| 1. |
- Oerlemans, Johannes, et al.
(författare)
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A model study of Abrahamsenbreen, a surging glacier in northern Spitsbergen
- 2015
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Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 9:2, s. 767-779
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Tidskriftsartikel (refereegranskat)abstract
- The climate sensitivity of Abrahamsenbreen, a 20 km long surge-type glacier in northern Spitsbergen, is studied with a simple glacier model. A scheme to describe the surges is included, which makes it possible to account for the effect of surges on the total mass budget of the glacier. A climate reconstruction back to AD 1300, based on ice-core data from Lomonosovfonna and climate records from Longyearbyen, is used to drive the model. The model is calibrated by requesting that it produce the correct Little Ice Age maximum glacier length and simulate the observed magnitude of the 1978 surge. Abrahamsenbreen is strongly out of balance with the current climate. If climatic conditions remain as they were for the period 1989–2010, the glacier will ultimately shrink to a length of about 4 km (but this will take hundreds of years). For a climate change scenario involving a 2 m year−1 rise of the equilibrium line from now onwards, we predict that in the year 2100 Abrahamsenbreen will be about 12 km long. The main effect of a surge is to lower the mean surface elevation and thereby to increase the ablation area, causing a negative perturbation of the mass budget. We found that the occurrence of surges leads to a faster retreat of the glacier in a warming climate. Because of the very small bed slope, Abrahamsenbreen is sensitive to small perturbations in the equilibrium-line altitude. If the equilibrium line were lowered by only 160 m, the glacier would steadily grow into Woodfjorddalen until, after 2000 years, it would reach Woodfjord and calving would slow down the advance. The bed topography of Abrahamsenbreen is not known and was therefore inferred from the slope and length of the glacier. The value of the plasticity parameter needed to do this was varied by +20 and −20%. After recalibration the same climate change experiments were performed, showing that a thinner glacier (higher bedrock in this case) in a warming climate retreats somewhat faster.
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| 2. |
- Parmhed, Oskar, et al.
(författare)
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Describing surface fluxes in katabatic flow on Breidamerkurjökull, Iceland
- 2004
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Royal meteorological Society. - 0035-9009 .- 1477-870X. ; 130:598, s. 1137-1151
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Tidskriftsartikel (refereegranskat)abstract
- For very stable boundary layers there is no well-accepted theory today. In this study, an improved Prandtl model with varying diffusivity is applied to less than ideal conditions for pure katabatic flow pertaining to very stable boundary layers. We find that the improved Prandtl model adequately describes the usual and persistent katabatic glacier wind on Breidamerkurjökull. This is true even for flows with very different heights and strengths of the jet. A theoretical estimate of the katabatic jet height, based on temperature deficit and lapse rate, is verified. The calculated surface fluxes compare well with the measured turbulence parameters. A possible reason for the robustness of the katabatic jet (and other low-level jets) is given in terms of the Scorer parameter. Copyright © 2004 Royal Meteorological Society.
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| 3. |
- Radic, Valentina, et al.
(författare)
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Analysis of scaling methods in deriving future volume evolutions of valley glaciers
- 2008
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Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 54:187, s. 601-612
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Tidskriftsartikel (refereegranskat)abstract
- Volume-area scaling is a common tool for deriving future volume evolutions of valley glaciers and their contribution to sea-level rise. We analyze the performance of scaling relationships for deriving volume projections in comparison to projections from a one-dimensional ice-flow model. The model is calibrated for six glaciers (Nigardsbreen, Rhonegletscher, South Cascade Glacier, Sofiyskiy glacier, midre Lovenbreen and Abramov glacier). Volume evolutions forced by different hypothetical mass-balance perturbations are compared with those obtained from volume-area (V-A), volume-length (V-L) and volume-area-length (V-A-L) scaling. Results show that the scaling methods mostly underestimate the volume losses predicted by the ice-flow model, up to 47% for V-A scaling and up to 18% for V-L scaling by the end of the 100 year simulation period. In general, V-L scaling produces closer simulations of volume evolutions derived from the ice-flow model, suggesting that V-L scaling may be a better approach for deriving volume projections than V-A scaling. Sensitivity experiments show that the initial volumes and volume evolutions are highly sensitive to the choice of the scaling constants, yielding both over- and underestimates. However, when normalized by initial volume, volume evolutions are relatively insensitive to the choice of scaling constants, especially in the V-L scaling. The 100 year volume projections differ within 10% of initial volume when the V-A scaling exponent commonly assumed, gamma = 1.375, is varied by -30% to +45% (gamma = [0.95, 2.00]) and the V-L scaling exponent, q = 2.2, is varied by -30% to +45% (q = [1.52, 3.20]). This is encouraging for the use of scaling methods in glacier volume projections, particularly since scaling exponents may vary between glaciers and the scaling constants are generally unknown.
