Diploma Thesis

Untersuchung der lokalen Einflüsse auf die meteorologischen Messungen an der Station ‚Weidenbrunnen' (Waldstein/Fichtelgebirge)

Alexander Mangold (11/1998-05/1999)

Support: Thomas Foken

The aim of this study is to characterize the influences of a complex, hilly, forested site on turbulence measurements. The site Weidenbrunnen is located in the Fichtelgebirge, near Bayreuth, Germany. This study is important for the ongoing or planned measurements with the eddy-correlation-technique or the relaxed-eddy-correlation technique at this site. The data were collected during July and August 1998 with an additional turbulence measuring set (CSAT3, KH20, Pt-150 Ohm). These data were compared and evaluated with those of the ongoing EUROFLUX-project at this site. The integral turbulence characteristics for the horizontal and vertical windcomponent were analysed dependent on stability and wind direction. The same was done with the fluxes of sensible and latent heat and the buoyancy flux. With the quality test according to FOKEN AND WICHURA (1996) and these parameters it is possible to characterize the influences of the underlying surface on the respective turbulent parameters. With the data for the standard deviation of the wind direction, the turbulence intensity and the wind vector slope a characterization of the horizontal wind field was done. The method of the integral turbulence characteristics to determine fluxes of trace gases was tested on applicability for the Weidenbrunnen. For the evaluation of the site also a detailed footprint-analysis according to the model of SCHMID (1997) was carried out.

With regard to the horizontal turbulent wind field the three sectors ESE-SSW, SSW-W and W-NNW could be separated against each other. The sector ESE-SSW showed clear higher values for the standard deviation of the wind direction and the wind vector slope in relation to the other sectors. The vertical windcomponent showed no sustained disturbances, neither for all analysed wind sectors (ESE-NNW) nor for the examined stability range (-0,5 < z/L < 0,5). For the horizontal windcomponent hints were found that it seems to be more appropriate to scale with the laws of the mixing heigth than with the laws of the surface layer. The three examined heat fluxes showed no dependency on wind direction. With the method of the integral turbulence characteristics the measured heat fluxes could be very well determined, especially in the unstable case. With the footprint-analysis it was able to divide the wind field in the three sectors named above. There was a strong relationship between the dimensions of the source areas and the quality of the integral turbulence characteristics for the heat fluxes. The site Weidenbrunnen itself contributes only to a small amount to the measured sensor signals. The different results between the horizontal and the vertical windcomponent indicate different areas of influence for scalars, respective fluxes. As a summary and with regard to a strict quality control it can be stated that it is possible to carry out turbulence measurements with high quality at the site Weidenbrunnen.

last modified 2003-12-12