Diploma Thesis

Parameterization of integral turbulence characteristics above and within a spruce stand

Tobias Biermann (02/2008-03/2009)

Support: Thomas Foken, Andrei Serafimovich

Integral turbulence characteristics, the normalized standard deviation of a turbulent quantity, can be used to describe the structure of turbulence. A comparison between measured and predicted values shows whether turbulence is fully developed or not and is therefore used in quality assessment. For this quality control and as an input for models parameterizations of integral turbulence characteristics and their profiles are needed. Since no uniform theory of parameterizations inside a forest is available, different approaches were tested with data collected during September and October 2007, the first intensive observation period (IOP 1), in the framework of the EGER (ExchanGE processes in mountainous Regions) project during which different physical, chemical and biological processes in the soil-vegetation-boundary-layer system were investigated. Therefore turbulence structure, advection, flux gradients of meteorological and chemical quantities were observed. Field experiments were performed at the BayCEER research site Waldstein/ Weidenbrunnen, a 23 m tall spruce (Picea abies) stand, located in the Fichtelgebirge Mountains in North-Eastern Bavaria, which are challenging for their heterogeneity and orographically structured terrain. The observations of turbulence structure were obtained by a vertical profile of sonic anemometers covering all parts of the forest up to the lower part of the roughness sublayer. Additionally Field observations are complemented by simulations of ACASA model (Advanced Canopy-Atmosphere-Soil Algorithm). The results of the comparison between measurements and recommended parameterization approaches indicate, that in order to parameterize the integral turbulence characteristics of the wind components and temperature inside the roughness sublayer a dimensionless height &zeta = hc L-1 should be used instead of &zeta = z L-1, which is used above short vegetation. Profiles of integral turbulence characteristics from different ecosystems show that the decrease inside the roughness sublayer is similar but that parameterizations of profiles can not be generalized due to different stand structures. Selecting the profiles of the integral turbulence characteristics by coupling situations between the atmosphere above and inside the stand did not reveal a significant different behavior than a selection according to stratification above the canopy. A comparison between the measured values and model results from the ACASA model showed a good agreement for the normalized wind speed but the integral turbulence characteristics of the wind components were usually overestimated above the canopy and underestimated inside the trunk space.

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last modified 2009-06-26