Silvia Trini Castelli

COMPARISON AMONG EMPIRICAL PROBABILITY DENSITY FUNCTIONS OF THE VERTICAL VELOCITY IN THE SURFACE LAYER BASED ON HIGHER ORDER CORRELATIONS

Vertical velocity fluctuations were measured in theatmospheric surface layer by means of an ultrasonic anemometer andhigher order correlations were calculated on two time series, recordedin unstable and neutral conditions, and selected for the wholemeasurement period on the basis of the inversion test (stationaritytest). Comparisons have been made between observed and predictedcorrelations by considering Gaussian joint-PDF and Gram-Charlierseries expansions truncated to the fourth and sixth order as doneearlier by Frenkiel and Klebanoff. A bi-Gaussian PDF, given by amixture of two Gaussian PDFs, has also been considered. This lasthas been constructed assuming that either the first three or the firstfour moments are given, and the relationships between correlationfunctions of different order are derived. The departure from Gaussianbehaviour in both stability conditions is derived. Though Gram-Charlier series expansions show a good correspondence toexperimental reality, their use as non-Gaussian probabilitydistributions cannot be suggested in theoretical approaches andshould be considered with care in practical applications, due topossible occurrences of small negative probabilities. The resultsshown in this paper support the applicability of the bi-Gaussian PDFcreated using up to the fourth moment.

COST 732 in practice: the MUST model evaluation exercise

The aim of this paper is to describe the use of a general methodology tailored to the evaluation of micro-scale meteorological models applied to flow and dispersion simulations in urban areas. This methodology, developed within COST 732, has been tested through a large modelling exercise involving many groups across Europe. The major test case used is the Mock Urban Setting Test (MUST) experiment representing an idealised urban area. It is emphasised that a full model evaluation is problem-dependent and requires several activities including a statistical validation that requires a careful choice of the metrics for the comparison with measurements.

Turbulence Closures In Neutral Boundary Layer Over Complex Terrain

In this work, three turbulence closure models, Mellor andYamada level 2.5, E - l and E - ∈ implemented in a circulation model, are compared in neutral condition over complex terrain. They are firstly applied to a one-dimensional case on flat terrain and then to a schematic two-dimensional valley. The simulation results, in terms of wind field and turbulent kinetic energy, are tested against measurements from a wind-tunnel experiment. The empirical constants defining the characteristic length scales of the closures are modified based on turbulence parameters estimated in the experiment. The formulation of the diffusion coefficients is analysed to explain the differences among the various closures in the simulation results. Regarding the mean flow, both on flat and complex terrain, all the closures yield satisfactory results. Concerning the turbulent kinetic energy, the best results are obtained by E - l and E - ∈ closures.

Characterization of Wind Meandering in Low-Wind-Speed Conditions

Investigation of low-wind cases observed during the Urban Turbulent Project campaign (Torino, Italy) and at the Santa Maria meteorological station (Santa Maria, Brazil) provides insight into the wind-meandering phenomenon, i.e. large, non-turbulent oscillations of horizontal wind speed and temperature. Meandering and non-meandering cases are identified through analysis of the Eulerian autocorrelation functions of the horizontal wind-velocity components and temperature. When all three autocorrelation functions oscillate, meandering is present. As with weak turbulence, meandering shows no dependence on stability but is influenced by presence of buildings and depends on wind speed. We show that, while the standard deviation of the horizontal velocity is always large in low-wind conditions, the standard deviation of the vertical velocity shows very different behaviour in meandering and non-meandering conditions. In particular, the value of the ratio of the standard deviations of the vertical and horizontal velocities typifies the meandering condition.

Development and sensitivity analysis of a Lagrangian particle model for long range dispersion

Abstract A new long range dispersion model of Lagrangian particle type (MILORD) has been recently developed at the “Istituto di Cosmogeofisica”. Its capabilities have been tested by comparing its predictions with the Cs-137 air concentrations recorded over Europe by many laboratories during the Chernobyl accident. MILORD sensitivity to variations in its parametrizations has been studied and, in order to ascertain the accuracy of the simulations, some widely used statistical indexes and graphs have been computed. The study has made possible the accomplishment of a set of model input parameters able to produce the best agreement between observations and predictions. It is shown that this model was able to reconstruct with a good accuracy the main characteristics of the radioactive cloud spread over Europe.

Evaluation of Local-Scale Models for Accidental Releases in Built Environments: Results of the Modelling Exercises in Cost Action ES1006

A main research task of COST Action ES1006 is the evaluation of atmospheric dispersion models by their comparison against test data from qualified field and laboratory experiments and by a model inter-comparison. The model comparison and evaluation carried out for three test cases is presented, addressing the performance of the different modelling approaches, quantifying the scatter of results when different models are applied and assessing the effect of uncertainties.

Simulations of the dispersion from a waste incinerator in the Turin area in three different meteorological scenarios

A numerical modelling study for the assessment of the air quality impact of a waste incinerator to be built in the city of Turin is presented, aimed at evaluating the ground level concentration distribution during adverse dispersion conditions, causing severe pollution episodes. The pollutant impact of the incinerator is evaluated with the three-dimensional modelling system RMS. This class of models is essential to get reliable simulations in 3-D complex conditions. A comparison vs. observed wind data is presented and various parameters elaborated from the concentration values are discussed for three episodes, in critical meteorological conditions from the pollutant dispersion viewpoint.

Evaluation of Air Pollution Models for Their Use in Emergency Response Tools in Built Environments: The ‘Michelstadt’ Case Study in COST ES1006 ACTION

The first results of a model validation test case, carried out in the research context of the COST ES1006 Action, are outlined and discussed. The validation exercise was established with an application-oriented approach, devoted to the investigation of the modeling performances in the emergency-response framework.

Effect of the Turbulence Parameterizations on the Simulation of Pollutant Dispersion with the RMS Modelling System

The effect of using in dispersion modeling different parameterizations for the wind velocity fluctuations standard deviations is investigated for low-wind conditions.

Reviving MILORD Long-Range Model for Simulating the Dispersion of the Release during Fukushima Nuclear Power Plant Accident

This work focuses on long range dispersion using the numerical model MILORD, a Lagrangian particle model capable of simulating transport, dispersion, removal and deposition of tracers. The chosen case study concerns the release of Caesium isotope 137Cs from Fukushima Daichi nuclear plant caused by the earthquake and the subsequent tsunami in March 2011. 137Cs deposition in the affected area is reproduced from 11 March until the end of that month. In order to evaluate and improve the model, simulations results are compared to station measurements and a sensitivity analysis is performed. A comparison with results of other models is briefly discussed based on a statistical analysis.