Turbulence Structures at a Forest Edge

During a field campaign near the FLUXNET site DE-Bay (Waldstein-Weidenbrunnen) in summer 2011, turbulent structures were investigated along and perpendicular to an approximately 300 m long forest edge between a 25 m high spruce forest and a clearing. To measure the horizontal gradients of temperature, moisture, radiation, carbon dioxide and ozone concentrations, a horizontal moving measuring system was applied. In addition to more than ten flux measuring points, measurements of carbon dioxide and ozone concentrations in particular were used as tracers.

Besides the investigation of the coupling of turbulent eddies in the horizontal and vertical scale, the role of the forest edge in the generation of local circulations was investigated with the aim of finding reasons for the unclosed energy balance. First findings show dominant ejections at the forest edge together with a positive mean vertical velocity at day time. During the night, fresh air with low carbon dioxide and high ozone concentrations was infiltrated at the forest edge, while inside the forest or above the clearing both concentrations show the opposite properties.

The coupling of eddies above the forest with those in the trunk space (several papers have already been published for this site) was similar to that found in previous studies, and at the forest edge similar conditions were found. The horizontal coupling of the trunk space with the clearing was negligible.

The data analysis is ongoing and, as well as an experimental overview, more results as mentioned above will be presented. The experimental study was accompanied by LES simulations (see contribution by S. Raasch) and ecological model studies by E. Falge.