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

Wednesday, 17 December 2014
Mathieu Reverdy1, Hélène Chepfer2, David P Donovan3, Vincent Noel4, Roger Marchand5, Grégory Cesana6, Christophe Hoareau7, Marjolaine Chiriaco8 and Sophie Bastin8, (1)Ecole Polytechnique, Palaiseau Cedex, France, (2)Laboratoire de Météorologie Dynamique Palaiseau, Palaiseau Cedex, France, (3)Royal Netherlands Meteorological Institute, De Bilt, Netherlands, (4)LMD, Palaiseau, France, (5)University of Washington, Department of Atmospheric Sciences, Seattle, WA, United States, (6)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (7)Laboratoire de Météorologie Dynamique, Palaiseau Cedex, France, (8)LATMOS Laboratoire Atmosphères, Milieux, Observations Spatiales, Paris Cedex 05, France
Today, the CALIOP lidar and CloudSat radar have collected more than seven years of observations, and will
hopefully still operate in 2016, after the EarthCARE-ATLID/CPR launch. Lidars and Radars in space provide
cutting edge information on the detailed vertical structure of clouds: a key element for both the evaluation of
the description of clouds in climate models, and the survey of the clouds inter-annual evolution in various
climatic 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 be
merged 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 and
relevance 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 their
ability 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 shallow
cumulus) 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 the
same clouds despite their differences (e.g. their sensitivities to noise). Finally, we use the COSP lidar and
radar simulator to predict the global scale cloud cover that ATLID, CALIOP, CloudSat and EarthCARE CPR
would observe if they were overflying the same atmosphere predicted by a GCM. Our results suggest that a
merged CALIOP/ATLID and CloudSat/CPR cloud climatology could be to be useful for clouds inter-annual
studies, if the post-launch sensitivity of EarthCARE instruments is in line with what is predicted today.