Nimbus 7 CZCS images as inputs in circulation modelling of the north Adriatic Sea

Summary The results of a first attempt at using satellite remotesensed images in numerical, circulation modelling is described. The Nimbus 7/CZCS (Coastal Zone Colour Scanner) image of 7 July 1979 enhanced in terms of total suspended matter (TSM) was geometrically adapted to the grid of the northern Adriatic model. The lack of data relative to salinity and temperature distributions necessitated the application of the barotropic version of the model in which the wind field was combined with the advection-diffusion equation to get the transport of a passive tracer. The simulation began around the same hour of the satellite overflight and carried on for a number of consecutive days. Output data, in agreement with the hypotheses, have recreated the marine structure comparable to those found in later images. Paper presented at the 1^o Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, Rome, June 19–22, 1984.     

Preliminary results from the ozone lidar at the University of L''aquila

Summary We describe the ozone lidar operated at the Department of Physics of the University of L'Aquila. Preliminary ozone profiles obtained with the DIAL (differential absorption lidar) technique are also reported and a comparison is made with ECC (electro chemical cell) sonde data obtained at the FISBAT, CNR in Bologna. Although this comparison is of limited value the two sets of data show a good agreement. The influence of the recent detected volcanic aerosols from the eruption of Pinatubo on these measurements is also discussed.     

Inertial circulation of the western Mediterranean sea

Summary The essential features of the steady circulation of the western Mediterranean are reproduced by means of a vertically integrated model. In the framework of barotropic theory, it is shown how the effects of the geometry of the basin, including the islands, of the variable bottom topography and of the forcing of the flow at the Gibraltar Strait concur in determining the circulation pattern. Some observed features in particular regions, such as the Ligurian Sea, which are not reproduced by the model, indicate where baroclinic and/or wind-driven dynamics are likely to dominate. Paper presented at the 1^o Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 19–22, 1984, Rome.     

Radar characterization of summer thunderstorms in the western Po Valley

Summary Data taken by aC-band conventional weather radar during 1979, 1980 and 1981 summer campaigns conducted in the western Po Valley, have been analysed in comparison with surface reports of hailfalls, indicating the location, time and estimated losses for each event. The aim of this paper is to determine the signature of thunder-storms on radar data,vs. the presence or absence of hail on the ground. Hail percentages of occurrence greater than 75% of all cases are experienced when reflectivity values of 55 dBZ are detected above 8000m. Detection criteria of this kind are easy to implement in real-time surveillance systems and can be used to elaborate short-time warnings.

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Riassunto Si presenta un'analisi di dati rilevati con un radar meteorologico tradizionale in bandaC durante campagne di osservazioni condotte nella parte occidentale della Valle Padana nelle estati 1979, 1980 e 1981. I dati a terra sono costituiti dallo segnalazioni di grandinate che specificano la località, l'ora e la stima dei danni arrecati alle colture agricole. S'intende con questo lavoro determinare criteri di discriminazione fra le caratte-ristiche dei segnali radar provenienti da eventi temporaleschi per cui sia stata segnalata grandine, rispetto ai casi di assenza di grandine. Percentuali di eventi grandinigeni maggiori del 75% sono state riscontrate quando valori di riflettività di almeno 55 dBZ sono stati rilevati sopra gli 8000 m di quota. Criteri di discriminazione di questo tipo sono di semplice implementazione in sistemi di sorveglianza in tempo reale e possono essere usati per elaborare messaggi di allarme a breve periodo.

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Резюме Проводится анализ данных, полученных при метеорологических радарных исследованиях в зонеC в период летних кампаний 1979, 1980 и 1981 г.г. в западной части долины По. Полученные данные сопоставляются с наземными сообщениями о выпадании града, отмечая месторасположение, время и расчетные потори для каждого события. Цель этой статьи— определить сигнатуру для гроз по радарным данным в зависимости от наличия или отсутствия града на земле. Вероятность вышадания града превышает 75% в том случае, когда детектируется величина отражательной способности ∼55 dBZ выше 8000 м. Критерии определения такого типа легко использовать в системах наблюдения в реальном времени и могут служить для предупреждения за короткий промежуток времени.

     

Low-cost and high-reliability control and data acquisition system for the operation of a solar plant with a long-term thermal storage capability

Summary A solar plant with a long-term thermal storage capability has been built up at the University of Calabria. In this paper it is described the control and data acquisition system for the operation of the plant. Some considerations on the control's schedule of the plant are developed.

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Riassunto Si descrive un sistema di controllo e acquisizione dati a basso costo ed elevata affidabilità per la gestione di un impianto solare dotato di accumulo di calore a lungo termine.

