Abstract
Abstract. A realistic simulation of snow cover and its thermal properties are important for accurate modelling of permafrost. We analyse simulated relationships between air and near-surface (20 cm) soil temperatures in the Northern Hemisphere permafrost region during winter, with a particular focus on snow insulation effects in nine land surface models, and compare them with observations from 268 Russian stations. There are large cross-model differences in the simulated differences between near-surface soil and air temperatures (ΔT; 3 to 14 °C), in the sensitivity of soil-to-air temperature (0.13 to 0.96 °C °C−1), and in the relationship between ΔT and snow depth. The observed relationship between ΔT and snow depth can be used as a metric to evaluate the effects of each model's representation of snow insulation, hence guide improvements to the model's conceptual structure and process parameterisations. Models with better performance apply multilayer snow schemes and consider complex snow processes. Some models show poor performance in representing snow insulation due to underestimation of snow depth and/or overestimation of snow conductivity. Generally, models identified as most acceptable with respect to snow insulation simulate reasonable areas of near-surface permafrost (13.19 to 15.77 million km2). However, there is not a simple relationship between the sophistication of the snow insulation in the acceptable models and the simulated area of Northern Hemisphere near-surface permafrost, because several other factors, such as soil depth used in the models, the treatment of soil organic matter content, hydrology and vegetation cover, also affect the simulated permafrost distribution.
Highlights
Present-day permafrost simulations by global climate models are limited and future projections contain high, modelinduced uncertainty (e.g. Slater and Lawrence, 2013; Koven et al, 2013)
These studies showed that the consideration of wet snow metamorphism and snow compaction, improved snow thermal conductivity and multilayer snow schemes can improve the simulation of snow dynamics and soil temperature
There is significant scatter in the observation-based relationship indicated by the interquartile range in T of 1.5–8.5 ◦C at specific snow depth and air temperature regimes, likely resulting from complicating factors such as snow pack density and moisture content variability over the winter, as well as observational errors
Summary
Present-day permafrost simulations by global climate models are limited and future projections contain high, modelinduced uncertainty (e.g. Slater and Lawrence, 2013; Koven et al, 2013). Langer et al, 2013; Dutra et al, 2012; Gouttevin et al, 2012; Essery et al, 2013; Wang et al, 2013; Jafarov et al, 2014) Most importantly, these studies showed that the consideration of wet snow metamorphism and snow compaction, improved snow thermal conductivity and multilayer snow schemes can improve the simulation of snow dynamics and soil temperature. The influence of snow thermal conductivity on soil temperature has been demonstrated by many model studies The snow insulation effect plays an important role for the Arctic soil temperature response to climate change and for future near-surface permafrost thawing and soil carbon vulnerability The model skill in atmosphere–soil coupling with the concomitant snow cover in the Arctic is an important factor in the assessment of limitations and uncertainty of carbon mobility estimates (Schaefer et al, 2011)
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