WAVY TEMPERATURE DISTRIBUTIONS IN SNOW

The process of heat transfer in snow is important in such fields of snow science as snow avalanches, thermoinsulation by snow in agriculture, permafrost and global energy exchange between the atmosphere and ground in northern regions. Theoretical and experimental results of investigations in this field have been published by Z. YOSIDA (Contrib. Inst. Low Temp. Sci., 7,19,1955), J. C. GIDDINGS and E. LACHAPELLE (J. Geophys. Res., 67,2377,1962), and Y.-Ch. YEN (J. Geophys. Res., 70,1821,1965). The purpose of such works was mostly determination of numerical values of the heat conductivity and water vapor diffusion coefficient in snow, required for any snow related physical calculations. However, published values of these physical quantities vary over a wide range and are sometimes even not in agreement with theory. The purpose of the present experimental work was to understand the mechanism of simultaneous heat and water vapor transfer in snow by systematic measurements of temperature distributions, density and structure change in snow under an applied temperature gradient. Experimental procedure and results : The experiments on heat and water vapor transfer in snow were done in a cold laboratory of the Institute of Low Temperature Science. The experimental runs were done with naturally compacted snow of density about 350kg・m^ and screened snow of densities from 200 up to 500kg・m^. Heat and water vapor fluxes were built in snow by sudden heating of one end of sample with initially uniform temperature and maintaining a temperature difference between the opposite ends for a prolonged period of time. The length of a sample was 10,20,30 or 40cm. Fine thermocouples were installed to measure temperatures in several points on the central axis of the sample, parallel to the direction of heat transfer. More details of the experimental set-up and results are reported elsewhere (S. A. SOKRATOV and N. MAENO, Snow Engineering : Recent Advances, ed. by M. IZUMI et al. Rotterdam, Balkema Publ., 49,1997). The obtained result could be expressed as a non-linear steady state temperature distribution in snow under temperature gradient, convex toward the warmer ends of snow samples. This result is explained by the simultaneous transport of heat and water vapor. In some snow samples, especially in the shortest ones (10cm), there were found some noticeable waves on temperature distribution curves. The measurements showed that the temperature distribution is not always monotonic in the direction of heat flux, but could fluctuate under some conditions. To study this phenomenon in more detail we did several runs of experiments with shorter distances between thermocouples. 30cm snow samples with density 400 and 500kg・m^ were used in these experiments, and heat and mass fluxes were built up in the horizontal or vertical (upward warm or downward warm) direction to check the possible effect of convection. These experiments showed that waves were formed in all the experimental runs and the wave length was about 5cm. The waves appeared during the first 10min of heating and did not change their positions during the run. This new finding strongly suggests that the process of heat and mass transfer can not be described by a simple conductive and diffusive mechanism. As waves were formed both in horizontal and vertical snow samples their formation can not be explained by possible convection in snow. Possible reasons for the wave formation could be the temperature increase of ice grains by the latent heat release due to condensation of supersaturated water vapor at the end of any one wave. The alternation of evaporation and condensation zones in the direction of heat transfer could explain the wavy character of temperature distributions. This explanation is in agreement with our obtained wavy density distributions. However, more experiments and careful analyses are necessary to determine the quantitative physical mechanism of wave formation in relation to the applied condition (temperature and temperature gradient) and snow properties (porosity, pore size, structure, etc.)

Spatial Variability of Snow Water Equivalent – The Case Study from the Research Site in Khibiny Mountains, Russia

The aim of the investigation was assessment of spatial variability of the characteristics of snowpack, including the snow water equivalent (SWE) as the main hydrological characteristic of a seasonal snow cover. The study was performed in Khibiny Mountains (Russia), where snow density and snow cover stratigraphy were documented with the help of the SnowMicropen measurements, allowing to determine the exact position of the snow layers’ boundaries with accuracy of 0.1 cm. The study site was located at the geomorphologically and topographically uniform area with uniform vegetation cover. The measurement was conducted at maximum seasonal SWE on 27 March 2016. Twenty vertical profiles were measured along the 10 m long transect. Vertical resolution depended on the thickness of individual layers and was not less than 10 cm. The spatial variation of the measured snowpack characteristics was substantial even within such a homogeneous landscape. Bulk snow density variability was similar to the variability in snow height. The total variation of the snowpack SWE values along the transect was about 20%, which is more than the variability in snow height or snow density, and should be taken into account in analysis of the results of normally performed in operational hydrology snow course SWE estimations by snow tubes

QUANTIFICATION OF ECONOMIC AND SOCIAL RISKS OF DEBRIS FLOWS FOR THE BLACK SEA COASTAL REGION OF THE NORTH CAUCASUS

Debris flows are the most frequent and disastrous natural hazards among other exogenic processes at the Black Sea coastal region of the North Caucasus. Numerous debris flow releases are reported every year between Novorossiysk and Krasnaya Polyana. The debris flows bring economic losses, and sometimes loss of human lives. Quantification of the economic, individual and collective debris flows risk is based on their spatial distribution, repeatability, debris flows’ regime, as well as economical and social characteristics of the territory accounted for. Estimation of the individual debris flow risk shows that the level of such risk corresponds to “allowable” and “acceptable” degrees [Vorob’ev, 2005] - less than 3,3 × 10-6. The maximal values of the economic debris flow risk are estimated in the Adler region - more than 1 mln. rub. per year

The Changing Face of Arctic Snow Cover: A Synthesis of Observed and Projected Changes

Analysis of in situ and satellite data shows evidence of different regional snow cover responses to the widespread warming and increasing winter precipitation that has characterized the Arctic climate for the past 40-50 years. The largest and most rapid decreases in snow water equivalent (SWE) and snow cover duration (SCD) are observed over maritime regions of the Arctic with the highest precipitation amounts. There is also evidence of marked differences in the response of snow cover between the North American and Eurasian sectors of the Arctic, with the North American sector exhibiting decreases in snow cover and snow depth over the entire period of available in situ observations from around 1950, while widespread decreases in snow cover are not apparent over Eurasia until after around 1980. However, snow depths are increasing in many regions of Eurasia. Warming and more frequent winter thaws are contributing to changes in snow pack structure with important implications for land use and provision of ecosystem services. Projected changes in snow cover from Global Climate Models for the 2050 period indicate increases in maximum SWE of up to 15% over much of the Arctic, with the largest increases (15-30%) over the Siberian sector. In contrast, SCD is projected to decrease by about 10-20% over much of the Arctic, with the smallest decreases over Siberia (<10%) and the largest decreases over Alaska and northern Scandinavia (30-40%) by 2050. These projected changes will have far-reaching consequences for the climate system, human activities, hydrology, and ecology

Photochemical Tuning of Tris-Bidentate Acridine- and Phenazine-Based Ir(III) Complexes

International audienc

Changing Arctic Snow Cover: A Review of Recent Developments and Assessment of Future Needs for Observations, Modelling, and Impacts

Snow is a critically important and rapidly changing feature of the Arctic. However, snow-cover and snowpack conditions change through time pose challenges for measuring and prediction of snow. Plausible scenarios of how Arctic snow cover will respond to changing Arctic climate are important for impact assessments and adaptation strategies. Although much progress has been made in understanding and predicting snow-cover changes and their multiple consequences, many uncertainties remain. In this paper, we review advances in snow monitoring and modelling, and the impact of snow changes on ecosystems and society in Arctic regions. Interdisciplinary activities are required to resolve the current limitations on measuring and modelling snow characteristics through the cold season and at different spatial scales to assure human well-being, economic stability, and improve the ability to predict manage and adapt to natural hazards in the Arctic region