstrom coefficient, whose values are consistent with submicrometer aerosol particles. Finally, Potenza lidar measurements of the aerosol layer base and top heights, the peak aerosol-scattering ratio and peak height, as well as of the aerosol scattering ratio at the cloud base appear to be consistent with measurements performed by other ground lidar stations in Europe during the LITE campaign as well as with the LITE data

Characterization of the planetary boundary layer height and structure by Raman lidar: comparison of different approaches

Abstract. The planetary boundary layer (PBL) includes the portion of the atmosphere which is directly influenced by the presence of the earth's surface. Aerosol particles trapped within the PBL can be used as tracers to study the boundary-layer vertical structure and time variability. As a result of this, elastic backscatter signals collected by lidar systems can be used to determine the height and the internal structure of the PBL. The present analysis considers three different methods to estimate the PBL height. The first method is based on the determination of the first-order derivative of the logarithm of the range-corrected elastic lidar signals. Estimates of the PBL height for specific case studies obtained through this approach are compared with simultaneous estimates from the potential temperature profiles measured by radiosondes launched simultaneously to lidar operation. Additional estimates of the boundary layer height are based on the determination of the first-order derivative of the range-corrected rotational Raman lidar signals. This latter approach results to be successfully applicable also in the afternoon–evening decaying phase of the PBL, when the effectiveness of the approach based on the elastic lidar signals may be compromised or altered by the presence of the residual layer. Results from these different approaches are compared and discussed in the paper, with a specific focus on selected case studies collected by the University of Basilicata Raman lidar system BASIL during the Convective and Orographically-induced Precipitation Study (COPS)