Wind lidars reveal turbulence transport mechanism in the wake of a tree

Abstract. Solitary trees are natural land surface elements, found in almost all climates, yet their influence on the surrounding air flow is poorly known. Here we use state-of-the-art, laser-based, remote sensing instruments to study the turbulent wind field in the near-wake region of a mature, open-grown oak tree. Our measurements provide for the first time a full picture of the mixing layer of high turbulence that surrounds the mean wind speed deficit. In this layer, we validate the eddy-viscosity hypothesis, a fundamental theory used in modelling the wind conditions. Using the mixing-length hypothesis we find that for this tree the corresponding turbulence length scale in that layer can be approximated by one, height-independent value. Further, the laser-based scanning technology used here was able to accurately reveal three-dimensional turbulent and spatially varying atmospheric flows over a large plane, without seeding or intruding the atmospheric flow. This capability points to a new and more exact way of exploring the complex earth-atmosphere interactions.