Boundary‐layer growth and advection of heat over snow and soil patches: modelling and parameterization

Essery, Richard; Granger, R. J.; Pomeroy, John W.

doi:10.1002/hyp.6122

Cited by 39 publications

(51 citation statements)

References 25 publications

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“…This may occur because the model only accounts for atmospheric advection of heat within and not between grid boxes. Warming of air by upwards sensible heat fluxes over snow-free patches and warming of snow by downwards heat fluxes as the air then passes over snow patches is a process that has been well documented at GB (Granger et al, 2002Essery et al, 2006). Figure 9 shows the southwest-facing slope on three dates during the first two weeks of the melt season; the red arrow points to a snow-free patch close to one of the transects that was small enough on 20 April to be contained within a single model grid box but had grown much larger by 27 April.…”

Section: Evaluation Of Distributed Simulationsmentioning

confidence: 99%

Modelled sensitivity of the snow regime to topography, shrub fraction and shrub height

Ménard

Essery

Pomeroy

2014

Hydrol. Earth Syst. Sci.

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Abstract. Recent studies show that shrubs are colonizing higher latitudes and altitudes in the Arctic. Shrubs affect the wind transport, accumulation and melt of snow, but there have been few sensitivity studies of how shrub expansion might affect snowmelt rates and timing. Here, a three-source energy balance model (3SOM), which calculates vertical and horizontal energy fluxes -thus allowing within-cell advection -between the atmosphere, snow, snow-free ground and vegetation, is introduced. The three-source structure was specifically adopted to investigate shrub-tundra processes associated with patchy snow cover that single-or two-source models fail to address. The ability of the model to simulate the snow regime of an upland tundra valley is evaluated; a blowing snow transport and sublimation model is used to simulate premelt snow distributions and 3SOM is used to simulate melt. Some success at simulating turbulent fluxes in point simulations and broad spatial pattern in distributed runs is shown even if the lack of advection between cells causes melt rates to be underestimated. The models are then used to investigate the sensitivity of the snow regime in the valley to varying shrub cover and topography. Results show that, for domain average shrub fractional cover ≤ 0.4, topography dominates the pre-and early melt energy budget but has little influence for higher shrub cover. The increase in domain average sensible heat fluxes and net radiation with increasing shrub cover is more marked without topography where shrubs introduce wind-induced spatial variability of snow and snow-free patches. As snowmelt evolves, differences in the energy budget between simulations with and without topography remain relatively constant and are independent of shrub cover. These results suggest that, to avoid overestimating the effect of shrub expansion on the energy budget of the Arctic, future large-scale investigations should consider wind redistribution of snow, shrub bending and emergence, and sub-grid topography as they affect the variability of snow cover.

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Section: Evaluation Of Distributed Simulationsmentioning

confidence: 99%

Modelled sensitivity of the snow regime to topography, shrub fraction and shrub height

Ménard

Essery

Pomeroy

2014

Hydrol. Earth Syst. Sci.

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“…This is particularly obvious when the total melting of the natural (and even groomed) snowpack in December and April made the ski slope an isolated snow patch in a mostly snow-free area with strong edge-effects. In such a situation the energy balance of the snowpack can be significantly affected by the modification of turbulent fluxes (Essery et al, 2006) and horizontal ground fluxes from snow-free areas in the vicinity (Lejeune et al, 2007). Since snow free areas have lower albedo values than the snow and are not limited to a 0 • C maximum temperature, they can become significantly warmer than the surrounding snow and advect heat to the snow through the air (and respectively the ground), providing additional sensible heat energy to the snowpack.…”

Section: Water Losses Due To Mechanical Effectsmentioning

confidence: 99%

Determination of snowmaking efficiency on a ski slope from observations and modelling of snowmaking events and seasonal snow accumulation

et al. 2017

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Abstract. The production of Machine Made (MM) snow is now generalized in ski resorts and represents the most common method of adaptation for mitigating the impact of a lack of snow on skiing. Most investigations of correlations between snow conditions and the ski industry's economy focus on the production of MM snow though not one of these has taken into account the efficiency of the snowmaking process. The present study consists of observations of snow conditions (depth and mass) using a Differential GPS method and snow density coring, following snowmaking events and seasonal snow accumulation in Les Deux Alpes ski resort (French Alps). A detailed physically based snowpack model accounting for grooming and snowmaking was used to compute the seasonal evolution of the snowpack and compared to the observations. Our results show that approximately 30 % of the water mass can be recovered as MM snow within 10 m from the center of a MM snow pile after production and 50 % within 20 m. Observations and simulations on the ski slope were relatively consistent with 60 % (±10 %) of the water mass used for snowmaking within the limits of the ski slope. Losses due to thermodynamic effects were estimated in the current case example to be less than 10 % of the total water mass. These results suggest that even in ideal conditions for production a significant fraction of the water used for snowmaking can not be found as MM snow within the limits of the ski slope with most of the missing fraction of water. This is due to site dependent characteristics (e.g. meteorological conditions, topography).