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| 4. |
- Radic, Valentina, et al.
(författare)
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Volume-area scaling vs flowline modelling in glacier volume projections
- 2007
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Ingår i: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 46:1, s. 234-240
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Tidskriftsartikel (refereegranskat)abstract
- Volume-area scaling provides a practical alternative to ice-flow modelling to account for glacier size changes when modelling future glacier evolutions, however, uncertainties remain as to the validity of the approach under non-steady conditions. We address these uncertainties by deriving scaling exponents in volume-area relationship from one-dimensional ice-flow modelling. We generate a set of 37 synthetic steady-state glaciers of different sizes, and then model volume evolutions due to climate warming and cooling as prescribed by negative and positive mass balance perturbations, respectively, on a century time scale. The scaling exponent derived for the steady-state glaciers (=1.56) differs from the exponents derived from the glaciers in transient (non-steady) state by up to 86%. Nevertheless, volume projections employing volume-area scaling are relatively insensitive to these differences in scaling exponents. Volume-area scaling agrees well with the results from ice-flow modelling and is able to simulate the approach of a glacier to a new steady state, if mass-balance elevation feedback is considered by adding or removing elevation bands at the lowest part of the glacier in response to mass balance variations. Provided area-changes are considered in the mass balance computations in this way, our results indicate that volume-area scaling is a powerful tool for glacier volume projections on multi-century time scales.
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| 5. |
- van Pelt, Ward, et al.
(författare)
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Inverse estimation of snow accumulation along a radar transect on Nordenskioldbreen, Svalbard
- 2014
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Ingår i: Journal of Geophysical Research - Earth Surface. - 2169-9003 .- 2169-9011. ; 119:4, s. 816-835
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Tidskriftsartikel (refereegranskat)abstract
- We present an inverse modeling approach to reconstruct annual accumulation patterns from ground-penetrating radar (GPR) data. A coupled surface energy balance-snow model simulates surface melt and the evolution of subsurface density, temperature, and water content. The inverse problem consists of iteratively calibrating accumulation, serving as input for the model, by finding a match between modeled and observed radar travel times. The inverse method is applied to a 16km GPR transect on Nordenskioldbreen, Svalbard, yielding annual accumulation patterns for 2007-2012. Accumulation patterns with a mean of 0.75meter water equivalent (mwe)a(-1)contain substantial spatial variability, with a mean annual standard deviation of 0.17mwea(-1), and show only partial consistency from year to year. In contrast to traditional methods, accounting for melt water percolation, refreezing, and runoff facilitates accurate accumulation reconstruction in areas with substantial melt. Additionally, accounting for horizontal density variability along the transect is shown to reduce spatial variability in reconstructed accumulation, whereas incorporating irreducible water storage lowers accumulation estimates. Correlating accumulation to terrain characteristics in the dominant wind direction indicates a strong preference of snow deposition on leeward slopes, whereas weaker correlations are found with terrain curvature. Sensitivity experiments reveal a nonlinear response of the mass balance to accumulation changes. The related negative impact of small-scale accumulation variability on the mean net mass balance is quantified, yielding a negligible impact in the accumulation zone and a negative impact of -0.09mwea(-1)in the ablation area.
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| 6. |
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| 7. |
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| 8. |
- van Pelt, Ward, et al.
(författare)
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Simulating melt, runoff and refreezing on Nordenskiöldbreen, Svalbard, using a coupled snow and energy balance model
- 2012
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Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 6:3, s. 641-659
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Tidskriftsartikel (refereegranskat)abstract
- A distributed energy balance model is coupled to a multi-layer snow model in order to study the mass balance evolution and the impact of refreezing on the mass budget of Nordenskioldbreen, Svalbard. The model is forced with output from the regional climate model RACMO and meteorological data from Svalbard Airport. Extensive calibration and initialisation are performed to increase the model accuracy. For the period 1989-2010, we find a mean net mass balance of -0.39 m w.e. a(-1). Refreezing contributes on average 0.27 m w.e. a(-1) to the mass budget and is most pronounced in the accumulation zone. The simulated mass balance, radiative fluxes and subsurface profiles are validated against observations and are generally in good agreement. Climate sensitivity experiments reveal a non-linear, seasonally dependent response of the mass balance, refreezing and runoff to changes in temperature and precipitation. It is shown that including seasonality in climate change, with less pronounced summer warming, reduces the sensitivity of the mass balance and equilibrium line altitude (ELA) estimates in a future climate. The amount of refreezing is shown to be rather insensitive to changes in climate.
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