Stratospheric heating due to El chicon volcanic eruption: Preliminary results using a 3D model

Summary Changes in the stratospheric temperature due to the presence of volcanic aerosols from E1 Chichon eruption have been calculated with the MIT-GIT quasi-geostrophic general circulation model with the addition of the continuity equation for the aerosols. Heating rates are calculated by taking into account the contribution of both solar and planetary radiation. The heating parametrization uses a method based on a simplified delta-Eddington approximation. The infra-red contribution is obtained calculating the emissivity for a given composition of dust. For this purpose a multiple scattering radiative code has been used assuming a 75% sulfuric-acid composition for the aerosols. Results are reported for the second month of our numerical experiment (about four months after the eruption). In particular an analysis is made of the temperature differences calculated between a control, unperturbed run and an interactive, perturbed run in which the aerosol-induced heating is taken into account. Paper presented at the 1° Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 19–22, 1984, Rome.     

Simulation of monthly mean circulation anomalies using a linear anomay model

Summary The El Ni?o event of 1982–1983 is studied using a linearized model derived from a complete GCM. The model describes the response to a heating distribution of an atmosphere with fully tridimensional basic state. The numerical results show that the 1983 circulation can be reasonably simulated by idealized heating distributions, but better results are obtained if heating derived from observed Outgoing Longwave Radiation (OLR) is used. The usage of a fully tridimensional basic state also improves the simulation over traditional zonally symmetric models. Extension of the simulations to other years (Januaries 1977–1984) yields some exceptional good case, but mixed results in most cases.     

Calibration with experimental data of a 2D sea breeze model by heating parametrization

Summary A new scheme of vertical distribution of sensible heat flux has been introduced in a bidimensional numerical sea breeze model which uses a prescribed flux at the ground. The scheme has been suggested by inspection of thermal and dynamical fields observed during a case study along the coast of northern Adriatic Sea. Agreement with data is shown to be considerably increased.

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Riassunto Un nuovo schema per la distribuzione verticale del flusso di calore sensibile è stato introdotto in un modello bidimensionale di brezza di mare in cui l’input termico è dato dal valore al suolo del flusso stesso. Lo schema è stato suggerito dall’analisi dei campi termici e dinamici osservati durante un ?case study? nel comprensorio Alto Adriatico, ed ha contribuito a migliorare sensibilmente i risultati della simulazione.

     

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.     

Preliminary results on a study of stratospheric aerosol loading by means of Lidar analysis of long- and short-time fluctuations

Summary Lidar stratospheric aerosol measurements have been carried out at IROE since April 1982, just after the eruption of the Mexican volcano El Chichon. Over two years evolution in stratospheric aerosol loading has been monitored and compared with data collected by other stations. Since the Lidar system can perform an average signature, every minute, also short-time fluctuations in Lidar signatures have been analysed in order to obtain information on stratospheric air turbulence and on the possible presence of gravity waves Paper presented at the 1^o Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 19–22, 1984, Rome.     

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.     

A simple model of summer atmospheric circulation in the Po Valley

Summary Through numerical integration of the primitive equations, we study the summer circulation in the Po Valley, Italy. We investigate separately the mountain slope effect and the sea-breeze effect. The results show that, because of the mountain slope, there is convergence early in the morning and divergence during the day in the lower atmosphere. Further-more, the sea breeze generated by the Adriatic Sea is confined to the eastern side of the Valley. These two phenomena are expected. However, the model suggests that the convergence due to the slope is organized in an area as large as the valley and that, even if the sea breeze is a boundary layer circulation, the perturbation introduced triggers a train of gravity waves as deep as the troposphere. These effects might be very important for the distribution of the summer thunderstorms. Further specific investigations. Experimental and theoretical, are needed. Paper presented at the 1° Congresso del Gruppo Nazionale per la Fisica dell'At-mosfera dell'Oceano, June 19–22, 1984, Rome.     

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.

     

Multiple equilibria and their stability in a baroclinic two-layer model

Summary We examine a two-layer highly truncated channel model with topography to study multiple equilibria and to discuss their stability. We find that all the Charney-Straus multiple equilibria require meridional temperature gradients which are highly baroclinically unstable. After a detailed study we demonstrate that the flux of angular momentum from tropical latitudes is able to produce one equilibrium which is baroclinically stable (in the low-layer model). For low values of the external radiation heating the stationary topographically forced wave alone satisfies all the balances, while for larger values of the external radiation forcing the stationary topographically forced wave collaborates with shorter, more baroclinically unstable, moving, synoptic-scale waves.

