Interfacial and structural relaxations of snow under isothermal conditions

摘要

We investigated the morphological evolution of laboratory snow under isothermalconditions at —3,-9 and —19°C, using X-ray tomography. We employed a two-point density correlationfunction to measure spatial fluctuations of the density of the bicontinuous ice/vapor system at differentlength scales. Length scales were derived from the correlation function to distinguish between interfacialcoarsening due to the minimization of surface energy on the smallest scales and anisotropic structural re-arrangements due to gravity on larger scales. On the smallest scales our data suggest a crossover betweenT= —9 and —19°C from evaporation/condensation to surface diffusion as the dominant transportmechanism. Anomalous growth was found for the slope of the correlation function at the origin, and itwas similar to those reported for the coarsening of fractal clusters. This is consistent with the observedpersistence of dendritic structures throughout an entire year. The dynamics of large-scale morphologywas characterized by the first zero-crossing of the correlation function which displays a nonmonotonicevolution with a pronounced anisotropy between the direction of gravity and horizontal directions.Since the correlation function naturally emerges in problems of scattering of radiation in snow, ourresults appear to be important for optical and remote-sensing methods.