Building a 15-Year Cloud Climatology using Lidar in Space Observations: CALIOP and CloudSat now, EarthCARE next.

International audienceToday, the CALIOP lidar and CloudSat radar have collected more than seven years of observations, and willhopefully still operate in 2016, after the EarthCARE-ATLID/CPR launch. Lidars and Radars in space providecutting edge information on the detailed vertical structure of clouds: a key element for both the evaluation ofthe description of clouds in climate models, and the survey of the clouds inter-annual evolution in variousclimatic conditions (El Nino, variation of North Atlantic Oscillations, polar regions, etc). For this purpose,the observations collected by CALIOP and by ATLID as well as CloudSat and EarthCARE CPR need to bemerged into a long-term (15 years) cloud climatology. Here, we examine the possibility of building such a climatology, with the aim of defining its accuracy andrelevance for cloud inter-annual studies. We examine the differences between the instruments (wavelengths,satellite’s altitudes, telescope fields of view, multiple scattering processes, spatial resolutions) and theirability to detect the same clouds consistently. Then, we define a set of cloud detection thresholds for ATLID,CALIOP, CloudSat and EarthCARE-CPR and test against synthetic cloud scenes (cirrus and shallowcumulus) over small areas (about 200km) produced by a lidar and radar instrument simulator (ECSIM)running on Large Eddy Simulations. Doing so, we verify that the fourth instruments will be able to detect thesame clouds despite their differences (e.g. their sensitivities to noise). Finally, we use the COSP lidar andradar simulator to predict the global scale cloud cover that ATLID, CALIOP, CloudSat and EarthCARE CPRwould observe if they were overflying the same atmosphere predicted by a GCM. Our results suggest that amerged CALIOP/ATLID and CloudSat/CPR cloud climatology could be to be useful for clouds inter-annualstudies, if the post-launch sensitivity of EarthCARE instruments is in line with what is predicted today