Spectral characteristics of wind and air pollution data in an industrial area

Summary A comparison is made between the spectral features of sulfur dioxide concentration and zonal and meridional components of wind speed over a highly industrialized area situated on the coast. The paper focuses on the characteristic times of the meso-synoptic scale. Diurnal and longer period oscillations were identified. Variations of ground-level SO₂ concentrations are attributed to local sea-breeze circulation and to the synoptic weather period of wind speed.     

Spectral analysis and trend of total ozone observations at Vigna di Valle

Summary Time series analyses of measurements of total ozone make possible an in-depth climatological study of this important stratospheric gas. The Italian Air Force's Vigna di Valle Observatory (42°N, 12°E, 262 m a.s.l.) provided a time series of monthly averages (January 1958–December 1988) of total ozone. Spectral analysis and running averages were combined to detect medium-(QBOs of estimated (4÷5) DU amplitudes) and long-term fluctuations (possible correlation to 11-year solar cycle) and to filter them, leaving any overlapping trends unaltered. Total ozone trend estimates produced by the present study were +0.1% per decade for the 1959–1987 period and a decrease of −0.4% per decade for the more recent 1970–1987 span, over which a pronounced ozone depletion caused mainly by CFCs is assumed. This study has supported by the CNR-ENEL Project ?Interaction of energy system with human health and environment?.     

Internal boundary layer at coastal sites

Summary The problem of the internal boundary layer (IBL) development at two Italian coastal sites (La Spezia and Montalto di Castro) has been investigated. Among the numerous IBl empirical models found in the literature, which are briefly introduced and discussed, we choose the Nanticoke model because it seems to deal with the physical problem in a more complete and satisfactory way. In fact it explicitly considers two different time scales (the advective and the diurnal one) contemporary acting on the phenomenon. The results of the comparison between the measured data and the ones calculated by means of the Nanticoke model were encouraging even if the influence of the complex topography and orography was felt.

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Riassunto Nel presente lavoro è stato affrontato e studiato lo sviluppo dello strato limite interno (IBL) in due siti costieri italiani (La Spezia e Montalto di Castro). Tra i numerosi modelli presenti in letteratura, che sono stati qui brevemente illustrati e discussi, è stato scelto il modello di Nanticoke. Tale modello infatti sembra essere quello che affronta il problema nel modo piú soddisfacente poiché considera esplicitamente due differenti scale temporali (quella avvettiva e quella diurna) che agiscono contemporaneamente sul fenomeno. I risultati del confronto tra i dati misurati e quelli calcolati per mezzo del modello di Nanticoke sono stati incoraggianti, nonostante fosse sensibile l'influenza delle complessità orografiche e topografiche.

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Резюме В этой работе исследуется проблема внутреннего пограничного слоя в двух точках итальянской береговой линии. Среди многочисленных эмпирических моделей внутреннего пограничного слоя, имеющинся в литературе, которые вкратце рассматриваются и обсуждаются, мы выбираем, модель Нантикука. Эта модель рассматривает физическую проблему более полно и последовательно, в ней учитываются два различных временных масштаба, одновременно влиьющих на исследуемое. явление. Результаты сравнения экспериментальных и расчетных данных являются обнадеживающими, несмтря на влияние сложной топографии и орографии.

     

Physical and mathematical analysis of a wind model

Summary We have carried out a mathematical and physical analysis of the instabilities present in a one-layer wind model. The single terms of the basic equation have been discussed, pointing out their influence on the accuracy of the solution and their relationship to the possible instabilities. Possible improvements of the model in different directions are indicated in the final discussion.

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Riassunto Si effettua un’analisi matematica e fisica delle instabilità presenti nel modello del vento ad uno strato. Si discutono i singoli termini dell’equazione di base, sottolineando la loro influenza sulla accuratezza della soluzione e la loro relazione con le instabilità possibili. Nella discussione finale si indicano possibili miglioramenti del modello in diverse direzioni.

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Резюме Проводится математический и физический анализ неустойчивостей, возникающих в одно-слойной модели ветра. Обсуждаются отдельные члены базисного уравнения. Отмечается влияние этих членов на точность решения и их связь с возможными неустойчивостями. Указываются возможные улучцения обсуждаемой модели в различных напавлениях.

     

Preliminary analysis of the turbidimetric characteristics of the Bruncu Spina (Sardinia) radiometer station

Summary Observations carried out at the radiometric station of Bruncu Spina (Sardinia, altitude 1825 m) for the determination of turbidimetric characteristics are analysed and discussed. Diurnal evolution of the turbidimetric parameters α and β is emphasized. The values of the turbidity coefficient β show particularly low aerosol concentration in the site. A comparison among turbidimetric characteristics of different radiometric stations confirms the existence of a correlation between the radius of aerosol particles and the altitude of the sites. An analysis of the spectral variations of optical thickness shows a characteristic diurnal variation and a fall of the optical depth in correspondence of the peak of the visible.

