Dino Zardi

Mechanisms of Up-Valley Winds

The basic physical mechanisms governing the daytime evolution of up-valley winds in mountain valleys are investigated using a series of numerical simulations of thermally driven flow over idealized three-dimensional topography. The three-dimensional topography used in this study is composed of two, two-dimensional topographies: one a slope connecting a plain with a plateau and the other a valley with a horizontal floor. The present two-dimensional simulations of the valley flow agree with results of previous investigations in that the heated sidewalls produce upslope flows that require a compensating subsidence in the valley core bringing down potentially warmer air from the stable free atmosphere. In the context of the three-dimensional valley‐plain simulations, the authors find that this subsidence heating in the valley core is the main contributor to the valley‐ plain temperature contrast, which, under the hydrostatic approximation, is the main contributor to the valley‐ plain pressure difference that drives the up-valley wind.

Diurnal Mountain Wind Systems

Diurnal mountain wind systems are local thermally driven wind systems that form over mountainous terrain and are produced by the buoyancy effects associated with the diurnal cycle of heating and cooling of the lower atmospheric layers. This chapter reviews the present scientific understanding of diurnal mountain wind systems, focusing on research findings published since 1988. Slope flows are examined first, as they provide a good introduction to the many factors affecting diurnal mountain wind systems. The energy budgets governing slope flows; the effects of turbulence, slope angle, ambient stability, background flows and slope inhomogeneities on slope flows; and the methods used to simulate slope flows are examined. Then, valley winds are reviewed in a similar manner and the diurnal phases of valley and slope winds and their interactions are summarized. Recent research on large-scale mountain-plain wind systems is reviewed, with an emphasis on the Rocky Mountains and the Alps. Winds occurring in closed basins and over plateaus are then discussed, and analogies between the two wind systems are outlined. This is followed by a discussion of forecasting considerations for diurnal mountain wind systems. Finally, the chapter concludes with a summary of open questions and productive areas for further research.

Structure of the Atmospheric Boundary Layer in the Vicinity of a Developing Upslope Flow System: A Numerical Model Study

Abstract The development of a morning upslope flow is studied by means of idealized numerical simulations. In particular, two cases are examined: a plane slope connecting a lower plain and an elevated plateau and a symmetric mountain in the middle of a uniform plain. The analysis examines various steepness cases and aims at understanding the processes occurring in the area of transition between the upslope flow region and the convective boundary layers (CBLs) growing nearby. A characteristic sequence of events is recognized in the simulations, and their relationship with the along-slope variability of the thermal energy and turbulent kinetic energy budgets is studied. Features occurring after the onset of the upslope wind include a transient depression in the boundary layer depth at the base of the slope and the formation of elevated turbulent layers above the CBL, caused by the divergence of turbulent flow from a thermal plume at the slope top. Numerical evidence agrees well with the results of previous ...

Daytime Heat Transfer Processes Related to Slope Flows and Turbulent Convection in an Idealized Mountain Valley

Abstract The mechanisms governing the daytime development of thermally driven circulations along the transverse axis of idealized two-dimensional valleys are investigated by means of large-eddy simulations. In particular, the impact of slope winds and turbulent convection on the heat transfer from the vicinity of the ground surface to the core of the valley atmosphere is examined. The interaction between top-down heating produced by compensating subsidence in the valley core and bottom-up heating due to turbulent convection is described. Finally, an evaluation of the depth of the atmospheric layer affected by the slope wind system is provided.

Management of atmospheric pollutants from waste incineration processes: the case of Bozen:

This article presents the case study of a waste incinerator located in a region rich in natural and environmental resources, and close to the city of Bozen, where there are about 100,000 inhabitants. Local authorities paid special attention to the effect of the plant on human health and the surrounding environment. Indeed, among the measures adopted to control the emissions, in 2003 an automatic sampling system was installed specifically to monitor polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD/F) emissions during the complete operation time of the plant. The continuous sampling system was coupled directly to aerosol spectrometers for the determination of fine and ultra-fine particles in the emissions of the plant. The measurement results suggest that the waste incineration plant of Bozen is not a significant source of PCDD/F, or fine and ultra-fine particles. Immission measurements from other monitoring systems confirmed these results.

