Showing papers on "Snowpack published in 1991"

Solute chemistry of snowmelt and runoff in an Alpine Basin, Sierra Nevada

Abstract: Snowpack runoff contributions to the hydrochemistry of an alpine catchment in the Sierra Nevada were evaluated in 1986 and 1987 by analyzing snowpack, meltwater, and stream water samples for major inorganic ions, conductance, acid neutralizing capacity (ANC), and silicate. An ionic pulse in meltwater with initial concentrations twofold to twelvefold greater than the snowpack average, varying with site and with ion, was measured in lysimeters placed at the base of the snowpack. Maximum concentrations of ions in meltwater were inversely related to the rate of snowmelt; melt-freeze cycles increased the concentration of solutes in meltwater. Hydrogen concentration in meltwater was buffered by ANC produced in part by the dissolution of particulates. The anionic pulse in meltwater was observed in stream waters during the first 30 days of snowpack runoff, with NO3− concentrations in stream waters at this time about 1.6-fold greater than the average NO3− concentration for the time period of snowpack runoff, Cl− about 1.5-fold greater and SO42− about 1.3-fold greater. Maximum H+ concentration during snowpack runoff (increase of 170% over winter concentrations) occurred near maximum discharge. ANC minima occurred at maximum discharge as a result of dilution, with a decrease from winter concentrations of 70% in 1986 and 60% in 1987. Interactions between snowpack runoff and soils were important to the chemistry of stream water. Eighty to ninety percent of the H+ stored in the snowpack was consumed before it reached the base of the catchment. Soils were a sink for NH4+ from snowpack meltwater, with less than 1% of the NH4+ released from snowpack storage exported from the basin as NH4+. Sulfate concentrations in stream waters were less variable than NO3− or Cl− concentrations; sorption processes in soils were a likely cause for the regulation of SO42− concentrations.

Stable Isotopes of Oxygen and Natural and Fallout Radionuclides Used for Tracing Runoff During Snowmelt in an Arctic Watershed

Abstract: Stable isotopes of oxygen, and natural and fallout radionuclides, have been used, respectively, to identify water sources and to quantify watershed fluxes of precipitation-borne solutes and particles that come in contact with tundra vegetation at Imnavait Creek, Alaska (68° 37′N, 149° 17′W). Oxygen 18/oxygen 16 ratios of water in the snowpack, stream, and unfrozen soil during the peak of snowmelt showed that less than ∼14% of streamwater was derived from sources other than snow. Within a month of snowmelt, 18O/16O ratios in the stream indicated that only negligible amounts of water derived from snow remained in the watershed, in contrast to the low degree of mixing between snow and underlying soil water, greater than 90% of the atmospherically derived 7Be (53-day half-life) that was deposited in the snowpack was adsorbed onto the surface 2–3 cm of frozen organic soils and vegetation. A slightly lower degree of absorption (∼2/3) on tundra was observed for atmospherically derived 35S (87-day half-life) released during snowmelt. These data indicate that atmospherically derived substances in the snowpack are often retained strongly by sorption or chemical interaction with vegetation and soil during snowmelt. This conclusion is also supported by the vegetation and soil inventories of 137Cs (30.2-year half-life), which are similar to values expected as a result of atmospheric deposition over the past 40 years.

Distributed Snowmelt Simulations in an Alpine Catchment: 2. Parameter Study and Model Predictions

Abstract: A distributed grid-based model is used (1) to analyze the importance of selected model parameters, (2) to simulate spatial distributions of snow cover properties in a small basin and (3) for a comparison with less sophisticated models as typically used in operational applications. Results indicate that variations of water equivalent with slope and local relief are of utmost importance for realistic distributed simulations but more moderately influence mean basin melt. Snow cover variables of which spatial distributions are simulated include the thermal and hydraulic state of the pack and hourly melt water release. All variables exhibit substantial variations in space and time. They are primarily controlled by topography and the delay of melt water in deep packs. The grid model is compared with a snow band model and a parametric model. The latter estimates the snowpack's areal extent from water equivalent. Simulated snow-covered areas suggest the grid model to be the most realistic. Differences in terms of mean basin melt derive from different assumptions associated with model structure.

Derivation of Snow Water Equivalent in Boreal Forests Using Microwave Radiometry

Abstract: Efforts have been made by several investigators to produce a reliable global microwave snow algorithm to estimate snow depth or snow water equivalent (snow volume) and snow extent. Complications arise when trying to apply a global algorithm to specific regions where the climate, snowpack structure and vegetation vary. In forest regions, the microwave emission from dense coniferous forests may overwhelm the emission from the underlying snow-covered ground. As a result, algorithms employing microwave data tend to underestimate snow depths. Preliminary results indicate that the amount of underestimation can be minimized when the fraction of forest cover can be accounted for and used as an additional input in microwave algorithms. In the boreal forest of Saskatchewan, the standard error between the measured and the estimated snow water equivalent was reduced from 2.7 to 2.1 cm by using a generalized snow retrieval algorithm that includes the percentage of forest cover. However, perhaps as much as 25% of the boreal forest of North America and Eurasia is too dense to enable satisfactory snow water equivalent determination to be made using passive microwave techniques alone. Key words: brightness temperature, boreal forest, microwaves, radiometer, snowpack

