Permafrost on the Tibetan Plateau (TP) is controlled by high-elevation and the complex hydrothermal processes and energy balance on the ground surface. To successfully model or map permafrost distribution, it is necessary to parameterize near-surface air or land-surface temperatures (Ta or LST) to ground surface temperature (GST) at local-, meso-, or macro-scale. Here, a long-term experimental observation (November 2010 to December 2018) was conducted for understanding the differences between Ta and GST at a plot with 26 sites at Chalaping to the south of the Sisters Lakes in the Source Area of the Yellow River, northeastern TP. Results show that GST varies considerably within an area of about 3.5 km2 under the combined thermal influences of surface vegetation, soil moisture conditions, and microtopography. Mean annual GST (MAGST) ranged from -0.55 to -3.02 degrees C, with an average of -1.35 +/- 0.63 degrees C. The surface offset varied from 1.01 to 3.90 degrees C, with an average of 2.72 +/- 0.70 degrees C. The difference between monthly Ta and monthly GST decreased from 4.64 +/- 2.09 degrees C in January to 1.09 +/- 1.34 degrees C in July and then gradually increased to 5.61 +/- 2.53 degrees C in November. The active layer thickness (ALT) calculated with the ground-surface thawing index ranged from 0.85 to 1.95 m, with an average of 1.51 +/- 0.33 m. Annual freezing N-factors and annual thawing N-factors were averaged at 0.58 +/- 0.12 and 1.31 +/- 0.28, respectively. Although weakly, hourly and daily GST values are positively correlated to NDVI, while ALT negatively correlated with NDVI. This study demonstrates the complex thermal regimes on the ground surface, even within a small area despite the relatively consistent topography. It will likely facilitate the parameterization of the upper thermal boundary of permafrost modeling or mapping on the TP where the landscapes are characterized by extensive presence of dwarf alpine meadow and alpine steppe, further contributing to the study in ecosystem feedbacks to the regional climate change.

Snow cover distribution has a profound impact on ground temperature, on thickness of the active layer, and on permafrost. The purpose of this study was to evaluate the effects of snow cover on soil thermal regimes in West Siberia and to characterize the meso- and micro-scale spatial variation of winter ground surface temperature (GST). Maximum snow cover thickness (> 80 cm) and duration (similar to 8 months) were recorded for the lower elevation areas and in the forest site (using a vertical array of Muttons). Shallow snow cover and a late snow formation characterized open raised areas with shallow permafrost. Our results indicate that 20 cm snow cover thickness is the minimum for generating a significant insulating effect. Date of snow cover formation with thickness > 20 cm had the strongest influence on soil temperature regimes. We found a significant negative correlation between winter GST and elevation. This relationship is indirectly controlled by snow cover redistribution. We additionally have shown that elevation, n-factor and winter GST are the variables most significantly affecting thaw depth in permafrost-affected soils. This research dictates the need for taking into account snowfall, and its redistribution due to the variability of local factors, in predicting the effects of climate change on soil temperatures and active layer depth. According to long-term meteorological data for West Siberia, a temporal trend in snowfall is not observed. Nevertheless, considerable interannual fluctuations in snow cover thickness can lead to interannual variations in the soil thermal regimes.

The Western Antarctic Peninsula region shows mean annual air temperatures ranging from -4 to -2 degrees C. Due to its proximity to the climatic threshold of permafrost, and evidence of recent changes in regional air temperatures, this is a crucial area to analyse climate-ground interactions. Freezing indexes and n-factors from contrasting topographic locations in Hurd Peninsula (Livingston Island) are analysed to assess the influence of snow cover on soil's thermal regime. The snow pack duration, thickness and physical properties are key in determining the thermal characteristics and spatial distribution of permafrost. The Temperature at the Top Of the Permafrost (TTOP) model uses freezing and thawing indexes, n-factors and thermal conductivity of the ground, as factors representing ground-atmosphere interactions and provides a framework to understand permafrost conditions and distribution. Eight sites were used to calculate TTOP and evaluate its accuracy. They encompass different geological, morphological and climatic conditions selected to identify site-specific ground thermal regime controls. Data was collected in the freezing seasons of 2007 and 2009 for air, surface and ground, temperatures, as well as snow thickness. TTOP model results from sites located between 140 and 275 m a.s.l were very close to observational data, with differences varying from 0.05 to 0.4 degrees C, which are smaller than instrumental error. TTOP results for 36 m a.s.l confirm that permafrost is absent at low altitude and thermal offsets for rock areas show values between 0.01 and 0.48 degrees C indicating a small effect of latent heat, as well as of advection. (C) 2016 Published by Elsevier B.V.

