Natural convection in the subarctic snow cover

Abstract

The purpose of this study was to determine if air convects in a natural snow cover. To detect convection, the temperature field in the subarctic snow cover in Fairbanks, Alaska, was measured hourly during three winters (1984)(1985)(1986)(1987) using an array of thermistors which were suspended on threads and allowed to be buried by snowfall. The results indicate that convection occurred sporadically in 1984-1985 and almost continuously in 1985-1986 and 1986-1987. The evidence was (1) simultaneous warming and cooling at different locations in a horizontal plane in the snow, and (2) horizontal temperature gradients of up to 16øC m -1 During the winter, warm and cold zones developed in the snow and remained relatively fixed in space. We interpret these zones to be the result of a diffuse plumelike convection pattern linked to spatial variations in the temperature of the snow-soil interface. Air flow was inferred to have been primarily horizontal near the base of the snow and vertical elsewhere, Calculated flow speeds were of the order of 0.2 mm s -l, with a maximum value of 2 mm s-1. The convective circulation was time-dependent, with perturbations such as high wind or rapid changes in air temperature triggering periods when horizontal temperature gradients were strongest, suggesting that these were also periods when the air flow was fastest. The coincidence of depth hoar crystals with horizontal c axes and the horizontal flow lines at the base of the snow suggests that convection may have affected crystal growth directions.

Evolution of the Snow Area Index of the Subarctic Snowpack in Central Alaska over a Whole Season. Consequences for the Air to Snow Transfer of Pollutants

“…First, it is much more permeable, as depth hoar is at least 10 times more permeable than windpacks (38). Second, active convection in the subarctic snowpack enhances exchanges (39). Third, ice layers of low permeability are less likely to last long in the subarctic snowpack, because the vigorous metamorphism rapidly transforms them into depth hoar of high permeability (39).…”

“…Second, active convection in the subarctic snowpack enhances exchanges (39). Third, ice layers of low permeability are less likely to last long in the subarctic snowpack, because the vigorous metamorphism rapidly transforms them into depth hoar of high permeability (39). Although such layers were not observed at Alert (82°N), they are often present at lower latitudes, such as Barrow (71°N).…”

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

“…Snow has a high permeability (Calonne et al, 2012;Zermatten et al, 2014), which facilitates diffusion of gases and, under appropriate conditions, airflow (Gjessing, 1977;Colbeck, 1989;Sturm and Johnson, 1991;Waddington et al, 1996). In a typical Antarctic and Greenland snow profile, strong interactions between the atmosphere and snow occur, especially in the first 2 m (Neumann and Waddington, 2004;Town et al, 2008), called the convective zone.…”

Tomography-based monitoring of isothermal snow metamorphism under advective conditions

“…Recent studies indicate that sublimation deposition is the dominant contribution for temperatures close to the melting point, whereas surface diffusion dominates at temperatures far below the melting point (Vetter et al, 2010). Snow has a high permeability, which facilitates diffusion of gases and, under appropriate conditions, airflow (Gjessing, 1977;Colbeck, 1989;Sturm and Johnson, 1991;Waddington et al, 1996). Both diffusion and advective airflow affect heat and mass transports in the snowpack (Cunningham and Waddington, 1993;Albert, 1993;McConnell et al, 1998).…”