Metamorphism during temperature gradient with undersaturated advective airflow in a snow sample

Pirmin Philipp Ebner,Aldo Steinfeld,Martin Schneebeli

doi:10.5194/tc-10-791-2016

Abstract

Abstract. Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. Time-lapse X-ray microtomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Cold saturated air at the inlet was blown into the snow samples and warmed up while flowing across the sample with a temperature gradient of around 50 K m−1. Changes of the porous ice structure were observed at mid-height of the snow sample. Sublimation occurred due to the slight undersaturation of the incoming air into the warmer ice matrix. Diffusion of water vapor opposite to the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible leading to a constant porosity profile. However, the strong recrystallization of water molecules in snow may impact its isotopic or chemical content.

Highlights

Snow has a complex porous microstructure and consists of a continuous ice structure made of grains connected by bonds and interconnecting pores (Löwe et al, 2011)
Various airflow conditions in a snow sample occur, namely, isothermal airflow, air cooling by a negative temperature gradient along the airflow leading to a local supersaturation of the air, and air warming by a positive temperature gradient along the airflow leading to a local undersaturation of the air (Fig. 1)
We studied the surface dynamics of snow metamorphism under an induced temperature gradient and saturated airflow in controlled laboratory experiments

Summary

Introduction

Snow has a complex porous microstructure and consists of a continuous ice structure made of grains connected by bonds and interconnecting pores (Löwe et al, 2011) It has a high permeability (Calonne et al, 2012; Zermatten et al, 2014) and under appropriate conditions, airflow through the snow structure can occur (Sturm and Johnson, 1991) due to variation of surface pressure (Colbeck, 1989; Albert and Hardy, 1995), simultaneous warming and cooling, and induced temperature gradients (Sturm and Johnson, 1991). When applying a temperature gradient, the effect of sublimation and deposition in the snow results from interaction between snow temperature and the local relative hu-

Results

Discussion

Conclusion