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

Abstract

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.

Thermal conductivity of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements

“…1a in Marchenko et al, 2017a) and the last one is derived by minimizing the misfit between temperature profiles measured in April 2015 by the thermistor strings installed in April 2014 and in April 2015. The firn pack at Lomonosovfonna is heavily influenced by the percolation and refreezing of meltwater (Marchenko et al, 2017b), which results in prominent variability of subsurface stratigraphy at the scale of 10 m (Marchenko et al, 2017a).…”

“…During the first two pe-riods it was once every 3 h; during the fourth period it was once every 1 h. During the third period the frequency varied and was once every 1 h during 17 April-31 July 2014 and 15 April-9 July 2015, once every 3 h during 1 August-31 October 2014 and once every 12 h from 1 November 2014 to 14 April 2015. The strings installed in 2012, 2013 and 2014 contained up to 128 thermistors covering a depth from 0.5 to 12 m with a vertical separation varying from 0.25 to 2 m (Marchenko et al, 2017b;see Fig. 2 therein).…”

Dynamic Response of a High Arctic Glacier to Melt and Runoff Variations

“…The front of Nordenskiöldbreen has retreated by 15-35 m/a since the end of the Little Ice Age, but retreat rates have been negligible since ∼2002 as the glacier is retreating on land (Allaart, 2016;Rachlewicz et al, 2007). Nordenskiöldbreen is a polythermal glacier ("type b" in Blatter & Hutter, 1991), with temperate conditions in the accumulation zone due to deep meltwater percolation and refreezing (Marchenko et al, 2016(Marchenko et al, , 2017Vega et al, 2016), and cold near-surface ice in the ablation area (Van Pelt et al, 2012). Nordenskiöldbreen is a polythermal glacier ("type b" in Blatter & Hutter, 1991), with temperate conditions in the accumulation zone due to deep meltwater percolation and refreezing (Marchenko et al, 2016(Marchenko et al, , 2017Vega et al, 2016), and cold near-surface ice in the ablation area (Van Pelt et al, 2012).…”

“…(Van Pelt et al, 2012). Nordenskiöldbreen is a polythermal glacier ("type b" in Blatter & Hutter, 1991), with temperate conditions in the accumulation zone due to deep meltwater percolation and refreezing (Marchenko et al, 2016(Marchenko et al, , 2017Vega et al, 2016), and cold near-surface ice in the ablation area (Van Pelt et al, 2012). Unlike neighboring outlet glacier Tunabreen, Nordenskiöldbreen is not a surge-type glacier, at least no surges have occurred since the termination of the Little Ice Age according to analysis of foreland landforms (Ewertowski et al, 2016).…”

Drivers of Firn Density on the Greenland Ice Sheet Revealed by Weather Station Observations and Modeling

“…Recent advances in firn modeling facilitated a move from empirical parameterizations of meltwater retention based on few climate parameter (Janssens & Huybrechts, 2000;Reijmer et al, 2012) to physical multilayer snow and firn models resolving multiple subsurface processes driven by weather observations (Charalampidis et al, 2015;Marchenko et al, 2017;Wever et al, 2014;Wever et al, 2016) or regional climate models (Langen et al, 2017;Steger et al, 2017). These models now allow identifying the contributions of various subsurface processes to a net observable change in firn structure and density and therefore allow a better understanding of the surface of the Greenland ice sheet and of its response to climate warming.…”