scholarly journals A continuum model for meltwater flow through compacting snow

2017 ◽  
Author(s):  
Colin R. Meyer ◽  
Ian J. Hewitt
Keyword(s):  
Surface Energy ◽  
Continuum Model ◽  
Water Storage ◽  
Greenland Ice Sheet ◽  
Percolation Process ◽  
Surface Mass ◽  
Run Off ◽  
Flow Through ◽  
Energy Balances ◽  
Mass And Energy Balances

Abstract. Meltwater is produced on the surface of glaciers and ice sheets when the seasonal surface energy forcing warms the snow to its melting temperature. This meltwater can run off the surface in streams or percolate through the porous snow and refreeze, which warms the subsurface through the release of latent heat. We model the percolation process from first principles using a continuum model that includes heat conduction, meltwater percolation and refreezing, as well as mechanical compaction. The model is forced by surface mass and energy balances. When the surface temperature reaches the melting point, we compute the amount of meltwater produced and allow it to percolate through the snow according to Darcy's law, or to run off the surface if the snow is already saturated. The model outputs the temperature, density, and water content profiles as well as the surface runoff and water storage. We compare the propagation of freezing fronts that occur in the model to observations from the Greenland ice sheet. The model applies to both accumulation and ablation areas and allows for a transition between the two as the surface energy forcing varies. The largest firn temperatures occur at intermediate values of the surface forcing when perennial water storage is predicted.

scholarly journals A continuum model for meltwater flow through compacting snow

2017 ◽  
Vol 11 (6) ◽  
pp. 2799-2813 ◽  
Author(s):  
Colin R. Meyer ◽  
Ian J. Hewitt
Keyword(s):  
Continuum Model ◽  
Pore Space ◽  
Water Storage ◽  
Greenland Ice Sheet ◽  
Percolation Process ◽  
Surface Mass ◽  
Run Off ◽  
Flow Through ◽  
Energy Balances ◽  
Mass And Energy Balances

Abstract. Meltwater is produced on the surface of glaciers and ice sheets when the seasonal energy forcing warms the snow to its melting temperature. This meltwater percolates into the snow and subsequently runs off laterally in streams, is stored as liquid water, or refreezes, thus warming the subsurface through the release of latent heat. We present a continuum model for the percolation process that includes heat conduction, meltwater percolation and refreezing, as well as mechanical compaction. The model is forced by surface mass and energy balances, and the percolation process is described using Darcy's law, allowing for both partially and fully saturated pore space. Water is allowed to run off from the surface if the snow is fully saturated. The model outputs include the temperature, density, and water-content profiles and the surface runoff and water storage. We compare the propagation of freezing fronts that occur in the model to observations from the Greenland Ice Sheet. We show that the model applies to both accumulation and ablation areas and allows for a transition between the two as the surface energy forcing varies. The largest average firn temperatures occur at intermediate values of the surface forcing when perennial water storage is predicted.

scholarly journals Changing surface–atmosphere energy exchange and refreezing capacity of the lower accumulation area, West Greenland

2015 ◽  
Vol 9 (6) ◽  
pp. 2163-2181 ◽  
Author(s):  
C. Charalampidis ◽  
D. van As ◽  
J. E. Box ◽  
M. R. van den Broeke ◽  
W. T. Colgan ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Surface Energy ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Balance Model ◽  
Surface Mass ◽  
Surface Energy Fluxes ◽  
Sheet Surface ◽  
Run Off ◽  
Negative Surface

Abstract. We present 5 years (2009–2013) of automatic weather station measurements from the lower accumulation area (1840 m a.s.l. – above sea level) of the Greenland ice sheet in the Kangerlussuaq region. Here, the summers of 2010 and 2012 were both exceptionally warm, but only 2012 resulted in a strongly negative surface mass budget (SMB) and surface meltwater run-off. The observed run-off was due to a large ice fraction in the upper 10 m of firn that prevented meltwater from percolating to available pore volume below. Analysis reveals an anomalously low 2012 summer-averaged albedo of 0.71 (typically ~ 0.78), as meltwater was present at the ice sheet surface. Consequently, during the 2012 melt season, the ice sheet surface absorbed 28 % (213 MJ m−2) more solar radiation than the average of all other years. A surface energy balance model is used to evaluate the seasonal and interannual variability of all surface energy fluxes. The model reproduces the observed melt rates as well as the SMB for each season. A sensitivity analysis reveals that 71 % of the additional solar radiation in 2012 was used for melt, corresponding to 36 % (0.64 m) of the 2012 surface lowering. The remaining 64 % (1.14 m) of surface lowering resulted from high atmospheric temperatures, up to a +2.6 °C daily average, indicating that 2012 would have been a negative SMB year at this site even without the melt–albedo feedback. Longer time series of SMB, regional temperature, and remotely sensed albedo (MODIS) show that 2012 was the first strongly negative SMB year, with the lowest albedo, at this elevation on record. The warm conditions of recent years have resulted in enhanced melt and reduction of the refreezing capacity in the lower accumulation area. If high temperatures continue, the current lower accumulation area will turn into a region with superimposed ice in coming years.

