Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 5 2006 10.5194/acpd-6-8681-2006 http://www.atmos-chem-phys-discuss.net/6/8681/2006/ http://www.atmos-chem-phys-discuss.net/6/8681/2006/acpd-6-8681-2006.html http://www.atmos-chem-phys-discuss.net/6/8681/2006/acpd-6-8681-2006.pdf 8681 8712 2006-09-13 First Odin sub-mm retrievals in the tropical upper troposphere: ice cloud properties P. Eriksson patrick.eriksson@chalmers.se M. Ekström B. Rydberg D. P. Murtagh Department of Radio and Space Science, Chalmers University of Technology, Gothenburg, Sweden There exists today no established satellite technique for measuring the amount of ice in thicker clouds. Sub-mm radiometry is a promising technique for the task, and a retrieval scheme for the first such instrument in space, Odin-SMR, is presented. Several advantages of sub-mm observations are confirmed, such as low influence of particle shape and orientation, and a high dynamic range of the retrievals. In the case of Odin-SMR, cloud ice amounts above ~12.5 km can be determined. The presented retrieval scheme gives a detection threshold of ~4 g/m² without saturation even for thickest observed clouds. The main retrieval uncertainty is the assumed particle size distribution. Initial results are found to be consistent with similar Aura MLS retrievals. It is then shown that important differences compared to atmospheric models exist. This first retrieval algorithm is limited to lowermost Odin-SMR tangent altitudes, and further development should improve the detection threshold and the vertical resolution.