A statistical approach to represent small-scale variability of permafrost temperatures due to snow cover

Gisnås, Kjersti; Westermann, Sebastian; Schuler, Thomas; Litherland, Tobias; Isaksen, Ketil; Boike, Julia; Etzelmüller, Bernd

doi:10.5194/tc-8-2063-2014

Cited by 89 publications

(116 citation statements)

References 51 publications

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“…1). "Bayelva", about 2 km west of NyÅlesund, is the main study site where multiyear in situ records on, for instance, the surface energy balance, permafrost thermal regime and snow distribution are available (Westermann et al, 2009;Gisnås et al, 2014;Boike et al, 2017). In addition, snow surveys for a single season (2016) are available from "Steinflåen plateau" and "Kvadehuksletta".…”

Section: Physical Characteristics and Climatementioning

confidence: 99%

“…This area has been the subject of extensive studies spanning permafrost Boike et al, 2008;Westermann et al, 2011a), the surface energy balance (Boike et al, 2003;Westermann et al, 2009), CO 2 exchange (Lüers et al, 2014;Cannone et al, 2016), ecology (Kohler and Aanes, 2004), snow (Bruland et al, 2001;Gisnås et al, 2014;López-Moreno et al, 2016), hydrology (Nowak and Hodson, 2013) and satellite retrieval validation (Westermann et al, 2011b. The surface cover at Bayelva and Kvadehuksletta alternates between bare soil, rocks and sparse low vegetation (Westermann et al, 2009), while the more elevated Steinflåen plateau is predominantly covered by loose rocks.…”

Section: Physical Characteristics and Climatementioning

confidence: 99%

“…While topography and vegetation are relatively fixed in time, the other controls vary strongly over a range of spatiotemporal scales. In unforested regions, snow tends to be affected by wind drift (e.g., Gisnås et al, 2014), leading to accumulation in areas with preferential deposition, such as topographic depressions or the lee side of a ridge. The scale of such features can vary dramatically across the landscape.…”

Section: Introductionmentioning

confidence: 99%

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Ensemble-based assimilation of fractional snow-covered area satellite retrievals to estimate the snow distribution at Arctic sites

et al. 2018

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Abstract. With its high albedo, low thermal conductivity and large water storing capacity, snow strongly modulates the surface energy and water balance, which makes it a critical factor in mid-to high-latitude and mountain environments. However, estimating the snow water equivalent (SWE) is challenging in remote-sensing applications already at medium spatial resolutions of 1 km. We present an ensemble-based data assimilation framework that estimates the peak subgrid SWE distribution (SSD) at the 1 km scale by assimilating fractional snow-covered area (fSCA) satellite retrievals in a simple snow model forced by downscaled reanalysis data. The basic idea is to relate the timing of the snow cover depletion (accessible from satellite products) to the peak SSD. Peak subgrid SWE is assumed to be lognormally distributed, which can be translated to a modeled time series of fSCA through the snow model. Assimilation of satellite-derived fSCA facilitates the estimation of the peak SSD, while taking into account uncertainties in both the model and the assimilated data sets. As an extension to previous studies, our method makes use of the novel (to snow data assimilation) ensemble smoother with multiple data assimilation (ES-MDA) scheme combined with analytical Gaussian anamorphosis to assimilate time series of Moderate Resolution Imaging Spectroradiometer (MODIS) and Sentinel-2 fSCA retrievals. The scheme is applied to Arctic sites near Ny-Ålesund (79 • N, Svalbard, Norway) where field measurements of fSCA and SWE distributions are available. The method is able to successfully recover accurate estimates of peak SSD on most of the occasions considered. Through the ES-MDA assimilation, the root-mean-square error (RMSE) for the fSCA, peak mean SWE and peak subgrid coefficient of variation is improved by around 75, 60 and 20 %, respectively, when compared to the prior, yielding RMSEs of 0.01, 0.09 m water equivalent (w.e.) and 0.13, respectively. The ES-MDA either outperforms or at least nearly matches the performance of other ensemble-based batch smoother schemes with regards to various evaluation metrics. Given the modularity of the method, it could prove valuable for a range of satellite-era hydrometeorological reanalyses.

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Section: Physical Characteristics and Climatementioning

confidence: 99%

Section: Physical Characteristics and Climatementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ensemble-based assimilation of fractional snow-covered area satellite retrievals to estimate the snow distribution at Arctic sites

et al. 2018

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“…Fiddes et al, 2015;Kurylyk et al, 2016;Westermann et al, 2015;Zhang et al, 2012). As exemplified by Gisnås et al (2014) for mountain permafrost environments in Norway, redistribution of snow due to wind drift could be a governing factor for the ground thermal regime also in palsa mires, especially since palsas and peat plateaus are elevated landscape elements which feature lower snow depths than the surrounding mire area (Seppälä, 1982). Tiling approaches that facilitate a statistical representation of subgrid variability of snow depths have been implemented in a regional permafrost model for the Norwegian mountain areas (Gisnås et al, 2016b), but the concept has not yet been applied to mire areas.…”

