Determination of Surface Layer Parameters at the Edge of a Suburban Area

Vertical wind and air temperature profile related parameters in the atmospheric surface layer at the edge of suburban area of the city of Zagreb (Croatia) have been considered. For that purpose the set of observations of wind speed and air temperature at 2 and 10 m above ground, recorded in 2005, have been used. The Monin-Obukhov theory is adopted for the purpose of estimation of the wind speed at 2 m above the ground, that is, for calculation of turbulence parameters following improvements that were introduced by Paulson (1970), Businger et al. (1971), Dyer (1974), Beljaars and Holtslag (1991) and Lee (1997). The effective roughness length z₀ concept is used in order to take into account the influence of different surface roughness (mainly due to urbanization) dependent on wind direction. One of the more important results here is the classification of z₀ according to wind direction. For this classification three methods are used: root mean squared errors between estimated and corresponding measured values of wind speed at 2 m above ground, relationship between the standard deviation of wind speed and z₀ as well as the relationship between median of wind gust factor and z₀. According to all three methods used, z₀ values obtained are higher for western than for eastern quadrants of wind direction, as expected. Three verification parameters for estimation of wind speed at 2 m: bias, mean absolute error and root mean squared error between measured and estimated values of wind speed are used. Taking into account the dependence of z₀ on wind directions, all three parameters (estimation errors) became smaller, especially the bias. The obtained results suggest that the wind observation at the standard level (10 m) is representative for the area of about one kilometer in the upwind direction. The wind data extrapolation at lower or higher levels, based on standard measurements at 10 m, can provide values of the wind representative for wider inhomogeneous (regarding surface roughness) suburban area of the city of Zagreb. These data can be used for atmospheric modeling, estimation of turbulent fluxes, wind energy, civil engineering and air pollution applications, etc.