A numerical model to simulate snow-cover stratigraphy for operational avalanche forecasting

AbstractLaws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature, density and liquid-water profiles of snow cover as a function of weather conditions.To establish these laws, the authors have summarized previous studies on temperature gradient and on wet-snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh-snow samples. An original formalism was developed to allow a description of snow with parameters evolving continuously throughout time.The introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow-covered albedo, which depend on the simulated stratigraphy, i.e. the type and size of snow grains of different layers of the snow cover.The model was tested during a whole winter season without any re-initialization. Comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail. The model proved itself to be very efficient in simulating accurately the evolution of the snow-cover stratigraphy throughout the whole winter season.

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A tracking algorithm to identify slab and weak layer combinations for assessing snow instability and avalanche problem type

10.5194/egusphere-egu21-1578 ◽

2021 ◽

Author(s):

Benjamin Reuter ◽

Léo Viallon-Galinier ◽

Stephanie Mayer ◽

Pascal Hagenmuller ◽

Samuel Morin

Keyword(s):

Snow Cover ◽

Winter Season ◽

Essential Element ◽

Problem Type ◽

Model Output ◽

Avalanche Forecasting ◽

Weak Layer ◽

Problem Types ◽

Snow Stratigraphy ◽

Wet Snow

Snow cover models have mostly been developed to support avalanche forecasting. Recently developed snow instability metrics can help interpreting modeled snow cover data. However, presently snow cover models cannot forecast the relevant avalanche problem types &#8211; an essential element to describe avalanche danger. We present an approach to detect, track and assess weak layers in snow cover model output data to eventually assess the related avalanche problem type. We demonstrate the applicability of this approach with both, SNOWPACK and CROCUS snow cover model output for one winter season at Weissfluhjoch. We introduced a classification scheme for four commonly used avalanche problem types including new snow, wind slabs, persistent weak layers and wet snow, so different avalanche situations during a winter season can be classified based on weak layer type and meteorological conditions. According to the modeled avalanche problem types and snow instability metrics both models produced weaknesses in the modeled stratigraphy during similar periods. For instance, in late December 2014 the models picked up a non-persistent as well as a persistent weak layer that were both observed in the field and caused widespread instability in the area. Times when avalanches released naturally were recorded with two seismic avalanche detection systems, and coincided reasonably well with periods of low modeled stability. Moreover, the presented approach provides the avalanche problem types that relate to the observed natural instability which makes the interpretation of modeled snow instability metrics easier. As the presented approach is process-based, it is applicable to any model in any snow avalanche climate. It could be used to anticipate changes in avalanche problem type due to changing climate. Moreover, the presented approach is suited to support the interpretation of snow stratigraphy data for operational forecasting.

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In situ effective snow grain size mapping using a compact hyperspectral imager

Journal of Glaciology ◽

10.1017/jog.2020.68 ◽

2020 ◽

pp. 1-9

Author(s):

Christopher Donahue ◽

S. McKenzie Skiles ◽

Kevin Hammonds

Keyword(s):

Spatial Variability ◽

Near Infrared ◽

Absorption Feature ◽

Micro Ct ◽

Band Area ◽

Snow Metamorphism ◽

Wet Snow ◽

Before And After ◽

Computed Microtomography ◽

Snow Samples

Abstract Effective snow grain radius (re) is mapped at high resolution using near-infrared hyperspectral imaging (NIR-HSI). The NIR-HSI method can be used to quantify re spatial variability, change in re due to metamorphism, and visualize water percolation in the snowpack. Results are presented for three different laboratory-prepared snow samples (homogeneous, ice lens, fine grains over coarse grains), the sidewalls of which were imaged before and after melt induced by a solar lamp. The spectral reflectance in each ~3 mm pixel was inverted for re using the scaled band area of the ice absorption feature centered at 1030 nm, producing re maps consisting of 54 740 pixels. All snow samples exhibited grain coarsening post-melt as the result of wet snow metamorphism, which is quantified by the change in re distributions from pre- and post-melt images. The NIR-HSI method was compared to re retrievals from a field spectrometer and X-ray computed microtomography (micro-CT), resulting in the spectrometer having the same mean re and micro-CT having 23.9% higher mean re than the hyperspectral imager. As compact hyperspectral imagers become more widely available, this method may be a valuable tool for assessing re spatial variability and snow metamorphism in field and laboratory settings.

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Simultaneous Measurements of Stability Indices and Characteristic Parameters Describing the Snow Cover and the Weather in Fracture Zones of Avalanches

Journal of Glaciology ◽

10.1017/s0022143000010595 ◽

1980 ◽

Vol 26 (94) ◽

pp. 65-74 ◽

Cited By ~ 9

Author(s):

H. Gubler

Keyword(s):

Snow Cover ◽

Winter Season ◽

Processing System ◽

Weather Conditions ◽

Fracture Zones ◽

Characteristic Parameters ◽

On Line ◽

Solar Powered ◽

Snow Temperature ◽

Stability Indices

AbstractStability indices at different slope aspects and characteristic parameters describing the snow cover and the weather conditions are recorded simultaneously and automatically in potential fracture zones of avalanches during the whole winter season. A remote, solar-powered system including measurements of snow depth, mass flux of wind-blown snow and of the snow temperature profile as well as on-line and off-line data processing has been developed and tested. The results show that this type of data-recording and processing system makes quantitative case studies of natural stability variations possible.

