Snow Trench Research Articles

Demiryolu Hatlarında Karla Mücadele

Bu çalışma ile demiryolu hatlarında karla mücadelenin araştırılması amaçlanmıştır. Bu çalışma kapsamında; demiryollarında yolun üzerini kapatan karın durumuna göre kar çeşitleri, demiryolu trafiğinin aksamadan işletilmesi için yağan karın demiryolu üstünü kapatma durumuna göre demiryolunda seçilecek olan kar temizleme yöntemleri, demiryolunun kardan korunması için imal edilen kar siperleri ve türleri, kar siperlerinin dolu veya delikli olmalarına göre kar siperinin ön ve arkasında karın toplanma şekilleri ele alınmıştır. Ana hatlarda karla kapanmaya en çok maruz kalan yerlerin tespiti için istatistiki bilgiler tutularak kar siperlerinin yapılacağı yerler tespit edilmeli ve kar siperleri bu doğrultuda inşa edilmelidir. Kar siperi olarak mümkün olduğunca hem yapım, hem de uzun vadeli bakım masraflarının düşük olması ayrıca kar mücadelesinde çok iyi sonuçlar alınması nedeniyle doğal kar siperlerin tercih edilmesinin faydalı olacağı düşünülmektedir. Ülkemizde raylı sistemler ulaşımı alanında ulusal düzeyde bilimsel, akademik eser sayısının az olduğu görülmekte olup bu çalışmanın literatüre katkısı olacağı düşünülmektedir.

Constraints on post-depositional isotope modifications in East Antarctic firn from analysing temporal changes of isotope profiles

Abstract. The isotopic composition of water in ice sheets is extensively used to infer past climate changes. In low-accumulation regions their interpretation is, however, challenged by poorly constrained effects that may influence the initial isotope signal during and after deposition of the snow. This is reflected in snow-pit isotope data from Kohnen Station, Antarctica, which exhibit a seasonal cycle but also strong interannual variations that contradict local temperature observations. These inconsistencies persist even after averaging many profiles and are thus not explained by local stratigraphic noise. Previous studies have suggested that post-depositional processes may significantly influence the isotopic composition of East Antarctic firn. Here, we investigate the importance of post-depositional processes within the open-porous firn (≳ 10 cm depth) at Kohnen Station by separating spatial from temporal variability. To this end, we analyse 22 isotope profiles obtained from two snow trenches and examine the temporal isotope modifications by comparing the new data with published trench data extracted 2 years earlier. The initial isotope profiles undergo changes over time due to downward advection, firn diffusion and densification in magnitudes consistent with independent estimates. Beyond that, we find further modifications of the original isotope record to be unlikely or small in magnitude (≪ 1 ‰ RMSD). These results show that the discrepancy between local temperatures and isotopes most likely originates from spatially coherent processes prior to or during deposition, such as precipitation intermittency or systematic isotope modifications acting on drifting or loose surface snow.

Layering of surface snow and firn at Kohnen Station, Antarctica: Noise or seasonal signal?

The density of firn is an important property for monitoring and modeling the ice sheet as well as to model the pore close-off and thus to interpret ice core-based greenhouse gas records. One feature, which is still in debate, is the potential existence of an annual cycle of firn density in low-accumulation regions. Several studies describe or assume seasonally successive density layers, horizontally evenly distributed, as seen in radar data. On the other hand, high-resolution density measurements on firn cores in Antarctica and Greenland showed no clear seasonal cycle in the top few meters. A major caveat of most existing snow-pit and firn-core based studies is that they represent one vertical profile from a laterally heterogeneous density field. To overcome this, we created an extensive dataset of horizontal and vertical density data at Kohnen Station, Dronning Maud Land on the East Antarctic Plateau. We drilled and analyzed three 90 m long firn cores as well as 160 one meter long vertical profiles from two elongated snow trenches to obtain a two dimensional view of the density variations. The analysis of the 45 m wide and 1 m deep density fields reveals a seasonal cycle in density. However, the seasonality is overprinted by strong stratigraphic noise, making it invisible when analyzing single firn cores. Our density dataset extends the view from the local ice-core perspective to a hundred meter scale and thus supports linking spatially integrating methods such as radar and seismic studies to ice and firn cores.

Impact of spatial averaging on radar reflectivity at internal snowpack layer boundaries

ABSTRACTMicrowave radar amplitude within a snowpack can be strongly influenced by spatial variability of internal layer boundaries. We quantify the impact of spatial averaging of snow stratigraphy and physical snowpack properties on surface scattering from near-nadir frequency-modulated continuous-wave radar at 12–18 GHz. Relative permittivity, density, grain size and stratigraphic boundaries were measured in-situ at high resolution along the length of a 9 m snow trench. An optimal range of horizontal averaging (4–6 m) was identified to attribute variations in surface scattering at layer boundaries to dielectric contrasts estimated from centimetre-scale measurements of snowpack stratigraphy and bulk layer properties. Single vertical profiles of snowpack properties seldom captured the complex local variability influencing near-nadir radar surface scattering. We discuss implications of scaling in-situ measurements for snow radiative transfer modelling and evaluation of airborne microwave remote sensing of snow.

Regional climate signal vs. local noise: a two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land

Abstract. In low-accumulation regions, the reliability of δ18O-derived temperature signals from ice cores within the Holocene is unclear, primarily due to the small climate changes relative to the intrinsic noise of the isotopic signal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based climate reconstructions, we studied the stable-water isotope composition of firn at Kohnen Station, Dronning Maud Land, Antarctica. Analysing δ18O in two 50 m long snow trenches allowed us to create an unprecedented, two-dimensional image characterising the isotopic variations from the centimetre to the 100-metre scale. Our results show seasonal layering of the isotopic composition but also high horizontal isotopic variability caused by local stratigraphic noise. Based on the horizontal and vertical structure of the isotopic variations, we derive a statistical noise model which successfully explains the trench data. The model further allows one to determine an upper bound for the reliability of climate reconstructions conducted in our study region at seasonal to annual resolution, depending on the number and the spacing of the cores taken.

