First Odin sub-mm retrievals in the tropical upper troposphere: ice cloud properties

[摘要] More accurate global measurements of the amount of ice in thickerclouds are needed to validate atmospheric models and sub-mmradiometry can be an important component in this respect. A cloudice retrieval scheme for the first such instrument in space,Odin-SMR, is presented here.Several advantages of sub-mmobservations are shown, such as low influence of particle shape andorientation, and a high dynamic range of the retrievals. In the caseof Odin-SMR, only cloud ice above ≈12.5 km can bemeasured. The present retrieval scheme gives a detection thresholdof about 4 g/m² above 12.5 km and does not saturate evenfor thickest observed clouds (>500 g/m²). The mainretrieval uncertainties are the assumed particle size distributionand cloud inhomogeneity effects.The overall retrieval accuracy isestimated to be ~75%. The retrieval error is judged to havelarge random components and to be significantly lower than this valuefor averaged results, but high fixed errors can not be excluded.However, a firm lower value can always be provided.Initial resultsare found to be consistent with similar Aura MLS retrievals, butshow important differences to corresponding data from atmosphericmodels. This first retrieval algorithm is limited to lowermostOdin-SMR tangent altitudes, and further development should improvethe detection threshold and the vertical resolution.It should alsobe possible to decrease the retrieval uncertainty associated withcloud inhomogeneities by detailed analysis of other data sets.

[学科分类] 大气科学