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Riassunto Abbiamo effettuato uno studio sugli equilibri multipli e sulla stabilità delle onde planetarie forzate dalla topografia in un modello quasi geostrofico a due livelli troncato. Abbiamo mostrato che tutti gli equilibri trovati da Charney-Straus sono baroclinicamente instabili rispetto ad alcune onde su scala sinottica. Dopo uno studio dettagliato abbiamo dimostrato che l’introduzione di un flusso di momento angolare dalle zone tropicali nelle medie latitudini è in grado di produrre un equilibrio baroclinicamente stabile. Per bassi valori del riscaldamento solare, l’onda forzata planetaria soddisfa da sola tutti i bilanci, mentre per valori piú grandi del riscaldamento solare l’onda forzata planetaria collabora con onde sinottiche.

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Резюме Исследуются множественные положения равновесия и их устойчивость относительно планетарных волн, форсированных топографией, в двух-слойной усеченной модели. Показывается, что все положения равновесия, обнаруженные Шане-Штраусом являются бароклинно неустойчивыми относительно волн синоптического масштаба. После подробного изучения, мы показываем, что поток момента из тропических широт создает положение равновесия, которое является бароклинно устойчиным (в двух-слойной модели). В случае малых величин внешнего излучения форсированная планетарная волна удовлетворяет всем соотношениям баланса, тогда как для больших значений внешнего излучения форсированная планетарная волна сотрудничает с синоптической волной.

     

Experimental results on atmospheric dynamical and thermal structures modeled in a rotating hydraulic channel

Summary The operation characteristics of a rotating hydraulic channel, designed for geophysical fluid-dynamic research, are described. The results of simulations concerning the conditions of motion and density stratification of the atmospheric planetary boundary layer, both stationary and in evolution, are then presented.

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Riassunto Si descrivono le caratteristiche funzionali di un canale idraulico rotante realizzato per ricerche di fluidodinamica geofisica. Vengono presentati i risultati delle simulazioni concernenti le condizioni di moto e di stratificazione di densità, stazionarie e in evoluzione, dello strato limite planetario dell'atmosfera.

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Резюме Описываются характеристики вращающегося гидравлического канала, сконструированного для исследования геофизической гидродинамики. Приводятся результаты моделирования, относящиеся к условиям движения и стратификации плотности атмосферных планетарных граничных слоев, во время эволюции и в стационарном случае.

     

Sensitivity analysis of a Monte Carlo atmospheric diffusion model

Summary A Monte Carlo model simulating atmospheric transport and diffusion in the PBL is presented. In a previous study, it was shown that it works well in homogeneous turbulence and fits well the Willis and Deardorff water tank simulations in convective nonhomogeneous conditions. In the present paper a sensitivity analysis aimed at estimating the importance and effectiveness of the model parameters is performed and discussed. Our model makes use of Hanna's scheme for the vertical structure of the turbulent parameters, and of an empirical parametrization of updrafts and downdrafts in convective unstable conditions. Emitting the particles either from a point source or uniformly distributed along the vertical we found that the model avoids the particle accumulation at the top and bottom of the PBL and recovers the Eulerian turbulent statistics. This demonstrates that our numerical scheme is consistent with the physical constraints,i.e. mass and energy are preserved and an initial uniform distribution remains so. Finally it is shown that considering the contribution of the cross-correlation term does not improve significantly the model performances.

