To better understand this influence of surface heterogeneity along a scintillometer path on the spatial variability of Cx2 was one of the main objectives of the LITFASS-2009 field experiment. This experiment was performed around the Meteorological Observatory Lindenberg of the German Meteorological Service (DWD) in July 2009, and combined eddy-covariance techniques, scintillometer observations, unmanned aircraft measurements and large eddy simulation (LES) modeling (Beyrich et al., 2012).
However, if spatial variability is investigated, one is interested in the influence of surface heterogeneity only rather than in the combined effect of turbulent variation and imposed spatial variations due to surface heterogeneity. Therefore, it is essential to decompose the two causes. A method to quantify the turbulent variation is to investigate the short time temporal variability of Cx2 at a given location (i.e. without any influence of spatial variability).
In this research we will focus on the short-time temporal variability of scalar structure parameters obtained by eddy-covariance measurements performed in the atmospheric surface layer during the LITFASS-2009 experiment: First, we investigate the shape of the probability density functions of the structure parameters near the surface. We search for a uniform behavior of the variability under different atmospheric conditions. Second, since Cx2 is derived over a certain time window, we have to quantify how the variance in the structure parameter depends on the size of this window. Furthermore, we show how the dimensionless standard deviation of Cx2, a measure of the temporal variability, behaves under unstable conditions. Finally, we will discuss implications for the interpretation of path-integrated structure parameters.
Cheinet, S and Siebesma, AP; 2009: Variability of Local Structure Parameter in the Convective Boundary Layer, Journal of the Atmospheric Sciences 66, 1002-1017
Beyrich, F, Bange, J, Hartogensis, OK, Raasch, S. and Braam, M, van Dinther, D, Gräf, D, van Kesteren, B, van den Kroonenberg, AC, Maronga, B, Martin, S and Moene, AF, 2012: Towards a validation of scintillometer measurements: The LITFASS-2009 experiment, Boundary Layer Meteorology DOI 10.1007/s10546-012-9715-8