Field investigation of near-surface metamorphism of snow

摘要

Buried surface hoar and near-surface faceted crystals are known to lead to deadlyavalanches. Over the course of three winter seasons a field investigation detailing the environmentalconditions leading to the formation of these crystals was performed. Weather stations on north- andsouth-facing aspects were established. The weather data were accompanied by detailed dailyobservations and grain-scale photographs of the snow surface. During the three seasons, 35 surfacehoar and 47 near-surface facets events were recorded. The mean weather conditions for the entiredataset (all three seasons and both stations) were compared to the nights when surface hoar formed.The comparison yielded five parameters that were statistically linked to the formation of surface hoar:incoming longwave radiation, snow surface temperature, wind velocity, relative humidity and theair/snow temperature difference. A similar comparison between the daytime mean values for alldays with near-surface facet events revealed three parameters with statistically significant differences.Thus, these parameters (short- and longwave radiation and relative humidity) could be statisticallylinked to facet formation. This research also suggests that environmental conditions in the daytimehours before and after surface hoar formation are statistically similar to the conditions causing near-surface facet formation.