Greenland Clouds Observed in CALIPSO-GOCCP: Comparison with Ground-Based Summit Observations

Abstract

Spaceborne lidar observations from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations ( CALIPSO) satellite provide the first-ever observations of cloud vertical structure and phase over the entire Greenland Ice Sheet. 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. Central Greenland is the cloudiest area in summer, at +7% and +4% above the Greenland-wide average for total and liquid cloud cover, respectively. Southern Greenland contains free-tropospheric thin ice clouds in 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 a positive liquid cloud cover anomaly (from +1% to +2%). In contrast, fewer clouds (−7%) are observed during low ice-sheet melt years (e.g., 2009).

Temporal Characteristics of Cloud Radiative Effects on the Greenland Ice Sheet: Discoveries From Multiyear Automatic Weather Station Measurements

“…The seasonal trend at Barrow, which is adjacent to the ocean and only covered by scattered snow in summer, is similar to that in the southern ablation zone of the GrIS. The seasonal cycle in the northern accumulation zone on the GrIS agrees with cloud fraction and liquid water content variabilities at Summit reported in Miller et al (), cloud fraction in northern and central Greenland reported in Starkweather (), and liquid cloud fraction in northern Greenland reported in Lacour et al (). On the rest of the GrIS, longwave CRE responds to clouds in an almost opposite manner to shortwave ↓ CRE throughout the season (Figure d).…”

“…Cloud fraction from the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) also increases throughout the melt season in the north. However, it slightly decreases from May to June in the south (Lacour et al, ). Liquid‐containing clouds, which contribute more to surface melt than ice‐only clouds (Bennartz et al, ; Kay et al, ; Miller et al, ), increase continually in both northern and southern Greenland during the melt season, with a larger variability in the north (Lacour et al, ).…”

“…The melt‐season average of cloud fraction from MODIS generally increases from north to south (Starkweather, ). The CALIPSO cloud fraction, dominated by liquid clouds, presents a high‐low‐high spatial pattern from summit to the coasts of Greenland (Cesana et al, ; Lacour et al, ). These differences in cloud properties and environmental conditions could cause dramatic shifts of CRE temporal characteristics across the GrIS.…”

Spatial Distribution of Melt Season Cloud Radiative Effects Over Greenland: Evaluating Satellite Observations, Reanalyses, and Model Simulations Against In Situ Measurements

“…For example, Cesana et al (2015) and Liu and Key (2016) use cloud retrievals from active sensors to evaluate reanalyses and model simulations. However, active sensor retrievals can only be cross-validated at Summit, the sole station with comprehensive cloud measurements inside Greenland (Lacour et al, 2017;Shupe, Turner, et al, 2013).…”

“…Shortwave cooling by clouds is weakest near Summit due to the constantly high albedo. Longwave warming is strongest there probably due to the dry atmosphere and prevalent low-level liquid-containing clouds (Lacour et al, 2017;Miller et al, 2015;Shupe, Turner, et al, 2013). These clouds most likely form by orographic lifting during warm southerly advection (Zygmuntowska et al, 2012) and are usually decoupled from the surface (Curry et al, 1996;Shupe, Persson, et al, 2013;Tjernström et al, 2014) as the boundary layer is drier at higher elevations.…”