ВІТРОВИЙ РЕЖИМ ВЕЛИКОГО МІСТА

Abstract

Big city wind regime is an important factor which influences on air pollution level and bioclimate of the territory. It forms as a result of climatic conditions influence and the impact of various objects (height and density of construction, road network, green zones, water bodies etc.) within the city. The article is devoted to the study and analysis of big city wind regime, as well as generalizing of the basic knowledge about air flow transformation in urban areas for future using this information in scientific research and for the correction of aeration regime of different territories. Wind speed reduction is the main feature of urban areas wind regime. Usually, wind velocity in the city is approximately 30 % lower compared to its neighbourhoods. Not only the mean wind speed is lower in urban areas, but also the vertical wind profile is characterized by some differences. Urban heat island existence leads to the formation of a mesoscale thermal circulation in the city – a rural breeze which is the most pronounced under conditions without wind or with weak wind speed. Transformation of air flow in an urban street canyon depends on the wind direction – when the wind is directed parallel to the canyon axis, wind within canyon has a higher velocity (according to the Venturi effect). In a street canyon which is oriented with its axis perpendicular to the wind direction, when air flows across the cross-section of a canyon, a vortex is formed and accordingly wind velocity is getting lower. Depending on the characteristics of the canyon (its height/width and length/width ratio) three distinct wind regimes may be identified in the canyon – isolated roughness flow regime, wake interference regime and skimming flow regime. Thus, the wind field has a very complex structure in the urban areas, because on airflow in the city influence a lot of factors.