scholarly journals Estimating Greenland ice sheet surface mass balance contribution to future sea level rise using the regional atmospheric climate model MAR

2012 ◽  
Vol 6 (4) ◽  
pp. 3101-3147 ◽  
Author(s):  
X. Fettweis ◽  
B. Franco ◽  
M. Tedesco ◽  
J. H. van Angelen ◽  
J. T. M. Lenaerts ◽  
...  
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
Climate Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Future Projections ◽  
Surface Mass ◽  
Run Off ◽  
Rcp 8.5

Abstract. We report future projections of Surface Mass Balance (SMB) over the Greenland ice sheet (GrIS) obtained with the regional climate model MAR, forced by the outputs of three CMIP5 General Circulation Models (GCMs) when considering two different warming scenarios (RCP 4.5 and RCP 8.5). The GCMs selected in this study have been chosen according to their ability to simulate the current climate over Greenland. Our results indicate that in a warmer climate (i) the mass gained due to increased precipitation over GrIS does not compensate the mass lost through increased run-off; (ii) the surface melt increases non-linearly with rising temperatures due to the positive feedback between surface albedo and melt, associated with the expansion of bare ice zones which, in addition, decreases the ice sheet refreezing capacity; (iii) most of the precipitation is expected to fall as rainfall in summer, which further increases surface melt; (iv) no considerable change is expected on the length of the melting season, since heavier winter snowfall dampens the melt increase at the end of spring; (v) the increase of meltwater run-off versus temperature anomalies is dependent of the GCM-forced MAR ability to simulate the current climate; (vi) the MAR-simulated SMB changes can be approximated using the annual accumulated snowfall and summer 600 hPa temperature increase simulated by the forcing GCMs. In view of the large range in the CMIP5 future projections for the same future scenario, the GCM-based SMB approximations allow us to estimate what future projections are most likely within the CMIP5 multi-model ensemble. In 2100, the ensemble mean projects a sea level rise, resulting from a GrIS SMB decrease, estimated to be +4 ± 2 cm and +9 ± 4 cm for the RCP 4.5 and RCP 8.5 scenarios, respectively. The GrIS SMB should remain positive with respect to RCP 4.5 scenario and becomes negative around 2070 in the case of the RCP 8.5 scenario since a global warming >+3 °C is needed. However, these future projections do not consider the positive melt-elevation feedback because the ice sheet topography is fixed through the whole simulation. In this regard, the MAR simulations suggest a cumulative ice sheet thinning by 2100 of ~100–200 m in the ablation zone. This highlights the importance of coupling climate models to an ice sheet model to consider the future response of both surface processes and ice-dynamic changes, and their mutual feedbacks to rising temperatures.

scholarly journals A numerical simulation of supraglacial heat advection and its influence on ice melt

1991 ◽  
Vol 37 (126) ◽  
pp. 296-300
Author(s):  
R. D Moore
Keyword(s):  
Heavy Rainfall ◽  
Water Layer ◽  
Glacier Surface ◽  
Rainfall Events ◽  
Heat Advection ◽  
Ice Melt ◽  
Run Off ◽  
Macro Scale ◽  
Energy Balances ◽  
Mass And Energy Balances

AbstractEnergy exchange between the atmosphere and a melting glacier surface is mediated by the presence of a water layer. Under conditions of rapid melt and/or heavy rainfall, the possibility exists that a supraglacial run-off layer can advect sensible heat and influence the spatial variations of melt. The potential magnitude of such advection was investigated by numerically solving differential equations expressing the mass and energy balances of a two-dimensional run-off layer. Solutions were obtained for conditions typical of rainfall events, in which the potential for supraglacial heat advection should be maximal. The solutions indicate that advection cannot influence macro-scale melt patterns and surface morphology, except perhaps under heavy rainfall and/or rapid melt conditions, but can possibly cause micro-scale variations in ice melt. One-dimensional energy-balance models, which have normally been applied over glacier surfaces, should remain valid for most conditions.

scholarly journals Meteorological drivers of ablation processes on a cold glacier in the semiarid Andes of Chile

