November 19, 2023

Clouds

The overlap of cloud structures in multi-layer clouds, which account for half of existing clouds, is the main uncertainty in determining short-wave radiation fluxes on the surface and long-wave radiation fluxes in the atmosphere. Combining lidar profiles with radiative budget measurements (CERES on EOS) improves radiation flux and warming rate measurement.

As a complement to EOS, CALIPSO affords better characterization of microphysical, optical and radiative cloud properties (optical thickness, phase, ice cloud asymmetry parameters, etc.), which enables large-scale statistical analysis to improve cloud modelling parametrization.

In particular, the combination of the CALIPSO lidar and infrared imager enable very interesting measurements for cirrus characterization. These thin clouds account for no less than 20% of global cloud cover. They are poorly detected by traditional methods and are very heterogeneous. Models simulating cirrus radiative impact are very sensitive to particle size and to small particles' major role. By measuring cirrus brightness temperature in two thermal infrared channels (required precision: 0.5 K) coupled with the altitude profile from the lidar, their emissivity (precision: 1%) and ice particles' effective radius can be calculated.