Measurements of Turbulent Energy Dissipation Rate with a CW Doppler Lidar in the Atmospheric Boundary Layer

Abstract

The results of a theoretical and experimental study of the feasibility of the turbulent energy dissipation rate ?T measurements with a continuous wave (CW) CO2 Doppler lidar in the atmospheric boundary layer are presented. Three methods of probing ?T are considered: 1) Doppler spectrum width, 2) the temporal spectrum (temporal structure function) of wind velocity measured by the Doppler lidar, and 3) spatial structure function. In these methods, information on the dissipation rate is extracted by means of analysis of the corresponding statistical characteristics of wind velocity in the inertial subrange of the turbulence, taking into account the spatial averaging of the measured wind velocity fluctuations over sounded volume. In the first and third methods, the spatial structure of the turbulence is analyzed directly. In the second method, to determine ?T from the measured temporal characteristics, it is necessary to use a model for the spatiotemporal correlation function of wind velocity. As a result of the study, it has been shown that in the case of large longitudinal size of sounded volume and weak side wind, Taylor?s hypothesis of ?frozen? turbulence cannot be accepted for the correlation function. The strict limitation on the longitudinal size of the sounded volume and therefore sounding height is the main restriction of the first method. The third method is free of such limitations. It allows one to obtain the information on the dissipation rate profile throughout the entire boundary layer. Comparison of the developed theory for statistical characteristics of wind velocity measured by the Doppler lidar with the obtained experimental data has demonstrated their good agreement. The vertical profiles of the turbulent energy dissipation rate retrieved from Doppler lidar data with the use of the methods described above do not contradict the known experimental results. This fact confirms the feasibility of application of lidar remote sensing methods to the study of the small-scale turbulence in the atmospheric boundary layer.