2013 ◽  
Vol 7 (2) ◽  
pp. 1833-1870 ◽  
Author(s):  
S. MacDonell ◽  
C. Kinnard ◽  
T. Mölg ◽  
L. Nicholson ◽  
J. Abermann
Keyword(s):  
Austral Summer ◽  
Longwave Radiation ◽  
Shortwave Radiation ◽  
Strongly Correlated ◽  
Glacier Surface ◽  
Surface Mass ◽  
Strong Winds ◽  
Sublimation Rates ◽  
Energy Balances ◽  
Mass And Energy Balances

Abstract. Meteorological and surface change measurements collected during a 2.5 yr period are used to calculate surface mass and energy balances at 5324 m a.s.l. on Guanaco Glacier, a cold-based glacier in the semi-arid Andes of Chile. Meteorological conditions are marked by extremely low vapour pressures (annual mean of 1.1 hPa), strong winds (annual mean of 10 m s−1), high shortwave radiation receipt (mean annual 295 W m−2) and low precipitation rates (mean annual 45 mm w.e.). Net shortwave radiation provides the greatest source of energy to the glacier surface, and net longwave radiation dominates energy losses. The turbulent latent heat flux is always negative, which means that the surface is always losing mass via sublimation, which is the main form of ablation at the site. Sublimation rates are most strongly correlated with net shortwave radiation, incoming shortwave radiation, albedo and vapour pressure. Low glacier surface temperatures restrict melting for much of the period, however episodic melting occurs during the austral summer, when warm, humid, calm and high pressure conditions restrict sublimation and make more energy available for melting. Low accumulation (131 mm w.e. over the period) and relatively high ablation (1435 mm w.e.) means that mass change over the period was negative (−1304 mm w.e.), which continued the negative trend recorded in the region over the last few decades.

scholarly journals A numerical simulation of supraglacial heat advection and its influence on ice melt

1991 ◽  
Vol 37 (126) ◽  
pp. 296-300 ◽  
Author(s):  
R. D Moore
Keyword(s):  
Heavy Rainfall ◽  
Water Layer ◽  
Glacier Surface ◽  
Rainfall Events ◽  
Heat Advection ◽  
Ice Melt ◽  
Run Off ◽  
Macro Scale ◽  
Energy Balances ◽  
Mass And Energy Balances

AbstractEnergy exchange between the atmosphere and a melting glacier surface is mediated by the presence of a water layer. Under conditions of rapid melt and/or heavy rainfall, the possibility exists that a supraglacial run-off layer can advect sensible heat and influence the spatial variations of melt. The potential magnitude of such advection was investigated by numerically solving differential equations expressing the mass and energy balances of a two-dimensional run-off layer. Solutions were obtained for conditions typical of rainfall events, in which the potential for supraglacial heat advection should be maximal. The solutions indicate that advection cannot influence macro-scale melt patterns and surface morphology, except perhaps under heavy rainfall and/or rapid melt conditions, but can possibly cause micro-scale variations in ice melt. One-dimensional energy-balance models, which have normally been applied over glacier surfaces, should remain valid for most conditions.

scholarly journals The modelled liquid water balance of the Greenland Ice Sheet

2017 ◽  
Vol 11 (6) ◽  
pp. 2507-2526 ◽  
Author(s):  
Christian R. Steger ◽  
Carleen H. Reijmer ◽  
Michiel R. van den Broeke
Keyword(s):  
Water Balance ◽  
Liquid Water ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Special Focus ◽  
Near Surface ◽  
Surface Mass ◽  
Run Off ◽  
Surface Melt ◽  
Western Side

Abstract. Recent studies indicate that the surface mass balance will dominate the Greenland Ice Sheet's (GrIS) contribution to 21st century sea level rise. Consequently, it is crucial to understand the liquid water balance (LWB) of the ice sheet and its response to increasing surface melt. We therefore analyse a firn simulation conducted with the SNOWPACK model for the GrIS and over the period 1960–2014 with a special focus on the LWB and refreezing. Evaluations of the simulated refreezing climate with GRACE and firn temperature observations indicate a good model–observation agreement. Results of the LWB analysis reveal a spatially uniform increase in surface melt (0.16 m w.e. a−1) during 1990–2014. As a response, refreezing and run-off also indicate positive changes during this period (0.05 and 0.11 m w.e. a−1, respectively), where refreezing increases at only half the rate of run-off, implying that the majority of the additional liquid input runs off the ice sheet. This pattern of refreeze and run-off is spatially variable. For instance, in the south-eastern part of the GrIS, most of the additional liquid input is buffered in the firn layer due to relatively high snowfall rates. Modelled increase in refreezing leads to a decrease in firn air content and to a substantial increase in near-surface firn temperature. On the western side of the ice sheet, modelled firn temperature increases are highest in the lower accumulation zone and are primarily caused by the exceptional melt season of 2012. On the eastern side, simulated firn temperature increases are more gradual and are associated with the migration of firn aquifers to higher elevations.

