Local-scale variability of snow density on Arctic sea ice

Abstract

Abstract. Local-scale variations in snow density and layering on Arctic sea ice were characterized using a combination of traditional snow pit and SnowMicroPen (SMP) measurements. In total, 14 sites were evaluated within the Canadian Arctic Archipelago and Arctic Ocean on both first-year (FYI) and multi-year (MYI) sea ice. Sites contained multiple snow pits with coincident SMP profiles as well as unidirectional SMP transects. An existing SMP density model was recalibrated using manual density cutter measurements (n=186) to identify best-fit parameters for the observed conditions. Cross-validation of the revised SMP model showed errors comparable to the expected baseline for manual density measurements (RMSE = 34 kg m−3 or 10.9 %) and strong retrieval skill (R2=0.78). The density model was then applied to SMP transect measurements to characterize variations at spatial scales of up to 100 m. A supervised classification trained on snow pit stratigraphy allowed separation of the SMP density estimates by layer type. The resulting dataset contains 58 882 layer-classified estimates of snow density on sea ice representing 147 m of vertical variation and equivalent to more than 600 individual snow pits. An average bulk density of 310 kg m−3 was estimated with clear separation between FYI and MYI environments. Lower densities on MYI (277 kg m−3) corresponded with increased depth hoar composition (49.2 %), in strong contrast to composition of the thin FYI snowpack (19.8 %). Spatial auto-correlation analysis showed layered composition on FYI snowpack to persist over long distances while composition on MYI rapidly decorrelated at distances less than 16 m. Application of the SMP profiles to determine propagation bias in radar altimetry showed the potential errors of 0.5 cm when climatology is used over known snow density.

On the performance of the snow model Crocus driven by in situ and reanalysis data at Villum Research Station in northeast Greenland

“…Parametrisation for SSA after Proksch et al (2015) was developed using the precise MicroCT while Calonne et al (2020) used measurements from the IceCube. We found that densities for Calonne et al (2020) and King et al (2020), whose parametrisation is for Arctic snow on sea ice with the SMP Version 4, differ only slightly. Simulated density is closest to results after King et al (2020) and Calonne et al (2020) and especially underestimated compared to densities after Proksch et al (2015).…”

“…We found that densities for Calonne et al (2020) and King et al (2020), whose parametrisation is for Arctic snow on sea ice with the SMP Version 4, differ only slightly. Simulated density is closest to results after King et al (2020) and Calonne et al (2020) and especially underestimated compared to densities after Proksch et al (2015). Simulated SSA agrees better with results after Calonne et al (2020) and is far off results after Proksch et al (2015).…”

“…We evaluated the model performance by comparing simulated and measured snow depth, snow density and SSA ( Vertical profiles of snow density and SSA were retrieved from a SnowMicroPen (SMP), a snow penetrometer measuring the bonding force between snow grains with a vertical resolution of 1.25 mm (Schneebeli et al, 1999). While the density retrieved from SMP measurements was calculated following Calonne et al (2020), Proksch et al (2015) and King et al (2020), SSA was obtained based on Calonne et al (2020) and Proksch et al (2015), as King et al (2020) In addition, on 03 April 2018, snow depth was measured with a ruler, and every 10 cm of the profile, snow density with a density cutter (60x30x56 mm) and SSA with an IceCube3. The optical system IceCube measures the hemispherical infrared reflectance of snow and converts the reflectance in SSA (Zuanon, 2013).…”

“…However, Calonne et al (2020) developed the parametrisation for the SMP Version 4 we used, while the parametrisation after Proksch et al (2015) was developed for SMP Version 2 (Calonne et al, 2020). King et al (2020) found large discrepancies between measured density with a density cutter and SMP after Proksch et al (2015) for snow on Arctic sea ice. Parametrisation for SSA after Proksch et al (2015) was developed using the precise MicroCT while Calonne et al (2020) used measurements from the IceCube.…”

“…8. While density calculated afterCalonne et al (2020) andKing et al (2020) showed some similarities, densities after Proksch et alhttps://doi.org/10.5194/tc-2021-100 Preprint. Discussion started: 7 April 2021 c Author(s) 2021.…”