Depth-hoar crystal growth in the surface layer under high temperature gradient

Abstract

The quick growth of depth-hoar crystals was observed at night-time just below the snow surface on a south-facing slope. This growth was due to a high temperature gradient (> 100 K m−1) near the snow surface under clear skies after a thin deposition of new snow on older and denser snow. The temperature gradient was greater when internal melting had taken place during daytime, keeping the sub-surface snow temperature at 0°C even after sunset until all liquid water had frozen. To understand the relationship between the crystal growth rate and the temperature gradient, a series of experiments was carried out in the laboratory. The snow sample was set under a constant temperature gradient between 100 and 300 K m− and sustained for about 50 h. The average crystal size increased linearly with time and the crystal growth rate increased as the given temperature gradient increased. The growth rates were in the order of 10−9 m s−1, which gave a good agreement with the results of the field observation.

Linking snowpack microphysics and albedo evolution

“…[51] Existing GCM representations of snow aging do not consider temperature gradient in albedo evolution, although this and several other studies [Marbouty, 1980;Fukuzawa and Akitaya, 1993;Sturm and Benson, 1997] show it to be very important. Investigations into the effects of blowing snow, wind ventilation, and frost formation are also needed for a thorough understanding of snow albedo evolution.…”

“…Observations of the largest crystals being surrounded by greater pore volumes [Akitaya, 1974;Colbeck, 1983a] imply greater vapor source for these particles and offer further evidence for the importance of particle spacing. Presumably, this is also why lower-density snow experiences more rapid growth [Marbouty, 1980;Fukuzawa and Akitaya, 1993]. Realizing the importance of irregularly spaced particles for growth, it is not surprising that growth occurs faster in greater temperature gradients [Marbouty, 1980;Fukuzawa and Akitaya, 1993], as enhanced vapor density gradients accentuate minute advantages in grain positioning.…”

“…Presumably, this is also why lower-density snow experiences more rapid growth [Marbouty, 1980;Fukuzawa and Akitaya, 1993]. Realizing the importance of irregularly spaced particles for growth, it is not surprising that growth occurs faster in greater temperature gradients [Marbouty, 1980;Fukuzawa and Akitaya, 1993], as enhanced vapor density gradients accentuate minute advantages in grain positioning. These realizations helped motivate the early capacitor models, but they have the burden of manually designating source and sink particles.…”

“…[32] Fukuzawa and Akitaya [1993] observe highly linear growth rates, whereas SNICAR predicts more rapid initial growth that tapers off. On the basis of our isothermal snow analysis, we used s g = 2.3, while snow produced by an iceslicer may be more homogeneously sized.…”

Prediction of temperature variation within a snowpack in open areas and under different canopy covers

“…Diurnal fluctuations of the air temperature are very important in influencing the temperature of the first 30-40 cm of snowpack (Armstrong and Williams, 1992;Fukuzawa and Akitaya, 1993;McClung and Schaerer, 1993;Birkeland, 1998;Birkeland et al, 1998;Ingolfsson and Grimsdottir, 2008). Therefore, the temperature profile within the snowpack is not linear (Koivusalo and Heikinheimo, 1999).…”