A Method to Determine the Capping Inversion of the Convective Boundary Layer

Abstract A simple mathematical algorithm is proposed to decipher the thermal structure of the convective boundary layer by means of best-fit analysis of soundings or airborne measurements with a smooth ideal profile. The latter includes a constant-potential-temperature mixed layer, a strongly stratified entrainment layer, and a constant-lapse-rate free atmosphere. The resulting profile depends on five parameters amenable, through simple mathematical relationships, to physical variables defining the vertical structure of the layers. The method allows objective evaluation of parameters involved in the test profile and easy comparison of measurements with theoretically expected structure.

PCDD/F enviromental impact from municipal solid waste bio-drying plant

The present work indentifies some environmental and health impacts of a municipal solid waste bio-drying plant taking into account the PCDD/F release into the atmosphere, its concentration at ground level and its deposition. Four scenarios are presented for the process air treatment and management: biofilter or regenerative thermal oxidation treatment, at two different heights. A Gaussian dispersion model, AERMOD, was used in order to model the dispersion and deposition of the PCDD/F emissions into the atmosphere. Considerations on health risk, from different exposure pathways are presented using an original approach. The case of biofilter at ground level resulted the most critical, depending on the low dispersion of the pollutants. Suggestions on technical solutions for the optimization of the impact are presented.

Analysis of the Urban Thermal Fingerprint of the City of Trento in the Alps

AbstractThe temperature contrasts typically marking urban heat island (UHI) effects in the city of Trento, Italy, located in an Alpine valley and inhabited in its inner urban area by a population of about 56 000, are investigated. Time series of air temperature data, collected at an urban weather station, in the city center, and at five extraurban stations are compared. The latter are representative of rural and suburban areas, both on the valley floor and on the valley sidewalls. It is found that the extraurban weather stations, being affected by different local-scale climatic conditions, display different temperature contrasts with the urban site. However, the diurnal cycle of the UHI is characterized by similar patterns of behavior at all of the extraurban weather stations: the UHI intensity is stronger at night, whereas during the central hours of the day an “urban cool island” is likely to occur. The diurnal maximum UHI intensity turns out to be typically of order 3°C, but under particularly favorabl...

Back-tracking water vapour contributing to a precipitation event over Trentino: a case study

The relation between individual precipitation patterns over an Alpine target area and the origin of the water vapour which contributes to them is investigated. Back-trajectories are calculated, starting from selected ending points over the target area, by means of the Lagrangian model FLEXTRA, on the basis of meteorological fields provided by ECMWF 4d-Var analysis data. Suitable clustering procedure is devised to identify representative flow patterns from calculated trajectories. The procedure is applied to a recent precipitation event (24-27 November 2002) adopted as a test case. The analysis allows to identify the contribution of various air streams to the precipitation, as well as the regions where most of the evaporation into the air streams occurred at various phases of the event.

Daytime Development of the Boundary Layer over a Plain and in a Valley under Fair Weather Conditions: A Comparison by Means of Idealized Numerical Simulations

AbstractThe daytime thermal structures of the valley boundary layer (VBL) and of the convective boundary layer (CBL) above a plain, as revealed by idealized large-eddy simulations, are compared. Simulations in the two environments consider similar thermal forcing, thus allowing an analysis of the atmospheric heating processes in the VBL and CBL in light of the volume-effect theory, traditionally invoked to explain the larger diurnal temperature ranges observed in valleys. It is found that, after an equal input of thermal energy, the atmospheric volumes affected by thermal perturbations in the CBL and in the VBL are comparable. Although the boundary layer top is higher in the VBL than in the CBL, the average VBL depth is approximately equal to the CBL depth, since the ground elevation is nonuniform in the valley. Accordingly, the volume-averaged potential temperature increments in the CBL and VBL are comparable. Nevertheless, surface air temperature variations are larger in the VBL, while differences in th...