Abstract
Abstract. Accurate measurements and simulations of Greenland Ice Sheet (GrIS) surface albedo are essential, given the role of surface albedo in modulating the amount of absorbed solar radiation and meltwater production. In this study, we assess the spatio-temporal variability of GrIS albedo during June, July, and August (JJA) for the period 2000–2013. We use two remote sensing products derived from data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS), as well as outputs from the Modèle Atmosphérique Régionale (MAR) regional climate model (RCM) and data from in situ automatic weather stations. Our results point to an overall consistency in spatio-temporal variability between remote sensing and RCM albedo, but reveal a difference in mean albedo of up to ~0.08 between the two remote sensing products north of 70° N. At low elevations, albedo values simulated by the RCM are positively biased with respect to remote sensing products by up to ~0.1 and exhibit low variability compared with observations. We infer that these differences are the result of a positive bias in simulated bare ice albedo. MODIS albedo, RCM outputs, and in situ observations consistently indicate a decrease in albedo of −0.03 to −0.06 per decade over the period 2003–2013 for the GrIS ablation area. Nevertheless, satellite products show a decline in JJA albedo of −0.03 to −0.04 per decade for regions within the accumulation area that is not confirmed by either the model or in situ observations. These findings appear to contradict a previous study that found an agreement between in situ and MODIS trends for individual months. The results indicate a need for further evaluation of high elevation albedo trends, a reconciliation of MODIS mean albedo at high latitudes, and the importance of accurately simulating bare ice albedo in RCMs.
Highlights
Over the past decade, the Greenland Ice Sheet (GrIS) has simultaneously experienced accelerating mass loss (van den Broeke et al, 2009; Rignot et al, 2011) and records for the extent and duration of melting (Tedesco et al, 2008, 2011, 2013; Nghiem et al, 2012)
Modèle Atmosphérique Régionale (MAR) v3.2 and the two Moderate Resolution Imaging Spectroradiometer (MODIS) data sets show coherent spatial patterns of JJA mean 2000–2013 albedo (Fig. 2) that are consistent with previous studies (e.g. Box et al, 2012), with low-elevation areas in the ablation area dominated by lower albedo values (< 0.7 on average, Table 3) due to the presence of meltwater and bare ice, and high elevation areas by relatively higher albedo (> 0.74)
Because any systematic biases in the satellite products are likely to be relatively consistent across space, it is likely that MAR v3.2 biases contribute to some of the elevational differences seen in Fig. 3b and Fig. 3c
Summary
The Greenland Ice Sheet (GrIS) has simultaneously experienced accelerating mass loss (van den Broeke et al, 2009; Rignot et al, 2011) and records for the extent and duration of melting (Tedesco et al, 2008, 2011, 2013; Nghiem et al, 2012). Due to the impact of albedo on the surface energy balance, it is crucial to assess the performance of models that simulate albedo over the GrIS and the quality of albedo estimates from remote sensing or in situ observations. These assessments are pivotal for improving our understanding of the physical processes leading to accelerating mass loss, and for improving future projections
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