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

Tenglong Shi,Quanliang Chen,Wei Pu,Xuelei Zhang,Xuanye Xu,Jiecan Cui,Xin Wang,Yang Chen,Yue Zhou

doi:10.5194/acp-21-6035-2021

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.

Highlights

Snow cover is one of the most reflective surfaces in the Earth system, and plays a crucial role in the atmospheric solar radiation energy budget via snow albedo feedbacks (DiMauro et al, 2020; Flanner et al, 2011; Jacobson, 2004; Usha et al, 2020; Xie et al., 2018)
The effects of dust particles on absorption coefficients and snow albedo were theoretically analyzed by combining asymptotic radiative transfer theory and Mie theory
We initially considered external mixing – when dust is present between ice grains – and variations of internal mixing of dust within ice grains

Summary

Introduction

Snow cover is one of the most reflective surfaces in the Earth system, and plays a crucial role in the atmospheric solar radiation energy budget via snow albedo feedbacks (DiMauro et al, 2020; Flanner et al, 2011; Jacobson, 2004; Usha et al, 2020; Xie et al., 2018). Previous studies have shown that light-absorbing particles (LAPs) effectively reduce snow albedo and enhance the absorption of solar radiation after deposition, these studies were based on in situ observations and model simulations (Casey et al, 2017; Hadley and Kirchstetter, 2012; Shi et al, 2020; Warren and Wiscombe, 1980; Yasunari et al, 2012; Yasunari et al, 2015). Numerous studies have assessed the potential effects of LAPs, such as black carbon (BC) and mineral dust, on snow albedo by assuming that LAPs mixed outside spherical snow grains (i.e., external mixing) (Flanner et al, 2007; Kokhanovsky, 2013; Libois et al, 2013; Wang et al, 2017; Warren and Wiscombe, 1980). Warren and Wiscombe (1980) calculated snow spectral albedo by solving a radiative transfer equation using Mie theory and δ-Eddington approximations, and found that 10–100 ng g−1 of BC and 1–10 μg g−1 of dust in old snow decreased albedo by 1%–7% and 2%–

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Discussion

Conclusion