DIURNAL TEMPERATURE-RANGE FOR A DOUBLED CARBON-DIOXIDE CONCENTRATION EXPERIMENT - ANALYSIS OF POSSIBLE PHYSICAL-MECHANISMS

An analysis of the results of a climate simulation for a doubling of a tmospheric carbon dioxide concentration over the European region is re ported. Physical mechanisms are sought which could explain possible ch anges in the diurnal temperature range (DTR) under conditions of incre ased atmospheric greenhouse gas content. We show that an important con tribution to changes in DTR is given by soil moisture.In areas where s oil moisture increases due to an increase in precipitation there is a positive change in latent heat flux and a decrease in sensible heat fl ux.As a result, in areas with increasing soil moisture, the increase i n maximum daytime temperature will be smaller than that in minimum tem perature, thereby causing a decrease in the DTR. The opposite occurs f or areas which undergo soil drying. This process amplifies the effect of cloud changes on surface solar and infrared radiation and dominates the direct effect of downward infrared radiation associated with incr easing greenhouse gas concentration. Because the soil water content is largely controlled by precipitation, our results are consistent with early observational findings of negative correlation between changes i n precipitation and in diurnal temperature range.