A Snow Density Dataset for Improving Surface Boundary Conditions in Greenland Ice Sheet Firn Modeling

Abstract

The surface snow density of glaciers and ice sheets is of fundamental importance in converting volume to mass in both altimetry and surface mass balance studies, yet it is often poorly constrained. Site-specific surface snow densities are typically derived from empirical relations based on temperature and wind speed. These parameterizations commonly calculate the average density of the top meter of snow, thereby systematically overestimating snow density at the actual surface. Therefore, constraining surface snow density to the top 0.1 m can improve boundary conditions in high-resolution firn-evolution modeling. We have compiled an extensive dataset of 200 point measurements of surface snow density from firn cores and snow pits on the Greenland ice sheet. We find that surface snow density within 0.1 m of the surface has an average value of 315 kg m −3 with a standard deviation of 44 kg m −3 , and has an insignificant annual air temperature dependency. We demonstrate that two widely-used surface snow density parameterizations dependent on temperature systematically overestimate surface snow density over the Greenland ice sheet by 17-19%, and that using a constant density of 315 kg m −3 may give superior results when applied in surface mass budget modeling.

Firn data compilation reveals widespread decrease of firn air content in western Greenland

“…To these, we added an additional 20 cores extracted in 2016 and 2017, for which firn density was measured at a 10 cm resolution following the same procedure as Machguth et al (2016). When nearsurface snow densities were missing, we assigned a density of 315 kg m −3 (Fausto et al, 2018b) to the top centimetre and interpolated over the remaining gaps in density profiles using a logarithmic function of depth fitted to the available densities.…”

Evaluation of CloudSat's Cloud‐Profiling Radar for Mapping Snowfall Rates Across the Greenland Ice Sheet

“…Based on RCM outputs, we estimate that this could introduce uncertainties of up to ±11%. Second, Koenig16 assume that the density of the upper meter of snow is 338 kg/m 3 , yet snow densities are known to vary across the ice sheet with a standard deviation of 44 kg/m 3 (Fausto et al, 2018). Third, many of the accumulation rates derived by Koenig16 are located at the margins of the ice sheet.…”

“…Contemporary snowfall observations with high temporal resolution are provided by automated weather stations (AWS; e.g., Fausto et al, 2018;Smeets et al, 2018). AWS are equipped with acoustic ranging sensors that record changes in surface elevation over hourly or shorter intervals (Steffen & Box, 2001).…”

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

“…Charalampidis (Ahlstrøm et al, 2008). Fausto et al (2018) indicate that such near-surface snow density is not realistic. We, on the contrary, attribute this underestimation to the compaction of snow and firn below a newly deposited snow layer and apply a correction factor to each increment found in the snow height record.…”

“…The fresh snow bucket is used to distinguish fresh snow from old snow, information needed for the parameterization of surface roughness length from Lefebre et al (2003). A fresh snow density of 315 kg/m 3 after Fausto et al (2018), which already accounts for the effect of wind, is preferred to the parameterization used in Langen et al (2017). Grain size of fresh snow is set to 0.1 mm as in Langen et al (2017) and Katsushima et al (2009).…”