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“…Furthermore, considering the locally strong effect of the advection of sensible heat, a consequent next step would be the implementation of advection processes in very highresolution energy balance models on a scale of less than 5 m, by following e.g. the idea of a boundary layer integration method provided by Essery et al (2006). This approach, however, needs to be augmented by the counteractive effect of SIBL development close to the melting snow surface.…”

Section: Turbulent Exchange Of Sensible Heat Above a Melting Snow Surmentioning

confidence: 99%

“…Several studies on local advection of sensible heat attempted to estimate the advective flux over snow fields by applying analytical methods (Shook et al, 1993;Shook, 1995), numerical atmospheric boundary-layer models (Liston, 1995;Essery, 1997), concepts of advection efficiency (Marsh and Pomeroy, 1996) or boundary layer integration methods (Granger et al, 2002;Essery et al, 2006). Measurements of either the effect of local advection of heat or the growth of internal boundary-layers above snow patches are extremely rare, except for the studies of Takahara and Higuchi (1985) and Granger et al (2006).…”

Section: Introductionmentioning

confidence: 99%

“…Measurements of either the effect of local advection of heat or the growth of internal boundary-layers above snow patches are extremely rare, except for the studies of Takahara and Higuchi (1985) and Granger et al (2006). Essery et al (2006) applied boundary layer principles and estimated the additional sensible heat flux to melting snow. Nevertheless, none of these studies demonstrated the direct effect of advective fluxes on the spatial distribution of snow ablation by measurements.…”

Section: Introductionmentioning

confidence: 99%

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Micrometeorological processes driving snow ablation in an Alpine catchment

Mott¹,

Egli²,

Grünewald³

et al. 2011

The Cryosphere

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Abstract. Mountain snow covers typically become patchy over the course of a melting season. The snow pattern during melt is mainly governed by the end of winter snow depth distribution and the local energy balance. The objective of this study is to investigate micro-meteorological processes driving snow ablation in an Alpine catchment. For this purpose we combine a meteorological boundary-layer model (Advanced Regional Prediction System) with a fully distributed energy balance model (Alpine3D). Turbulent fluxes above melting snow are further investigated by using data from eddy-correlation systems. We compare modeled snow ablation to measured ablation rates as obtained from a series of Terrestrial Laser Scanning campaigns covering a complete ablation season. The measured ablation rates indicate that the advection of sensible heat causes locally increased ablation rates at the upwind edges of the snow patches. The effect, however, appears to be active over rather short distances of about 4-6 m. Measurements suggest that mean wind velocities of about 5 m s −1 are required for advective heat transport to increase snow ablation over a long fetch distance of about 20 m. Neglecting this effect, the model is able to capture the mean ablation rates for early ablation periods but strongly overestimates snow ablation once the fraction of snow coverage is below a critical value of approximately 0.6. While radiation dominates snow ablation early in the season, the turbulent flux contribution becomes important late in the season. Simulation results indicate that the air temperatures appear to overestimate the local air temperature above snow patches once the snow coverage is low. Measured turbulent fluxes support these findings by suggesting a stable internal boundary layer close to the snow surface causing a strong decrease of the sensible heat flux towards the snow cover.Correspondence to: R. Mott (mott@slf.ch) Thus, the existence of a stable internal boundary layer above a patchy snow cover exerts a dominant control on the timing and magnitude of snow ablation for patchy snow covers.

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Boundary‐layer growth and advection of heat over snow and soil patches: modelling and parameterization

Cited by 39 publications

References 25 publications

Modelled sensitivity of the snow regime to topography, shrub fraction and shrub height

Modelled sensitivity of the snow regime to topography, shrub fraction and shrub height

Determination of snowmaking efficiency on a ski slope from observations and modelling of snowmaking events and seasonal snow accumulation

Micrometeorological processes driving snow ablation in an Alpine catchment

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