C32B-01
Neither Dust Nor Black Carbon Causing Apparent Albedo Decline in Greenland’s Dry Snow Zone; Uncorrected Sensor Degradation Impacting MODIS C5 Results
Wednesday, 16 December 2015: 10:20
3007 (Moscone West)
Chris Polashenski1, Jack E Dibb2, Mark Flanner3, Justin Chen4, Zoe Courville5, Alexandra Lai6, James J Schauer6, Martin M Shafer7 and Michael Howard Bergin8, (1)Dartmouth College, Thayer School of Engineering, Hanover, NH, United States, (2)University of New Hampshire Main Campus, Durham, NH, United States, (3)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (4)Hanover High School, Hanover, NH, United States, (5)CRREL, Hanover, NH, United States, (6)University of Wisconsin Madison, Madison, WI, United States, (7)Univ Wisconsin-Madison, Madison, WI, United States, (8)Duke University, Durham, NC, United States
Abstract:
Observations suggest the Greenland ice sheet albedo has declined since 2001, even in the dry snow zone (DSZ). We seek to explain the apparent DSZ albedo decline. We analyze samples representing 2012-2014 snowfall across NW Greenland for absorbing impurities (black carbon and dust) and model their impacts on snow albedo. Albedo reductions due to absorbing impurities are small, averaging 0.003, with episodic enhancements resulting in reductions of 0.01-0.02. No significant increase in black carbon or dust concentrations relative to recent decades is indicated. Enhanced deposition of absorbing impurities is not, therefore, causing significant albedo reduction in the DSZ or driving recent melt events. Analysis of MODIS surface reflectance indicates that the decline and spectral shift in DSZ albedo seen in C5 MODIS data contains contributions from uncorrected Terra sensor degradation. The discrepancies between Terra and Aqua are generally below the stated accuracy of MODIS products (0.05), but since discussions of Greenland albedo trends below this level are common in the literature, the identification of these discrepancies likely requires revisiting conclusions about the trends and spectral signature of Greenland DSZ albedo after C6 data is released.