Recording microscale variations in snowpack layering using near-infrared photography

AbstractDeposition of snow from precipitation and wind events creates layering within seasonal snowpacks. The thickness and horizontal continuity of layers within seasonal snowpacks can be highly variable, due to snow blowing around topography and vegetation, and this has important implications for hydrology, remote sensing and avalanche forecasting. In this paper, we present practical field and post-processing protocols for recording lateral variations in snow stratigraphy using near-infrared (NIR) photography. A Fuji S9100 digital camera, modified to be sensitive to NIR wavelengths, was mounted on a rail system that allowed for rapid imaging of a 10 m long snow trench excavated on the north side of Toolik Lake, Alaska (68°38′ N, 149°36′ W). Post-processing of the images included removal of lens distortion and vignetting. A tape measure running along the base of the trench provided known locations (control points) that permitted scaling and georeferencing. Snow layer heights estimated from the NIR images compared well with manual stratigraphic measurements made at 0.2 m intervals along the trench (n = 357, R2 = 0.97). Considerably greater stratigraphic detail was captured by the NIR images than in the manually recorded profiles. NIR imaging of snow trenches using the described protocols is an efficient tool for quantifying continuous microscale variations in snow layers and associated properties.

Chemical and radio-chemical composition of freshsnow samples from northern slopes of Himalayas (Cho Oyu range, Tibet)

In September and October 2000, during a scientific and mountaineering expedition (Rome 8000), a continuous series of daily snowfalls have been sampled during the final monsoon and post-monsoon season. The sampling sites were the Gyabrag glacier and the Mt. Cho Oyu west buttress, in the northern slope of the Himalayas range. Samples of freshsnow were collected at different altitudes, ranging from 5700 to 6400 m a.s.l. in the same day and for the same precipitation. Contemporarily, some snow trenches were dug and snow layers were studied and sampled. Conductivity, pH and the major inorganic ions have been analysed with their relative field blanks. The results obtained in the Cho Oyu area have been compared to the ones reported in literature for the southern slopes of the Himalayas range. The comparison shows a substantial homogeneity of main ions concentrations in freshsnow, not depending on the geographical location but only on the monsoon alternation. Freshsnow data showed differences between the monsoon season, with values not substantially influenced by anthropogenic inputs, and the extra-monsoon (post-monsoon, winter and pre-monsoon) season characterised by the influence of dust from central Asia. Some experimental results of in situ radioactivity measurements, obtained with a portable γ-ray detector, are also presented.

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

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.

Harmonic analysis of snow temperatures

Introduction. Fourier technique was employed in this analysis to reduce snow temperature data collected between 1961 and 1963 at Camp Century, Greenland. The effects of radiation and pressure fluctuations on the heat transfer processes in the snow were not considered because the experimental site was located 600 cm from top surface in the floor of a completely covered snow trench. Fourier coefficients derived from the analysis will not only provide the variation in the amplitude of the temperature wave with depths and times of temperature extremes, but they will also give insight into the mechanism of the heat transfer processes and the thermal-physical properties of the medium under study.

Subsurface transportation methods in deep snow: G. Abele. Cold Regions Research and Engineering Lab. Hanover N.H. Technical Report

Abstract : During the 1962 test season in Greenland, a study was performed on subsurface transportation methods. A 1600 ft long, covered test trench containing horizontal curves and a 400 ft long processed snow floor section was constructed. Wheel trafficability tests on the snow trench floor were conducted with two types of low-pressure tires as well as with standard truck tires. An M-54 5-ton truck with a 5-ton load was used as the test vehicle. Skid tests were performed with the three types of tires on the processed snow floor, and the coefficient of friction between the tires and a hard snow surface was determined. A 1300 ft long, standard gage railroad track was installed in the trench after completion of the wheel traffic tests. A standard size flatcar with a 30-ton load, towed by a 5-ton truck equipped with rail wheels, was used as the test vehicle for the rail traffic tests. It was determined that the natural, unprocessed snow surface in a trench 26 ft below the snow surface is not suitable for extensive traffic with vehicles such as 5-ton trucks even when equipped with low-pressure flotation tires. However, a Peter plow-processed, age-hardened snow surface is capable of supporting a virtually unlimited amount of vehicle traffic using standard tires. Indications are that even heavier wheeled vehicles could be easily supported by a processed-snow trench floor. The coefficient of friction between rubber tires and a hard snow surface was found to be in the general range of 0.2 to 0.3. (Author)

On the isothermal flow of air into a rectangular snow trench

For isothermal, steady, two-dimensional flow with constant permeability, an expression has been derived for the quantity of air flowing into a partially cased rectangular snow trench. The formula, which is readily evaluated for any flow geometry, is Q = (K′;/2K) (k/μ) 〈ρ〉 (ps - pw), where Q is the mass flow rate, K′/2K is a configuration factor, 〈ρ〉 is the average air density calculated at mean pressure, and ps and pw are the air pressures at the snow surface and the uncased trench walls, respectively. For field conditions for which permeability is a known function of depth, the above expression, in which k/μ is replaced by 〈k/μ〉 = dt−1∫0dt(k/μ) dy, where dt is the depth of the trench, predicts a flow within 3 per cent of the value obtained from a more exact solution in which numerical techniques are used to account for variable permeability.