The LITFASS-98 experiment: Fluxes over a heterogeneous land surface

The German Weather Service (DWD) currently runs a research project (LITFASS='Lindenberg Inhomogeneous Terrain - Fluxes between Atmosphere and Surface: a Long-term Study') in order to develop and to test a strategy for the determination of the area-averaged turbulent fluxes of heat, momentum, and water vapour over a heterogeneous landscape. The fluxes shall be representative for a horizontal scale of about 10 km (while the typical patch scale is between 102 to 103 m) corresponding to the size of a grid cell in the present operational numerical weather prediction model of the DWD. LITFASS consists of three components: - the development of a non-hydrostatic micro-a-scale model with a grid-size of 100 m - experimental investigations of land surface - atmosphere exchange processes and boundary layer structure within a 20 km x 20 km area around the Meteorological Observatory Lindenberg (MOL) - operation of a data base as an interface between measurement and modeling activities.

The overall project strategy has been tested over a four weeks period in May / June 1998 during the LITFASS-98 field experiment. The paper will present a brief description of the experimental setup and some initial results focusing on the behaviour of the turbulent fluxes. These have been determined using a variety of different techniques and methods covering six magnitudes of spatial sampling scales (profile measurements, eddy-correlation measurements, scintillometry, helicopter and aircraft measurenments). Results to be shown include - the behavior of the turbulent fluxes over different surface types within the LITFASS area, - vertical profiles of turbulent fluxes as derived from measurements at a 100m tower, - an intercomparison of the local and area-integrated values of turbulent fluxes. Finally, first modelling results for the experimental episode and aspects of an operationalisation of parts of the LITFASS measurement programme will be discussed.