Contributions of Clouds to Greenland's Surface Melt
The impact of clouds on Greenland's surface melt is difficult to quantify due to harsh observing conditions. To better quantify cloud radiative effects (CRE), we exploit 29 automatic weather stations (AWS), and for the first time, provide a multi-year analysis on seasonal and hourly timescales across both accumulation and ablation zones. Longwave CRE shows that a bimodal distribution of clouds occurs on the diurnal timescale. The close relationship between CRE and albedo over dark surfaces suggests a stabilizing feedback: net CRE is negative at low albedo caused by snow melt and snow metamorphism, and thus tends to increase albedo and decelerate surface melt. We also intercompare Greenland CRE spatial distributions estimated from AWS, satellite, reanalyses, and a global climate model (MERRA2, ERA-Interim, CERES, ASR, and CESM). With AWS as "ground truth", we identify better and worse CRE distributions from the gridded datasets, and identify the physical causes of discrepencies. AWS observations show that clouds enhance surface melt in the higher accumulation zone and reduce surface melt in the lower ablation zone.