The effect of wind on the snow cover

Sokratov, Sergey; Sato, Atsushi

doi:10.3189/172756401781819436

Cited by 16 publications

(6 citation statements)

References 20 publications

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“…Overall, the internal energy changes of the snowpack are believed to be accurately determined for the specific location of the measurement array, however little information as to the spatial distribution of energy within the snow is known. Forced convection within the snowpack, or ''wind pumping'' (Colbeck 1989) has been observed to influence thermal field within the snow (e.g., Albert and McGilvary 1992;Albert and Hardy 1995;Sokratov and Sato 2001;Albert and Schultz 2002). This has been commonly attributed to pressure gradients caused by small-surface topographical features (Colbeck 1989;Waddington et al 1996;Albert 2002).…”

Section: E Causes Of the Energy Imbalancementioning

confidence: 99%

Problems Closing the Energy Balance over a Homogeneous Snow Cover during Midwinter

Helgason

Pomeroy

2012

Journal of Hydrometeorology

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Application of the energy balance approach to estimate snowmelt inherently presumes that the external energy fluxes can be measured or modeled with sufficient accuracy to reliably estimate the internal energy changes and melt rate. However, owing to difficulties in directly measuring the internal energy content of the snow during melt periods, the ability to close the energy balance is rarely quantified. To address this, all of the external energy balance terms (sensible and latent heat fluxes, shortwave and longwave radiation fluxes, and the ground heat flux) were directly measured and compared to changes of the energy content within an extensive, homogeneous, snowpack of a level field near Saskatoon, Saskatchewan, Canada. The snow was observed to lose significant amounts of energy because of a persistent longwave radiation imbalance caused by low incoming fluxes during cold, clear-sky periods, while solar heating of the snow surface caused an increase in the outgoing fluxes. The sum of the measured turbulent heat fluxes, ground heat flux, and solar radiation fluxes were insufficient to offset these losses, however the snowpack temperatures were not observed to cool. It was concluded that an unmeasured exchange of sensible heat was occurring from the atmosphere to the snowpack. The exchange mechanism for this is not known but would appear to be consistent with the concept of a windless exchange as employed to close the energy balance in various snow models. The results suggest that caution should be exercised when using the energy balance method to determine changes in internal energy in cold snowpacks.

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Section: E Causes Of the Energy Imbalancementioning

confidence: 99%

Problems Closing the Energy Balance over a Homogeneous Snow Cover during Midwinter

Helgason

Pomeroy

2012

Journal of Hydrometeorology

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“…The entire snow season's average hourly maximum wind speed of 6 m s −1 is in the range, when snow particles are broken to smaller fragments (McClung and Schaerer, 2006). Also mechanical wind pressure leads to a densification of the near-surface part of the snowpack (Sokratov and Sato, 2001). Thus significant cornice accretion occurs during storm events with significantly higher wind speeds than the snow season's average.…”

Section: Cornice Accretion and Scouringmentioning

confidence: 99%

Cornice dynamics and meteorological control at Gruvefjellet, Central Svalbard

2012

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Abstract. Cornice fall avalanches endanger life and infrastructure in Nybyen, a part of Svalbard's main settlement Longyearbyen, located at 78 • N in the High Arctic. Thus, cornice dynamics -accretion, cracking and eventual failure -and their controlling meteorological factors were studied along the ridgeline of the Gruvefjellet plateau mountain above Nybyen in the period 2008-2010. Using two automatic time-lapse cameras and hourly meteorological data in combination with intensive field observations on the Gruvefjellet plateau, cornice process dynamics were investigated in larger detail than previously possible. Cornice accretion starts directly following the first snowfall in late September and October, and proceeds throughout the entire snow season under a wide range of air temperature conditions that the maritime winter climate of Svalbard provides. Cornice accretion is particularly controlled by distinct storm events, with a prevailing wind direction perpendicular to the ridge line and average wind speeds from 12 m s −1 . Particularly high wind speeds in excess of 30 m s −1 towards the plateau ridgeline lead to cornice scouring and reduce the cornice mass both vertically and horizontally. Induced by pronounced air temperature fluctuations which might reach above freezing and lead to midwinter rainfall events, tension cracks develop between the cornice mass and the plateau. Our measurements indicate a linear crack opening due to snow creep and tilt of the cornice around a pivot point. Four to five weeks elapsed between the first observations of a cornice crack until cornice failure. Throughout the two snow seasons studied, 180 cornice failures were recorded, of which 70 failures were categorized as distinctive cornice fall avalanches. A clear temporal pattern with the majority of cornice failures in June was found. Thus only daily air temperature could determine avalanche from nonavalanche days. Seven large cornice fall avalanches reached the avalanche fans on which the Nybyen settlement is located. The size of the avalanches was primarily determined by the size of the cornice that detached. The improved process understanding of the cornice dynamics provides a first step towards a better predictability of this natural hazard, but also highlights that any type of warning based on meteorological factors is not an adequate measure to ensure safety of the housing at risk.

