Enhanced light absorption and reduced snow albedo due to internally mixed mineral dust in grains of snow

Abstract

Abstract. Mineral dust is a major light-absorbing aerosol, which can significantly reduce snow albedo and accelerate snow/glacier melting via wet and dry deposition on snow. In this study, three scenarios of internal mixing of dust in ice grains were analyzed theoretically by combining asymptotic radiative transfer theory and (core–shell) Mie theory to evaluate the effects on absorption coefficient and albedo of the semi-infinite snowpack consisting of spherical snow grains. In general, snow albedo was substantially reduced at wavelengths of <1.0 µm by internal dust–snow mixing, with stronger reductions at higher dust concentrations and larger snow grain sizes. Moreover, calculations showed that a nonuniform distribution of dust in snow grains can lead to significant differences in the values of the absorption coefficient and albedo of dust-contaminated snowpack at visible wavelengths relative to a uniform dust distribution in snow grains. Finally, using comprehensive in situ measurements across the Northern Hemisphere, we found that broadband snow albedo was further reduced by 5.2 % and 9.1 % due to the effects of internal dust–snow mixing on the Tibetan Plateau and North American mountains. This was higher than the reduction in snow albedo caused by black carbon in snow over most North American and Arctic regions. Our results suggest that significant dust–snow internal mixing is important for the melting and retreat of Tibetan glaciers and North American mountain snowpack.

Modelling light-absorbing particle–snow–radiation interactions and impacts on snow albedo: fundamentals, recent advances and future directions

“…6). Assuming dust external mixing with snow spheres, dust can lead to broadband snow albedo reductions of up to 0.3 with 100 ppm dust content in aged snow (snow grain radius of 1000 μm) (Dang et al 2015;He et al 2019;Shi et al 2021). Dust in snow leads to a springtime regional mean surface radiative forcing of up to 5 W m −2 over the globe, with particularly strong forcing (>10 W m −2 ) over the polluted mid-latitude seasonal snowpack (Painter et al 2010;Skiles et al 2018;Dumont et al 2020;Shi et al 2022a).…”

“…Recent studies pointed out that dust can also be internally mixed with snow grains through dust atmospheric wet deposition (e.g. serving as ice nuclei; Hoose and Möhler 2012), which enhances dust-induced snow albedo reductions by up to 40% (Liou et al 2014;He et al 2019;Shi et al 2021). For example, He et al (2019) estimated that dust-snow internal mixing leads to about 20% higher snow albedo reductions in the Colorado River Basin (US) than external mixing, which is equivalent to an increase of 6-16 W m −2 for dust-induced springtime surface radiative effects.…”

“…For example, He et al (2019) estimated that dust-snow internal mixing leads to about 20% higher snow albedo reductions in the Colorado River Basin (US) than external mixing, which is equivalent to an increase of 6-16 W m −2 for dust-induced springtime surface radiative effects. Shi et al (2021) further tested the impact of three different dust-snow internal mixing configurations for spherical snow grains, including dust distributed uniformly, in the centre or in the peripheral within each snow grain. They found that the uniform dust-snow internal mixing configuration leads to smaller snow albedo reductions than the central internal mixing configuration but larger albedo reductions than the peripheral internal mixing configuration.…”

“…Some recent studies explored the effects of dust and BC internally mixed with snow grains and snow non-sphericity through modelling experiments (e.g. Flanner et al 2012;Dang et al 2016;He et al 2017aHe et al , 2019Shi et al 2021), which however have not been validated by direct observations. Currently, no theoretical or observational studies on BrC/ash/algae-snow mixing structures and impacts on snow albedo are available.…”

Fluorescence characteristics, absorption properties, and radiative effects of water-soluble organic carbon in seasonal snow across northeastern China

“…Snowpack BC and MD have been the focus of considerable research in snow-covered regions worldwide (Li et al, 2021a;Zhang et al, 2018;Antony et al, 2014;Hegg et al, 2010;Doherty et al, 2014;Wang et al, 2015). As the most important LAP (Bond et al, 2013;Doherty et al, 2010;Wang et al, 2014b), the radiative efficiency of snowpack BC can be more than three times greater than that of carbon dioxide (Flanner et al, 2007), and MD, another important snowpack LAP, is also known to alter the cryospheric environment owing to its light-absorbing properties (Di Mauro et al, 2015;Painter et al, 2007;Sarangi et al, 2020;Shi et al, 2021). Recently, researchers have also begun evaluating the influence of biomes on global snow albedo (Hotaling et al, 2021).…”