     

Analysis of solar-radiation characteristics at the EURELIOS power plant of Adrano

Summary Two years of experimental data, measured with high resolution at Adrano, have been analysed. The behaviour of the radiation changes on short time intervals, the cumulative distributions, the statistical properties and the influence of the integration time have been studied in detail. The distributions of daily collected energy in different periods andvs. power thresholds have been computed together with the differences between the average and the most favourable periods. In order to allow the optimum dimensioning of the storage system, a study on the statistical properties of excess (**) and recurrence time intervals has been developed. Work carried out under contract with the Italian Electricity Board (ENEL).     

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.     

An analytical model for a screen evaluation of the environmental impact from a single point source

Summary A screening model (CISP) is presented for the calculation of maximum predicted concentrations from a single point source, which is particularly useful in situations where on-site meteorological measurements are limited or unavailable. CISP utilizes an analytical solution of the advection diffusion equation which is non-Gaussian in form. CISP performance in evaluating maximum ground-level concentrations was compared with that of the Environmental Protection Agency (EPA) Regulatory PTPLU2 Gaussian model.     

A laboratory experiment on the development of cyclogenesis in the lee of a mountain

Summary One of the most intriguing problems concerning the interaction of subsynoptic and synoptic atmospheric flows with topographic features is orographic cyclogenesis. A fully satisfactory prediction theory is not yet available, but a lot of efforts have been made by theoreticians to implement reliable numerical models simulating the different phases of this complex phenomenon. An attempt to perform a laboratory experiment to simulate physically this kind of interaction has been made by us, through the generation of a baroclinic frontal system in the rotating hydraulic platform of the ?Coriolis Laboratory—LEGI-IMG—Grenoble?. The adopted technique consists in a device which produces, at the interface separating two water layers of different density (ϱ₁ and ϱ₂), a stream of stratified fluid whose density has an intermediate value ϱ₁ < ϱ_m < ϱ₂. This stream is generated at the height of the interface between the two layers; due to the rotation of the platform, the attainment of geostrophic equilibrium brings about an intermediate-water flow running along a wall, giving rise to a three-layer baroclinic structure which can represent some of the main outstanding features of an atmospheric frontal system impinging on a mountain. In a well-defined range of the Rossby and Burger numbers, the instability of this current gives rise to a couple of persistent cyclonic and anticyclonic vortices, whose horizontal dimensions and vertical extents reproduce quite faithfully the synoptic situation supporting the onset of the orographic cyclogenesis, with its characteristic cold front stretching between the two vortex structures. It is enough to place an obstacle of a suitable size in the proper geographic position, to make the cyclogenesis start. The first results of our simulations have been encouraging, showing the occurrence of lee cyclogenesis when the stream conditions in our model correspond to the synoptic features which have been recognized as the precursors of orographic cyclogenesis in the lee of the Alps.     

A study about the environmental impact of a large particulate matter source by means of a sampling station interactive with the environment

Summary The contribution of the particulate matter relapsed from a large oil-fired power plant into the surrounding environment was investigated by means of an automated sampling station interactive with the environment. This station performs real-time measurements of some meteorological parameters and of the concentrations of some gaseous pollutants, thus carrying out aerosol samplings only in situations of environmental interest such as fumigation or blank conditions. Elemental composition of the fractionated particulate matter and morphological observations on single particles were obtained using PIXE (particle-induced X-ray emission) and SEM (scanning electron microscopy) techniques.

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Riassunto Il contributo all’inquinamento dovuto all’emissione di materiale particolato da una centrale termoelettrica ad olio combustibile è stato studiato utilizzando una stazione di prelievo funzionante in modo interattivo con l’ambiente. Questa stazione è in grado di effettuare prelievi di aerosol atmosferico pilotati da prefissati valori di parametri ambientali, sia di tipo meteorologico che di concentrazione di alcuni inquinanti gassosi, che permettono di discriminare situazioni di ricaduta del pennacchio da situazioni tipicamente di fondo. La composizione elementare del particolato, frazionato nelle diverse classi dimensionali, è stata ottenuta mediante la tecnica multielementare PIXE (emissione di raggi X indotte da particelle), mentre osservazioni morfologiche sulle particelle campionate sono state effettuate mediante SEM (microscopia elettronica a scansione).

