Inhaltszusammenfassung

Land surface heterogeneity effects on the sub-grid scale of regional climate and numerical weather prediction models are of vital interest for the energy and mass exchange between the surface and the atmo¬¬spheric boundary layer. High-resolution numerical model simu¬la¬tions can be used to quantify these effects, and are a tool to obtain area-averaged surface fluxes over heterogeneous land surfaces. The present paper presents high-resolution model simu¬la¬tions for the LITFASS area near Berli...Land surface heterogeneity effects on the sub-grid scale of regional climate and numerical weather prediction models are of vital interest for the energy and mass exchange between the surface and the atmo¬¬spheric boundary layer. High-resolution numerical model simu¬la¬tions can be used to quantify these effects, and are a tool to obtain area-averaged surface fluxes over heterogeneous land surfaces. The present paper presents high-resolution model simu¬la¬tions for the LITFASS area near Berlin during the LITFASS-2003 experiment. Model simulations were carried out using the non-hydro-static model FOOT3DK of the University of Köln with horizontal resolutions of 1 km and 250 m. The LITFASS-2003 experimental data set is used for an intercomparison. The screen level quantities show a good quality for the simulated pressure, temperature, humidity and wind speed and direction. Averaged over the four weeks experimental period, simulated surface energy fluxes at land stations show a small bias for the turbulent heat fluxes and an underestimation of the net radiation caused by excessive cloudiness in the simulations. For eight selected days with low cloud amounts, the net radiation bias is close to zero, but the sensible heat flux shows a strong positive bias. Large differences are found for latent heat fluxes over a lake, which are partly due to local effects in the measurements, but an additional problem seems to be the overestimation of the turbulent exchange under stable conditions in the daytime internal boundary layer over the lake. In the area average over the LITFASS area of 20x20km², again a strong positive bias of 70 W m-2 for the sensible heat is present. For the low soil moisture conditions during June 2003, the simulation of the turbulent heat fluxes is sensitive to variations in the soil type and its hydrological properties. Under these conditions, the supply of ground water to the lowest soil layer should be accounted for. Different area-averaging methods are tested. The experimental set up of the LITFASS-2003 experiment is found to be well-suited for the computation of area-averaged turbulent heat fluxes.» weiterlesen» einklappen

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DDC Sachgruppe:
Naturwissenschaften