Determination of diurnal daylight courses for a central European region

Abstract

The diurnal course of daylight (exterior illuminance) during winter and summer in a central European town, Bratislava, Slovakia, is studied. By using multivariate statistical methods (Factor and Cluster Analysis), the most significant types of the diurnal variations of illuminance are determined. The database used consists of mean 5-min values of global horizontal illuminance for the 14-year period 1994–2007. Two sets of data (sunrise-noon, noon-sunset) are utilized for each season, consisting of the anomalies of the semi-diurnal courses of illuminance with respect to the mean semi-diurnal course on each calendar day of the year. For winter, six typical semi-diurnal courses for sunrise-noon and nine for noon-sunrise are found, and for summer, six for sunrise-noon and seven for noon-sunset. For each type of semi-diurnal course, the most representative day is selected. Finally, for a verification of the results the atmospheric circulation patterns near the surface and at the 500-hPa level, the distribution of precipitation over Europe as well as the meteorological observations are presented, for these days.The purpose of the present study is to achieve an objective determination of the main diurnal daylight courses observed in a central European region. The results can be useful to engineers for a rational use of daylight in buildings, which may significantly contribute towards energy saving.