Enhanced Snow Absorption and Albedo Reduction by Dust‐Snow Internal Mixing: Modeling and Parameterization

Abstract

We extend a stochastic aerosol-snow albedo model to explicitly simulate dust internally/ externally mixed with snow grains of different shapes and for the first time quantify the combined effects of dust-snow internal mixing and snow nonsphericity on snow optical properties and albedo. Dust-snow internal/external mixing significantly enhances snow single-scattering coalbedo and absorption at wavelengths of <1.0 μm, with stronger enhancements for internal mixing (relative to external mixing) and higher dust concentrations but very weak dependence on snow size and shape variabilities. Compared with pure snow, dust-snow internal mixing reduces snow albedo substantially at wavelengths of <1.0 μm, with stronger reductions for higher dust concentrations, larger snow sizes, and spherical (relative to nonspherical) snow shapes. Compared to internal mixing, dust-snow external mixing generally shows similar spectral patterns of albedo reductions and effects of snow size and shape. However, relative to external mixing, dust-snow internal mixing enhances the magnitude of albedo reductions by 10%-30% (10%-230%) at the visible (near-infrared) band. This relative enhancement is stronger as snow grains become larger or nonspherical, with comparable influences from snow size and shape. Moreover, for dust-snow external and internal mixing, nonspherical snow grains have up to~45% weaker albedo reductions than spherical grains, depending on snow size, dust concentration, and wavelength. The interactive effect of dust-snow mixing state and snow shape highlights the importance of accounting for these two factors concurrently in snow modeling. For application to land/climate models, we develop parameterizations for dust effects on snow optical properties and albedo with high accuracy.Plain Language Summary Mineral dust is one of the most common and abundant aerosols by mass, playing a key role in the Earth/climate system. Dust can significantly reduce snow albedo and accelerate snow/glacier melting after deposition. Previous modeling studies have mainly assumed dust mixed outside spherical snow grains, whereas in reality dust can also be mixed inside nonspherical snow grains. Thus, it is imperative to understand and quantify the effects of dust-snow mixing type (outside vs. inside snow grains) and snow grain shape (spherical vs. nonspherical) on snow albedo. This study uses an advanced snow albedo model to simulate dust mixed with snow grains of different shapes. Results show that dust mixed with snow grains can enhance snow absorption of sunlight and hence reduce snow albedo. Dust reduces snow albedo more when mixed inside snow grains than when mixed outside snow grains, while dust reduces snow albedo less when mixed with nonspherical snow grains than when mixed with spherical snow grains. This intertwined effect from dust-snow mixing type and snow shape highlights the importance of including these two factors simultaneously in snow models. This study further develops parameterizations to account for dust effects on snow albedo for co...

Modulation of springtime surface sensible heating over the Tibetan Plateau on the interannual variability of East Asian dust cycle

“…On one hand, an increase in dust aerosols would result in a decrease of solar heating at surface, and thus a decrease in temperature, turbulence, and sensible heat flux through dust direct effect (Miller et al, 2004;Heinold et al, 2007;Xie et al, 2018a). On the other hand, previous studies indicate that dust deposited on the snow over the TP region reduces the visible surface albedo and warms the surface of the TP through the snow-darkening effect (Flanner et al, 2009;Qian et al, 2011Qian et al, , 2015He et al, 2018;Xie et al, 2018b;Shi et al, 2019).…”

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

“…The code of (core-shell) Mie theory used in this study can be found at http://eodg.atm.ox.ac.uk/MIE/mie_single. html (last access: 20 April 2021, Earth Observation Data Group, 2021) and http://gwest.gats-inc.com/software/bhcoat.pro (last access: 20 April 2021, Hervig, 2021).…”

Biomass-Derived Provenance Dominates Glacial Surface Organic Carbon in the Western Himalaya

“…[5][6][7] Impurities that darken the ice surface and directly increase the heat absorption and thus enhance ice melting comprise dust, BC (black carbon, e.g., soot), and other forms of OC not derived from combustion. [8][9][10][11] In this study, OC refers to the total organic 51 carbon that comprises the entire pool of organic carbon including both organic and elemental 52 carbon. Further, we classify the OC as OC ff (fossil fuel) and OC bio (biomass) referring to OC derived from either fossil fuel or biomass sources, such as biomass burning derived particles, atmospheric organic matters, and glacial microbes.…”