Measuring Coherent Structures in the Horizontal Wind Field using dual Doppler Lidar

Coherent structures are quasi-periodic patterns in turbulent flow fields. Many researchers regard those structures as important for boundary layer processes, such as the transport of momentum, heat, and trace gases. For the detection of coherent structures, high temporal and spatial resolution measurements of the turbulent wind field are needed and so the acquisition of coherent structures in the atmospheric boundary layer is challenging. The Institute of Meteorology and Climate Research (IMK-TRO) of Karlsruhe Institue of Technology (KIT) is operating within the KITcube integrated mobile observation system two powerful ground based Doppler lidars. Using both Doppler lidars simultaneously we have the exceptional possibility to probe the turbulent horizontal wind field in low altitudes applying dual-Doppler techniques to explore up to now hidden details of the boundary layer. During spring 2013 IMK-TRO participated in the HOPE field campaign of HD(CP)2 in Juelich (Germany). More than 300 hours of horizontal wind field data with a spatial resolution of less than 100 m and a temporal resolution of 12 sec have been sampled during HOPE. Technical details of the dual Doppler system and the used scan algorithm will be given in the presentation. The data set was analyzed systematically to gain information on the characteristics and the development processes of coherent structures in the surface layer. Three case studies about the development of coherent structures during different atmospheric conditions will be presented.