A new albedo parameterization for the Antarctic ice sheetkuipe117/docs/KuipersMunneke_EGU2011… ·...
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Published as: Kuipers Munneke, P. et al. (2011). A new albedo parameterization for use in climate models over the Antarctic ice sheet. J. Geophys. Res., 116, D05114, doi: 10.1029/2010JD015113 Other references: Flanner, M.G. and C.S. Zender (2006) JGR 111, D12208, Gardner, A.S. and M.J. Sharp (2010) JGR 115, F01009 This is EGU poster 2011-114 2001 | 2002 2000 | 2001 2002 | 2003 0.70 0.75 0.80 0.85 0.90 0.95 2003 | 2004 0.70 0.75 0.80 0.85 0.90 0.95 Albedo 1999 | 2000 0 50 Nov Dec Jan Feb Net SW radiation [W m -2 ] Mean/RMS: -1.1/18.4 Nov Dec Jan Feb -50 0 50 Mod. - Obs. [W m -2 ] -1.9/17.5 Nov Dec Jan Feb -5.7/24.8 Nov Dec Jan Feb -8.7/18.4 Nov Dec Jan Feb -3.5/21.0 Validation The computed albedo is validated against observed albedo at Neu- mayer, a site with high-quality solar radiation measurements. The agree- ment between RACMO2.1 (dashed lines in figure 4 to the right) and observations (solid lines) is very good. Over a summer season, net shortwave radiation is underesti- mated by 2.7 W m-2. The seasonal cycle, the variability due to cloud cover, and the feedback between albedo and melt are well represented. Validation Apart from solar elevation and cloudiness, albedo is determined mainly by the size of the snow grains. A computation of the evolution of snow grain size was implemented in RACMO2.1, based on Flanner and Zender (2006). It takes into account (1) dry snow metamorphism (2) wet snow metamorphism (3) fresh snowfall (4) refreezing of meltwater, processes that each influence snow grain size. Figure 2 demon- strates the evolution of snow grain size in an Antarctic summer season, for three very different locations. Figure 3 shows the evolution of snow grain size during one summer on the entire Antarctic continent. Lastly, formulas by Gardner and Sharp (2010) are used to trans- late snow grain size, solar elevation and cloud cover to snow albedo. The solution 0 200 400 600 800 Oct Nov Dec Jan Feb Mar Apr May Snow grain size r e (μm) 2003 2002 Snow grain size of the first full snow layer (r e,1 ) Neumayer Larsen C ice shelf South Pole Figure 2 (above): Snow grain size in an Antarctic summer at the Larsen C ice shelf (Antarctic Peninsula), Neumayer (coastal East Antarctica), and South Pole (Antarctic plateau). Figure 3 (right): Snow grain size in an Antarctic summer over the entire continent. (a) October, (b) November, (c) December, (d) January, (e) February, (f) March. In coastal Antarctica, the energy budget of the snowpack is domi- nated by solar radiation. How much solar radiation is absorbed depends on the albedo of the snow surface. Albedo is involved in a strong positive feedback: when snow melts, albedo drops, causing more radiation to be available for melting. The challenge It is thought that ponding of meltwater has led to the break-up of the Larsen A (1995) and B (2002, see images) ice shelves. Also, meltwater extent is mea- sured by satellites and used as a climate change indicator. If you want to simulate meltwater produc- tion realistically (and indeed the entire surface energy budget), the key is to have the parameterization of albedo right. The challenge is to implement a good parameterization of albedo in our regional climate model RACMO2.1 Peter Kuipers Munneke*, Michiel van den Broeke*, Jan Lenaerts*, Mark Flanner**, Alex Gardner**, and Willem Jan van de Berg* *Institute for Marine and Atmospheric Research Utrecht (IMAU) **Dept. of Atmospheric, Oceanic, and Space Sciences, Univ. Michigan, Ann Arbor Contact: [email protected], +31 30 253 3274 A new albedo parameterization for the Antarctic ice sheet
Transcript of A new albedo parameterization for the Antarctic ice sheetkuipe117/docs/KuipersMunneke_EGU2011… ·...