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Riassunto Si discutono una serie di osservazioni condotte con un fotometro a tre canali relative alla determinazione del contenuto in aerosol dell'atmosfera in località ?Bruncu Spina? (Monte Gennargentu 1825 m s.l.m. Sardegna). I dati di osservazione sono analizzati e si dà una preliminare valutazione delle caratteristiche turbidimetriche del sito, con particolare riferimento alla variazione diurna del contenuto di aerosol ed alle caratteristiche della variazione spettrale dello spessore ottico. Un confronto fra le caratteristiche dimensionali delle particelle di aerosol di diverse stazioni radiometriche mostra una correlazione tra raggio delle particelle e quota delle stazioni.

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Резюме Анализируются и обсуждаются результаты наблюдений, проведенных на радиометрической станции ?Брунку Спина? (в Сардинии, на высоте 1825 м). для определения нефелометрических характеристик. Отмечается суточное изменение нефелометрических параметров α и β. Значения коэффициента мутности β, в частности, показывают низкую концентрацию аэрозоля в этом месте. Сравнение нефелометрических характеристик, полученных на различных радиометрических станциях, подтверждает существование корреляций между радичсом аэрозольных частиц и высотой расположения станций. Анализ спектральных изменний оптических толщин обнаруживает характерное суточное изменение и уменьшение оптической толщины, соответствующее пику видимости.

     

Climatological study of air trajectories arriving at three alpine sites

Summary Within the frame of the EUROTRAC project and in collaboration with ENEL/C.R.T.N. of Milan, a research activity aiming at a meteorological interpretation of smaples of trace chemical compounds collected in alpine glaciers started. With reference to that, availing ourselves of a wind data set coming from the ECMWF analysis, backward air trajectories arriving at three alpine sites six hours for five years (1981–1985) have been computed. The origin of the trajectories at various distances has been evidentiated through their partition in sectors and in altitude.     

Spectral transfer for scalars in inhomogeneous turbulence

Summary The two-point correlation equation is constructed for reactant and product of reaction and it is shown that for this case, certain terms can be interpreted as transfer terms, even for a general inhomogeneous turbulence. This result is also true for any correlation between scalars (temperature, humidity, carbon dioxide, concentration of tracer or contaminant, ect.) and correlation between scalar and velocity field.     

Observations and simulations with linked numerical PBL and air pollution models and a Gaussian model under low wind speed conditions: a case study of the urban-industrial Linz area

Summary A one-week-long field study was carried out to investigate dispersion conditions and SO₂ patterns under low wind speed conditions in the industrial city of Linz. Meteorological fields generated with the URBMET PBL model were used as input for a 28 hour simulation of the SO₂ concentrations with a Eulerian model. Results were compared with the operational Gaussian model of the Austrian meteorological service. On the basis of balloon soundings at two sites, horizontal temperature profiles evaluated from car trips and the stationary observational network wind, temperature and SO₂ patterns were analysed and used to evaluate model results. Paper presented at the GNFAO/EURASAP Meeting, Turin, September 1989. To speed up publication, proofs were not sent to the authors and were supervised by the Scientific Committee.     

Pluviometric pattern of the Island of Sardinia with regard to extreme precipitations related to meteorological and climatological conditions

Summary The pluviometric characteristics of Sardinia are given by the analysis of the island’s geomorphological pattern and of the various types of weather mostly affecting such Mediterranean area during autumn and winter seasons.     

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.     

Model of mesoscale wind field obtained from SAR marine images

Summary Wind parameters are directly extracted from marine SAR images by deducing wind stress intensity from a model of pixel statistics, and wind vector at 10 m height from spectral analysis of the mesoscale turbulence present in the stress signature.

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Riassunto I parametri del vento frizionale sono estratti direttamente da immagini SAR deducendo la velocità frizionale da un modello che si basa sulla statistica dei pixel. La direzione e la stabilità atmosferica da una analisi della turbolenza a mesoscala ricavata da appropriate sub-immagini.

