Diploma Thesis

Investigation of advection and the wind field in a spruce forest

Martina Hunner (02/2008-04/2009)

Support: Thomas Foken, Lukas Siebicke, Johannes Lüers

This work investigates advection and the wind field in a spruce forest at the Waldstein/Weidenbrunnen site located in the Fichtelgebirge Mountains in Northern Ba-varia. During the experiments EGER (ExchanGE processes in mountainous Regions) different physical, chemical and biological processes in the soil-vegetation-boundary-layer system were investigated and turbulence structure, advection and flux gradients were observed within two intensive observation periods in September and October 2007 (IOP 1) and in June and July 2008 (IOP 2). Measurements of a sonic anemometer includ-ing vertical velocity are available for two longer periods, September 2007 to February 2008 and May 2008 to October 2008. Beyond a general characterization of the experimental site according to the wind field and advection regime a particular focus was put on the calculation of vertical advection. Vertical advection is determined by a CO2 concentration gradient and mean vertical ve-locity. The small values of the later cause a high source of uncertainty to vertical advec-tion calculation. To correct influences of sensor misalignment, obstacles or local topo-graphy, the planar fit coordinate rotation was carried out. The influence of time span and classification in wind sectors as well as the effect of data quality on the correction of ver-tical velocity and therefore on the calculation of vertical advection were examined. Final-ly the effect on total advection and net ecosystem exchange (NEE) was determined. Results show that at the Waldstein/Weidenbrunnen site nocturnal subsidence and drai-nage flows exist. Vertical advection is positive or negative, depending on the method of applying planar fit rotation, but horizontal advection is positive throughout the day lead-ing to a high contribution to NEE. Comparing the methods of planar fit correction, the influence of time span is more important than the application of quality criteria. However the classification in wind direction sectors also improves the nullification of vertical ve-locity. Using Aubinet’s advection scheme the advection regime at the Waldstein/Weidenbrunnen site can be classified as a convergence situation with increas-ing source intensity or divergence situation in 2007, depending on the planar fit method, and as convergence situation in summer 2008.

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last modified 2011-09-30