Clouds

The recovery of cloud structures in the multi-layer clouds, which represent half the clouds, constitutes the main uncertainty in the determination of short-wave radiation fluxes on the surface, and long-wave radiation fluxes in the atmosphere. The association of Lidar profiles with radiative budget measurements (CERES on board EOS) will improve radiation flux and warming rate measurement.

As complement of the EOS, CALIPSO brings a better characterization of microphysical, optical, and radiative cloud properties (optical thickness, phase, ice cloud asymmetry parameters, etc.) which will enable a large-scale statistical analysis leading to the improvement of cloud modelling parametrization.

Particularly, the association of the CALIPSO Lidar and infrared imager enable very interesting measurements for the cirrus characterization. Those thin clouds represent no less than 20% of the global cover. They are poorly detected by classical methods and are very heterogeneous. The cirrus radiative impact simulation models show a very great sensitivity to particle size and to small particles' major role. Thanks to the measurement of cirrus brightness temperature in two thermal infrared channels (required precision: 0.5 K) coupled with the altitude profile given by the Lidar, their emissivity (precision: 1%) and ice particles' real radius can be calculated.