21st century high-resolution downscaling of the Antarctic surface mass balance from global circulation models

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EGU 2011 - 5, April 2011

Vincent Favier, Christophe Genthon, Gerhard Krinner, Hubert Gallée

of Antarctic surface mass balance

from global circulation models

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1

Antarctic Surface Mass Balance

(van de Berg et al., 2006)

Coastal areas :

snowy and windy

Antarctic Plateau :

cold and dry

4000 2000 1000 700 500 300 200 100 50 20 0 -400 mm w.e. a-1

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1

Antarctic Surface Mass Balance

(van de Berg et al., 2006)

4000 2000 1000 700 500 300 200 100 50 20 0 -400 mm w.e. a-1

Climate models:

major SMB changes expected in coastal areas

Coastal areas :

snowy and windy

Antarctic Plateau :

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SMB Downscaling : Why ?

Spatial extent

Antarctica (5600 km x 5600 km)

➙_{Reduced computation time needed} Time extent

~800 yrs (1980-2200 * 2 Scenarios * 2 Boundary conditions)

SMB estimation

Precipitation, Sublimation, Melting, Refreezing, Blowing snow

GCM resolution : ~ 60 km _{Required resolution :}_≤ _{15 km}

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Sublimation

_HIDEP

Melting

_HiDEP

Refreezing

_HiDEP

HiDEP

GCM Outputs :

P, T, Qv, U, V, W

3D Fields

Time step : 6H

Surface Fields

Time step : 3H

Rain

_HIDEP

Snow

_HiDEP

Precipitation

Surface Energy Balance

High-resolution topography

The HiDEP model

High-Resolution Downscaling of surface Energy balance and Precipitation

OUTPUTS (15 KM RES.)

INPUTS (~50 KM RESOLUTION)

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4

Upward wind ➙ Adiabatic cooling ➙ ρsat ↓

Integration of the Clausius-Clapeyron equation at saturation :

Precipitation downscaling :

an orographic precipitation model

Precipitation rate = Δρ

sat

/Δt = F (ρ

sat

,T,P) × W

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Orographic precipitation :

Determination of the vertical wind W

At the surface : the wind is tangent to the topography ➙_{new vertical wind at the surface}

➙

_{Computation for W : resolution of mountain gravity wave}

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High-resolution Total Precip.

Low-res. Total Precip. (Interpolated from GCM)

+

High-resolution Orographic Precip.

Low-res. NON-Orographic Precipitation

−

Low-resolution Orographic Precip.

Total precipitation :

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Total precipitation :

Orographic + Non-Orographic

GCM Grid (~50 km res.) HiDEP Grid (15 km res.)

GCM Topography GCM Interpolated Topography GCM Precipitation Interpolation

Low-res. Oro. Precip.

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Total precipitation :

Orographic + Non-Orographic

GCM Topography GCM Interpolated Topography GCM Precipitation Interpolation High-res. Topography

High-res. Oro. Precip. Low-res. Oro. Precip.

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Total precipitation :

Orographic + Non-Orographic

GCM Topography GCM Interpolated Topography GCM Precipitation Interpolation Interpolation High-res. Topography

High-res. Oro. Precip. Low-res. Oro. Precip.

Low-res. Total Precip.

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Surface Energy Balance

×

z Var

×

Extrapolation of GCM surface fields against the topography

Surface Scheme

Sublimation

Melting

Refreezing

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Application to LMDZ4 : 1980-2007

4000 2000 1000 700 500 300 200 100 50 20 0 -400 mm w.e. a-1

van de Berg et al, 2006

Arthern et al, 2006

HiDEP-LMDZ4

SMB

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Validation with a quality-controlled SMB

data-set (Magand et al., 2007) : 90° – 180°E

0 0,2 0,4 0,6 0,8 1,0 0 500 1000 1500 2000 2500 3000 3500 4000

R2 weighted by the number of observation in LMDZ4 grid boxes

Elevation range of Observations (m)

R2 LMDZ4 vs. Obs HiDEP-LMDZ4 vs. Obs 10 0 30 60 90 120 0 500 1000 1500 2000 2500 3000 3500 0 80 160 240 320 Nb. of Obs. Cum. Nb. of Obs.

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Extension of the data quality-control to the rest of Antarctica :

Work in progress at LGGE

(In charge : Soazig Parouty, Vincent Favier)

Validation with a quality-controlled SMB

data-set (Magand et al., 2007) : 90° – 180°E

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Grounded SMB 1980-2007

208.6 mm w.e. a

-1

_{= kg m}

-2

_a

-1

⇔

6.7 mm a

-1

sea level equivalent

Present SMB (1950-2000) :

‣

_{Range : 4.1 to 6.4 mm a}

-1

_{sea level equivalent}

(Monaghan et al., 2006)

175.2 mm w.e. a

-1

_{= kg m}

-2

_a

-1

⇔

6.0 mm a

-1

sea level equivalent

LMDZ4

P-E

HiDEP-LMDZ4

SMB

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0

50

100

150

200

250 SMB

Snow

Rain

Melt

Sublim.

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Projection for the 21

century (A1B)

First results

LMDZ4 HiDEP-LMDZ4 1980-2007 2071-2099

mm w

.e. a

-1 Grounded ice-sheet

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Projection for the 21

century (A1B)

First results

1980-2007

2070-2099

Melt HiDEP

₄₀₀₀ 2000 1000 700 500 300 200 100 50 20 0 -400 mm w.e. a-1

Melt

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Conclusion

• High-resolution SMB (15 km) obtained from LMDZ4 downscaling

Partial validation for present :

✦ Increased performance Downscaled SMB close to LMDZ4 SMB

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15

Conclusion

Further validation :

• Extended quality-controlled data set over all Antarctica

Model development in progress :

• More detailed Surface Scheme

• High-resolution SMB (15 km) obtained from LMDZ4 downscaling

Partial validation for present :

✦ Increased performance Downscaled SMB close to LMDZ4 SMB

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