Snow, dim
systems
Florent Domine
Takuvik joint international Labo niversite Laval and CNRS Quebec City, Canada
1 - Snow affects the albedo of the surface
2 - Snow affects the temperature of the underlying soil
20 10 0
40 em
S0
-0.3°C
-2.6°C
■    ■■wmH- ■ ■■■■■ - :.
-3.9°C -6.9°C ,
Snow prevents ground freezing Impact on nutrient cycling and carbon accumulation
3 - Snow affects wildlife
Snow and wildlife
4 - Climate affects snow
3-oct.    2-nov.   2-déc.   1-janv.  31-janv. 1-mars 31-mars 30-avr.
5 - Vegetation affects snow
Thin snowpack on tundra
Thick snowpack in forest
northern Quebec
0,4 0,2
0,0 1-oct.
i -nov. 2-déc. 2-janv. 2-févr. 5-mars 5-avr.  6-mai 6-juin
7-juil.
Outline
— How climate affects snow physical properties
^ Snow metamorphism
— Snow-albedo feedback 1: sea ice and snow thermal conductivity
— Snow-albedo feedback 2: precipitation and the albedo of Antarctica
— Snow-albedo feedback 3: permafrost, vegetation and snow
— Conclusions
a Depth hoar
Taiga snow
Taiga snowpack
Tundra snow
Barrow, Alaska
Tundra snowpack
4- 50
0.2
Tundra
4- 40
Faceted crystal
□ Mixed forms
0.25
4- 30
0.4
4-20
QÜÜ    Ü    □   □ q
y' y ' ' y   y y> y y / y
y
4-10
0.25
1 0
y
a a a a a ä" a a aa a a a
aaaaa a a
a aaa a a aa a a a  a a a
—7—7
Tundra
—/ /
a Depth hoar
Windspeed Tundra
high: 10 m/s
2-nov.   2-déc.   1-janv.  31-janv. 1-mars 31-mars 30-avr.
30
20
Alpine / maritime snowpacks
Maritime / Alpine snowpacks
Visible properties and physical conditions of snowpacks
Geographical distribution of snowpacks
Snow metamorphism
^ Snow is not in thermodynamic equilibrium, its S/V ratio is too high
— Snow crystals evolve over time
— The changes are dictated by physical variables: temperature, temperature gradient, wind , etc.
Physical changes undergone by snow under environmental conditions
Snow metamorphism
What drives metamorphism ?
A   I I
Albedo = 0.90
lSpecif»c surface area
SSA = 86cmJ/9
Specific surface area
SSA = 930 cm2/g
to
Albedo = ^6
Light penetration ?
8 = 5 cm
' TOT»?.. ft
Under temperate climates
Snow : High surface area
Surf. Energy : 109 mJ/m2 Thermodynamically unstable
T = -3°C
200 Mm
\3
rc = 10 |jm PH2O= 517.72 Pa
_^_c._
PH2O gradient= 0.15 Pa/cm
rc = 1000
PH2O= 517
Under cold climates
T= -22°C Ph2q = 84 pa
p (T1) = P0 exp
Rapid grain growth
T= -15°C
PH2Q = 163 Pa
PH2Q gradient = 4 Pa/cm
T= -3°C Ph2q = 470 Pa
Effect of T and T gradient
isothermal warm) metamorphism
Wind and metamorphism
sublimation
Wind raises snow
$0/
rounding size decrease
"i ■••V »•
- Light snow y_ow cohesion i/k
impactionP^^. sintering
Dense cohesive snow
L_"■ ■ .     ■ ■
Effect of wind
Low wind (+ cold)
Climate and snowpack type
Warm
cold
Low wind Maritime/Alpine
Taiga
High wind Prairie
Tundra
Metamorphism and physical properties of the snowpack
albedo : energy budget of the surface
e-folding depth : photochemical
activity
thermal Energy budget conductivity : of the soil,
Sea ice growth
permeability : Release of
chemical species Sensible heat transfer
Climate, metamorphism and snow physics
Snow climate feedback 1: The growth of sea ice and the thermal conductivity of snow
Heat flux from ocean to atmosphere
KongsFjord, West coast of Spitsbergen
and limits the growth of the ice pack
20 cm of snow
Insulating power of snow
But during the night, enormous amounts of snow fell, so that arms and men lying down were covered. Pack animals were hobbled by the snow. There was great hesitation in getting up, because the snow was keeping the men lying down warm, except when it had slipped off their shoulders.
Xenophon of Athens, Anabasis, Book IV, Chapter IV, Sentence 11 (400 BP)
Insulating power of snow and climate
cm 50
40
30
February 2005 (cold)
Facted crystals
-10
-20
-30
2006 2005
Oct.     Nov.    Dec.     Jan.     Feb.     Mar. Apr.