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“…We thus expect snow to be the main source of water in high mountains. A significant portion of the snow that falls on steep slopes does not accumulate due to redistribution by wind and transport by gravity (Sokratov and Sato, 2001;Mott et al, 2010). Previous studies suggested that snow accumulation on steep rock slopes is inversely proportional to the slope angle and that above a certain slope angle, snow does not accumulate (Sommer et al, 2015;Blöschl et al, 1991;Winstral et al, 2002;Gruber Schmid and Sardemann, 2003;Haberkorn et al, 2015).…”

Section: Estimating Snow Accumulation and Snowmelt On Steep Slopesmentioning

confidence: 98%

Estimating surface water availability in high mountain rock slopes using a numerical energy balance model

Ben-Asher

Magnin

Westermann

et al. 2022

Preprint

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Abstract. Water takes part in most physical processes that shape the mountainous periglacial landscapes and initiation of mass wasting. An observed increase in rockfall activity in several mountainous regions was previously linked to permafrost degradation in high mountains, and water that infiltrates into rock fractures is one of the likely drivers of these processes. However, there is very little knowledge on the quantity and timing of water availability for infiltration in steep rock slopes. This knowledge gap originates from the complex meteorological, hydrological and thermal processes that control snowmelt, and also the challenging access and data acquisition in the extreme alpine environments. Here we use field measurement and numerical modeling to simulate the energy balance and hydrological fluxes in a steep high elevation permafrost affected rock slope at Aiguille du Midi (3842 m a.s.l), in the Mont-Blanc massif. Our results provide new information about water balance at the surface of steep rock slopes. Model results suggest that only ~25 % of the snowfall accumulates in our study site, the remaining ~75 % are redistributed by wind and gravity. Snow accumulation depth is inversely correlated with surface slopes between 40° to 70°. Snowmelt occurs between spring and late summer and most of it does not reach the rock surface due to the formation of an impermeable ice layer at the base of the snowpack. The annual effective snowmelt, that is available for infiltration, is highly variable and ranges over a factor of six with values between 0.05–0.28 m in the years 1959–2021. The onset of the effective snowmelt occurs between May and August, and ends before October. It precedes the first rainfall by one month on average. Sublimation is the main process of snowpack mass loss in our study site. Model simulations at varying elevations show that effective snowmelt is the main source of water for infiltration above 3600 m a.s.l.; below, direct rainfall is the dominant source. The change from snowmelt-dominated to rainfall-dominated water availability is nonlinear and characterized by a rapid increase in water availability for infiltration. We suggest that this elevation of water availability transition is highly sensitive to climate change, if snowmelt-dominated permafrost-affected slopes experience an abrupt increase in water input that can initiate rock slope failure.

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The effect of wind on the snow cover

Cited by 16 publications

References 20 publications

Problems Closing the Energy Balance over a Homogeneous Snow Cover during Midwinter

Problems Closing the Energy Balance over a Homogeneous Snow Cover during Midwinter

Cornice dynamics and meteorological control at Gruvefjellet, Central Svalbard

Estimating surface water availability in high mountain rock slopes using a numerical energy balance model

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