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Riassunto Si presenta un modello Monte Carlo atto a simulare il trasporto e la diffusione nello strato limite atmosferico che era stato validato in uno studio precedente ove si era trovato che esso lavora bene in condizioni di turbolenza omogenea e riproduce bene i risultati delle misure in vasca idraulica di Willis e Deardorff relativi a condizioni di turbolenza non omogenea. Nel presente lavoro è stata effettuata un'analisi di sensitività del modello volta alla valutazione dell'importanza ed efficacia dei parametri del modello stesso. Esso utilizza lo schema di Hanna per la descrizione dell'andamento verticale dei parametri turbolenti in atmosfera ed una parametrizzazione empirica delle celle convettive in condizioni instabili. Emettendo le particelle sia da una sorgente puntiforme, sia distribuite uniformemente lungo la verticale si è trovato che il modello evita l'accumulo di particelle ai limiti superiore ed inferiore del PBL e conserva la statistica euleriana delle grandezze turbolente. Ciò dimostra che il nostro schema numerico è fisicamente consistente dato che soddisfa i seguenti vincoli fisici: la massa e l'energia sono conservate ed una distribuzione iniziale uniforme rimane tale. Infine, si è mostrato che il considerare il contributo del termine di cross-correlazione non migliora in modo significativo le prestazioni del modello.

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Резюме Предлагается модель Моите Карло для моделирования процессов диффузии и переноса в атмосфере. Ранее было показано, что эта модель хорошо работает в условиях однородной турбулентности и хорошо воспроизводит результаты Виллиса и Дирдорфа измерений в водоеме при условиях неоднородной турбулентности. В данной статье проводится и обсуждается анализ чувствительности с целью определения важности и эффективности параметров модели. В предложенной модели используется схема Хана для вертикальной структуры параметров турбулентности атмосферы и эшпирическая параметризация для конвективных ячеек в нестационарных условиях. Испуская частиы либо из точечного источника, либо из однородно распределенных источников вдоль вертикали, мы находим, что модель не дает накапливания частиц на верхней и нижней границах PBL и сохраняет Эйлерову статистику турбулентности. Мы показываем, что наша численная схема согласуется с физическими ограничениями: масса и энергия сохраняются и начальное однородное распределение остается тем же. В заключение покаывается, что рассмотрение вклада перекрестного члена значительно не улучшает характеристики модели.

     

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.     

Development of a boundary layer model for evaluation of dispersion in complex terrain

Summary Trajectories in the turbulent boundary layer have been computed using a dynamic model, for a separating and a nonseparating case. The turbulent kinetic energy, the eddy diffusion coefficient and the hill factor have been evaluated along the trajectories, to get some insight into the different dispersion properties of such flows. Paper presented at the IV Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 22–24, 1987, Rome.     

A climatological diffusion model for ground level and elevated emissions in a weak-wind area

Summary This paper presents a climatological diffusion model for computing seasonal sulphur dioxide concentrations. The area under investigation is located in the Po Valley (Northern Italy), and is characterized by prevailing conditions of weak winds, with the presence of mountain and valley breeze. A large number of sulphur dioxide sources are located in this area: they are both urban emissions (due to home heating) and industrial emissions. A physical parametrization of the planetary boundary layer was achieved by using the results of experimental campaigns in the site. A detailed source inventory was compiled in order to supply correct input to the model. The paper presents the results obtained by simulations over a period of 2 years. The agreement between measured and computed concentrations confirms the soundness of the physical parametrizations of the model and makes it suitable to use it for planning future urban and industrial emissions in the area.

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Riassunto In questo lavoro si presenta un modello climatologico per lo studio della concentrazione media stagionale di anidride solforosa al suolo. L'area in esame è situata nella pianura Padana ed è caratterizzata da condizioni prevalenti di vento debole, con la presenza di brezze di monte e di valle. In questa zona sono presenti un numero elevato di sorgenti di diversa origine: emissioni urbane (dovute al riscaldamento domestico) ed emissioni industriali. La parametrizzazione fisica dello strato limite planetario è stata resa possibile dalla disponibilità di dati provenienti da campagne di misura effettuate in sito. Allo scopo di fornire al modello un corretto input si è dovuto effettuare un grosso sforzo per compilare un inventario delle sorgenti. In questo articolo si presentano i risultati ottenuti simulando un periodo di due anni. L'accordo tra i dati sperimentali e le concentrazioni simulate dimostra la corretta parametrizzazione del modello e lo rende disponibile come strumento di pianificazione delle emissioni urbane ed industriali nell'area in esame.

     

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.     

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.     