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Investigation on Wet-Snow Metamorphism in Respect of Liquid-Water Content

Annals of Glaciology ◽

10.3189/s0260305500007576 ◽

1989 ◽

Vol 13 ◽

pp. 22-26 ◽

Cited By ~ 37

Author(s):

E. Brun

Keyword(s):

Growth Rate ◽

Water Content ◽

Liquid Water ◽

Liquid Water Content ◽

Snow Metamorphism ◽

Wet Snow ◽

The Mean ◽

Water Saturated ◽

Warming Device ◽

Snow Samples

Up to the present time, quantitative investigations on wet-snow metamorphism have mostly been conducted on water-saturated snow, because of the difficulty in getting large enough wet-snow samples at a uniformly low liquid-water content. Using the dielectric properties of snow at a frequency in the range 20–100 kHz, a warming device has been developed which has enabled us to bring samples of 7 × 10−3 m3 snow to any desired liquid-water content. A maximum value of 8% by volume was reached within 2 h.The warming device was used to reproduce natural wetness conditions in the laboratory in order to investigate wet snow metamorphism at low liquid-water content. Snow samples were brought to different liquid-water contents and held in that condition for about 2 weeks, during which grain-size was characterized using a picture-analysis system able to derive the mean radius of curvature of the cluster circumference. At any given liquid-water content value, the growth rate of the mean volume of the crystals building the clusters was constant, a pattern which has also been observed in water-saturated snow by previous investigators. This growth rate is well described by a power function of liquid-water content.

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Simulating snow instability in complex terrain

10.5194/egusphere-egu2020-19589 ◽

2020 ◽

Author(s):

Bettina Richter ◽

Alec van Herwijnen ◽

Mathias W. Rotach ◽

Jürg Schweizer

Keyword(s):

Spatial Variability ◽

Snow Cover ◽

Complex Terrain ◽

Laser Scanning ◽

Winter Season ◽

Temporal Variations ◽

Full Potential ◽

Avalanche Forecasting ◽

Snow Stratigraphy ◽

Operational Forecasting

Numerical snow cover models are increasingly used in operational avalanche forecasting. While these models can provide snow stratigraphy and some snow instability information, their full potential is not yet exploited in forecasting. We investigated, how well the snow cover model Alpine3D simulated spatial and temporal variations in snow instability. Therefore, simulations were performed in highly varying complex terrain for the winter season 2016-2017 in the region of Davos, Switzerland for an area of about 21 km x 21 km. Alpine3D was forced with data from several automatic weather stations within the region, which were interpolated to a resolution of 100 m. To reproduce observed spatial variability, we scaled precipitation input with snow height measurements derived with airborne laser scanning. For comparison, we also simulated the snowpack without scaling. The simulation with scaling precipitation showed significantly higher spatial variability in modeled snow instability than the simulation without scaling. However, when information was aggregated to aspect and elevation dependent information for the whole region, as it is done for operational forecasting, this variability vanished and scaling precipitation seems unnecessary. At the beginning of the season and towards the end, snow instability depended on aspect, while in the winter months December to March, differences between different aspects were small. The simulations with scaling precipitation revealed a strong influence of snow depth on snow instability, although the various snow instability criteria provided inconsistent results. Simulated profiles, which were classified as rather favourable were rated as rather unstable and vice versa. A comparison to traditional snow profiles shows that snow stratigraphy was reproduced well, but assessing snow instability from stratigraphy alone is not feasible.

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New categories for the climatic division of snowy areas in Japan

Annals of Glaciology ◽

10.3189/1998aog26-1-131-137 ◽

1998 ◽

Vol 26 ◽

pp. 131-137 ◽

Cited By ~ 3

Author(s):

Masaaki Ishizaka

Keyword(s):

Temperature Gradient ◽

Snow Cover ◽

Air Temperature ◽

Snow Depth ◽

Winter Season ◽

Critical Values ◽

Absolute Value ◽

Mean Temperature ◽

Wet Snow ◽

The Absolute

New categories for the climatic division of snowy areas according to their snow-cover character in mid-winter are proposed. They are a wet-snow region, a dry-snow region, an intermediate snow region and a depth-hoar region. The wet-snow region is defined as the region in which every layer of deposited snow is wet due to percolation of snowmelt water throughout the winter. In contrast, areas in which the snow cover is dry, at least in the coldest period of the winter season, are classified into two categories, that is the dry-snow region and the depth-hoar region. In the latter region, the small snow depth and low air temperature induce development of depth hoar. The intermediate snow region was introduced to indicate an intermediate character between the dry-snow and wet-snow regions. From the climatic dataset calculated by the Japanese Meteorological Agency and from snow surveys, it has been found that in snowy areas, which have a climatic monthly mean temperature in January (Tjan) higher than 0.3°C, snow would be expected to be wet throughout the winter and, in areas that have Tjan, lower than −1.1°C, to be dry at least in the coldest period. Snow covers, where Tjan is between these two values, are expected to have intermediate characters. Therefore, these temperatures are supposed to be critical values among the wet, dry and intermediate snow regions. The criterion that separates the depth-hoar region from the dry-snow areas was found to be given by a climatic mean temperature gradient. This value lies between 10 and 12°Cm−1, which is derived by dividing the absolute value of the average of the climatic monthly mean air temperature, which is always below 0°C, by the average of the monthly maximum snow depth during January and February.

