| 1. |
- Gusmeroli, Alessio, et al.
(författare)
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Vertical distribution of water within the polythermal Storglaciären, Sweden
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115:F4, s. F04002-
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of water content and its distribution in polythermal glaciers is required to model their flow and thermal state. However, observ of water content variations with depth in polythermal glaciers are scarce. Water content can be estimated from radio wave speed because they depend on one another. We obtained continuous profiles of radio wave speed variations with depth from zero-offset radar profiles collected in boreholes approximately 80 m deep in the upper ablation area of Storglaciaren, northern Sweden. These profiles show that the microcrystalline water system in the temperate ice is relatively homogeneous. The overall hydrothermal structure at this location is composed of a 20 m thick upper layer of cold, water-free ice, underlain by a temperate ice layer whose average water content is 0.6% +/- 0.3%. These results are corroborated by surface radar and thermistor measurements, which show that the depth of the cold temperate transition is 21 m and the calculated water content at that transition is 0.6% +/- 0.1%. These findings imply that the whole temperate ice layer is from 3 to 4 times softer than the cold ice and, consequently, that realistic ice flow models of polythermal glaciers should include the effect of water content on viscosity.
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| 2. |
- Løkkegaard, Anja, et al.
(författare)
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Greenland and Canadian Arctic ice temperature profiles database
- 2023
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Ingår i: The Cryosphere. - : Copernicus Publications. - 1994-0416 .- 1994-0424. ; 17:9, s. 3829-3845
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Tidskriftsartikel (refereegranskat)abstract
- Here, we present a compilation of 95 ice temperature profiles from 85 boreholes from the Greenland ice sheet and peripheral ice caps, as well as local ice caps in the Canadian Arctic. Profiles from only 31 boreholes (36 %) were previously available in open-access data repositories. The remaining 54 borehole profiles (64 %) are being made digitally available here for the first time. These newly available profiles, which are associated with pre-2010 boreholes, have been submitted by community members or digitized from published graphics and/or data tables. All 95 profiles are now made available in both absolute (meters) and normalized (0 to 1 ice thickness) depth scales and are accompanied by extensive metadata. These metadata include a transparent description of data provenance. The ice temperature profiles span 70 years, with the earliest profile being from 1950 at Camp VI, West Greenland. To highlight the value of this database in evaluating ice flow simulations, we compare the ice temperature profiles from the Greenland ice sheet with an ice flow simulation by the Parallel Ice Sheet Model (PISM). We find a cold bias in modeled near-surface ice temperatures within the ablation area, a warm bias in modeled basal ice temperatures at inland cold-bedded sites, and an apparent underestimation of deformational heating in high-strain settings. These biases provide process level insight on simulated ice temperatures.
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| 3. |
- Roth, Aurora, et al.
(författare)
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Modeling Winter Precipitation Over the Juneau Icefield, Alaska, Using a Linear Model of Orographic Precipitation
- 2018
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Ingår i: Frontiers in Earth Science. - : Frontiers Media S.A.. - 2296-6463. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Assessing and modeling precipitation in mountainous areas remains a major challenge in glacier mass balance modeling. Observations are typically scarce and reanalysis data and similar climate products are too coarse to accurately capture orographic effects. Here we use the linear theory of orographic precipitation model (LT model) to downscale winter precipitation from the Weather Research and Forecasting Model (WRF) over the Juneau Icefield, one of the largest ice masses in North America (>4,000 km(2)), for the period 1979-2013. The LT model is physically-based yet computationally efficient, combining airflow dynamics and simple cloudmicrophysics. The resulting 1 kmresolution precipitation fields show substantially reduced precipitation on the northeastern portion of the icefield compared to the southwestern side, a pattern that is not well captured in the coarse resolution (20 km) WRF data. Net snow accumulation derived from the LT model precipitation agrees well with point observations across the icefield. To investigate the robustness of the LT model results, we perform a series of sensitivity experiments varying hydrometeor fall speeds, the horizontal resolution of the underlying grid, and the source of the meteorological forcing data. The resulting normalized spatial precipitation pattern is similar for all sensitivity experiments, but local precipitation amounts vary strongly, with greatest sensitivity to variations in snow fall speed. Results indicate that the LT model has great potential to provide improved spatial patterns of winter precipitation for glaciermass balance modeling purposes in complex terrain, but ground observations are necessary to constrain model parameters to match total amounts.
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