Understanding inter-site temperature differences at the KNMI terrain in De Bilt (the Netherlands)

From May 2003 through June 2005 a field experiment was carried out at the KNMI terrain in De Bilt. At five sites, including the operational site, temperature and wind speed were measured at a height of 1.5 m every minute, using identical instruments. The temperature differences between the sites have been studied in connection with the wind speed differences and operationally meas-ured weather variables. During the experiment (in October 2004) a renovation of the nature area just west of the operational temperature screen took place. The renovation introduced an inho-mogeneity in the temperature time series at the operational site. The inter-site temperature differ-ences are largest in summer and smallest in winter. Except for the most enclosed site, these tem-perature differences have opposite signs for daily maximum and minimum temperatures. As could be expected, the magnitudes of the differences strongly depend on the weather conditions. The understanding of these dependencies is an important condition for improving the homogenization of daily temperature series.