Numerical Simulation of Spectral Albedos of Glacier Surfaces Covered with Glacial Microbes in Northwestern Greenland

摘要

To clarify the effect of light absorbing impurities including glacial microbes spectral albedo measurements using a spectrometer for spectral domains of the ultraviolet, visible and near-infrared have been carried out on ablation area in Qaanaaq Glacier in northwestern Greenland in July 2011. The almost glacier surfaces in the ablation area were covered with cryoconite (biogenic dust) on thin ice grain layer above bare ice. There were also snow-covered surfaces including red snow (snow algae). The measured spectral albedos had a remarkable contrast between red snow surface and cryoconite-covered ice surface in the spectral domain from the ultraviolet to the visible, where red snow albedo increased rapidly with the wavelength, while the cryoconite albedo was relatively flat to the wavelength. We simulated the spectral albedos of these surfaces with a radiative transfer model for the atmosphere-snow system. The single scattering properties are calculated with Mie theory by assuming red snow gains to be spherical and with geometric optics by assuming ice grains of cryoconite surface to be non-spherical Voronoi aggregates. We calculated the effect of glacial microbes as snow (ice) impurities using a mineral dust model by changing the imaginary part of refractive index so as to fit the theoretically calculated spectral albedo to the measurement. Finally the imaginary part of refractive indices for red snow and cryoconite at the wavelengths less than 1.0 μm were retrieved. It was found that cryoconite has uniformly higher light absorption compared to mineral dust and red snow has strong light absorption at the wavelengths less than 0.6 μm.