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Sunday, April 3, 2016

"The implication of nonradiative energy fluxes dominating Greenland ice sheet exceptional ablation area surface melt in 2012," by Robert Fausto et al., GRL 43 (2016); doi: 10.1002/2016GL067720

Geophysical Research Letters, 43 (March 2016), DOI: 10.1002/2016GL067720

The implication of nonradiative energy fluxes dominating Greenland ice sheet exceptional ablation area surface melt in 2012

Robert Fausto, Dirk van As, Jason E. Box and Ruth Mottram


During two exceptionally large, July 2012, multi-day, Greenland ice sheet, melt episodes, non-radiative energy fluxes (sensible, latent, rain, and subsurface collectively) dominated the ablation area surface energy budget of the southern and western ice sheet. On average, the non-radiative energy fluxes contributed up to 76% of daily melt energy at nine automatic weather station sites in Greenland. Comprising 6% of the ablation period, these powerful melt episodes resulted in 12–15% of the south and west Greenland automatic weather station annual ablation totals. Analysis of high resolution (~5 km) HIRHAM5 regional climate model output indicates widespread dominance of non-radiative energy fluxes across the western ablation area during these episodes. Yet HIRHAM5 still underestimates melt by up to 56% during these episodes due to a systematic underestimation of turbulent energy fluxes typical of regional climate models. This has implications for underestimating future melt, when exceptional melt episodes are expected to occur more frequently.


Understanding the Greenland ice sheet surface climate response is crucial for reducing uncertainties in future predictions of both magnitude and rate of global sea level change [Dutton et al., 2015] and freshwater flux [Lenaerts et al., 2015]. The rate of Greenland ice sheet mass loss has accelerated over the past decades [Tedesco et al., 2013; Khan et al., 2015], and in recent years, the surface components of the ice sheet’s mass budget have become the dominant source of ice loss, outpacing the ice dynamic component [Enderlin et al., 2014; Andersen et al., 2015]. Partly due to two exceptional melt episodes in July 2012, new records for ice sheet surface melt area and ice mass loss were set [Tedesco et al., 2013]. Satellite observations revealed more than 98% of the ice sheet surface was melting on 12 July 2012, which was unprecedented in the 1978 to present satellite record [Nghiem et al., 2012]. This widespread melt in the accumulation area was enhanced by low-level liquid clouds [Bennartz et al., 2013] promoted by the advection of anomalously warm and moist air over Greenland [Neff et al., 2014], which decreased the firn’s ability to retain meltwater [Machguth et al., 2016]. Deposition of wildfire black carbon further promoted melt through enhanced sunlight absorption [Keegan et al., 2014]. Projections suggest that such melt episodes will become increasingly frequent in coming decades [Collins et al., 2013; McGrath et al., 2013].

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