Estimation of the boundary layer height in the southern region of Brazil

Abstract

Understanding the behavior of the planetary boundary layer is fundamental to better comprehend some phenomena such as the dispersion of pollutants in urban areas. This study aims at estimating the characteristic parameters and the spectral properties of the atmospheric turbulence on the surface boundary layer, especially the height of the atmospheric boundary layer in the south of Rio Grande do Sul state, in Brazil, based on data collected by micrometeorological instruments placed close to the surface. The characteristic parameters and the spectral properties were analyzed in the light of Monin-Obukhov’s similarity theory in different stability conditions. The boundary layer height was determined by using the turbulent spectra of the zonal wind velocity whose data was collected from August 28th to November 11th, 2006, on a tower located 20 km south of Rio Grande. Results of the turbulence kinetic energy, the friction velocity and Obukhov’s length are in agreement with the findings of other studies carried out in the region. After making adjustments regarding the atmospheric stability, the roughness length properly represented the characteristics of the landscape in the region where the data collection tower was placed. The spectral analysis showed that Monin and Obukhov’s similarity theory is not appropriate to describe the spectral characteristics of the turbulence in the somewhat unstable conditions in the region. Mean values of 1168.87 m and 291.90 m were obtained for the heights of the convective and the nocturnal boundary layers, respectively. The methodology that was used to estimate the boundary layer height was satisfactory to represent both its diurnal and its nocturnal evolution.