Trends in Nordic and Arctic temperature extremes and ranges

The national meteorological institutes in the Nordic countries have produce d a comprehensive dataset of climatic extreme temperatures (monthly mean da ily maximum and minimum, and monthly absolute highest and lowest temperatur es) comprising stations from Fenno-Scandia, the Nordic Seas, and Greenland. Mean maximum and minimum temperatures show statistically significant negat ive trends in western coastal Greenland during the period 1950-95, while ov er the Nordic Seas and Fenno-Scandia the trends are generally positive. The diurnal temperature range (DTR) is decreasing significantly throughout the study area and is unrelated to regional temperature trends, which show bot h warming and cooling. The opposite temperature trends between western coas tal Greenland and Fenno-Scandia since the 1950s are in accordance with a st rengthening of the North Atlantic Oscillation (NAO). However, the simple NA O index fails to explain the decrease of DTR. In Fenno-Scandia, the reliabl e long-term mean maximum and minimum temperatures show cooling in winter an d warming in spring and summer during the period 1910-95. Simultaneously, D TR has been decreasing in all seasons except winter. Most of the decrease h as occurred since the 1940s. Atmospheric circulation indices defined by zon al and meridional sea level pressure differences, along with sea level pres sure and cloud cover anomalies were used to build a multiple linear regress ion model for the Fenno-Scandian DTR. During the period 1910-95 the model e xplains from 53% (winter) to 80% (summer) of the variation in DTR and repro duces the statistically significant decreasing trend on annual level. Cloud cover is the dominant predictor, while circulation provides substantial im provement in explanation.