Motion of dust particles in dry snow under temperature gradient metamorphism

Pascal Hagenmuller,Frederic Flin,Isabel Peinke,François Tuzet,Edward Ando,Didier Voisin,Philippe Lapalus,Sabine Rolland Du Roscoat,Pascal Charrier,Laurent Pézard,Jacques Roulle,Marie Dumont,Anne Dufour

doi:10.5194/tc-13-2345-2019

Abstract

Abstract. The deposition of light-absorbing particles (LAPs) such as mineral dust and black carbon on snow is responsible for a highly effective climate forcing, through darkening of the snow surface and associated feedbacks. The interplay between post-depositional snow transformation (metamorphism) and the dynamics of LAPs in snow remains largely unknown. We obtained time series of X-ray tomography images of dust-contaminated samples undergoing dry snow metamorphism at around −2 ∘C. They provide the first observational evidence that temperature gradient metamorphism induces dust particle motion in snow, while no movement is observed under isothermal conditions. Under temperature gradient metamorphism, dust particles can enter the ice matrix due to sublimation–condensation processes and spread down mainly by falling into the pore space. Overall, such motions might reduce the radiative impact of dust in snow, in particular in arctic regions where temperature gradient metamorphism prevails.

Highlights

Dust in snow is an important driver of snowpack evolution (Dumont et al, 2014; Ginot et al, 2014; Painter et al, 2018; Skiles et al, 2018)
The anisotropy factor Q remained constant under isothermal conditions whereas temperature gradient metamorphism led to an increase in Q between 50 and 150 h due to the formation of ice structures that tend to be more aligned with the water vapor fluxes (Fig. 2c)
This study presents the first in operando microscopic observation of the interactions between dust and snow metamorphism

Summary

Introduction

Dust in snow is an important driver of snowpack evolution (Dumont et al, 2014; Ginot et al, 2014; Painter et al, 2018; Skiles et al, 2018). Mineral dust primarily affects the snow optical properties by lowering the albedo, which governs the amount of solar energy that is absorbed in the visible wavelengths (Warren and Wiscombe, 1980) This albedo decrease leads to accelerated metamorphism and possibly faster melt rates (Flanner et al, 2007; Tuzet et al, 2017). While several studies have quantified the radiative impact of dust on snow evolution (e.g., Skiles et al, 2012; Painter et al, 2012), large uncertainties remain They pertain in particular to (i) uncertainties of the dust refractive index (due to the influence of its geometry and chemical composition) (Caponi et al, 2017), (ii) poor knowledge of the mixing state of the dust particles in the ice matrix (Flanner et al, 2012) and (iii) imperfect representation of the vertical distribution of dust in the snowpack and related impacts (Dumont et al, 2014; Tuzet et al, 2017).

Methods

Results

Conclusion