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...     

Heuristic considerations pertaining to hailstone size distributions in the plain of Friuli-Venezia Giulia

In this work, the hailstone size distributions at the ground in the plain of Friuli-Venezia Giulia are presented, as revealed through a network of polystyrene pads (hailpads), managed by volunteers, which has been active since 1988. The aim of this work is to highlight possible differences in the diurnal and seasonal behavior of hail at the ground, both from Friuli-Venezia Giulia and other countries, in order to improve the knowledge of this meteorological phenomenon.In the comparison between different countries, differences are found between the yearly size distributions of Friuli-Venezia Giulia and those of North-East Colorado, measured during the National Hail Research Experiment (NHRE). The size distributions obtained in South West France and in Friuli-Venezia Giulia are quite similar and they are slightly different from those of the Grossversuch experiment.In the comparison between different periods of the year, relevant differences are found between April and May and the other months. In particular, thunderstorms are less efficient in producing big hailstones during the former months. The most prolific month in producing hailstones is June, followed by September. This feature is interpreted as due to a form of synergy between the frequency of the synoptic forcing of storms and the amount of available energy at the ground.Analyzing the size distributions at different times of the day, the greatest differences are found in the intervals [00–06] and [06–12] in local time (respectively, [22–04] and [04–10] in UTC). These differences cannot be ascribed to the melting of the hailstones during their fall.     

Cautious neotectonic hypotheses for assessing the seismic hazard in northeastern Italy

A simplified tectonic scheme for hazard purposes was recently adopted for northeastern Italy, introducing large generalized seismogenic areas containing systems of complex geometry faults. This scheme considers only major faults with documented seismic activity. In the present analysis, a different tectonic scheme, with linear elements as seismogenic sources, is presented. The assessment of the regional seismic hazard is done with the fault rupture model, its most important advantage being the recognition that the length of fault rupture during an earthquake is an important consideration in probabilistic calculations of seismic hazard. Moreover, some structures with no associated seismicity but with notable neotectonic activity are considered, and their contribution to the results investigated. Important uncertainties such as those in the maximum possible magnitude of future earthquakes, in the location of the fault, in the focal depth, and in the attenuation law are accounted for in the calculations and their influence studied. The results identify a seismic belt running from Lake Garda to Friuli and along the Yugoslav coast and are very similar to those already known for Friuli, with the largest values corresponding to the zone around Gemona. Some slight differences in the shape of the areas of equal acceleration are probably due to the delineation of the seismic sources of the proposed model. For a cautious elaboration, some neotectonic lines without present seismicity were added into the fault model. Their contribution is negligible in the areas of highest acceleration, but increases remarkably in the areas where acceleration is not expected to exceed the medium values.     

Computing the flux of moisture from net radiation and soil wetness

A study has been made of the time evolution of the flux of moisture E over grassland. The parameterization of E has been examined in order to formulate an equation depending on the net radiation flux and on bulk parameters which depend on the daily average meteorological situation and soil conditions. In particular the gradient of soil moisture has been recognized as playing a fundamental role in the time evolution of E(t). A time-dependent equation is proposed to compute in a statistical sense the irrigation needs or to forecast the hourly values of E(t), the maximum value E ₀ and the time at which this maximum happens.     

The sea breeze at Venice,as related to daily global solar radiation

Although the sea breeze at Venice and on her hinterland is influenced by orography - mainly the Alps — to the north and the Po Valley to the west, the search for a correlation between the frequency of development of the sea breeze and the daily global solar radiation seems to be desirable, and may be useful for the management of emissions from the industrial area near Venice. Three different cases are examined: (i) the sea breeze occuring in the absence of any appreciable gradient wind; (ii) the sea breeze superimposed on a prevailing wind; (iii) the sea breeze not developing at all. The frequency distributions of these cases related to the global solar radiation at Venice are discussed.     

Contents of Volume 53

Volume Contents

Contents of Volume 53     

The Role of Data Processing and Uncertainty Management in Seismic Hazard Evaluations: Insights from Estimates in the Garfagnana–Lunigiana Area (Northern Italy)

Significantly different estimates of seismic hazard may result for the same site as aneffect of different methodological choices underlying the adopted procedures. In orderto explore this aspect, two approaches devoted to probabilistic seismic hazard assessment are considered for the evaluation of hazard in a seismic area in Northern Italy. In particular, results of a standard procedure are compared with those obtained by an innovative approach. Fundamental features of this last methodology are the extensive use of intensity data relative to seismic effects observed at the site of interest during past earthquakes and the basic role attributed to the parameterisation of uncertainty which affects the considered pieces ofinformation. The analysis indicates that the new approach supplies results significantlydifferent from those obtained from standard methodology and that these differences strongly depend on strategies adopted for data processing and for the management of uncertainties which affect input parameters.     