Section: Implications For Permafrost Modelling and Mappingmentioning

confidence: 99%

Strong degradation of palsas and peat plateaus in northern Norway during the last 60 years

et al. 2017

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Abstract. Palsas and peat plateaus are permafrost landforms occurring in subarctic mires which constitute sensitive ecosystems with strong significance for vegetation, wildlife, hydrology and carbon cycle. Firstly, we have systematically mapped the occurrence of palsas and peat plateaus in the northernmost county of Norway (Finnmark, ∼ 50 000 km 2 ) by manual interpretation of aerial images from 2005 to 2014 at a spatial resolution of 250 m. At this resolution, mires and wetlands with palsas or peat plateaus occur in about 850 km 2 of Finnmark, with the actual palsas and peat plateaus underlain by permafrost covering a surface area of approximately 110 km 2 . Secondly, we have quantified the lateral changes of the extent of palsas and peat plateaus for four study areas located along a NW-SE transect through Finnmark by utilizing repeat aerial imagery from the 1950s to the 2010s. The results of the lateral changes reveal a total decrease of 33-71 % in the areal extent of palsas and peat plateaus during the study period, with the largest lateral change rates observed in the last decade. However, the results indicate that degradation of palsas and peat plateaus in northern Norway has been a consistent process during the second half of the 20th century and possibly even earlier. Significant rates of areal change are observed in all investigated time periods since the 1950s, and thermokarst landforms observed on aerial images from the 1950s suggest that lateral degradation was already an ongoing process at this time. The results of this study show that lateral erosion of palsas and peat plateaus is an important pathway for permafrost degradation in the sporadic permafrost zone in northern Scandinavia. While the environmental factors governing the rate of erosion are not yet fully understood, we note a moderate increase in air temperature, precipitation and snow depth during the last few decades in the region.

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“…Several studies have been undertaken on this topic in European mountains (Haeberli, 1973;Grüber and Hoelzle, 2001;Luetschg et al, 2008;Farbrot et al, 2011Farbrot et al, , 2013Hasler et al, 2011;Pogliotti, 2011;Gisnås et al, 2014;Ardelean et al, 2015;Magnin et al, 2016;Beniston et al, 2017), in Japan (Ishikawa, 2003;Ishikawa and Hirakawa, 2000), in the Canadian Rocky Mountains (Harris, 1981;Lewkowicz and Ednie, Lewkowicz et al, 2012;Bonnaventure et al, 2012;Hasler et al, 2015), and most recently in the Andes (Apaloo et al 2012). The snow cover acts as a buffer layer controlling heat loss at the ground interface.…”

Section: Introductionmentioning

confidence: 99%

Wind-driven snow conditions control the occurrence of contemporary marginal mountain permafrost in the Chic-Choc Mountains, south-eastern Canada: a case study from Mont Jacques-Cartier

et al. 2017

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Abstract. We present data on the distribution and thermophysical properties of snow collected sporadically over 4 decades along with recent data of ground surface temperature from Mont Jacques-Cartier (1268 m a.s.l.), the highest summit in the Appalachians of south-eastern Canada. We demonstrate that the occurrence of contemporary permafrost is necessarily associated with a very thin and wind-packed winter snow cover which brings local azonal topo-climatic conditions on the dome-shaped summit. The aims of this study were (i) to understand the snow distribution pattern and snow thermophysical properties on the Mont JacquesCartier summit and (ii) to investigate the impact of snow on the spatial distribution of the ground surface temperature (GST) using temperature sensors deployed over the summit. Results showed that above the local treeline, the summit is characterized by a snow cover typically less than 30 cm thick which is explained by the strong westerly winds interacting with the local surface roughness created by the physiography and surficial geomorphology of the site. The snowpack structure is fairly similar to that observed on windy Arctic tundra with a top dense wind slab (300 to 450 kg m −3 ) of high thermal conductivity, which facilitates heat transfer between the ground surface and the atmosphere. The mean annual ground surface temperature (MAGST) below this thin and wind-packed snow cover was about −1 • C in 2013 and 2014, for the higher, exposed, blockfield-covered sector of the summit characterized by a sporadic herbaceous cover. In contrast, for the gentle slopes covered with stunted spruce (krummholz), and for the steep leeward slope to the southeast of the summit, the MAGST was around 3 • C in 2013 and 2014. The study concludes that the permafrost on Mont Jacques-Cartier, most widely in the Chic-Choc Mountains and by extension in the southern highest summits of the Appalachians, is therefore likely limited to the barren windexposed surface of the summit where the low air temperature, the thin snowpack and the wind action bring local cold surface conditions favourable to permafrost development.

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A statistical approach to represent small-scale variability of permafrost temperatures due to snow cover

Cited by 89 publications

References 51 publications

Ensemble-based assimilation of fractional snow-covered area satellite retrievals to estimate the snow distribution at Arctic sites

Ensemble-based assimilation of fractional snow-covered area satellite retrievals to estimate the snow distribution at Arctic sites

Strong degradation of palsas and peat plateaus in northern Norway during the last 60 years

Wind-driven snow conditions control the occurrence of contemporary marginal mountain permafrost in the Chic-Choc Mountains, south-eastern Canada: a case study from Mont Jacques-Cartier

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