Fully coupled snowpack/ atmosphere simulations of snowfall ...Study: High resolution Large Eddy...

Fully coupled snowpack/atmosphere simulations of snowfall and blowing snow in alpine terrain

V. Vionnet1,2,3, H. Bellot4, G. Guyomarc’h3, C. Lac3, E. Martin4, V. Masson3, F. Naaim Bouvet4, A. Prokop5  

 1 Centre for Hydrology, University of Saskatchewan, Saskatoon, Canada

2 Environmental Numerical Prediction Research, Dorval, Canada 3 Météo – France - CNRS, CNRM, UMR 3589, Grenoble and Toulouse, France

4IRSTEA, Grenoble and Aix en Provence, France 5UNIS, Svalbard, Norway 

Snow/atmopshere coupling processes during blowing snow events

• Influence of near-surface atmospheric turbulence and the saltation dynamics • Blowing snow sublimation and feedbacks on the SBL • Evolution of physical properties of surface snow (roughness, cohesion, …)

A fully coupled snowpack/atmosphere model


Atmospheric model: Meso-NH

• 3D Turbulence Scheme • Cloud microphysical scheme

Lafore et al. (1998), Lac et al. (2018)





Synoptic Wind

Simulation of complex and turbulent atmospheric flow in alpine terrain





SBL



Snowpack model: Crocus++

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oo

••

◻◻

ΛΛ


• Detailed layering of the snowpack

• Metamorphism laws

Brun et al. (1989, 1992), Vionnet et al. (2012)


SBL


Crocus

Sedimentation

Turbulentdiffusion

SnowpackType of grains

Threshold windlspeed

SublimationMeso-NH

2 parametergamma

distribution

Saltation layer

Surface boundarylayer

Canopy

2nd level atmospheric model

WindTemp.ReHu

SURFEX

N S q S,

Radius (m)

1st level atmospheric model


Snowpack model: Crocus++

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oo

••

◻◻

ΛΛ

Blowing snow scheme


• Detailed layering of the snowpack

• Metamorphism laws

Brun et al. (1989, 1992), Vionnet et al. (2012)Vionnet et al. (2014)


SBL

Spatial variability of snow accumulation during snowfall

▪ Orographic snowfall ▪ Preferential deposition of falling snow ▪ Wind-induced transport of deposited snow

(salation/suspension)




- What is the relative importance of these processes? - Can atmospheric models provide useful informations?




- What is the relative importance of these processes? - Can atmospheric models provide useful informations?

Study: High resolution Large Eddy Simulation of Snow Accumulation in Alpine Terrain (Vionnet et al., JGR-A, 2017)

▪ Case study: 24-h blowing snow event with concurrent snowfall in Feb. 2011 around Col du Lac Blanc

Model configuration10

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(km

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Elevation (m)

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(m)

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Elevation (m)

1000 2000 3000 40000(m)

Alpe d'Huez

Col du Lac Blanc

150-m grid

50-m grid

a)

b)

Lac Blanc

SarennesDome

Pic Bayle3465 m

Pic Blanc3323 m

Muzelle

Sarennes glacierAWS

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Elevation (m)

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Alpe d'Huez

Col du Lac Blanc

150-m grid

50-m grid

a)

b)

Lac Blanc

SarennesDome

Pic Bayle3465 m

Pic Blanc3323 m

Muzelle

Sarennes glacierAWS

Downscaling the meteorology to the local scale: ➢ 3 nested grids from operational analysis at 2.5 km down to 50-m grid spacing

Atmospheric conditions

2000 2200 2800 3000 3200 3400

Elevation (m)2400 2600

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(m)

0

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18 m s-1Wind vector

R1

R2B1

B2

C1

Wind field at 1st atmos. level at 09:00 15 Feb.

➢ Main structures of atmospheric flow in alpine terrain ➢ Good agreement around CLB ➢ Strong overestimation of wind speed at Sarennes AWS

010

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030

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a) AWS Dome

Win

d di

rect

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(°)

Model 50 mObservation

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d di

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(°)


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(°)


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dom_50[, 4]

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(m s−1

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eed

(m s−1

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pera

ture

(°C

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pera

ture

(°C

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pera

ture

(°C

)

1500 2100 0300 0900

Total solid precipitation

10 20 30 40 50 600

a) Total b) Snow c) Graupel

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3000

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1000

1000 2000 3000 4000 1000 2000 3000 4000 1000 2000 3000 4000

0 5 10 15 20 0 10 20 30 40Accumulated precipitation (mm we)

0 10 20 30 40 50 60

0 5 10 15 20 2525 0 10 20 30 40

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010

2030

4050

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Cumulated solid precip. (14/02 15h−15/02 12h)

