3D growth rates from tomographic images: local measurements for a better understanding of snow metamorphism

Abstract:

Once deposited on the ground, snow forms a complex porous material whose microstructure constantly transforms over time. These evolutions, which strongly impact the physical and mechanical properties of snow (e.g. Srivastava et al, 2010; Calonne et al, 2014) need to be considered in details for an accurate snowpack modeling. However, some of the physical mechanisms involved in metamorphism are still poorly understood.
To address this problem, several investigations combining X-ray tomography and 3D micro-modeling have been carried out (e.g. Flin et al, 2003; Kämpfer and Plapp, 2009; Pinzer et al, 2012) but precise comparisons between experimentation and modeling remain difficult. One of the difficulties comes from the lack of high resolution time-lapse series for experiments occurring with very well-defined boundary conditions, and from which precise measurements of the interfacial growth rates can be done.
Thanks to a recently developed cryogenic cell (Calonne et al, 2015), we conducted in situ time-lapse tomographic experiments on several snow and ice samples under various conditions (isothermal metamorphism at -7°C, temperature gradient metamorphism at -2°C under a TG of 18 K/m, air cavity migration in a single crystal at -4°C under a TG of 50 K/m). The non-destructive nature of X-ray microtomography yielded series of 8 micron resolution images that were acquired with a 2 to 12 h time step. An image analysis method was then developed to estimate the normal growth rates on each point of the ice-air interface and applied to the series obtained.
The analysis of the results and their comparison to those of existing models (e.g. Flin et al, 2003; Flin and Brzoska, 2008) give interesting outlooks for the understanding of the physical mechanisms involved in snow metamorphism.

References:
Calonne, N., et al (2015), Geophys. Res. Lett., 42, 3911-3918.
Calonne, N., et al (2014), The Cryosphere, 8, 2255-2274.
Flin, F. and J.-B. Brzoska (2008), Ann. Glaciol., 49, 17-21.
Flin, F., et al (2003), J. Phys. D. Appl. Phys., 36, A49-A54.
Kämpfer, T. U., and M. Plapp (2009), Phys. Rev. E, 79 (3), 031502.
Pinzer, B., et al (2012), The Cryosphere, 6, 1141-1155.
Srivastava, P., et al (2010), Annals of Glaciology, 51 (54), 73-82.