Single level turbulence measurements to determine roughness parameters of complex terrain

Abstract

An attempt was made to determine roughness length z0 and zero‐plane displacement height d0 from single level turbulence measurements over a complex area in tropical monsoon environment where standard procedures to derive those parameters were found difficult to apply. The value of d0 was derived from the nondimensional standard deviation of temperature ϕθ and of vertical wind speed ϕw by making use of the fact that ϕθ and ϕw versus atmospheric stability relationship is sensitive to the d0 value, by following and by extending the proposal of Rotach [1994]. This method was applied to the two turbulence data sets obtained at 30 and 60 m above a complex terrain in central part of Thailand, and they produced d0 = 15.7 m. However, investigations into the accuracy of the d0 value obtainable by this method have revealed that it is probably of the order of meters and thus a simultaneous application of the method to both vertical wind speed and temperature data are recommended to allow an intercomparison of the derived d0 values to enhance the reliability of the result. The z0 value was also determined from the single level turbulence data by a method in which the z0 value that produced the best agreement of the friction velocity values obtained from the eddy correlation method and those from a wind profile equation with the derived d0 value, the given value of z0 and single level wind speed data, was selected. This method is not very sensitive to the exact value of d0 and z0 = 0.31 m was obtained. Overall, single level turbulence data were found useful to evaluate roughness parameters of a complex area.