Coupled conduit and atmospheric dispersal dynamics of the AD 79 Plinian eruption of Vesuvius

The AD 79 eruption of Vesuvius is certainly one of the most investigated explosive eruptions in the world. This makes it particularly suitable for the application of numerical models since we can be quite confident about input data, and the model predictions can be compared with field-based reconstruction of the eruption dynamics. Magma ascent along the volcanic conduit and the dispersal of pyroclasts in the atmosphere were simulated. The conduit and atmospheric domain were coupled through the flow conditions computed at the conduit exit. We simulated two different peak phases of the eruption which correspond to the emplacement of the white and gray magma types that produced Plinian fallout deposits with interlayered pyroclastic flow units during the gray phase. The input data, independently constrained and representative of each of the two eruptive phases, consist of liquid magma composition, crystal and water content, mass flow rate, and pressure–temperature–depth of the magma at the conduit entrance. A parametric study was performed on the less constrained variables such as microlite content of magma, pressure at the conduit entrance, and particle size representative of the eruptive mixture. Numerical results are substantially consistent with the reconstructed eruptive dynamics. In particular, the white eruption phase is found to lead to a fully buoyant eruption plume in all cases investigated, whereas the gray phase shows a more transitional character, i.e. the simultaneous production of a buoyant convective plume and pyroclastic surges, with a significant influence of the microlite content of magma in determining the partition of pyroclast mass between convective plumes and pyroclastic flows.     

History of the Long Series of Daily Air Temperature in Padova (1725–1998)

The history of the origin of the study of meteorology in Padova and its connection to the major developments of this science in Italy and the international context are presented. Special topics are: the scientific legacy of Galileo Galilei and the Accademia del Cimento,the birth of the first meteorological networks, i.e., Ferdinand II and Leopold de' Medici who created the Rete Medicea, J. Jurin and the network of the RoyalSociety, London, L. Cotte and the Société Royale de Médicine, Paris, J. J. Hemmerand the Societas Meteorologica Palatina, Mannheim. After outliningthe cultural background that favoured the development of meteorology, emphasis is given to the plurisecular time series of meteorological observations, taken in Padova since 1725, in its national and international context. This long series includes barometric pressure, air temperature, wind direction and speed; state of the sky and occurrence of meteorological events and precipitation. Special reference is made to indoor and outdoor temperature observations. Solar radiation falling on each exposure has been modelled in order to know when data were fully reliable and when they were less so. A vertical profile of air temperature has allowed corrections of the change of instrument level, when necessary. In terms of homogeneity, the series can be divided into several periods, during which instruments and operational methods, position, general criteria were unchanged: origins in homes of the first observers (1725–1767); the First Period at the Specola(1768–1812); the Second Period at the Specola (1813–1864); the Third and Fourth Periodsat the Specola (1865–1937); the Last Measurements at theSpecola (1938–1962); the Giovanni Magrini Observatoryof the Water Magistrate (1920–today); the Gino Allegri Airport(1926–1990), the Botanical Gardens (1980–today), the CNR (1984–1986; 1993–today). The latestperiod with the birth of new weather stations, is the most affected byanthropic effect. The simultaneous presence of an urban and a rural weather station pointed out local effects which dominate the urban heat island.     

Errors in Early Temperature Series Arising from Changes in Style of Measuring Time, Sampling Schedule and Number of Observations

Study of the Padova series (1725–today) is a useful example, of general interest, of a critical revision of long time series. These are composed of a number of inhomogeneous parts, each of them with mean daily values, and extremes, computed in different ways, based on observations taken at different times, or with the time expressed in different styles. Imprecise clocks, little care for the schedule established for meteorological readings, changing style of evaluating time, inappropriate choice of observing schedules, too small a number of readings to compute the daily average, generated errors that caused significant departures in time series, that could be interpreted as a climate signal. In the past, average values were obtained with only a few daily measurements. The first problem is to correct the data and extrapolate the hourly temperatures needed to evaluate the daily minimum, maximum and average values in a homogeneous way. The change of style in temporal reference introduced spurious seasonal changes. Styles (or combinations of styles) used were: Italian time in use till 1789, in which the hours werecomputed starting from twilight; apparent solar time based on theactual motion of the sun; mean solar time based on the average motion of the sun; local time referred to the actual passage of thesun across the local meridian (local culmination); French timestarting at midnight and regulated on the local culmination; Western European Time regulated on theculmination of fictitious average solar motion on a reference meridian 15° East. A test was performed to verify whether the times chosen for readings were appropriate, in particular when observations were performed not close to the daily minimum and maximum. In effect, in the early period with Morgagni and Toaldo, the choice of schedule of observations was good, but afterwards the introduction of new observations, not always established at the most appropriate schedule, reduced the representativity of the data. The error in calculating the daily average temperature after a given number of observations taken at different hours of the day has been analysed. National, and especially international recommendations have been particularly important in the choice of observations times, and in determining averages. These recommendations have been simultaneously applied on a large number of sites, causing an in-homogeneity that may be misinterpreted as a well-documented, widespread climate change.