Numerical simulations of localized boundary layer circulations affecting eddy covariance measurements in inhomogeneous terrain

The Energy Balance Network during the COPS campaign 2007 included 11 eddy covariance stations distributed in the Black Forest region, Germany. A detailed analysis of the data record showed multiple situations in which the surface energy balance was not closed. Prior studies in cases with flat terrain identified large scale O(1000m) quasi-stationary flow structures that carried a part of latent and sensible heat fluxes. This portion of the energy balance is not seen by the eddy covariance measurements. Beside its complex orography the Black Forest region is characterized by its inhomogeneous land use. Both features are known to create and maintain boundary layer circulations. In this study an attempt was made to determine the influence of these boundary layer circulations on the measurements of the COPS Energy Balance Network using Large Eddy Simulations. It was found that indeed these local quasi-stationary circulations could contribute a main part to the deficit in the measurements.