Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Modelling, measurements and observations of physical processes in cirrus clouds

The dominant role of clouds in modulating and interacting with radiative energy transport within the atmosphere, in providing precipitation, transporting water, and influencing air-chemical processes is still not understood well enough to be accurately represented within atmospheric circulation and climate models over all regions of the globe. Also, the extraction of real-world cloud properties from satellite measurements still contains uncertainties. Therefore, various projects have been developed within the global energy and water cycle experiment (GEWEX), to achieve more accurate solutions for this problem by direct measurements within cloud fields and other complementary studies. They are based on the hypothesis that most relevant properties of cloud fields can be parametrized on the basis of the prognostic field variables of atmospheric circulation models, and that the cloud microphysical properties can directly be related, with additional parameters on the particle shapes, etc, to the radiative transfer properties.

One of these projects has been the European cloud and radiation experiment (EUCREX) with its predecessor the International cirrus experiment (ICE). The EUCREX and ICE provided a common platform for research groups from France, Germany, Sweden and the United Kingdom to concentrate their efforts primarily on high, cold cirrus. They showed, with data from satellites, that this cloud species enhances the atmospheric greenhouse-effect. Numerical mesoscale models were used in sensitivity studies on cloud developments. In-situ measurements of cloud properties were made during more than 30 aircraft missions, where also in-flight comparisons of various instruments were made to ensure the uniqueness of data sets measured from different aircraft. The particle sampling probes, used for in-cloud measurements, showed a disagreement in total number density in all ranges between about 20 to 50%, while all other instruments agreed satisfactorily. A few measured holographic data provided information on typical ice-crystal shapes, which were used in numerical simulations of their absorption and scattering properties.

Several new instruments for both in-situ and remote measurement, such as a polar nephelometer, a chopped pyrgeometer and an imaging multispectral polarimeter (POLDER) for cloud and radiation measurements were tested and improved. New algorithms were developed for cloud classifications in multispectral satellite images and also for simulations of the scattering of radiation by non-spherical particles.

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