Greenland, Canadian and Icelandic land-ice albedo grids (2000–2016)

Abstract

Albedo, Latin for ‘whiteness’, is a term used to describe the amount of sunlight reflected by the ground. Fresh snow albedo can exceed 85%, making it among the most reflective natural substances. Warm conditions promote snow crystal metamorphosis that, like the presence of liquid water, bring snow albedo down below 65%. With the darkening, caused by the metamorphosis, absorbed solar energy thus increases by roughly a factor of two. Seasonal snow melts over the lower reaches of a glacier leading to the exposure of bare ice with albedo below 55%. Impurities such as dust, black carbon or microbes can bring glacier-ice albedo below 30%, meaning that snow ablation gives way to impurity-rich, bare glacier ice which increases absorbed sunlight by more than a factor of three. The thickness of the winter snow layer and the intensity of spring melt are important determinants of the annual glacier-ice melt, as the amount of snow cover governs the timing of darker ice exposure; the earlier the exposure, the more ice can melt. Because snow and ice albedo properties make it an amplifier of climate change, surface albedo has been designated as an Essential Climate Variable and a Target Requirement for climate monitoring (WMO 2011). Polar orbiting satellites facilitate albedo mapping with Arctic coverage multiple times per day in clear-sky conditions. Satellite-based retrievals of surface albedo depend on accurate compensation of the intervening atmosphere. Thus, without ground truth, the satellite retrievals are uncertain. In Greenland, snow and ice albedo is monitored by automatic weather stations (AWSs) from The Greenland Climate Network (GC-Net; Steffen et al. 1996) since 1995 and after 2007 from The Programme for Monitoring of the Greenland Ice Sheet (PROMICE; van As et al. 2013). Using the GC-Net data, satellite-derived albedo values are compared with ground data (e.g. Stroeve et al. 2013). Here, we present comparisons of daily GC-Net and PROMICE albedo data to satellite-derived albedo from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) MOD10A1 product (Hall et al. 1995). MOD10A1 data have been available since May 2000 and are here de-noised, gap-filled and calibrated into a daily 500 × 500 m grid covering Greenland, Iceland and the Canadian Arctic glaciers (Fig. 1).