Parallel air temperature measurements at the KNMI-terrain in De Bilt (the Netherlands) May 2003 - April 2005

From May 2003 through April 2005 a field experiment is being carried out at the terrain of KNMI in De Bilt. The objectives of the experiments are to study the representativeness of the current operational air temperature measurements site and to explore the possibility of using present-day paral- lel measurements to correct for inhomogeneities, caused by changes in the surroundings and a relocation of the thermometer screen in 1951. At five locations, including the operational location, temperature and wind speed are measured at a height of 1.5 m every minute, using identical instru- ments. The temperature differences between the sites are studied in connec- tion with wind speed differences and operationally measured weather vari- ables. The experiment is part of the KNMI-program 'Hisklim' (HIStorical CLIMate).

The present interim report presents the results of the first phase of the ex- periment (May 2003–April 2004). The report is meant to serve as a basis for deciding upon the optimal future location of the current operational temperature site. A Final report will be published at the end of the experi- ment.