The effect of buildings on atmospheric turbulence in open spaces in Western São Paulo State, Brazil

Abstract

[EN] This paper seeks to identify a pattern of air turbulence that reflects the effect of buildings on air turbulence characteristics measured in open spaces in Western São Paulo State, Brazil. Atmospheric turbulence was estimated using high-frequency observations of the three orthogonal wind components (u, v, w). A CSAT3 sonic anemometer from Campbell Scientific Inc. (CSI) was deployed on the roof of a building, and the turbulent components (u', v', w') were systematically measured and recorded at 0.1 s and 5 min intervals, respectively, over 100 days between the end of summer (March 2015) and beginning of winter (July 2015) with a CR3000 automatic data acquisition system (CSI). The data analysis took into account the diurnal and nocturnal variability of the turbulence, and the experimental results revealed the existence of a daily vertical circulation pattern. The w component varied between 15 and 45 cm.s-1 on average, and the turbulent fluctuations observed indicated that an ascending component with a speed of up to 1 m.s-1 predominated during the middle of the day and early afternoon. Throughout the night until the early hours of the morning, a less robust, subsiding component with a speed of up to 0.5 m.s-1 was observed. The mean horizontal flow (u, v) was low-speed (around 1 m.s-1) and predominantly from the southeast. There was a consistent change in the direction of this wind, which changed to easterly during the morning as the ascending branch developed. We propose a model for air circulation close to the surface in which this change in direction of the wind is the main effect of the building on the observed turbulence.