Estimation of flux parameters from sodar wind profiles

Abstract

The estimate of flux-parameters and sensible heat flux is required in many boundary-layer modelling applications. A method based on the Monin-Obukhov similarity theory has been used to derive the flux parameters from the sodar wind profiles during stable and unstable stratification. The data we used have been collected during a field experiment in the Tiber valley during the summer of 1992. As the sodar provides a poor description of the surface layer, preliminary work was required to understand the limitations in determining flux parameters from sodar wind profiles. The behaviours of friction velocity and the Monin-Obukhov length were found to be in good agreement with the expected values for the area under investigation, while the roughness length was always overestimated. The variations in roughness are explained in terms of wind direction. Using the flux parameters derived from sodar wind profiles and the parameterization equations available in the literature on free convection regime, the vertical velocity variance has been computed and compared with the variance values measured directly by the sodar. The results show an underestimation of sodar variance during the day. In case of free convection, the sensible heat flux has been compared with the results obtained with a method which uses the variance of vertical velocity fluctuations.