14.1 INTEGRATION OF HUMIDITY FLUCTUATION SENSORS INTO THE LINDENBERG BOUNDARY LAYER MEASUREMENT FACILITIES: EXPERIENCES, PROBLEMS, AND FUTURE REQUIREMENTS

A comprehensive boundary layer measurement program has been set up at the Meteorological Observatory Lindenberg (MOL) of the German Meteorological Service (DWD) over the last five years. The measurements are aimed at the investigation of atmosphere land surface interaction processes over a heterogeneous landscape. Moreover, boundary layer data form an integral part of the "Lindenberg Column", a reference data set created operationally at MOL in order to characterize the vertical structure of the whole troposphere with high vertical and temporal resolution (Neisser et al., 2002). The experimental boundary layer facilities comprise, i.a., a boundary layer field site (in German: Grenzschichtmessfeld, GM) at Falkenberg equipped with a 99m tower, various measurement complexes for the determination of air ~, soil ~ and radiation parameters, and a sodar / RASS and a network of up to seven micrometeorological stations (energy budget measurement networkEBMN) operated over different surfaces in an area of about 20 * 20 km around the MOL site (Weisensee et al., 2001). In addition to a great variety of standard meteorological sensors, these facilities have been equipped with instruments for the operational determination of heat and momentum fluxes continuously throughout the year (profile mast, ultrasonic anemometer-thermometers, laser scintillometer). The operational determination of the latent heat flux based on direct humidity fluctuation measurements, however, is a much more challenging task and has been performed during field experiments only in the past using Ly-α-, Kryptonor infrared hygrometers (Foken et al., 1998). Current activities are directed towards the integration of different fast-response hygrometers in the existing micrometeorological measurement systems at MOL. In connection with this, a number of problems have to be solved which partially originate from contradictions between operational requirements and sensor characteristics. With respect to long-term operation, the 99m tower and the EBMN both essentially need sensors with low maintenance requirements.