     

Dispersion simulation of a wind tunnel experiment with Lagrangian particle models

Summary A particle model LAMDA suitable for dealing with the atmospheric dispersion is presented. The reliability of the model is tested comparing the results of its simulations to the wind tunnel measurements by Khurshudyanet al. (1981). Two versions of the model, both based on the Langevin equation and askewed distribution of the vertical wind velocity fluctuations, are considered. To develop the second version of the model we derived a proper scheme to produce skewed distributions of particle velocities consistent with the observed first and second moments of turbulent fluctuating velocities, with their horizontal and vertical derivatives, and their cross-correlations. The 2D geometry of the obstacle (in the wind tunnel experiment considered) allowed some simplifications. Due to the lack of some input data (such as the vertical profiles of crosswind standard deviation of wind velocity fluctuations and of the Lagrangian time scales) we looked for three different parametrizations. It was found that particular combinations of measured and parametrized data could give rise to critical vertical regions in which the derived scheme for the generation of random vertical velocity fluctuations cannot be applied. The best vertical distributions of the Lagrangian time scales (third parametrization) were estimated by fitting simple formulations for the average plume height and lateral variances to the measured data. The main results of this work were the model performance in simulating dispersion in shear flow over flat terrain, and its sensivity to the shape of the crosscorrelation term .     

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.

     

A diagnostic study of turbulence features in wind tunnel flow over simple topographic shapes

Summary The turbulence features observed in wind tunnel experiments of flow over isolated simple-shaped two-dimensional hills and valleys are analysed in the light of transport equations of Reynolds stresses in the streamline coordinate system. The analysis has shown that near the surface the streamwise pressure gradient is the driving parameter for all the stresses. At higher levels, the effects of streamline curvature and streamwise pressure gradient act differently on the source terms of stresses, showing that the shear stress is the most sensitive to streamline curvature, whereas the streamwise stress is the most sensitive to streamwise pressure gradient. Although two of the considered topographies are specular images, the turbulence response is not so, since it depends on the sequence of curvatures to which it is subjected. The information and analysis presented will constitute a valuable resource to those seeking an understanding of atmospheric boundary layer development over complex terrain. It will also provide a support for the development and validation of more rigorous turbulence models.     

Nondimensional temperature and wind profiles and their changes under the influence of terrain and stability conditions

Summary The object of this paper is to present some of the results obtained by the analysis of the set of vertical profile measurements of momentum and temperature fluxes, of the mean wind speed and temperature. The conditions of validity of the Monin-Obukhov theory over a complex terrain are discussed. Paper presented at the GNFAO/EURASAP Meeting, Turin, September 1989. To speed up publication, proofs were not sent to the author and were supervised by the Scientific Committee.     

The Chernobyl accident: the radioactive contamination in the area of Lake Como and in other Northern Italy sites

Summary The radioactive cloud released during the Chernobyl accident reached the Po Plain and Lombardy in the night of April 30, 1986; the cloud remained in the northern Italian skies for a few days and then disappeared either dispersed by winds or washed by rains. The evidence in the atmosphere of radionuclides as tellurium, iodine, cesium was promply observed by the Istituto di Fisica. The intense rain, in the first week of May, washed the radioactivity and the fallout contaminated the land, soil, grass and vegetables. The present work concerns the overall contamination of the Northern Italy territory and in particular the radioactive fallout in the Alpine region. Samples of soil have been measured at the gamma-spectroscope; a linear correlation is found between the radionuclide concentration in soil samples and the rain intensity, when appropriate deposition models are considered. A number of measurements has been done on Lake Como ecosystem: sediments, plankton, fishes and the overall fallout in the lake area have been investigated.

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Riassunto La nube radioattiva sprigionatasi nel corso dell'incidente al reattore nucleare di Chernobyl si è dispersa nei cieli lombardi fra la notte del 30 aprile 1986 e i primi giorni di maggio. La presenza di radioelementi nell'aria—tellurio, iodio, cesio—è stata osservata dalle numerose stazioni operanti nella pianura padana. Le piogge dei primi giorni di maggio, cadute soprattutto nelle zone prealpine, hanno trascinato al suolo consistenti quantità di radioelementi. Al fine di rilevare la correlazione fra pioggia e ricadute sono stati prelevati oltre un centinaio di campioni di terreno; i contenuti di radioelementi, e in particolare il cesio, sono misurati a mezzo di spettrometro gamma e risultano in buon accordo con i modelli di deposizione. Si rilevano particolarmente elevati i livelli di ricaduta nella zona del lago di Como e delle adiacenti vallate; un esame dei contenuti di radioelementi nell'ecosistema lacustre completa l'analisi.

     

Characteristics of high-frequency atmospheric eddies over the mediterranean area in different seasons

Summary We examine the properties of atmospheric eddies over Europe and the Mediterranean, as revealed by an analysis of high-pass filtered time series of geopotential height. The data used are seven years of 6-hourly initialized analyses, prepared at ECMWF. The application of a time-filter with cut-off around 6 days allows us to isolate the variability associated with travelling eddies, which generally come from the Atlantic and whose properties (spatial structure, propagation characteristics) are deeply modified when they pass over the Mediterranean region. Different statistical indicators have been derived to reveal these modifications, that are particularly evident in the lower troposphere. It appears that the orography surrounding the Mediterranean region is the main factor influencing eddy behaviour. This conclusion is supported, among other considerations, by the comparison between winter and summer statistics: notwithstanding the different climatological properties of the mean atmospheric circulation and of the surface heat fluxes in the two seasons, some peculiar properties of the high-frequency components over the European and Mediterranean region, such as the vertical and horizontal structure, do not vary much as a function of the season.

