Graph of the Day: Anomaly Map of Greenland Melting Days for 2010

Anomaly map of Greenland melting days for 2010 derived from passive microwave data. Hatched regions indicate where MAR-simulated meltwater production exceeds the mean by at least two standard deviations. Abstract: Analyses of remote sensing data, surface observations and output from a regional atmosphere model point to new records in 2010 for surface melt and albedo, runoff, the number of days when bare ice is exposed and surface mass balance of the Greenland ice sheet, especially over its west and southwest regions. Early melt onset in spring, triggered by above-normal near-surface air temperatures, contributed to accelerated snowpack metamorphism and premature bare ice exposure, rapidly reducing the surface albedo. Warm conditions persisted through summer, with the positive albedo feedback mechanism being a major contributor to large negative surface mass balance anomalies. Summer snowfall was below average. This helped to maintain low albedo through the 2010 melting season, which also lasted longer than usual. … Surface melting over the Greenland ice sheet, which can be estimated from satellite data, ground observations or models (Abdalati and Steffen, 1997, Mote, 2007, Nghiem et al., 2001, Hall et al., 2009, Tedesco, 2007, Hanna et al., 2008, Fettweis et al., 2010b, Ettema et al., 2010) was also exceptional in 2010 (Box et al., 2010). Results obtained applying the algorithm reported in Tedesco (2007) to spaceborne microwave brightness temperatures (e.g., Armstrong et al., 1994, Knowles et al., 2002) are consistent with those reported in Box et al. (2010), showing that large areas of the ablation zone in south Greenland underwent melting up to 50 days longer in 2010 compared to the 1979 – 2009 average, with melting in 2010 starting exceptionally early at the end of April and ending quite late in mid September (above figure). These results are confirmed by surface measurements. Near-surface air temperature is often used as a proxy for surface 49 melting. Previous studies have analyzed exceptional melting events mainly focusing on the relationship between melt and near surface temperatures (e.g., Mote 2007, Tedesco 2007). However, melting and, consequently the surface mass balance (SMB), also depend on accumulation, radiation conditions, refreezing and sublimation, the latter relatively small and constant in time (Box and Steffen, 2001; Fettweis, 2007; Van den Broeke et al., 2008). Surface melt and albedo are intimately linked: as melting increases, so does snow grain size, leading to a decrease in surface albedo which then fosters further melt. Also, changes in accumulation can affect the seasonal evolution of surface albedo, that influences the SMB. It is hence not sufficient to analyze near-surface temperature trends to understand the driving mechanisms of extreme mass loss and studying the role of albedo and accumulation becomes crucial to provide a more robust understanding of the exceptional melting detected by satellite microwave sensors.

In this study, we report results derived from spaceborne sensors, surface glaciological observations and regional atmospheric model outputs regarding the surface albedo, accumulation and bare ice exposure over the Greenland ice sheet during the summer of 2010. Our results indicate that negative surface albedo anomalies were especially prominent over west Greenland, with bare ice exposed earlier than previous years. In addition, increased runoff and reduced accumulation likely contributed to a strongly negative SMB. …

M Tedesco, et al., 2011 Environ. Res. Lett. 6 014005, The role of albedo and accumulation in the 2010 melting record in Greenland [pdf]