The impact of atmospheric mineral aerosol deposition on the albedo of snow &amp;amp; sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?

M L Lamare,J Lee-Taylor,M D King

doi:10.5194/acp-16-843-2016

Abstract

Abstract. Knowledge of the albedo of polar regions is crucial for understanding a range of climatic processes that have an impact on a global scale. Light-absorbing impurities in atmospheric aerosols deposited on snow and sea ice by aeolian transport absorb solar radiation, reducing albedo. Here, the effects of five mineral aerosol deposits reducing the albedo of polar snow and sea ice are considered. Calculations employing a coupled atmospheric and snow/sea ice radiative-transfer model (TUV-snow) show that the effects of mineral aerosol deposits are strongly dependent on the snow or sea ice type rather than the differences between the aerosol optical characteristics. The change in albedo between five different mineral aerosol deposits with refractive indices varying by a factor of 2 reaches a maximum of 0.0788, whereas the difference between cold polar snow and melting sea ice is 0.8893 for the same mineral loading. Surprisingly, the thickness of a surface layer of snow or sea ice loaded with the same mass ratio of mineral dust has little effect on albedo. On the contrary, the surface albedo of two snowpacks of equal depth, containing the same mineral aerosol mass ratio, is similar, whether the loading is uniformly distributed or concentrated in multiple layers, regardless of their position or spacing. The impact of mineral aerosol deposits is much larger on melting sea ice than on other types of snow and sea ice. Therefore, the higher input of shortwave radiation during the summer melt cycle associated with melting sea ice accelerates the melt process.

Highlights

The albedo of snow and sea ice has a large influence on the surface energy budget of polar regions, impacting the Earth’s climate system (e.g. Barry et al, 1993; Curry et al, 1995; Jacobson, 2004; Serreze and Barry, 2005)
The results are presented in three sections: the effect of different types of mineral aerosol deposits on albedo of polar snow and sea ice, the variation of albedo with increasing loading of mineral aerosol deposits and the effect of layers of mineral aerosol deposits in snow
Helens light grey ash reaches 0.0268 in cold polar snow and 0.1444 in first-year sea ice as shown in Fig. 5, where the albedo of different snow and sea ice types is shown for an increasing mass ratio of mineral aerosol deposits

Summary

Introduction

The albedo of snow and sea ice has a large influence on the surface energy budget of polar regions, impacting the Earth’s climate system (e.g. Barry et al, 1993; Curry et al, 1995; Jacobson, 2004; Serreze and Barry, 2005). The albedo of snow and sea ice has a large influence on the surface energy budget of polar regions, impacting the Earth’s climate system Variation in albedo is linked to several factors, such as the physical properties of snow and sea ice, morphology, surface roughness, thickness and light-absorbing impurities Previous studies have defined wavelength integrated and spectral albedos for a variety of snow and sea ice types Albedo is influenced by the physical structure of snow or sea ice and by the amount and type of lightabsorbing impurities in the snow and sea ice (Warren and Wiscombe, 1980). Small amounts of light-absorbing impurities are needed to achieve changes in snow or sea ice albedo

Methods

Results

Discussion

Conclusion