Published as: Kuipers Munneke, P. et al. (2011). A new albedo parameterization for use in climate models over the Antarctic ice sheet. J. Geophys. Res., 116, D05114, doi: 10.1029/2010JD015113
Other references: Flanner, M.G. and C.S. Zender (2006) JGR 111, D12208, Gardner, A.S. and M.J. Sharp (2010) JGR 115, F01009 This is EGU poster 2011-114
2001 | 20022000 | 2001 2002 | 20030.70
0.75
0.80
0.85
0.90
0.95
2003 | 20040.70
0.75
0.80
0.85
0.90
0.95
Albe
do
1999 | 2000
0
50
Nov Dec Jan Feb
Net S
W ra
diat
ion
[W m
-2]
Mean/RMS: -1.1/18.4Nov Dec Jan Feb
-50
0
50
Mod. - O
bs. [W m
-2]-1.9/17.5Nov Dec Jan Feb
-5.7/24.8Nov Dec Jan Feb
-8.7/18.4Nov Dec Jan Feb
-3.5/21.0
Validation
The computed albedo is validated against observed albedo at Neu-mayer, a site with high-quality solar radiation measurements. The agree-ment between RACMO2.1 (dashed lines in figure 4 to the right) and observations (solid lines) is very good. Over a summer season, net shortwave radiation is underesti-mated by 2.7 W m-2. The seasonal cycle, the variability due to cloud cover, and the feedback between albedo and melt are well represented.
Validation
Apart from solar elevation and cloudiness, albedo is determined mainly by the size of the snow grains. A computation of the evolution of snow grain size was implemented in RACMO2.1, based on Flanner and Zender (2006). It takes into account(1) dry snow metamorphism(2) wet snow metamorphism(3) fresh snowfall(4) refreezing of meltwater,processes that each influence snow grain size. Figure 2 demon-strates the evolution of snow grain size in an Antarctic summer season, for three very different locations. Figure 3 shows the evolution of snow grain size during one summer on the entire Antarctic continent.
Lastly, formulas by Gardner and Sharp (2010) are used to trans-late snow grain size, solar elevation and cloud cover to snow albedo.
The solution
0
200
400
600
800
Oct Nov Dec Jan Feb Mar Apr May
Snow
gra
in s
ize r
e (
µm)
20032002
Snow grain size of the
first full snow layer (re,1
)
Neumayer
Larsen C ice shelf
South Pole
Figure 2 (above): Snow grain size in an Antarctic summer at the Larsen C
ice shelf (Antarctic Peninsula), Neumayer (coastal East Antarctica), and
South Pole (Antarctic plateau).
Figure 3 (right): Snow grain size in an Antarctic summer over the entire
continent. (a) October, (b) November, (c) December, (d) January, (e)
February, (f) March.
In coastal Antarctica, the energy budget of the snowpack is domi-nated by solar radiation. How much solar radiation is absorbed depends on the albedo of the snow surface. Albedo is involved in a strong positive feedback: when snow melts, albedo drops, causing more radiation to be available for melting.
The challenge
It is thought that ponding of meltwater has led to the break-up of the Larsen A (1995) and B (2002, see images) ice shelves. Also, meltwater extent is mea-sured by satellites and used as a climate change indicator.
If you want to simulate meltwater produc-tion realistically (and indeed the entire surface energy budget), the key is to have the parameterization of albedo right. The
challenge is to implement a good parameterization of albedo in our regional climate model RACMO2.1
Peter Kuipers Munneke*, Michiel van den Broeke*, Jan Lenaerts*, Mark Flanner**, Alex Gardner**, and Willem Jan van de Berg*
*Institute for Marine and Atmospheric Research Utrecht (IMAU) **Dept. of Atmospheric, Oceanic, and Space Sciences, Univ. Michigan, Ann Arbor
Contact: [email protected], +31 30 253 3274
A new albedo parameterizationfor the Antarctic ice sheet