     

On the radiative cooling of a surface during dew formation

Summary From the energy balance of a radiant surface with zero mass and perfectly insulated from below, the equilibrium temperature is calculated as a function of both sensible and latent heat transfer resistance. Under the hypothesis of Robinson,r _L=r _H is the air in contact with the surface is saturated, the equilibrium temperature is estimated as a function of air temperature, dew temperature and wind speed. This result could be useful to calculate night-time temperature of passive solar collectors or the yield of dew collectors. Paper presented at the 1^o Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 19–22, 1984, Rome.     

Analysis of a feedback system governed by the diffusion equation

Summary In this paper the three-dimensional diffusion equation for a pollutant's source whose discharge depends lienarly on the concentration of the pollutant at a given point is solved analytically. The situation is that one corresponding to a linear feedback system applied to a partial differential equation. The obtained results show that this system is very robust to possible changes occurring in the eddy diffusion coefficient. Furthermore, a stability analysis for the feedback solution is carried out.

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Riassunto Si risolve analiticamente l'equazione tridimensionale della diffusione per uno scarico la cui portata inquinante è fatta dipendere linearmente dal valore della concentrazione dell'inquinante ad una certa distanza dalla sorgente. La situazione descritta corrisponde alla meassa a punto di un sistema a ?retroazione? retto da una equazione alle derivate parziali. I risultati ottenuti mostrano che un tale tipo di sistema è poco sensibile alle possibili variazioni del parametro di diffusività turbolenta. Si dà inoltre un'analisi di stabilità per la soluzione del sistema reazionato.

     

Influence of a sea structure on the surrounding wind field

Summary We have experimentally studied the kinematic influence of an oceanographic tower on the surrounding wind field. The tower is located in the open sea in the northern Adriatic. The paper describes the tests carried out in a wind tunnel and their results.

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Riassunto Abbiamo studiato sperimentalmente l'influenza cinematica di una struttura sul campo di vento circostante. La struttura è una piattaforma oceanografica situata nel nord Adriatico. La nota descrive i test eseguiti in galleria del vento ed i risultati ottenuti.

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Резюме Мы экспериментально исследуем кинематическое влияние океанографической платформы на окружающее поле ветров. Платформа расположена в открытом море в северной части Адриатики. В статье описывается проверка, проведенная в ветряном туннеле, и приводятся полученные результаты.

     

Climatological implications of a satellite-borne SAR imaging the sea surface

Summary A methodology in the climatological interpretation of marine SAR images of the Italian seas is sought for. In particular, in condition of low wind SAR images may lead to the mapping of tropospheric mesoscale eddies. In conditions of high wind SAR images should reveal the deviating and shadowing effects of coastal obstacles in the wind field.

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Riassunto Si passano in rassegna gli effetti dell'interazione aria-mare in condizioni di vento debole e forte osservati col SAR montato su satellite, in vista della possibile definizione di una metodologia per l'uso del SAR come strumento climatologico.

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Резюме Анализируется методология при климатологической интерпретации изобразеиий SAR Итальянских морей. В частности, при условии слабого ветра изобразения SAR могут приводить к отобразению тропосферных вихрей. При условии сильоого ветра изобразения SAR долзны обнарузивать зффекты затенения объектов на поберезъе в поле ветра.

     

Experimental test of the EEC wind climatology model in a Mediterranean coastal area

Summary The analysis of 18 months of meteorological measurements collected in three stations located in Sardinia (Italy), is presented. The experimental wind distributions for 12 sectors of 30 degrees each have been fitted with the Weibull distribution function. The experimental Weibull parameters have been compared with the ones simulated by using the model produced within the EEC programme ?Wind Atlas for Europe?. Discrepancies between the experimental and simulated wind distributions have been discussed. Time series of the three stations have been compared to study the modification of the characteristics of the air flow from the coast to inland. Statistics of the atmospheric stratification, based on the concept of Pasquill stability classes has been produced by using semi-empirical methods. Further developments have been suggested.     

Synthesis of time series for the clearness index using a reordering algorithm

Summary Two insolation series, 4 and 8 years long, collected in different sites of the country, are used to contrast the behaviour of a statistical model for the clearness index, developed by the authors. This model is based on the independence between the stationary and the sequential statistic of clearness index series. A set of prospective clearness index coefficients is reordered until acquiring the sequential behaviour. A computer code has been developed to this end.     

The double cascade as a necessary mechanism for the instability of steady equivalent-barotropic flows

Summary In this paper we show that for a large class of steady solutions of the two-dimensional Euler equation and of the equation of conservation of potential vorticity for equivalent-barotropic flows, instabilities can grow only if their energy concentrates at length scales larger than that of the steady state. This possible growth of energy at large scales is accompanied by a corresponding growth of enstrophy at small scales. Such a distribution of energy and enstrophy, which is well known in the different context of two-dimensional turbulence, is therefore found to constitute a necessary mechanism for instability.