20
10
0
Sea ice
Wind slab
Depth hoar
snow of 2005 = 2 boards of styrofoam
	
	
J	US
StorFjord, East cosat of Spitsbergen	
0
0.07
0.46
0.06
Insulating power of snow and climate
Snow of 2006 = 1/2 board of styrofoam snow of 2005 = 2 boards of styrofoam
Snow will save sea ice from global warming !!
Snow climate feedback 2: Precipitation and the albedo of Antarctica
Snow albedo is the main factor in the energy budget and climate in Antarctica
Ghislain Picard Glaciology Lab. Grenoble
Picard et al. (2012) Nature Climate Change, 2, 795
Snow and albedo
Visible Visible
Consequence of snow cover decrease: more absorbed radiation
• Snow-climate positive feedback
The main snow-albedo feedback
Stronger warming
snow
\
/
Surface albedo decreases
Positive feedback
Are there negative feedbacks ?
Snow albedo
Albedo determined by I • Scattering : increases with decreasing grain size
• Absorption : increases with increasing impurity content
W. 4,
scattering
In Antarctica, snow is clean
Albedo is determined by grain size only*
absorption
■7 ...nt
Aerosol
*almost
Snow albedo
Snow with small grains has the highest albedo
Snow with large grains has a lower albedo
Albedo of pure snow
d= diameter of snow grains, approximated as spheres
Climate warming More small grains Surface cools down
% # ^ ft
More precipitation Albedo increases
Our question : with warming, which effect will predominate ?
What is the sign of the snow-albedo feedback in Antarctica ?
Climate warming Grains grow faster Surface heats up
%      #        % #
Metamorphism is faster Larger grains
Monitor snow physical properties using passive microwave sensing at 89 and 150 GHz
Ü TB of top 7 cm
TMIOi/SSSS^MMlUBKKK^BIKM —> tb of top 20 cm
Brightness Temperature Snow Temperature
= f(frequency)
Emissivity= AMSU*
Dielectric properties of the medium F^^^^H
=f(frequency, grain size) VI^H
89 GHz^^^B^^^^J
~20cm
*Advanced Microwave Sounding Unit (AMSU)
MSU data at Dome C
Jul 2003Jan 2004Jul 2004 Jan 2005Jul 2005Jan 2006Jul 2006Jan 2007Jul 2007
220 r i i i i i i i i
89 GHz
150 GHz
Difference "89 - 150"
Jul 2003Jan 2004Jul 2004 Jan 2005Jul 2005Jan 2006Jul 2006Jan 2007Jul 200^
30 K differences in TB cannot be explained by changes in Tsnow only Changes in £ must be invoked, and £ changes over time
To reduce temperature effects, we define the Grain Index
TB ~1B
l
GI
We test that GI in fact reflects grain size in the range 0-7 cm
Test of hypothesis: microwave emission model
Inverse model of microwave signal to determine mean grain sizes at 0-7 cm and 7-20 cm
Test of hypothesis: thermodynamic snow model
Rapid grain growth start of summer
Precipitation, winter
2601-
) £
1 Q.
'S
Jul-2008 Dec-2008 Jul-2009 Dec-2009 Jun-2010
After JM Barnola
Jul-2008
Dec-2008
Jul-2009
Dec-2009
Jun-2010
T strings measurements at 40 levels
Test of hypothesis: snow model + measurements
Run snow model to simulate grain growth
Measurements at 11 cm
	250 r
	200 -
-4.	150 :.
uo	
	
	100
a:	
	50 -
	
Snow model @ 11 cm
Microwave model Microwave model
-----*........
Snow model @ 5 cm
Measurements at 5 cm
i*   ^ ^ oO^°    .0v°  .0^ oO^°
^    \*   ^ o<**   $fi*   oe° *eX>  ^ ^
Annual accumulation : 10 cm of snow
8
0.2 0.15
0.1 0.05 0
-0.05
Sep-08 Oct-08 Nov-08 Dec-08
T TTTTTT
GI decreases^
GI is low
GI is low
150 GHz (7 cm)
GI increases ^
End of winter, year 1    Little precip, Start of winter precip
1st December 15 January 15 February
Small winter grains     Summer grain growth Small winter grains
End of winter, year 2 1st December Small winter grains
m
c 0
Confirmation with interannual variability: winter
Confirmation with interannual variability: summer
Impact of albedo increase on surface temperature
High summer precipitation => albedo increase of 0.03 Use LMDz GCM to calculate effect of albedo increase of 0.03
Summer mean
Future impact of this snow - albedo feedback
By 2100:
20 % increase in precipitation 3 K temperature rise
(SRES A1B GHG emission scenario)
mean albedo increase of 0.004 => -1.5 W m-2 forcing
=> -0.5 °C in summer => -0.3 °C in annual mean
10% negative feedback
Temperature drops
Stops snow metamorphism
\
Albedo remains high
b Grains remain small
Snow will save Antarctica from global warming !
