Аннотация:Effect of the snow thermal resistance on soil freezing is comparable to the
influence of mean temperature in the cold period. The thermal resistance of
snow cover depends on the thermal conductivity of snow. The scatter of snow
thermal conductivity in 2-3 times arises from differences in the microstructure of
snow at a given density. Our measurements have shown that average value of
coefficient of efficient thermal conductivity of the depth hoar with density of 280
kg/m3 is 0.12 W/(m K) that in 3 times smaller than the same coefficient of
granular frozen together snow with density of 370–390 kg/m3.
The thermal conductivity of snow depends on the contacts between ice
crystals. The larger the contact area, the better the heat transfer from one layer
to another. But the strength characteristics of snow, and especially its hardness,
depend on the bonds between ice crystals, so the thermal conductivity and
hardness of snow depend on the structure of snow. Note, that measurements of
snow hardness are less laborious than measurements of its thermal conductivity.
The results of experimental investigation of thermal conductivity of snow on
the Svalbard archipelago in the conditions of natural occurrence are considered.
The observations were carried out in the spring of 2013–2015 in the vicinity of
the meteorological station “Barentsburg”. The obtained data were processed
using the Fourier equation of thermal conductivity. That allowed deriving
relationship between thermal conductivity and snow hardness and determination
of the coefficient of thermal conductivity of the snow with different structure and
density. To verify the reliability of the approach to the determination of snow
thermal conductivity, numerical experiments were performed on a mathematical
model, which did show good convergence of the results. The obtained formulas
for the coefficient of thermal conductivity of very loose, loose, medium and hard
snow (according to the international classification of seasonal snow falls) are
compared with the data of other studies. It was found that when the snow
density is within the range 0.15–0.40 g/cm3 these formulas cover the main
variety of thermal conductivity of snow. This allows estimating the coefficient of
thermal conductivity and to determine the thermal resistance of snow cover in
the field by measuring the density and hardness of different layers of snow.
The thermal conductivity of snow with a density of 200 kg/m3 at different
hardness varies by 3-4 times, for snow with a density of 300 kg/m3 - by 2.5 times
and for snow with a density of 400 kg/m3 - by 1.7 times.
The effect of the snow cover hardness on dynamics of the soil freezing is
analyzed with the use of numerical modeling. Model calculations show that soil
freezing depth differs by 2.9 and 2.1 times for snow of different hardness at a
snow cover height 0.5 m and an average negative air temperature of –5 and -15
°C. With a snow cover height of 1 m, this ratio increases to 3-4 times. The results
of calculations show that for a more accurate assessment of the depth of soil
freezing it is necessary to take into account the structure of snow cover.
The mathematical modeling was carried out according to the framework of
fundamental scientific studies within the project reg. № 0148-2019-0004, field
studies on Svalbard were conducted with financial support from the state
assignment and logistical assistance of the Russian Scientific Center on
Spitsbergen (RSCS), processing and analysis of experimental data was supported
by the Russian Foundation for Basic Research, grant No 18-05-60067.