Characteristics of Cμ2 derived from ultrasonic anemometer in an urban boundary layer

Abstract

Fast-response observations of three components of wind and air temperature have been applied to calculate the refractive index function coefficient (Cμ2 ), which is needed to describe optical wave propagation in a turbulent medium. These were measured by 3D ultrasonic anemometer installed on the roof of the building of Atmospheric Science Department which is 19 m above ground level. Refractive index function coeffi cient was calculated for various periods of three seasons: winter, spring and summer.Diurnal variations of (Cμ2) have been made at the surface layer for these seasons. The results show that high values ofmean (Cμ2) occurred during the day time more than at night, also they occurred more in summer than in winter and spring. The results of (Cμ2) found to change with atmospheric stability, whereas they inversely decrease under unstable conditions, approximately constant at neutral cases, and increase under stable conditions. Values of (Cμ2) on average appears to be lower during the rainy and foggy weather cases compared to those of clear sky.