Showing papers by "Matthew Sturm published in 1993"

Structure and wind transport of seasonal snow on the Arctic slope of Alaska

Abstract: The invention provides a marine winch driven by a central operating spindle coupled at its lower end to drive reduction gearing in turn coupled to an outer casing of the winch to rotate said casing at one of two alternative output ratios selectable on rotating the operating spindle in opposite directions. The operating spindle has a separate upper portion movable vertically relative to a lower portion and in splined driving engagement therewith. When the upper part of the operating spindle is lowered it is coupled directly to drive the outer casing so as to provide a third, 1:1, output ratio. Unidirectional stepless clutch means are provided in the drive lines to enable the three output ratios to be acheived and also to enable the outer casing to over run.

Passive microwave measurements of tundra and taiga snow covers in Alaska, U.S.A.

Abstract: The microwave emissivity of two snow covers was measured in Alaska in March, 1990. Observations were made on taiga snow near Fairbanks that was 0.83 m thick with a 0.55 m thick basal layer of depth hoar. Other measurements were made on the tundra snow cover at Imnaviat Creek north of the Brooks Range which was 0.27 to 0.64 m thick and consisted of two or more wind slabs overlying a depth hoar layer 0.14 to 0.26 m thick. Density, crystal structure, and grain size were similar in tundra and taiga depth hoar layers. Emissivity was measured at 18.7 and 37 GHz using radiometers mounted on a 1.5 m tall bipod. Measurements were made on undisturbed snow, and then several snow layers were removed and additional measurements were made. This sequence was repeated until all snow had been removed. Effective emissivity values for the full snow depth ranged from 0.6 (37 GHz, H-pol) to 0.95 (18.7 GHz, V-pol) and were similar for both taiga and tundra snow covers. For both snow covers, there was a marked reduction in the effective emissivity (eeff) from that of the underlying ground with a maximum reduction of about 30%. All of the reduction was found to occur within the depth hoar layer. Maximum reduction in eeff could be caused by a depth hoar layer 0.3 m thick. Overlying wind slab or new snow were nearly “invisible”, increasing the effective emissivity only by a small amount due to self-emittance. Thus, it was difficult to distinguish the two different snow covers on the basis of their emissivity, since both contained 0.3 m of depth hoar or more.

Rain‐induced water percolation in snow as detected using heat flux transducers

Abstract: The percolation of water through snow is shown to be detectable with heat flux transducers (HFTs) at the base of, or embedded within, the snow. Theory indicates that the arrival of water at a HFT will result in a rapid drop in heat flow to negative values, followed by an exponential rise. Laboratory and field tests verify that the theory correctly predicts the form of the signal, and consideration of conditions in a snow cover suggest that it is unlikely the signal can be generated in any other way. Large (15×15 cm) HFTs were installed at the snow/ground interface at three locations in Alaska where rain on snow is common. During three winters, heat flux signals indicative of water percolating to the base of the snow were detected 23 times, often simultaneously at two or more sites. All signals were coincident with rain-on-snow events, though not all rain-on-snow events (there were a total of 27) were associated with distinctive heat flux signals. Signals were observed only when rainfall rates exceeded 1.5 cm d−1, and the character of the signal differed if the snow/ground interface was at or lower than 0°C. Observed delays between the start of rain and the arrival of water at the base of the snow ranged between 2 and 40 hours. A geometric analysis was used to calculate the spacing of percolation fingers or columns necessary to produce the observed number of times that water percolated onto the HFTs. The number of times there were abrupt changes in the temperature of thermistors installed in the snow adjacent to the HFTs was used in a similar manner. Results from both analyses suggest percolation columns with a mean spacing of about 25 cm, which is consistent with observations of these features in snow trenches.

Gas Gun Experiments to Determine Shock Wave Behavior in Snow: Methods and Data

Abstract: : A laboratory study of the behavior of snow under shock wave loading and unloading conditions was conducted using a 200-mm-diameter gas gun to generate loading waves in snow samples with initial densities of 100 to 520 kg m-3 at temperatures of -2 to -23 deg C. Stress levels were 2 to 40 MPa. The response of snow to shock wave loading was measured as a function of distance from the impact plane using embedded stress gauges. Large impedance differences between snow and the stress gauges produced complex stress histories. A finite element model, along with a simple analytical model of the experiment, was used to interpret the stress histories. Snow deformation was not affected by initial temperature, but was found to be rate dependent. The initial density of the snow determined its pressure-deformation path. The pressure needed to compact snow to a specific final density increases with decreasing initial density. The release moduli increased nonlinearly from 50 MPa at a snow pressure of about 15 MPa to 2700 MPa at a snow pressure of about 40 MPa.... Attenuation, Porous ice, Shock wave propagation in snow, Experimental methods, Shock waves, Snow