No abstract

ABSTRACT. M easurements from the sub arctic snowpack are used to explore the relation ship hctween grain growth and vapor flow, th e fundamental processes of dry-snow m eta m or phi sm. Du e to extreme temperature grad ients, the suba rctic pack undergoes extensive deplh-hoa r m etamorphi sm. By the end of the winter a fi ve-l ayered stru ctu re with a pronounced weak laye r near th e base of the snow evolves. Grain-size increases by a factor of 2-3, wh i le t he number of g ra i ns per unil mass d ecreases by a fac tor of 10. Obse rved growth rates require significant net inter-particle vapor fluxes. Stable-isoto pe ratios show that there are a lso significa nt net layer-to -I aye r vapor flu xes. Soil moi sture enters the base of th e p ack and mixes wit h the bottom 10 cm of snow, while iso topieally light water vapor fractionates from the basal layer a nd is d eposiled up to 50 cm high er in the p ack. End-of-winter density profi les for snow on the gro und, eomf,ared with snow on tabl es, indi cate th e ne t layer-to-laye r vapor flu x averages 6 x 10 kg m -2 S-I, th ough detail ed measurements show the net flu x is episod ic a nd varies with time and height in the pack, with peak net fl uxes ten tim es higher th a n average. A model, driven by observed temperatu re profiles, reproduces th e layer-lo-layer flu x pattern a nd predicts the observed weak layer at the base of the snow. Calcu lated layer-to-Iaye r vapor fluxes a re ten times higher than inter-particle flu xes, which implies that depth-hoar g rain g rowt h is limited by factors other than the vapor supply. This finding suggesls that gain and loss of water molecules due to sublimation from g rains ta kes place at a rate m a ny times hi gher than th e rate at which gr ains grow, a nd it expl ains why g rain s can meta morphose into different form s so r eadily.

No abstract

The hydrologic cycle of an arctic watershed is dominated by such physical elements as snow, ice, permafrost, seasonally frozen soils, wide fluctuations in surface energy balance, and phase change of snow and ice to water. Hydrologic data collected over a 5-year period (1985-1989) from an arctic watershed in northern Alaska are presented. Processes related to snow accumulation, redistribution, ablation, evaporation and subsequent snowmelt-generated runoff are discussed. The total water content of the snowpack at the end of winter has comprised between 28 and 40% of the annual precipitation. Redistribution of snow on the ground by the wind is a major factor in increasing the snowmelt runoff. Much of the redistributed snow accumulates in the valley bottom along the stream and also along depressions on the hillslopes. These depressions are small surface drainage channels that are referred to as water tracks. Partitioning of the snowmelt into runoff, evaporation and increased soil water storage in the active layer was carried out on the plot and watershed scale. Over a 5-year period, the volume of snowmelt runoff varied from 50 to 66% of the average watershed snowpack, while evaporation varied from 20 to 34% and soil moisture storage increased between 10 and 19%. Much greater variation in these hydrologic components occurred at the plot scale. Plotstream and subsequent slush flows follow as a channel is carved finally to the headwaters of the basin. Woo and 1974. Lewkowicz, A. G., and H. M. French, The hydrology of small runoff plots in an area of continuous permafrost, Banks Island, in Proceedings Fourth Canadian Permafrost Conference, Calgary, Alberta, edited by H. M. French, pp. 153-162, National Research Council of Canada, Ottawa, Ontario, 1982. Liston, G. E., Seasonal snow cover of the foothills region of Alaska's Arctic Slope: A survey of properties and processes, M.S. thesis, Univ. of Alaska, Fairbanks, 1986. Marsh, P., and M. K. Woo, Annual water balance of small high Arctic basins, in Canadian Hydrology Symposium: 79, Proceedings, Vancouver, British Columbia, Associate Committee on Hydrology, pp. 536-546, National Research Council of Canada, Ottawa, Ontario, 1979. Ohmura, A., Evaporation from the surface of the Arctic tundra on Axel Heiberg Island, Water Resour. Res., 18, 291-300, 1982. Osterkamp, T. E., and M. W. Payne, Estimates of permafrost thickness from well logs in northern Alaska, Cold Reg. Sci. Technol., 5, 13-27, 1981. Rouse, W. R., Microclimate at Arctic tree line, 3, The effects of regional advection on the surface energy balance of upland tundra, Water Resour. Res., 20, 74-78, 1984. Santeford, H. S., Snow soil interactions in Interior Alaska, in Modeling of Snow Cover Runoff, edited by S. Colbeck and M. Ray, pp. 311-318, U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, N.H., 1978.

No abstract