Permafrost and varying land surface properties greatly complicate modelling of the thermal response of Arctic soils to climate change. The forest-tundra transition near Nadym in west Siberia provides an excellent study area in which to examine the contrasting thermal properties of soils in a forested ecosystem without permafrost and peatlands with permafrost. We investigated the effects of forest shading, snow cover and variable organic soil horizons in three common ecosystems of the forest-tundra transition zone. Based on the year-round temperature profile data, the most informative annual parameters were: (1) the sum of positive average daily temperatures at depths of 10 and 20cm; (2) the maximum penetration depth of temperatures above 10 degrees C; and (3) the number of days with temperatures below 0 degrees C at a depth of 20cm. The insulative effect of snow cover in winter was at least twice that of the shading and cooling effect of vegetation in summer. In areas with shallow permafrost, the presence of a thick organic horizon, with an extremely low thermal diffusivity, creates a very steep temperature gradient that limits heat penetration to the top of the permafrost in summer. Copyright (c) 2015 John Wiley & Sons, Ltd.

Soil temperature regimes were studied in three ecosystems of the north of Western Siberia in the zone of isolated permafrost: the forest ecosystem with gleyic loamy sandy podzol (Stagnic Albic Podzol), the flat-topped peat mound ecosystem with humus-impregnated loamy sandy to light loamy peat cryozem (Histic Oxyaquic Turbic Cryosol (Arenic)), and the peat mound (palsa) ecosystem with oligotrophic destructive permafrost-affected peat soil (Cryic Histosol). Annual temperature measurements in the soil profiles demonstrated that these soils function under different temperature regimes: very cold permafrost regime and cold nonpermafrost regime. The following annual temperature characteristics proved to be informative for the studied soils: sums of above-zero temperatures at the depths of 10 and 20 cm, the maximum depth of penetration of temperatures above 10A degrees C, and the number of days with daily soil temperatures above (or below) 0A degrees C at the depth of 20 cm. On the studied territory, the insulating effect of the snow cover in winter was at least two times more pronounced than the insulating effect of the vegetation cover in summer. Cryogenic soils of the studied region are characterized by the high buffering towards changing climatic parameters. This is explained by the presence of the litter and peat horizons with a very low thermal diffusivity and by the presence of permafrost at a relatively shallow depth with temperature gradients preventing penetration of heat to the permafrost table.

The frost table depth is a critical state variable for hydrological modelling in cold regions as frozen ground controls runoff generation, subsurface water storage and the permafrost regime. Calculation of the frost table depth is typically performed using a modified version of the Stefan equation, which is driven with the ground surface temperature. Ground surface temperatures have usually been estimated as linear functions of air temperature, referred to as n-factors' in permafrost studies. However, these linear functions perform poorly early in the thaw season and vary widely with slope, aspect and vegetation cover, requiring site-specific calibration. In order to improve estimation of the ground surface temperature and avoid site-specific calibration, an empirical radiative-conductive-convective (RCC) approach is proposed that uses air temperature, net radiation and antecedent frost table position as driving variables. The RCC algorithm was developed from forested and open sites on the eastern slope of the Coastal Mountains in southern Yukon, Canada, and tested at a high-altitude site in the Canadian Rockies, and a peatland in the southern Northwest Territories. The RCC approach performed well in a variety of land types without any local calibration and particularly improved estimation of ground temperature compared with linear functions during the first month of the thaw season, with mean absolute errors <2 degrees C in seven of the nine sites tested. An example of the RCC approach coupled with a modified Stefan thaw equation suggests a capability to represent frozen ground conditions that can be incorporated into hydrological and permafrost models of cold regions. Copyright (c) 2015 John Wiley & Sons, Ltd.