The Impact of Extratropical Cyclones on the Greenland Ice Sheet

2020 ◽  
Author(s):  
Luca Maffezzoni ◽  
Laura Edwards ◽  
Tom Matthews
Keyword(s):  
Surface Energy ◽  
Sensible Heat Flux ◽  
Ice Sheet ◽  
Warm Season ◽  
Greenland Ice Sheet ◽  
Surface Energy Budget ◽  
Extratropical Cyclones ◽  
Positive Contribution ◽  
Surface Mass ◽  
The Impact

<p>The Greenland Ice Sheet (GrIS) stores enough freshwater to raise global sea level by more than 7 m, so its response to climate variability and change is of considerable societal significance. In this context, extratropical cyclones are known to impact the surface mass budget (SMB) via their influence on precipitation and the surface energy budget (SEB). However, there has so far been limited research on these pathways. We address this by expanding process-based knowledge of cyclones and their influence on the GrIS. Using a 58-year integration of the Model Atmospherique Regional (MAR) along with a cyclones`dataset covering the Northern Hemisphere for the same period, we show the mean standardized anomalies of SMB and SEB over the GrIS when cyclones are in close proximity. Overall, our results, show a positive contribution of extratropical cyclones to the SMB during warm and cold seasons alike, especially via snowfall. In both winter and summer, cyclones enhance the downwelling longwave radiative flux due to higher temperatures and increased humidity. In summer an increase (decrease) of long-wave downward and relative humidity (sensible heat flux and temperature) is observed. In winter the impact on these surface energy variables is similar, apart for temperature which have an opposite sign. Overall, cyclones suppress melt and run-off, especially in the ablation zone and peripherals areas of the Ice Sheet during the warm season. Results from this study will contribute to better understanding of how the GrIS may respond in terms of SMB and SEB to changes in the North Atlantic storm tracks under global warming scenarios.</p>

Innovative energy and mass balance of a continuous evaporating crystallizer

2019 ◽  
pp. 646-654
Author(s):  
Jan Iciek ◽  
Kornel Hulak ◽  
Radosław Gruska
Keyword(s):  
Energy Balance ◽  
Mass Balance ◽  
Working Conditions ◽  
Crystallization Process ◽  
Heat Losses ◽  
Inert Gas ◽  
Gas Removal ◽  
Energy Balances ◽  
Heat Released ◽  
Mass And Energy Balances

The article presents the mass and energy balances of the sucrose crystallization process in a continuous evaporating crystallizer. The developed algorithm allows to assess the working conditions of the continuous evaporating crystallizers and the technological and energy parameters. The energy balance algorithm takes into account the heat released during the crystallization of sucrose, which was analyzed in this study, heat losses to the environment and heat losses due the vapor used for inert gas removal.

scholarly journals Reconstruction of historical surface mass balance, 1984–2017 from GreenTrACS multi-offset ground-penetrating radar

2020 ◽  
pp. 1-10
Author(s):  
Tate G. Meehan ◽  
H. P. Marshall ◽  
John H. Bradford ◽  
Robert L. Hawley ◽  
Thomas B. Overly ◽  
...  
Keyword(s):  
Mass Balance ◽  
Ground Penetrating Radar ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Surface Mass Balance ◽  
Snow Density ◽  
Surface Mass ◽  
Age Model ◽  
Ground Penetrating ◽  
Good Agreement

Abstract We present continuous estimates of snow and firn density, layer depth and accumulation from a multi-channel, multi-offset, ground-penetrating radar traverse. Our method uses the electromagnetic velocity, estimated from waveform travel-times measured at common-midpoints between sources and receivers. Previously, common-midpoint radar experiments on ice sheets have been limited to point observations. We completed radar velocity analysis in the upper ~2 m to estimate the surface and average snow density of the Greenland Ice Sheet. We parameterized the Herron and Langway (1980) firn density and age model using the radar-derived snow density, radar-derived surface mass balance (2015–2017) and reanalysis-derived temperature data. We applied structure-oriented filtering to the radar image along constant age horizons and increased the depth at which horizons could be reliably interpreted. We reconstructed the historical instantaneous surface mass balance, which we averaged into annual and multidecadal products along a 78 km traverse for the period 1984–2017. We found good agreement between our physically constrained parameterization and a firn core collected from the dry snow accumulation zone, and gained insights into the spatial correlation of surface snow density.

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