Snow metamorphism under alternating temperature gradients: Morphology and recrystallization in surface snow

Abstract

[1] The composition of the lower atmospheric boundary layer can be strongly influenced by snow photochemistry. Surface snow, where air-snow interactions take place, is viewed as slowly changing quasi-isothermal snow, implied by the observation of mainly rounded snow crystals. The role of snow for photochemistry is therefore expected to be purely geometric. However, large temperature gradients are often observed in these layers, which would imply high recrystallization and faceting. In controlled laboratory experiments we showed that temperature gradients on the order of 100 K m À1 do not lead necessarily to faceting if their sign changes with a daily cycle. The shape of snow crystals does not reflect necessarily the metamorphic process. With time-lapse X-ray tomography, recrystallization rates as high as 60% of the total ice mass were observed during 12 hours. The high recrystallization rates in apparently isothermal snow not only contradict the current understanding of snow metamorphism, they also might influence chemical air-snow interactions. Citation: Pinzer, B. R., and M. Schneebeli (2009), Snow metamorphism under alternating temperature gradients: Morphology and recrystallization in surface snow, Geophys. Res. Lett., 36, L23503,

Influence of snowpack internal structure on snow metamorphism and melting intensity on Hansbreen, Svalbard

“…Process occurs efficiently until the difference in the snowpack temperature is at least 0.1-0.2ºC cm -1 (Colbeck 1982). The formation of faceted crystals was also observed at the temperature gradient of 0.03ºC cm -1 (Flin and Brzoska 2008), and even under isothermal conditions (Dominé et al 2003), however this process is then significantly prolonged in time (Pinzer and Schneebeli 2009). Destructive metamorphism takes place at a steady temperature.…”

Experimental observation of transient <i>δ</i><sup>18</sup>O interaction between snow and advective airflow under various temperature gradient conditions

“…The intensity of the recrystallization is dictated by the temperature gradient and this can occur under midlatitude or polar conditions. Temperature and geometrical factors (porosity and specific surface area) also play a significant role (Pinzer and Schneebeli, 2009;Pinzer et al, 2012).…”

Vertical profile of the specific surface area and density of the snow at Dome C and on a transect to Dumont D'Urville, Antarctica – albedo calculations and comparison to remote sensing products

“…The effect of alternating temperature gradients on the rate of SSA change has been little documented. Besides unexpected grain shapes (Pinzer and Schneebeli, 2009), this could lead to sublimation of snow grains and to condensation of atmospheric water vapor onto them, with effects on SSA that are difficult to predict. Today there is therefore insufficient data to understand the effect of many processes prevalent in Antarctica on snow SSA.…”

“…In any case, none of those studies treat many processes to which the snow was subjected to. These include the effects of wind and wind transport on SSA, and also the effect of diurnally alternating temperature gradients (Pinzer and Schneebeli, 2009). On the Antarctic plateau, the accumulation rate is so low that a given snow layer is exposed to wind action and alternating temperature gradients for a long time before it is finally sheltered from those effects.…”