In situ observations of the microphysical properties of upper-tropospheric contrails and cirrus clouds have been performed during more than 15 airborne missions over central Europe. Experimental and technical aspects concerning in situ characterization of ice clouds with the help of optical and nonoptical detection methods (preferably FSSP-300 and Hallet-type replicator) are addressed. The development of contrails into cirrus clouds on the timescale of 1 h is discussed in terms of a representative set of number densities, and size distributions and surface area distributions of aerosols and cloud elements, with special emphasis on small ice crystals (diameter Ͻ20 m). Contrails are dominated by high concentrations (Ͼ100 cm Ϫ3) of nearly spherical ice crystals with mean diameters in the range 1-10 m. Young cirrus clouds, which mostly contain small regularly shaped ice crystals in the range 10-20-m diameter and typical concentrations 2-5 cm Ϫ3 , have been observed. Measurement results are compared to simple parcel model calculations to identify parameters relevant for the contrail-cirrus transition. Observations and model estimates suggest that contrail growth is only weakly, if at all, affected by preexisting cirrus clouds.

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.

No abstract

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.

No abstract