Greenland clouds observed in CALIPSO-GOCCP: comparison with ground-based Summit observations.

Abstract

paceborne lidar observations from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) provide the first-ever observations of cloud vertical structure and phase over the entire Greenland icesheet. This study leverages CALIPSO observations over Greenland to pursue two investigations. First, the GCM-Oriented-CALIPSO Cloud Product (CALIPSO-GOCCP) observations are compared with collocated ground-based radar and lidar observations at Summit, Greenland. The liquid cloud cover agrees well between the spaceborne and ground-based observations. In contrast, ground satellite differences reach 30% in total cloud cover and 40% in cloud fraction below 2 km Above Ground Level, due to optically very thin ice clouds (IWC < 2.5?10-3 g m-3) missed by CALIPSO-GOCCP. Those results are compared with satellite cloud climatologies from the GEWEX cloud assessment. Most passive sensors detect fewer clouds than CALIPSO-GOCCP and the Summit ground observations, due to different detection methods. Second, the distribution of clouds over the Greenland is analyzed using CALIPSO-GOCCP. The central Greenland is the cloudiest area in summer: +7% and +4% above Greenland-wide average for respectively total and liquid cloud cover. South Greenland contains free troposphere thin ice clouds all seasons, and liquid clouds in summer. In northern Greenland, fewer ice clouds are detected than in other areas, but the liquid cloud cover seasonal cycle in that region drives the total Greenland cloud annual variability with a maximum in summer. In 2010 and 2012, large ice-sheet melting events have positive liquid cloud cover anomaly (+1 to 2%). In contrast, less clouds (-7%) are observed during low ice-sheet melt years (e.g., 2009).