Optical properties of dust deposited in mountain snow

What is it about?

In this article we present an inversion method to retrieve the imaginary part of complex refractive index, which describes absorption, of dust deposited in snow cover of the Rocky Mountains, CO. We use a high resolution snow sampling and observation dataset described in a related article, coincidentally published in the Journal of Glaciology titled ‘Daily evolution in dust and black carbon content, snow grain size, and snow albedo during snowmelt, Rocky Mountains, Colorado.’ This method is unique in that it was developed to use measured reflectance and particle size distributions of dust from snow, is validated with measured snow albedo, and specifically aims to improve radiative transfer modeling of snow containing dust at high spectral resolution across the full range of snow reflectance. Using the values retrieved by this method to update dust optical properties in a snow + aerosol radiative transfer model reduces errors in springtime albedo modeling by 50–70%.

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Why is it important?

Mineral dust is a critical component of the Earth system that impacts atmospheric radiative transfer, biogeochemistry, and snow/ice melt from regional to continental scales. However, the optical properties of dust are poorly constrained observationally. Dust deposition has been observed in almost all snow and ice covered environments, but is most prevalent in the mid-latitudes where it has been shown to shift snowmelt runoff timing and intensity through surface darkening and the initiation of snow albedo feedbacks. Modeling radiative forcing by dust, or any other light absorbing impurity, in snow requires an understanding of the optical properties of both snow and impurities. Although the optical properties of snow are well understood and spatially consistent, the optical properties of dust vary regionally and have never been determined for dust samples collected from snow.