Characterization of ?ngstr?m''s turbidity parameters in the Po Valley area for summer conditions of the atmosphere

Summary Measurements of direct solar irradiance were taken at the San Pietro Capofiume station in the centre of the Po Valley using two examples of the multispectral sun photometer, model UVISIR, on several clear-sky days of late spring and early summer in the years 1989 and 1990. Realistic evaluations of aerosol optical thickness at several sun-photometric wavelengths were obtained from these measurements by i) using values of the calibration constants carefully found by following both the Langley plot method and the spectral-correction procedure, which had previously been applied with satisfactory results to the sun-photometric measurements carried out in Antarctica and ii) taking into account the extinction effects produced by Rayleigh scattering and absorption due to ozone, water vapour and nitrogen dioxide on the solar radiation passing through the atmosphere. By examining a wide set of spectral series of the aerosol optical thickness in terms of the well-known Ångstr?m formula, a large number of pairs of atmospheric-turbidity parameters α and β was obtained, presenting a range of the mean daily values of α from 1.0 to 1.7 (with the median of 1.48) and a range of the mean daily values of β from 0.10 to 0.30 (with the median of 0.15). Using the particulate extinction models CR (for continental particles) and TR (for small tropospheric particles and large rural particles), the aerosol mass loading of the atmosphere calculated for these values of α and β was estimated to vary between 0.09 and 0.31 g m⁻² (with the median of 0.21 g m⁻²) during the measurement period of 1989 and between 0.09 and 0.41 g m⁻² (with the median of 0.13 g m⁻² for model CR and of 0.21 g m⁻² for model TR) during June and July 1990. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Transport of Volcano Etna emissions towards the alpine region using ECMWF data

Summary ECMWF data have been utilised to study the Volcano Etna contribution to the sulphur deposition in the alpine region. Air mass trajectories starting from Etna during the whole 1989 have been computed. Firstly a cluster analysis was applied in order to objectively classify them. Then the total deposition (wet and dry) over Northern Italy of sulphur coming from Volcano Etna was estimated. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

The modelling of short waves in shallow waters and in the surf zone

Summary Two different flow models of the surf zone wave current dynamics based on Boussinesq and Serre equations have been implemented and tested. Good results were obtained while testing the models against many different wave and current data sets. Highly satisfactory reproduction of the experimental current patterns have been obtained by the model based on the Serre equations. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Modelling a river delta growth: Evaluations on some partly deterministic 2D simulations

Summary A bidimensional explicit finite-difference simulation of a river delta growth, based on Pelnard-Considère continuity equation, considering long-shore sediment transport as given by CERC formula, has been developed and fed by sets of marine events generated by means of a general Markovian-process simulator. The simulation was restricted to the final stage of the sea-beach interaction, remaining it limited, seaward, to the consideration of pairs of values representing wave power and direction of wave motion. This kind of formulation allowed a computationally efficient way to represent persistent phenomena. River sand supply has been modelled by means of a simply stationary stochastic process. The operativeness of the model has been evaluated on some fixed conditions:a) beach length 20 km;b) non-erodible edges;c) river supply in the middle. In general, wave power ranged up to some unit·10³ W/m, while sand river supply up to near 7·10⁻² m³/s. Some models were left to evolve for 500 y, a time interval in which some significant event should occur. The results show how: 1) for long-time estimations a spatial resolution of 500 m could be a reasonable choice; 2) time step should be kept as small as possible, even in the absence of numerical instability; 3) wave-approaching angles simulation scheme impacts on final delta morphology; 4) sea status persistence strongly influences the final results; 5) even a simple (t/const) time adimensionalization may influence the results when high river sand supply meets low wave power conditions; 6) neglecting on/off-shore sediment transport reflects in a marked triangular equilibrium delta shapes; 7) the cuspate aspect of a river delta could be an indication of a non-erosion-dominated stage or of a growing one. Although for predictive engineering purpose 2D longshore formulations appear to be less attractive than 3D ones, it has been pointed out how some hypotheses can be tested, in an earth science operating context, using either moderate-complexity software or easily avilable computing devices. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Study of aerosol particle transport by means of particulate-matter elemental composition

Summary Results of two measurement campaigns on particulate-matter concentration and composition aimed at studying dispersion and transport of aerosol particles in areas of different typology are reported. Local and regional aerosol transport affects particulate-matter concentration in a rural prealpine area, in particular the regional background is a main component of sulphur compounds. A long-range transport episodic event has been also detected. In the urban area of Milan, under good mixing conditions, the concentration of particulate matter has been found to be nearly constant up to 100 metres. The measurements of elemental-concentration values for a time series of particulate-matter samples collected simultaneously at different sites or altitudes proved to be an effective method for the investigation of transport phenomena. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Cosmic-ray spectrum and composition: Ground observations

Summary This paper summarizes the most interesting results obtained from ground-based experiments investigating cosmic-ray spectrum and composition. The contributed measurements cover a range of primary energy of about 7 decades, from ∼10¹³ eV up to ∼10²⁰ eV, allowing us to gain deeper insight into a large variety of phenomena including: source and acceleration mechanisms, propagation and diffusion in the Galaxy, extragalactic sources and their location. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Interannual variability of the sea level at Trieste

Summary Some aspects of the interannual variability of the sea level at Trieste are studied by investigating the monthly arrangement of sea level peaks and their evolution from 1939 to 1991. The analysis is carried out by means of level thresholds, which allow to select sets of marked low and high daily mean sea level events. Extreme events correspond to well-defined weather synoptic configurations. As a result, the events tend to be concentrated in the first and last three months of the year, respectively, and their time evolution is sensitive to that of the annual mean sea level. Finally, the different mean duration of low- and high-level episodes is pointed out. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Ozone measurements in atmosphere and correlations with7Be in an Italian alpine valley

Summary Since 1990 our Institute has been conducting⁷Be measurements in the atmosphere in order to use it as a tracer for air coming from the upper layers of the atmosphere and for the stratospheric ozone. In this paper we present the results on⁷Be measurements and ozone concentrations obtained with a one-year monitoring campaign carried out in Sondrio, an alpine twon in Northern Italy. For a few interesting events correlations between beryllium and ozone is observed.⁷Be reveals itself as a good marker which reaches ground level during particularly rare events such as stratospheric intrusions. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Water-sediment thermal interaction in a lagoon exchanging water with the sea (winter case)

Summary In this paper the thermal behaviour of both a shallow and well-mixed layer of water and its underlying sediment (e.g. a lagoon) is described. The water-sediment thermal interaction is analytically obtained by assuming a sinusoidal trend for the water depth. During the first half-period, the water leaves the lagoon at temperatureT(t) and in the second half-period the water comes back but at a constant temperatureT ^*. In this study theoretical results in a case without the solar flux will be shown (i.e. the case correponds to a typical winter case). Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.