SO2 cooling and detection of the greenhouse effect

Summary Greenhouse effect calculations normally take into account the greenhouse gases’s (CO₂ mainly) warming effect. Only recently the inclusion of the cooling effect due to different gases (SO₂ mainly) has been suggested. Zecca and Brusa have proposed that the historical evolution of SO₂ production might have caused the apparent global cooling in the period 1940–1970 and might still now hinder the detection of greenhouse warming. In this paper it is shown that the SO₂ hypothesis could lead to a definite detection of the greenhouse warming provided that the globally averaged minimum daily and maximum daily temperatures were studied.     

Atmospheric CO2 and destructivity of the land biota: Seasonal variations

Summary The seasonal variations of the carbon content in the ocean are shown to be small as compared to those taking place in the atmosphere. Atmospheric meridional mixing is not intense enough to compensate for the variations of the atmospheric CO₂. If we assume meridional mixing to be zero, then the seasonal variations of carbon in the atmospheric column should be equal to those of carbon in the continental bionass but opposite to them in sign. This latter value is essentially the difference between productivity and destructivity of the land biomass Productivity of humid areas at any latitude is proportional to the diurnal mean solar radiation flux at that latitude. In the present study the temporal variations of this flux are harmonically approximated. Further, an harmonic approximation is found for expressing the temporal course of biomass destructivity at various latitudes. Productivity/destructivity oscillations appear to be almost in couterphase but amplitudinally close to each other.

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Riassunto Le variazioni stagionali del contenuto di carbonio nell'oceano sono piccole rispetto a quelle che si verificano nell'atmosfera. Il mescolamento atmosferico meridionale non è abbastanza intenso da compensare le variazioni del CO₂ atmosferico. Se si ammette che il mescolamento sia zero, le variazioni stagionali del carbonio nella colonna atmo-sferica dovrebbero essere uguali a quelle del carbonio nella biomassa continentale ma opposte a queste ultime come segno. Quest'ultimo valore è essenzialmente la differenza tra la produttività e la distruttività nella biomassa terrestre. La produttività delle aree umide ad ogni latitudine è proporzionale al flusso di radiazione solare diurno medio a quella latitudine. In questo studio si approssimano armonicamente le variazioni temporali di questo flusso. Inoltre si trova un'approssimazione armonica per esprimere l'andamento temporale della distruttività della biomassa a varie latitudini. Le oscillazioni di producttività/distruttività sembrano quasi in controfase ma prossime l'una all'altra per quanto riguarda l'ampiezza.

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Резюме Показано, что сезонные изменения содержания углерода в океане малы по сравнению с изменениями в атмосфере. Меридионаляное перемешивание атмосферы не успевает выравнивать атмосферные колебания CO₂. В приближении нулевого меридионляного перемешиваиия сезонные колебания содержания углерода в атмосферном столбе равны по величине и противололожны по знаку изменению содерзания углерода в континентальной биомассе, иоторое равно разности продуктивности и деструктивности. Продуктивность гумидных областей на разных широтах пропорционаляна среднесуточному потоку солнечной радиации на зтих широтах. В работе найдено гармоническое привлижение для изменения во времени последних величин. С помощью зтих данных определено гармоническое приближение для поведения во времени деструктивности на ражных широтах. Колебание продуктивности и деструктивности оказались происходящими почти в противофазя с близкими по величине амплитудами.

     

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.

     

Measurements of vertical kinematic eddy sensible heat flux by means of a doppler sodar and a cryogenic radiometer

Summary Radiative and dynamical energy exchanges in the planetary boundary layer are investigated by the simultaneous operation of a triaxial Doppler sodar, a zenith-pointing cryogenic radiometer with a bandpass centred around 850 μm wavelength, and additional meteorological equipment for near-ground reference. The two instruments provide measurements of the wind field and of the atmospheric radiative temperature, respectively. Two measurement campaigns were carried out in the Rome area in the periods 12–18 Sept. 1990 and 16–22 Sept. 1991. Data were analysed for correlation and used to calculate kinematic eddy sensible heat fluxes. Depending on the meteorological conditions, high values of correlation were found between the fluctuations of the height-averaged (300 m) vertical wind speed and the radiative temperature, in the presence of clear-sky convection. The highest values of correlation were obtained for delays of a few minutes, as expected in agreement with typical dimensions of convective structures in the boundary layer. Estimates of the kinematic eddy sensible heat flux gave average values as high as 0.14 K m s⁻¹ in daytime and 0.005 K m s⁻¹ at night.