Sensitivity of ground thermal regime and surface energy fluxes to tundra snow density in northern Alaska

Abstract

Regional snow densities are primarily controlled by winter air temperature and wind speed and change spatially and temporally. However, the impact of variations in snow density on the ground thermal regime and surface energy balance has received relatively little attention. This study examines the effect of variations in tundra snow density on surface energy fluxes and thermal regime of the active layer and permafrost in northern Alaska by using a one-dimensional heat transfer model with phase change. The model is driven through surface energy balance as the upper boundary condition. The baseline inputs were obtained at Barrow, Alaska, from 1995 to 1998. A snow bulk density of 362 kg m− 3 was used and a snow density factor was defined to modify the changes with respect to the baseline snow density. Based on the previous studies for tundra snow density in the Arctic, five simulation cases were conducted by setting the snow density factor to 0.7, 0.85, 1.0, 1.1, and 1.2, respectively, in the snow season of 1997–1998. Results show that variations in tundra snow density can strongly affect the near-surface ground temperature and conductive heat flux in northern Alaska. Simulation results indicate that an increase in snow density by 20% during the snow season of 1997–1998 would result in a decrease in the maximum temperature at the ground surface by 3.0 °C, at a depth of 0.29 m by 2.2 °C, at a depth of 5.0 m by 0.6 °C, and an increase in the magnitude of conductive heat flux by 31%. A decrease in the snow density by 30% would lead to the maximum temperature increase on the ground surface by 4.5 °C, at 0.29 m depth by 3.8 °C, and at 5.0 m depth by 1.5 °C, and a decrease in the magnitude of conductive heat flux by 38%. Increase of snow density by 20% would result in a decrease in mean annual ground surface temperature by up to 0.7 °C, whereas a decrease in snow density by 30% would lead to an increase in the mean annual ground surface temperature by approximately 1.6 °C. Variations in tundra snow density have very limited influence on snow surface temperature and active layer depth, and have insignificant impact on the sensible and latent heat fluxes.