Abstract. The impact of contrail-induced cirrus clouds on regional climate is estimated for mean atmospheric conditions of southern Germany in the months of July and October. This is done by use of a regionalized onedimensional radiative convective model (RCM). The in¯uence of an increased ice cloud cover is studied by comparing RCM results representing climatological values with a modi®ed case. In order to study the sensitivity of this eect on the radiative characteristics of the ice cloud, two types of additional ice clouds were modelled: cirrus and contrails, the latter cloud type containing a higher number of smaller and less of the larger cloud particles. Ice cloud parameters are calculated on the basis of a particle size distribution which covers the range from 2 to 2000 lm, taking into consideration recent measurements which show a remarkable amount of particles smaller than 20 lm. It turns out that a 10% increase in ice cloud cover leads to a surface temperature increase in the order of 1 K, ranging from 1.1 to 1X2 K in July and from 0.8 to 0X9 K in October depending on the radiative characteristics of the air-trac-induced ice clouds. Modelling the current contrail cloud cover which is near 0.5% over Europe yields a surface temperature increase in the order of 0X05 K.

Abstract. The impact of contrail-induced cirrus clouds on regional climate is estimated for mean atmospheric conditions of southern Germany in the months of July and October. This is done by use of a regionalized onedimensional radiative convective model (RCM). The in¯uence of an increased ice cloud cover is studied by comparing RCM results representing climatological values with a modi®ed case. In order to study the sensitivity of this eect on the radiative characteristics of the ice cloud, two types of additional ice clouds were modelled: cirrus and contrails, the latter cloud type containing a higher number of smaller and less of the larger cloud particles. Ice cloud parameters are calculated on the basis of a particle size distribution which covers the range from 2 to 2000 lm, taking into consideration recent measurements which show a remarkable amount of particles smaller than 20 lm. It turns out that a 10% increase in ice cloud cover leads to a surface temperature increase in the order of 1 K, ranging from 1.1 to 1X2 K in July and from 0.8 to 0X9 K in October depending on the radiative characteristics of the air-trac-induced ice clouds. Modelling the current contrail cloud cover which is near 0.5% over Europe yields a surface temperature increase in the order of 0X05 K.

Abstract. A satellite based method for deriving spatial distributions of erythemally weighted UV irradiance at the surface has been developed. The effects of ozone column amount and cloud optical thickness on UV were taken into account by the combined usage of the new European-Space-Agency's GOME (Global-OzoneMonitoring-Experiment) sensor onboard the EuropeanResearch-Satellite-2 (ERS-2) and the NOAA/AVHRR instrument, respectively. As an example for application, horizontal distributions of surface UV irradiances are derived in a region covering the area of Southern Germany on two days 22. July and 13. August 1996. These two days represent clear and cloudy conditions, respectively. For the cloud free day 22. July 1996 the surface UV measurements at Garmisch-Partenkirchen and Hohenpeissenberg (Southern Germany) were about 4.5% lower than those derived from satellite measurements. In addition, the accuracy of the method in case of the cloudy day is discussed.