Detection of objects buried in wet snowpack by an FM-CW radar

Abstract: A real-aperture FM-CW radar system was developed for the detection of objects buried in heavily wet snowpack. This radar uses the L-band microwave frequency with a maximum output power of 100 mW and utilizes digital signal processing techniques. A laboratory simulation and two field experiments were carried out to detect and map various objects embedded in the snowpack. It was possible to map a metallic pipe 3 cm in diameter at a depth of 70 cm and a 10*60-cm metallic plate at a depth of 90 cm in natural snowpack. Fundamental detection results are presented. >

Millimeter‐wave radar scattering from snow: 2. Comparison of theory with experimental observations

Abstract: Using a truck-mounted platform, backscatter measurements were made at 35, 95, and 140 GHz for a variety of snow conditions to evaluate the radar response to incidence angle, surface roughness, and liquid water content. Good agreement was obtained between the experimental observations and theoretical calculations based on the numerical solution of the radiative transfer equation presented in the preceding paper. A notable exception is when the snowpack is in the refreezing phase of the diurnal cycle, during which the snowpack is characterized by a dry surface boundary with wet layers underneath. To accommodate this type of condition, a hybrid first-order numerical solution is proposed. The hybrid approach provides excellent agreement between theory and experiment.

Links Between Snowpack Physics and Snowpack Chemistry

Abstract: Seasonal snow at the Earth’s surface contains a record of the chemistry in the atmosphere during snow crystal formation and subsequent snow pack accumulation. Solutes and other contaminants are incorporated into snow during crystal formation in the clouds, by scavenging and riming as the particles fall, and then by dry deposition. An established snow cover may represent the total chemical load on the environment integrated over several months. It is a widespread observation that this chemical load may be removed from the pack as an ionic pulse, with as much as 80 percent of the solutes eluting with the first 20 percent of the melt.

Physics-Based Models of Snow

Abstract: This chapter is a review of current physics-based techniques for modeling snowmelt Mixture theory is used to develop the equations of conservation of mass, momentum and energy for snow treated as a two-component, three-phase mixture of ice, water, water vapor, and air The constitutive laws and boundary conditions required to complete a general snowmelt model are then described, with particular attention to the energy balance at the upper boundary of a snowpack

Snowpack and the Subnivean Environment for Different Aspects of an Open Meadow in Jackson Hole, Wyoming, U.S.A.*

Abstract: Snowpack characteristics of an open meadow habitat were examined by students of the Teton Science School's Winter Ecology Course. Characteristics evaluated are inherent in snowpacks throughout circumpolar regions. Snowpits were sampled for 9 yr on a north-facing slope, a valley bottom, and a south-facing slope (situated in the same locations all years). Snow was deepest on the north-facing slope and shallowest on the valley bottom each year. Snowpack thermal index values less than 200 in some years in the valley bottom and on the south-facing slope indicated a possible failure to provide temperature buffering of the nivean environment. Despite lower air temperatures, ground temperatures of the north-facing slope snowpits appear to be higher than the other two aspects, especially in colder years. Temperature gradient snow (TG, depth hoar, or pukak) was well developed in all years for all aspects. We speculate that the depth of formation of cohesionless TG crystals has been sufficient for small mammal movem...

Microwave radiometry of snow-covered terrains

Abstract: In polar and mid- to high-latitude regions, snow accumulates every year which covers the Earth's surface. In order to carry out geophysical work in such regions, prior knowledge of snow thickness is essential. In the present paper, the emitted brightness temperature based on an incoherent approach has been calculated for various two-layered snowpack models representative of the snow-covered terrains. The effect of snow surface roughness caused by local winds and snow melting on passive microwave remote-sensing response has also been studied. The comparison of theoretically calculated brightness temperature with the measured data shows good agreement. The results presented in this paper will be useful in the analysis and interpretation of microwave remote-sensing data of snow-covered terrains.

The influence of a simulated transport corridor on snowpack characteristics, Fort Norman, N.W.T., Canada

Abstract: Between November 1985 and February 1989, six snowpack sampling sessions were completed (at least annually) at the Studies of the Environmental Effects of Disturbances in the Subarctic (SEEDS) site ...

Acidification potential of snowpack in sierra nevada

Abstract: Snowpack accumulates water and acid anions from atmospheric deposition. During the snowmelt, the rapid release of acid anions can cause an episodic pH depression in surface water. The potential for the snowmelt to acidify the surface water of the Sierra Nevada was investigated at the Eastern Brook Lane watershed. The acidification potential of snowpack is determined by the anion release rate, which is difficult to measure directly. Limited measurements of snowpack were combined with a mathematical model to calculate the solute flux in snowmelt runoff. In the springs of 1984–1986, the snowpack accumulated an average of 40 cm of water. It stored 80 equivalents per hectare of acidic anions. The melting rate of the snowpack was 0.5 cm of water equivalent per day and the anion release rate was 1.4 equivalents per hectare per day. This anion release rate was one‐tenth that of the Woods Lake watershed in the Adirondacks, New York.