An EarthCARE/ATLID simulator to evaluate cloud description in climate models

International audienceClouds still remain the largest source of uncertainty in model-based predictions of future climate, thus the description of the clouds in climate models needs to be evaluated. In particular, the cloud detailed vertical distribution that impacts directly the cloud radiative effect needs to be evaluated. Active satellite sensors directly measure the cloud vertical distribution with high accuracy; their observations should be used for model evaluation together with a satellite simulator in order to allow fair comparison between models and observations. The next cloud lidar in space, EarthCARE/ATLID, is planned for launch in 2018, while the current spaceborne cloud lidar CALIPSO/CALIOP is expected to stop collecting data within the next coming years. Here we describe the characteristics of the ATLID lidar onboard the EarthCARE satellite (spatial resolution, SNR, wavelength, field of view, PRF, orbit, HSRL) that need to be taken into account to build a COSP/ATLID simulator. We then present the COSP/ATLID simulator, and the Low, Mid, High level cloud covers it produces, as well as the zonal mean cloud fraction profiles and the Height-intensity histograms that are simulated by COSP/ATLID when overflying an atmosphere predicted by LMDZ5 GCM. Finally, we compare the clouds simulated by COSP/ATLID with those simulated by COSP/CALIPSO when overflying the same atmosphere. As the main differences between ATLID and CALIOP are taken into account in the simulators, the differences between COSP/ATLID and COSP/CALIPSO clouds covers are less than 1% in night time condition