Enhancement of snow albedo reduction and radiative forcing due to coated black carbon in snow

Wei Pu,Xin Wang,Jiecan Cui,Yang Chen,Yue Zhou,Tenglong Shi

doi:10.5194/tc-15-2255-2021

Abstract

Abstract. When black carbon (BC) is mixed internally with other atmospheric particles, the BC light absorption effect is enhanced. This study explicitly resolved the optical properties of coated BC in snow based on the core / shell Mie theory and the Snow, Ice, and Aerosol Radiative (SNICAR) model. Our results indicated that the BC coating effect enhances the reduction in snow albedo by a factor ranging from 1.1–1.8 for a nonabsorbing shell and 1.1–1.3 for an absorbing shell, depending on the BC concentration, snow grain radius, and core / shell ratio. We developed parameterizations of the BC coating effect for application to climate models, which provides a convenient way to accurately estimate the climate impact of BC in snow. Finally, based on a comprehensive set of in situ measurements across the Northern Hemisphere, we determined that the contribution of the BC coating effect to snow light absorption exceeds that of dust over northern China. Notably, high enhancements of snow albedo reduction due to the BC coating effect were found in the Arctic and Tibetan Plateau, suggesting a greater contribution of BC to the retreat of Arctic sea ice and Tibetan glaciers.

Highlights

Snow is the most reflective natural substance on the surface of Earth and covers more than 30 % of the global land area (Cohen and Rind, 1991)
Eabs varies with the wavelength and increases with the core / shell ratio, in contrast to the default Eabs value employed in the original SNICAR model, which remains constant
This occurs because compared to the nonabsorbing shell, the absorbing shell, it absorbs additional incident photons, causes fewer photons to reach the core, so that the photons absorbed by the lensing effect and black carbon (BC) core are reduced

Summary

Introduction

Snow is the most reflective natural substance on the surface of Earth and covers more than 30 % of the global land area (Cohen and Rind, 1991). Snow albedo feedback is considered one of the major energy balance factors of the climate system. LAPs play a major role in the alteration of snow morphology and snowmelt processes and yield important effects on local hydrological cycles and global climate (Qian et al, 2009). Warren and Wiscombe (1980) developed a radiative forcing model based on the Mie theory and the δ-Eddington approximation and reported that snow albedo at visible wavelengths could be reduced by 5 %–15 % with 1000 ng g−1 BC in snow. In addition to BC, the SNICAR model considers the potential effects of dust particles and volcanic ash on snow albedo. Nonspherical snow grains attain a lower albedo reduction than that due to spherical snow grains (He et al, 2018c; Dang et al, 2016)

Methods

Results

Conclusion