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Riassunto In questo lavoro mostriamo che, per una vasta classe di soluzioni stazionarie dell'equazione di Eulero bidimensionale e dell'equazione della conservazione della vorticità potenziale per flussi quasi geostrofici, le instabilità possono crescere solo se la loro energia si concentra a scale con lunghezza caratteristica piú grande di quella della soluzione stazionaria. Questa possibile crescita di energia a grande scale è accompagnata da una corrispondente crescita di enstrofia a piccola scala. Tale distribuzione di energia ed entrofia, ben nota in turbolenza bidimensionale, si dimostra essere un meccanismo necessario per l'instabilità.

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Резюме В этой работе мы показываем, что для большого класса стационарных решений двумерного уравнения Эйлера и уравнения сохранения потенциальной завихренности для эквивалентных баротропных потоков неустойчивости могут возрастатъ толъко в том случае, если их энергия концентрируется на масштабах с длинами, много большими, чем характерные длины стационарного состояния. Это возможное увеличение энергии на больших масштабах сопровождается соответствующим ростом ?энстрофии? на малых масштабах. Следовательно, указанное распределение энергии и ?энстрофии?, хорошо известное в двумерной турбулентости, представляет необходимый механизм для неустойчивости.

     

On sufficient conditions for global asymptotic stability of the barotropic fluid on a sphere

Summary Sufficient conditions are obtained for the global asymptotic stability of solutions to the vorticity equation for a forced barotropic viscous fluid on a rotating sphere. The Sundstr?m's requirements to the smoothness of the basic solution are weakened here, which makes it possible to apply these conditions to a wider class of the solutions, for example, modons, having continuous derivatives up to the second order only. The author of this paper has agreed to not receive the proofs for correction.     

Modelling the thermal pattern of a statue or column exposed to periodic lighting conditions

Summary In the case of monuments, the thermal effects due to periodic lighting conditions in the long run may be very dangerous. In this article the thermal response of a column or a statue cylindrically shaped and subjected to periodic lighting conditions is studied. Two sources are considered: in the first the intensity is time dependent according to a sinusoid (i.e. diffuse solar radiation from a skylight or window or partially closed outdoor environments); in the second according to a square-wave law (i.e. spot-light switched on and off). The model shows some characteristic features as a function of a dimensionless parameter μ, expressed as the ratio between the radius of the cylinder and its penetration depth, which takes into account the thermal properties of the substance and the lighting period. For high values of μ, the amplitude is poorly dependent on azimuth. The shadowed part is practically insensitive to the azimuth variation. For small values of μ the amplitudes of the thermal wave are very large, causing enhanced thermohydrometric cycles on the bodies. The phase lags between the different point depths increase with μ. The phase lags behave differently in three zones of the cylinder: i) the part facing the light, ii) the two transition zones, iii) the shadowed part. For small lighting durations and small μ the switching on or off of artificial light causes sudden and dangerous variations of temperature. Some hours after the switching off, all the surface of a cylinder with small μ reaches a homogeneous temperature. The mathematical analysis of the thermal behaviour of a cylinder shows how a physical simulation can be made, by changing radius, substance and lighting period, separately or together. Paper presented at the IV Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 22–24, 1987, Rome.     

A study of the global distribution of sulfate aerosols with a 2D model including microphysics

Summary The global distribution of sulfate aerosols in the troposphere and lower stratosphere has been calculated using a two-dimensional model. The chemistry includes the main families (NO _x , NO _y , HO _x ) plus the sulfur compounds, while the heterogeneous processes are modelled with a microphysics code which takes into account nucleation, condensation and coagulation. The results are compared with experimental data wherever available. A too low concentration of sulfuric acid is predicted by the model in the troposphere and this is explained by too large a flux of condensation nuclei and partly by the absence of sulfate production from methane sulfuric acid (MSA) in our scheme. Aerosol concentration and size distribution are comparable to observations; however the calculations show a more complex meridional structure than observed, while the size distribution is somewhat shifted toward smaller sizes. This fact is also attributed to the presence of a large number of nuclei and to the absence of any mechanism for evaporation of aerosol particles back to the core. We have also perturbed the anthropogenic fluxes of SO₂, CS₂ and the OCS ground mixing ratios to asses the sensitivity of the aerosol concentration: we have found very little changes in the aerosol distribution because H₂SO₄ chemistry is dominated by heterogeneous processes.