Snow climate feedback 3: Permafrost, vegetation and snow
I
Permafrost
i
= ground that remains frozen for at least 2 consecutive years
— Organic carbon reservoir : 1600 Pg C
Atmosphere : 730 Pg C
Warming
/
Permafrost thawing
Emission as
I CO2 et CH41
Carbon mineralisation
Continuous permafrost >90% area coverage
Discontinuous/sporadic 10-90% coverage
Isolated patches
^ How will the thermal regime of permafrost evolve ?
^ What is the fate of carbon in thawing permafrost ?
Factors affecting the energy budget of permafrost
Vegetation, wind speed and turbulent fluxes
Wind speed w = 10 m/s
Sensible heat flux : H x w Latent heat flux : L x w
6 m/s
4 ;;. i
4 m/s
Factors affecting the energy budget of permafrost
Vegetation and snowpack height
Factors affecting the energy budget of permafrost
Radiative budget
Albedo : 0.4
^      Albedo : 0.8
*
*
Hj ^ >|< ^
** *
Result: impact of vegetation on the energy budget of permafrost
Tundra
Taiga
3
=^> Vegetation destabilizes permafrost
Tundra snow
Barrow, Alaska
Thermal budget of snow
t—r    aground   Tsnowsurface
F=—^- J
R
T
0 0.05
kT, W m-1 K-1
0.1 0.15 0.2
0.25 0.3
RTundra = (3.7 ± 1	.8;	i m K W-
		
RTaiga = (17.3 ± 4.0) m2 K W-1		
10
20
30
40
50
60
0
Taiga, Finland
Tundra, Alaska
Result: impact of vegetation on the energy budget of permafrost
Partial quantification of the impact of vegetation
Land surface model (ORCHIDEE) to simulate the thermal regime of the ground and the dynamics of carbon stored in soils. ORCHIDEE forced by 20th century climate.
Testing the impact of snow physical properties : VARIED - CONTROL
VARIED	Tundra	Taiga
Density	330	200
Conducti.	0.25	0.07
CONTROL	Tundra	Taiga
Density	330	330
Conducti.	0.20	0.20
■12
-S
-4
-3 -2 _I_
■1 0 _I_
8
12
AT, °C
100°W
0°
100°E
Gouttevin et al. (2012) JGR, 117, D02020
More insulating snow
Carbon Mineralisation
rost tha
Snow will accelerate permafrost thawing !
Conclusion
— Snow is the most reflective surface on Earth and affects the radiation budget
— Snow forms an insulating layer on the ground
— Snow physical properties are highly dependent on climate and ecosystems
— There are many snow-climate feedbacks, some positive, some negative
— Predicting climate change, especially in polar regions, requires a more detailed understanding of the many complex snow feedbacks.
Polar research can be dangerous to your health
Physical properties of the snowpack
Energy budget of the soil Permafrost extent Sea ice growth
Roles de la neige sur la banquise
Isolation thermique: limite le refroidissement de l'ocean et la croissance de la glace de mer Refroidit la surface: reflechit la lumiere solaire
Contient des impuretes: favorise des reactions chimiques, destruction de l'ozone I ROle chimique Contient des bacteries: modifie la composition de l'atmosphere       | Role biologique
Role physique
Albedo : 80%
Perte de chaleur
Refroidit la surface
[isolation thermique*
Thermal conductivity, kT
1,0 0,8 0,6 0,4 0,2 0,0
Flux
-50 -40
-30 -20 T, °C
-10
0
sis
,1»
Sol
Material	kT Wnr1K"1
Air	0.023
Wood	0.04 -0.4
Water	0.6
Glass	1.1
Limestone	0.5
Ice	2.3
Stainless steel	15
Aluminium	237
Copper	401
Diamond	1000
F
High T gradient (cold) Depth hoar
kice kair
2.3 W/mK   0.023 W/mK
kT = 0.10 W m-1 K-1
Low T gradient (warm) Fine grained snow
Cm* \
1
air
kT = 0.40 W m-1 K-1
Insulating power of snow and climate
Weaker warming
ating snc
\
/
Faster sea ice growth
Negative feedback Are there positive feedbacks ?