Abstract
Abstract. We present 5 years (2009–2013) of automatic weather station measurements from the lower accumulation area (1840 m a.s.l. – above sea level) of the Greenland ice sheet in the Kangerlussuaq region. Here, the summers of 2010 and 2012 were both exceptionally warm, but only 2012 resulted in a strongly negative surface mass budget (SMB) and surface meltwater run-off. The observed run-off was due to a large ice fraction in the upper 10 m of firn that prevented meltwater from percolating to available pore volume below. Analysis reveals an anomalously low 2012 summer-averaged albedo of 0.71 (typically ~ 0.78), as meltwater was present at the ice sheet surface. Consequently, during the 2012 melt season, the ice sheet surface absorbed 28 % (213 MJ m−2) more solar radiation than the average of all other years. A surface energy balance model is used to evaluate the seasonal and interannual variability of all surface energy fluxes. The model reproduces the observed melt rates as well as the SMB for each season. A sensitivity analysis reveals that 71 % of the additional solar radiation in 2012 was used for melt, corresponding to 36 % (0.64 m) of the 2012 surface lowering. The remaining 64 % (1.14 m) of surface lowering resulted from high atmospheric temperatures, up to a +2.6 °C daily average, indicating that 2012 would have been a negative SMB year at this site even without the melt–albedo feedback. Longer time series of SMB, regional temperature, and remotely sensed albedo (MODIS) show that 2012 was the first strongly negative SMB year, with the lowest albedo, at this elevation on record. The warm conditions of recent years have resulted in enhanced melt and reduction of the refreezing capacity in the lower accumulation area. If high temperatures continue, the current lower accumulation area will turn into a region with superimposed ice in coming years.
Highlights
Glaciers and ice caps have dominated the cryospheric component to global average sea level rise during the past century (0.5 mm yr−1 or about 70 % of the total cryospheric component for the period 1961–2003; Solomon et al, 2007) due to their relatively short response times to climate variability
Our aim is to assess the sensitivity of surface mass budget (SMB) to atmospheric forcing in the lower accumulation area by using automatic weather stations (AWSs) measurements as input for a surface energy balance (SEB) model
We found that the AWS tripod and stake assembly are prone to sinking somewhat into warm, melting firn during the second part of the melt season
Summary
Glaciers and ice caps have dominated the cryospheric component to global average sea level rise during the past century (0.5 mm yr−1 or about 70 % of the total cryospheric component for the period 1961–2003; Solomon et al, 2007) due to their relatively short response times to climate variability. The largest freshwater reservoir in the Northern Hemisphere is the Greenland ice sheet, which would cause. The average sea level rise contribution from the ice sheet has increased from 0.09 mm yr−1 over the period 1992–2001 to 0.6 mm yr−1 over the period 2002–2011, according to the latest IPCC report (Vaughan et al, 2013). The sheer volume of the ice sheet and the relatively large warming of the polar regions may yield an increasingly dominant contribution to cryospheric mass loss in coming decades
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