ICAM/MAP Brig 19-23 May 2003 1
Ten years of operational numerical simulations of snow and mountain weather conditions and
recent developments at Météo-France.
Y. Durand, G. Guyomarc'h, L. Mérindol, G. Giraud, E. Brun, E. Martin.
Météo-France, Centre d'Études de la Neige (CNRM), 1441 rue de la Piscine, F 38406 Saint Martin d'Hères.
1) Introduction
2) The Safran/Crocus/Mepra (SCM) suite
3) Operational use of SCM (analysis and forecast modes)
4) Research use of SCM
5) Current developments
6) Conclusion
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Main Characteristics/Limitations of the Operational SCM massif-scale
avalanche hazard modeling.
• -homogeneous massifs (~400 km2) with different elevations (~10), aspects (7) and slopes(3)
• -hourly simulation of a lot of complete snow profiles (T, Z, , LWC, stratigraphy, stability) under the assumption that, at that scale, the snowpack evolution is completely controlled by the atmospheric forcing
• -no realistic orography but « idealized » slopes• -use only of « atmospheric » observations (no use of data concerning the
snow cover)• -use of NWP models: ARPEGE / ALADIN• -no local small scale features forcing • -crude simulation of snowdrift effects (in fresh snow crystal modification
only)
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Regional avalanche forecasting tool
Analyse and forecast of the snow pack evolution by massif, elevation, aspect and slope
Meteorological Data : Observations,meteo model…
SAFRAN
Meteorological analysisCROCUS
Snow model
MEPRAExpert system model
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SAFRAN• Meteorological
analysis for mountain regions
• notions of massif, altitude, aspect
• 2 days forecast version by adaptation of NWP models
• OI and variationnal methods used
MeteorologicalNWP model
Snow and weather observations
Classical meteo Observations and atmospheric sounding
Analysis /6H
24H Analysis for précipitation
Hourly Interpolation for all the parameters
Hourly meteorological parameters affecting snowpack evolution
Radar (in dev.)Satellite
•temperature and humidity•wind velocity/ direction•radiative fluxes•snow and rain precipitation•cloudiness
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SAFRAN « PRACTICAL » VERSION
• O/I scheme and Intermittent Analysis (6h) with ARPEGE or ALADIN as guess-field for :
1. Wind (Div. + Rot.) (verticale profile + surface)2. Humidity (verticale profile + surface)3. Cloudiness (3 layers)4. Temperature (verticale profile + surface)
• 24h Rainfall Analysis based on climatology and typical synoptic patterns.
• Variational Analysis at 1 hour step on 6h windows.
• Several algorisms and modelling for :
1. Radiations 2. Diurnal Variations
3. Vertical Snow-Rain Limits
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CROCUS
2
1D numerical snow model
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MEPRA1D mechanical analysis
– Additional mechanical characteristics , – Ram resistance profile – Shear strength profile (C)
– Estimation of the applied shear stress (n for snow,sfor skier)– Wet snow instability– Slab occurrence in superficial layers, presence of buried weak layer
• Natural stability index
• Accidental stability index
• Natural avalanche risk on a 6 level scale (very low, low, moderate increasing, moderate decreasing, high, very high)
• Accidental avalanche risk on a 4 level scale (very low, low, moderate,high)
• Avalanche types (fresh dry, fresh wet, fresh mixed, surface slab, surface wet, bottom wet)
n
CS
sn
CS '
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SAFRAN Results (2)
24h analyzed rainfalls
(15/11/02)
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24h forecated rainfall(11/01/99)
SAFRAN Results (3)
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3/5
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Tests on annual rainfall climatology
(SIM Projet).
Year 2000.
Symposium Zoning
Safran with full observation network.
Safran with real-time observation network.
3/5
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CROCUS results (1)
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CROCUS results (2)
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Scatter diagrams of measured and simulated means snow depth on 37 test sites during 4 different months over 10 winter seasons
10 years of measured (dotted) and simulated (solid) snow depths at the Tignes ski resort, Vanoise massif, 2080m.
Safran-Crocus Validation (1)
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Safran-Crocus Validation (2)
Comparisons between observed and numerically simulated snowpack structures during the 1996-97 winter at the ski resort of "La Plagne" (Vanoise massif) on the snow pit location of "Montchavin" (2100m, NE). The different panels illustrate the weekly observed snow pits and the corresponding computed profile. The vertical axis (in cm) represents the snow depth and the blue and green curves respectively temperature and density profiles (with two different scales on the horizontal axis in °C and %V). On the right side of each profile , the stratigraphic profile is illustrated by color code while vertical hachures show crusts.
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MEPRA operational results (1)
MEPRA : detection of an unstable layer
In this case (1st January 1996), the model has detected a snow structure favourable to an avalanche triggering by overloading (e.g. skiers). A weak layer is buried under 40 cm of new snow constituting a slab after some cohesion processes.
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MEPRA operational results (2)
MEPRA : risk of spontaneous (natural) avalanches due to an unstable fresh snow amount
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Mepra results (3)
Symbolic representation (elevation/aspects) of MEPRA natural
avalanche risks in a typical spring situation (9 March 94, 12 UTC)
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Snow and Climate Change
Snow duration (1500 m)
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Avalanches and climate change
• Rainfall +10% Température +1.8°C
a
0
0,2
0,4
0,6
0,8
1
1,2
1,4
Nov. Dec. Jan. Feb. Mar. Apr. May June
ind
ex
Ref.
PT
Tc
0
0,2
0,4
0,6
0,8
1
1,2
1,4
Nov. Dec. Jan. Feb. Mar. Apr. May June
ind
ex
Ref.
PT
T
All avalanches Melting Avalanches
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Local avalanche forecasting tools
CrocusMepra PCCrocusMepra PC
-Local simulation of the internal state and the mechanical stability of the snow pack
- Analyse and forecast mode
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SCALE DEFINITIONS
Downscaling
Massif scale : ~ 500 km2
Time step : 1 hour
Symbolic topography
Local scale : ~ 1 km2
Time step : 30 min
Fine scale orography
Avalanche path scale : ~ 100 m2
Time step : ~ 5 min
100 200 300 400 500 600
100
200
300
400
500
600
700
800
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Snow Drift
• Slab formation, effects of snow accumulation and erosion… • Objectives :
– Better estimation of accidental avalanche risks
– Better localisation of avalanche risks
• Experimentation in a specialized field laboratory• Modelling:
- SAMVER : surface wind field estimation
- SYTRON1 : wind transport at the massif scale (nearly operationnal)
- SYTRON2 : wind transport at local scale
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Snow Drift
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Snow depth differences due to snow drift effects
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Safran/Crocus/Mepra
chain• Valuable avalanche forecasting tool for regional forecasters :
meteo, snow, stability and risks• « analyse » mode with all the snow/meteorological data• 24 and 48 H forecast with the runs of the ALADIN and
ARPEGE meteorological models and analyses by a nearest neighbour method
• Validations : – Meteorological (Col de Porte, Lac Blanc)
– Snow depths
– Snow profiles
– By the avalanche forecasters
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Conclusion (1)
The SCM chain is presently running over:24 alpine massifs23 Pyrenean massifs12 islandic areas
It is operationally used by numerous forecasters.
It is still under development (snow drift, …)
It is also a research tool (climate ….)
It is used in related applications (hydrology, …)
Good skiing and thank you for your attention
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Conclusion (2)