ASYMMETRIC DIURNAL TEMPERATURE-CHANGE IN THE ALPINE REGION

By now there is general agreement that the annual mean temperature of earth's surface has increased during the last century. Recently, it ha s become obvious that this warming is quite inhomogeneous in various r espects. Besides the spatial and seasonal variability of the temperatu re trend a diurnal asymmetry of increase has been observed. In large c ontinental regions the annual mean of the daily minimum temperature ha s increased noticeably faster than the annual mean of the daily maximu m. The same behaviour is found in the present study for low-lying stat ions in Central Europe. However, data from mountain top stations show a similar increase for both minimum and maximum of daily temperatures. No diurnal asymmetry was observed for these stations. The good agreem ent of the time series from different mountain stations leads us to be lieve that the observed trends of minimum and maximum temperature are not caused by particular local influences or observation errors. An an alysis of monthly and seasonal means shows that most of the warming to ok place in fall.