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Analysis of the turbulence parameterisations for the atmospheric surface layer
Caggio, Matteo ; Bodnár, Tomáš
The purpose of this short communication is to present a method that aims to express the turbulent variables in the atmospheric surface-layer in function of the stability of the atmosphere. The case of very stable conditions (strong strati cation), where theoretical approaches provide conflicting results (see Luhar et al. [11]), is analysed in detail to provide some insight into the limits of applicability for some of the most popular models of turbulence. The problem of the existence of the critical flux Richardson number is also taken into account.
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Urban Ventilation Dependence on Geometric Configuration
Kukačka, Libor ; Jaňour, Zbyněk (advisor) ; Carpentieri, Matteo (referee) ; Uruba, Václav (referee)
Title: Urban Ventilation Dependence on Geometric Configuration Author: RNDr. Ing. Libor Kukačka Department: Department of Atmospheric Physics Supervisor: prof. RNDr. Zbyněk Jaňour, DrSc., Academy of Sciences of the Czech Republic, Institute of Thermomechanics, v. v. i. Abstract: The main goal of the thesis is to investigate the impact of urban geometry on the urban ventilation using wind-tunnel modelling. To measure the pollutant transport, both advective and turbulent, within complex urban geometries with a high temporal resolution a special measurement method was developed. At first, the pollution of a simplified urban area was simulated by a ground-level point source and the ventilation of the intersection with respect to four wind directions was studied. Later, the pollution of other simplified and complex urban areas was simulated by a ground-level line source and the ventilation of three different street canyons with respect to wind direction perpendicular and oblique to their along-canyon axis was investigated. The clear impact of urban complexity and wind direction on street canyon ventilation is demonstrated at lateral and top openings of all investigated canyons and the intersection. Whilst the dominance of the pollutant advection is demonstrated at the eaves of pitched roofs, at the roof ridges...
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Use of the ceilometer data to explainig changes in pollutants concetration gradient in the air during the day
Komínková, Kateřina ; Holoubek, Ivan
For the interpretation of air pollutants concentrations, the one of the key parameter is the atmospheric boundary layer (ABL) evolution during a day and night. The ABL is a broad concept that includes different states of airflow dynamics in the part of troposphere closest to the Earth's surface (0-2 km above the surface), which has an effect in this area. A lot of air flow changes occur in the ABL during the day. For the measurement of substances concentrations in the air the development of mixing layer (ML) in the light part of the day is very important. A lot of ground remote sensing methods was developed for determination of ABL height during the day, one of them which can be very simply operated is to use data from ceilometer. However, the obtained outputs cannot be directly interpreted. In addition, in the case of the terrain measurements a lot of cases when ABL height values cannot be determined because the ceilometer measurement is disturbed can occur.\n\n
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Flow and diffusion characteristics inside the urban area
Chaloupecká, Hana ; Jaňour, Zbyněk (advisor) ; Brechler, Josef (referee)
Title: Flow and diffusion characteristics inside the urban area Author: Hana Chaloupecká Department: Department of meteorology and enviroment protection Supervisor: prof. RNDr. Zbyněk Jaňour, DrSc., IT AS CR, v. v. i. Supervisor's e - mail: janour@it.cas.cz Abstract: Uniqueness of different towns, consists of various shapes of buildings. The main topic of this work is to compare concentration diffusion within groups of buildings of various types. We pursued houses made of single blocks of two different lengths - they were placed parallel or in courtyards. For research of pollution diffusion within the housing estates a method of physical modelling has been used. For this purpose we summarized a theory of atmospheric boundary layer and physical modelling at first. Then we pursued experiments. Measuring took place in a model in scale 1 : 300 inside an aerodynamic wind tunnel of the Institute of Thermomechanics AS in Nový Knín. We checked out the requirements placed on similarity of the real boundary layer and boundary layer modelled in the tunnel. By the measuring of concentration in urban areas we weren't watching a plume from the pollution source but we were studying an inversion task. We measured concentrations in two fixed points from different point sources inside the defined areas. A sensitivity of...
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Microscale flow and diffusion characteristics inside the urban area
Kukačka, Libor
Title: Microscale flow and diffusion characteristics inside the urban area Author: Libor Kukačka Department: Department of meteorology and enviroment protection Supervisor: prof. RNDr. Zbyněk Jaňour, DrSc., IT AS CR, v.v.i. Supervisor's e-mail address: janour@it.cas.cz Abstract: Dispersion of pollutants in the atmosphere of urban areas is the important task in environmental sciences. The main goal was the quantitative studying of a flow in a symmetrical urban built-up area depending on a running on flow direction. There was given a theoretical base of the physical modelling of the atmospheric boundary layer in this work. The measurement was done with a model of the urban build-up area at a scale of 1:200 in the aerodynamic wind tunnel of the IT AS CR, v.v.i. in Nový Knín. The requirements to the similarity to a real atmospheric boundary layer and a model boundary layer in the wind tunnel were accomplished. Velocity fields, concentration fields and fields of scalar fluxes were measured in the area of a rectangular intersection. Results of the experiment showed significant sensitivity of the velocity field about the running on flow direction that extensively influenced ventilation of street canyons. Keywords: air pollution, atmospheric boundary layer, physical modelling, dispersion of passive contaminant,...
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