Elevation (m)

Prec

ipita

tions

(mm

)

AggregatesGraupelTotal

➢ Spatial variability of total solid precipitation ➢ Different contributions of snowflakes and graupel (rimed particles) ➢ Graupel: higher terminal fall velocity, reduced downwind transport

Detailed cloud processes

2500

2635

2770

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3040

3175

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3445

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Ele

vati

on (

m)

Ele

vati

on (

m)

0 533 1065 1598 2131 2664 0 533 1065 1598 2131 2664

0 533 1065 1598 2131 26640 533 1065 1598 2131 2664

0 533 1065 1598 2131 2664

Distance (m) Distance (m)

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2635

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b) Vertical Wind speed (m s-1)

c) Graupel mixing ratio (g kg-1) d) Cloud droplets mixing ratio (g kg-1)

e) Riming rate (10-6 s-1) f) Dry growth rate (10-6 s-1)

a) Cumulated graupel (mm)

-7

-6

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➢ Strong updrafts producing supercooled cloud droplets ➢ Growth of snowflakes by riming of cloud droplets ➢ Local maximal production of graupel

➢ Local microphysical processes can potentially affect the spatial distribution of snowfall in alpine terrain (similar results as Mott et al. 2014)

➢ Overestimation of near-surface fluxes for intermediate wind speeds ➢ Influence of falling snow flakes on the vertical profile of flux

Blowing snow fluxes at Col du Lac Blanc

Snow Particles Counters (SPC)

Hau

teur

(m)

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Flux de particules (kg m−2 s−1)

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Flux de particules (kg m−2 s−1)

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U= 12 ms−1

● ObservationsModèle TNVModèle PAV

Hei

ght (

m)

Hei

ght (

m)

Particle Flux (kg m-2 s-1) Particle Flux (kg m-2 s-1)

Observations

Blown snowparticles only

With falling snow flakes

Simulated fluxes:

Wind-induced snow redistribution

➢ Strong spatial variability when including snow transport ➢ Main source of variability of snow accumulation

Model limitations

➢ Spatial resolution (50 m) is not sufficient to capture fine-scale patterns of snow accumulation

➢ Parameterizations in the blowing snow scheme: saltation layer, representation of non-steady processes, …

➢ Uncertainties in the representation of cloud processes at high-resolution

0.6

Laser : 28/02/11 - 17/02/11

dHS (m)0.6

Laser : 28/02/11 - 17/02/11

dHS (m)

Meso-NH/Crocus : 18/03/11 23h - 01h

30

dSWE (kg m-2)

12

3

4

5

6

7

Vionnet et al (2014)

Conclusion and perspectives

• Meso-NH/Crocus: a numerical lab. to investigate coupling processes between the atmosphere and the snow surface in alpine terrain (available in Meso-NH 5.4 mesonh.aero.obs-mip.fr).

http://mesonh.aero.obs-mip.fr

Conclusion and perspectives

• Representation of physical processes: •Interactions between local and non-local atmospheric turbulence and blowing snow

dynamics (ejections, splash, …) (Paterna et al., 2016; Comola and Lehning, 2017; Askamit and Pomeroy, 2018)

•Evolution of snow surface properties during blowing snow events: surface roughness (Amory et al. 2015), fragmentation (Comola et el. 2017) and hardening (Sommer et al., 2017)

• Models at temporal and spatial scales relevant for avalanche hazard and hydrological forecasting

• Model evaluation with multiple sensors (TLS, ALS, Radar, Wind Lidar, SPC, …)

• Meso-NH/Crocus: a numerical lab. to investigate coupling processes between the atmosphere and the snow surface in alpine terrain (available in Meso-NH 5.4 mesonh.aero.obs-mip.fr).

Future challenges for blowing snow models in alpine terrain (in general)

http://mesonh.aero.obs-mip.fr

Thanks for your attention!

Case study: 14-15 February 2011

➢ Cold front crossing France ➢ Southern flow ahead of the front ➢ Snowfall over the Alps (limit rain/snow 1200 m)

Synoptic conditions

Wind field and specific humidity at 700 hPa on 14 February 2011 12:00

Case study: 14-15 February 2011

➢ Cold front crossing France ➢ Southern flow ahead of the front ➢ Snowfall over the Alps (limit rain/snow 1200 m)

Synoptic conditions

Wind field and specific humidity at 700 hPa on 14 February 2011 12:00

Local conditions at CLB (2700 m)

➢ Non-erodable initial snow cover ➢ Snowfall (around 15 cm) ➢ Wind-induced redistribution of falling snow

Southern Winds

Fully coupled snowpack/ atmosphere simulations of snowfall ...Study: High resolution Large Eddy...

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