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New categories for the climatic division of snowy areas in Japan

Annals of Glaciology ◽

10.1017/s0260305500014695 ◽

1998 ◽

Vol 26 ◽

pp. 131-137 ◽

Cited By ~ 4

Author(s):

Masaaki Ishizaka

Keyword(s):

Temperature Gradient ◽

Snow Cover ◽

Air Temperature ◽

Snow Depth ◽

Winter Season ◽

Critical Values ◽

Absolute Value ◽

Mean Temperature ◽

Wet Snow ◽

The Absolute

New categories for the climatic division of snowy areas according to their snow-cover character in mid-winter are proposed. They are a wet-snow region, a dry-snow region, an intermediate snow region and a depth-hoar region. The wet-snow region is defined as the region in which every layer of deposited snow is wet due to percolation of snowmelt water throughout the winter. In contrast, areas in which the snow cover is dry, at least in the coldest period of the winter season, are classified into two categories, that is the dry-snow region and the depth-hoar region. In the latter region, the small snow depth and low air temperature induce development of depth hoar. The intermediate snow region was introduced to indicate an intermediate character between the dry-snow and wet-snow regions. From the climatic dataset calculated by the Japanese Meteorological Agency and from snow surveys, it has been found that in snowy areas, which have a climatic monthly mean temperature in January (Tjan ) higher than 0.3°C, snow would be expected to be wet throughout the winter and, in areas that have Tjan, lower than −1.1°C, to be dry at least in the coldest period. Snow covers, where Tjan is between these two values, are expected to have intermediate characters. Therefore, these temperatures are supposed to be critical values among the wet, dry and intermediate snow regions. The criterion that separates the depth-hoar region from the dry-snow areas was found to be given by a climatic mean temperature gradient. This value lies between 10 and 12°Cm−1, which is derived by dividing the absolute value of the average of the climatic monthly mean air temperature, which is always below 0°C, by the average of the monthly maximum snow depth during January and February.

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Investigation on Wet-Snow Metamorphism in Respect of Liquid-Water Content

Annals of Glaciology ◽

10.1017/s0260305500007576 ◽

1989 ◽

Vol 13 ◽

pp. 22-26 ◽

Cited By ~ 55

Author(s):

E. Brun

Keyword(s):

Growth Rate ◽

Water Content ◽

Liquid Water ◽

Liquid Water Content ◽

Snow Metamorphism ◽

Wet Snow ◽

The Mean ◽

Water Saturated ◽

Warming Device ◽

Snow Samples

Up to the present time, quantitative investigations on wet-snow metamorphism have mostly been conducted on water-saturated snow, because of the difficulty in getting large enough wet-snow samples at a uniformly low liquid-water content. Using the dielectric properties of snow at a frequency in the range 20–100 kHz, a warming device has been developed which has enabled us to bring samples of 7 × 10−3 m3 snow to any desired liquid-water content. A maximum value of 8% by volume was reached within 2 h. The warming device was used to reproduce natural wetness conditions in the laboratory in order to investigate wet snow metamorphism at low liquid-water content. Snow samples were brought to different liquid-water contents and held in that condition for about 2 weeks, during which grain-size was characterized using a picture-analysis system able to derive the mean radius of curvature of the cluster circumference. At any given liquid-water content value, the growth rate of the mean volume of the crystals building the clusters was constant, a pattern which has also been observed in water-saturated snow by previous investigators. This growth rate is well described by a power function of liquid-water content.

Download Full-text

Simultaneous Measurements of Stability Indices and Characteristic Parameters Describing the Snow Cover and the Weather in Fracture Zones of Avalanches

Journal of Glaciology ◽

10.3189/s0022143000010595 ◽

1980 ◽

Vol 26 (94) ◽

pp. 65-74 ◽

Cited By ~ 1

Author(s):

H. Gubler

Keyword(s):

Snow Cover ◽

Winter Season ◽

Processing System ◽

Weather Conditions ◽

Fracture Zones ◽

Characteristic Parameters ◽

On Line ◽

Solar Powered ◽

Snow Temperature ◽

Stability Indices

AbstractStability indices at different slope aspects and characteristic parameters describing the snow cover and the weather conditions are recorded simultaneously and automatically in potential fracture zones of avalanches during the whole winter season. A remote, solar-powered system including measurements of snow depth, mass flux of wind-blown snow and of the snow temperature profile as well as on-line and off-line data processing has been developed and tested. The results show that this type of data-recording and processing system makes quantitative case studies of natural stability variations possible.

Download Full-text