Detecting Surface Layer Coherent Structures with Dual-Doppler Lidar and Tower Measurements: A Comparative Study

Coherent structures in the atmospheric surface layer arise as regular patterns in the turbulent fields of velocity and temperature. Their contribution to turbulent fluxes remains under investigation with respect to energy balance closure and subgrid-scale parameterizations in models. Coherent structures have in recent years been mainly investigated using tower measurement data with wavelet analysis methods to detect characteristic ramp structures in the windfield components (Barthlott, 2007, Boundary-Layer Meteorol.; Segalini, 2011, Boundary-Layer Meteorol.). But even though tower measurements offer high time resolution time series of both wind speed and temperature, they contain only extremely limited spatial information. On the other hand, methods were developed to investigate coherent structures from Dual-Doppler Lidar scans, which allow for the extraction of the horizontal windfield on an area of several square kilometers. The goal of the study presented here is to establish a connection between both detection methods. High resolution LES wind field data is employed to generate wind speed time series data from virtual towers, and to simulate Dual-Doppler lidar measurements with a lidar simulation algorithm. The respective detection methods are then applied to the virtual measurements. The comparison of results reveals the aptitudes and limits of both detection methods. This can contribute to an improved interpretation of previous measurements and assessments of turbulent flux contributions from surface layer coherent structures.