Thermal tracing of retained meltwater in the lower accumulation area of the Southwestern Greenland ice sheet

Charalampidis, Charalampos; As, Dirk van; Colgan, William; Fausto, Robert S.; MacFerrin, Michael; Machguth, Horst

doi:10.1017/aog.2016.2

Cited by 31 publications

(42 citation statements)

References 49 publications

(79 reference statements)

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“…This justifies utilization of the empirical data for constraining the suggested schemes describing deep water percolation and validating the modeling results. In a broader context it also proves the potential of temperature tracking of melt water in snow and firn packs (Conway and Benedict, 1994;Pfeffer and Humphrey, 1996;Humphrey et al, 2012;Cox et al, 2015;Charalampidis et al, 2016).…”

Section: Discussionmentioning

confidence: 59%

Parameterizing Deep Water Percolation Improves Subsurface Temperature Simulations by a Multilayer Firn Model

et al. 2017

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Deep preferential percolation of melt water in snow and firn brings water lower along the vertical profile than a laterally homogeneous wetting front. This widely recognized process is an important source of uncertainty in simulations of subsurface temperature, density, and water content in seasonal snow and in firn packs on glaciers and ice sheets. However, observation and quantification of preferential flow is challenging and therefore it is not accounted for by most of the contemporary snow/firn models. Here we use temperature measurements in the accumulation zone of Lomonosovfonna, Svalbard, done in April 2012-2015 using multiple thermistor strings to describe the process of water percolation in snow and firn. Effects of water flow through the snow and firn profile are further explored using a coupled surface energy balance -firn model forced by the output of the regional climate model WRF. In situ air temperature, radiation, and surface height change measurements are used to constrain the surface energy and mass fluxes. To account for the effects of preferential water flow in snow and firn we test a set of depth-dependent functions allocating a certain fraction of the melt water available at the surface to each snow/firn layer. Experiments are performed for a range of characteristic percolation depths and results indicate a reduction in root mean square difference between the modeled and measured temperature by up to a factor of two compared to the results from the default water infiltration scheme. This illustrates the significance of accounting for preferential water percolation to simulate subsurface conditions. The suggested approach to parameterization of the preferential water flow requires low additional computational cost and can be implemented in layered snow/firn models applied both at local and regional scales, for distributed domains with multiple mesh points.

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Section: Discussionmentioning

confidence: 59%

Parameterizing Deep Water Percolation Improves Subsurface Temperature Simulations by a Multilayer Firn Model

et al. 2017

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“…Other snow/firn temperature records are available from the Greenland Climate Network (GC-Net; Steffen and Box, 2001) and for the western percolation zone (Humphrey et al, 2012;Charalampidis et al, 2016). The latter two data sets, which cover the periods 2007-2009 and 2009-2013, also indicate substantial warming of the upper ∼ 10 m firn caused by latent heat release from refreezing.…”

Section: Model Evaluation With Firn Temperature Measurementsmentioning

confidence: 99%

“…The closest available record is from the KAN_U automatic weather station of the Greenland Analogue Project (GAP) and the Programme for Monitoring of the Greenland Ice Sheet (PROMICE), which is located in the lower accumulation zone of Basin 6. There, firn temperature increased by approximately 4.7 • C during 2012 (Charalampidis et al, 2016). To discuss changes in the vertical firn properties over the simulation period in more detail, we present cross sections of firn density, temperature and volumetric water content along a southern GrIS transect (Fig.…”

Section: Refreezing and Latent Heat Releasementioning

confidence: 99%

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The modelled liquid water balance of the Greenland Ice Sheet

2017

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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.

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“…Challenges in determining runoff are largest due to the uncertainties in quantifying retention in snow and firn, as this is the only component that takes place at depth (in the order of meters), thus out of sight and reach of basic, direct observational methods . Indirect methods have existed for decades, such as determining changes in density/stratigraphy from repeat snow pits (e.g., Techel and Pielmeier, 2011) or firn cores (e.g., Vallelonga et al, 2014), continuous subsurface temperature measurements for capturing the release of latent heat from refreezing Charalampidis et al, 2016), or radar systems capable of identifying strong reflectors in porous snow or firn as ice layers (e.g., Koenig et al, 2016). Such methods are excellent for determining the location and quantity of the retained mass, but do not allow us to track and comprehend all physical processes involved in percolation and refreezing.…”

Section: Introductionmentioning

confidence: 99%

Challenges of Quantifying Meltwater Retention in Snow and Firn: An Expert Elicitation

Box

Fausto

2016

Front. Earth Sci.

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Thirty-four experts took part in a survey of the most important and challenging topics in the field of meltwater retention in snow and firn, to reveal those topics that present the largest potential for scientific advancement. The most important and challenging topic to the expert panel is spatial heterogeneity of percolation, both in measurement and model studies. Studying percolation blocking by ice layering, particularly in modeling, also provides large potential for science advancement, as well as hydraulic conductivity and capillary forces in snow/firn. Model studies can benefit from improved initialization, and improved calculation of accumulation and liquid water at the surface. Firn coring should be performed more often, though we argue that also data that are relatively simple to collect, but of great importance to retention such as surface accumulation, density and temperature, are too sparse due to the high logistical expenses involved in field campaigns. Generally speaking, retention changes are expected to be of importance to the climatic (surface) mass balance and thus ice loss in coming decades, more so for Greenland than Antarctica or ice masses elsewhere.

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Thermal tracing of retained meltwater in the lower accumulation area of the Southwestern Greenland ice sheet

Cited by 31 publications

References 49 publications

Parameterizing Deep Water Percolation Improves Subsurface Temperature Simulations by a Multilayer Firn Model

Parameterizing Deep Water Percolation Improves Subsurface Temperature Simulations by a Multilayer Firn Model

The modelled liquid water balance of the Greenland Ice Sheet

Challenges of Quantifying Meltwater Retention in Snow and Firn: An Expert Elicitation

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