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Riassunto Sono esaminate le proprietà dei vortici atmosferici sull'Europa e il Mediterraneo, mediante un'analisi di serie temporali di altezza di geopotenziale, filtrate con un filtro passa alto. I dati utilizzati sono costituiti da sette anni di analisi inizializzate, disponibili ad intervalli di 6 ore, preparate dal Centro Europeo di Previsione Meteorologica a Medio Termine (ECMWF). L'applicazione di un filtro temporale con un periodo di taglio di circa 6 giorni permette di isolare la variabilità associata con vortici viaggianti che generalmente provengono dall'Atlantico e le cui proprietà (struttura spaziale, caratteristiche di propagazione) sono profondamente modificate allorquando essi transitano sopra la regione mediterranea. Sono stati calcolati diversi indicatori statistici allo scopo di rivelare tali modifiche, che sono particolarmente evidenti nella bassa troposfera. L'orografia che circonda la regione mediterranea rappresenta il fattore principale che influenza il comportamento dei vortici. Questa conclusione è rafforzata, fra l'altro, dal confronto tra le statistiche riferite ai periodi invernale ed estivo: nonostante le differenti proprietà climatologiche della circolazione atmosferica media e dei flussi di calore alla superficie durante le due stagioni, alcune proprietà peculiari delle componenti di alta frequenza della circolazione sulla regione europea e mediterranea, quali la struttura orizzontale e verticale, non variano molto in funzione della stagione.

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Резюме Мы исследуем свойства атмосферных вихрей над Европой и над Средиземным морем, которые были обнаружены при анализе фильтрованных временных последовательностей для геопотенциальной высоты. Данные собирались в течение семи лет. Применение временного фильтра с обрезанием в 6 дней позволяет нам выделить изменчивость, связанную с перемещаюимися вихрями, которые обычно приходят из Атлантики и чьи свойства (пространственная структура, характеристики распространения) сильно изменяются, когда вихри проходят над областью Средиземного моря. Используются различные статистические индикаторы, чтобы обнаружить эти изменения, которые наблюдаются в нижней части тропосферы. Оказывается, что орография, окружающая область Средиземного моря, является основным фактором, влияющим на поведение вихрей. Это утверждение подтверждается также сравнением зимней и летней статистик: несмотря на различные климатологические свойства средней атмосферной циркуляции и поверхностных потоков в течение двух сезонов, некоторые свойства высокочастотных компонент над Европой и областью Средиземного моря, такие как вертикальная и горизонтальная структуры, существенно не изменяются в зависимости от сезона.

     

A note on instabilities of a Kelvin-Helmholtz velocity profile in different approximations

Summary The Kelvin-Helmholtz problem deals with the stability of superposed fluids in relative motion. For a basic discontinuity in the velocity of 2U and a constant Brunt-V?is?l? frequencyN it has been found that in the Boussinesq approximation small perturbations with a horizontal wavenumberk, such thatk ²>N ²/2U ², are unstable. When the fluid is assumed to be compressible and taking into account the variation of the density in all the equations we find that there are also instabilities fork ²<N ²/2U ². However, the growth rate of these instabilities is small. The horizontal phase velocities of the instabilities are also different from those obtained in the Boussinesq approximation. But again the difference is small. On the other hand, in the hydrostatic approximation, which takes into account the compressibility too, all instabilities disappear.     

Dependence of the wind profile power law exponent on the Pasquill stability classes and height interval in a stably stratified surface boundary layer.

Summary Using the logarithmic wind profile under stable stratification, a classification scheme was obtained for the Monin-Obukhov stability length and for the wind profile power law exponent in terms of the surface roughness length and the PasquillD-G stability classes, anywhere in the surface layer.     

Climatologies of tides at mid-latitudes in the lower thermosphere

Summary Time variations of the semi-diurnal and diurnal tides observed at Budrio (45°N, 12°E) in the wind structure of the lower thermosphere ((80÷110) km) throughout the period 1976–1990 are herewith represented as monthly contours of both amplitudes and phasesvs. height. The semi-diurnal tide has more marked seasonal variations, showing amplitudes generally larger than the diurnal ones ((10÷30) m/svs. (5÷15) m/s). The vertical wavelengths are longer in summer than in winter, at least below 100 km. Agreement with new numerical models for semi-diurnal tide at 50°N appears to be satisfactory.