DIURNAL TEMPERATURE-RANGE AND CLOUD COVER IN THE NORDIC COUNTRIES - OBSERVED TRENDS AND ESTIMATES FOR THE FUTURE

A simple regression model relating local monthly mean diurnal temperat ure range (DTR) and cloudiness at 10 synoptic stations in the Nordic r egion to monthly mean large-scale tropospheric flow has been construct ed. The tropospheric how data, which is input to the model, includes b oth 500 hPa height and 500/1000 hPa thickness fields which are compres sed via an EOF-technique. The regression coefficients are calculated f rom a 27 year record of analysed flow and locally observed DTR and clo udiness. The regression model has been used to down-scale the large-sc ale flow produced in a CO2 sensitivity experiment with a coupled ocean -atmosphere climate model (ECHAM-1). The down-scaled ''high CO2'' DTR is generally smaller than found when down-scaling the corresponding cl imate model control experiment. The opposite statement applies to clou diness. DTR-anomalies of the order 2 Kelvin (K) are obtained in the ce ntral/northern parts of Fenno-Scandia in the middle of the 21st centur y while anomalies much closer to zero are found over the Iceland/South ern Greenland region. Consistent with this picture the cloudiness anom alies in the high CO2 case are predicted highest near the central/nort hern parts of Fenno-Scandia. The results presented here indicate that periods observed to be anomalously warm on a large-scale - correspondi ng to high CO2 concentrations - are also observed to be more cloudy an d it is argued that clouds may have a thermostatic effect. We have cal culated DTR and cloud cover trends at the 10 stations used in the regr ession model in order to assess if they are consistent with the predic ted estimates and as such reflect a forcing of the climate system, We find that none of the stations show DTR/cloud cover trends significant ly different from zero in the period 1961-1987. We do, however, see a negative DTR trend and a positive cloud trend when we consider a sligh tly longer time series (1950-1992) at Reykjavik. All statements about trends are, however, very uncertain because the observed records in ad dition to any trends reflect a large natural variability on decadal ti me scales as well as possible observational inhomogeneities.