Equipment

The basic instruments of the Japanese system are another LI-COR LI-6262 fast response IRGA and a three dimensional fast response sonic anemometer-
thermometer (Kaijo-Denki, model DA-600). Air inlet tubes were mounted at 10 m and 3 m to perform both concentration gradient and eddy covariance measurements. A programmable timer is used to switch between the air inlet tubes and the calibration gases. Different pumps are used to suck air from the measuring levels and the calibration gas tanks. The IRGA, its pumps (one for 10 m and one for 3 m), the timer and the calibration gases are located in a ventillated box near the 10 m mast allowing a very short air inlet tubing. Raw voltage data detected by the fast response sensors are collected and digitised by means of a TEAC datalogger at exact 5 Hz. The data are written to magneto-optical disks in binary format. The disks are brought to Budapest for data processing once a month.

Before 13 April, 1999 the system worked in two separate modes: it performed gradient measurements and eddy covariance measurements by turns. The data acquisition program allowed us to calculate 16 minute averages of gradient data and 16 minute averages of eddy covariance data (with 2 minutes overlapping). This measuring routine turned out inadequate since the ogive functions (see section ) of the data did not converge during the 16 minute periods. For this reason, the measuring regime had been changed. The new measuring cycle consists of four 6 hour long periods, with each period begins with a 16 minute air sampling from the 10 m level (air inlet is installed near the existing 10 m inlet of the profiling system), with eddy covariance sampling during the rest of the 6 h period. The sampling of the 10 m level makes it possible to compare the profile system and the Japanese system.

Data coverage between 1 March 1999 and 18 December 2001 was 71%, after data screening it reduced to 65%.