AOMIP coordinated experiment with the NYU ice-isopycnal
OGCM
Petteri Uotila and David M. Holland
New York University
Courant Institute of Mathematical Sciences
email: [email protected]
June 11, 2004
Configuration (MICOM)
• Horizontal resolution 0.5◦,
isotropic grid,
grid size
103×134
• 11 vertical layers
• no diapycnal mixing
• shallowest ocean points at -50m
• minimum mixed layer thickness
is 25 m
• coupler time step = 4 h
• baroclinic time step = 24 min
• barotropic time step = 48 s
Figure 1: Model mask and bathymetry.
P. Uotila, http://cims.nyu.edu/˜uotila/
1
Configuration (CICE)
four ice thickness categories
three vertical layers
time step = 4 h
subcycling time step for
dynamics = 120 s
elastic
Ice categories in March 1953
0.45
0.45
0.4
0.4
0.35
0.35
0.3
0.25
0.2
0.15
0.3
0.25
0.2
0.15
0.1
0.1
0.05
0.05
0
0
P. Uotila, http://cims.nyu.edu/˜uotila/
Ice categories in September 1953
0.5
Average coverage [ratio]
•
•
•
•
Average coverage [ratio]
0.5
2
4
Thickness [m]
0
0
2
4
Thickness [m]
2
Initial Conditions
01/1948, Ice Thickness
Based on SST < Tf + 1◦C
0
1
2
3
4
Ice is relatively thin in 01/1948
P. Uotila, http://cims.nyu.edu/˜uotila/
3
Results
Mean Ocean Temperature
2
degC
1.8
1.6
1.4
1.2
1950
1955
1960
1965
1950
1955
1960
1965
psu
1970
1975
1980
1985
1990
1995
2000
1970
1975
1980
1985
1990
1995
2000
1980
1985
1990
1995
2000
1995
2000
1995
2000
Mean Ocean Salinity
34.9
34.8
34.7
34.6
0.1
Mixed Layer Volume Fraction
%
Restoring ends
0.05
0
1950
1955
1960
1965
1970
6
x 10
03/72, 1.1e7 km2
5
0
08/95, 3.2e6 km2
1950
1955
1960
1965
1970
4
3
km
3
1975
Ice Area
10
km
2
15
x 10
1975
1980
Ice Volume
1985
1990
3
04/71, 2.5e4 km
• Evident trends appear
after restoring
• Arctic becomes warmer
and fresher
• mixed layer becomes
thinner → MICOM ?
• Too little initial and
summer ice
• Too much ice in the
winter
• Ice
variability
as
expected, but higher
than observed
2
1
2
08/95, 8.0e3 km
0
1950
1955
1960
1965
1970
1975
P. Uotila, http://cims.nyu.edu/˜uotila/
1980
1985
1990
4
Inter-annual Ice variability
Ice Area in March
1.2
km2
1.1
1
0.9
0.8
1950
1955
1960
1965
1970 1975 1980 1985
Ice Area in September
1990
1995
2000
1950
1955
1960
1965
1970 1975 1980 1985
Ice Volume in March
1990
1995
2000
1950
1955
1960
1965
1970 1975 1980 1985
Ice Volume in September
1990
1995
2000
1950
1955
1960
1965
1990
1995
2000
6
km
2
5
4
3
km3
2.5
• Especially (winter) ice
volume decreases
2
1.5
km3
1.5
1
0.5
1970
1975
1980
P. Uotila, http://cims.nyu.edu/˜uotila/
1985
5
Ice Drift
01/2001, Ice velocity field
0
0.1
0.2
0.3
0.4
P. Uotila, http://cims.nyu.edu/˜uotila/
01/2003, Ice velocity field
0
0.1
0.2
0.3
0.4
6
Results: Ocean, surface circulation
01/2001, Ocean surface velocity field
0
0.1
0.2
0.3
P. Uotila, http://cims.nyu.edu/˜uotila/
0.4
01/2003, Ocean surface velocity field
0
0.1
0.2
0.3
0.4
7
Results: SSS
01/1948, Salinity at the surface
34
34.5
35
01/2003, Salinity at the surface
35.5
10 15
Note scale change !!
P. Uotila, http://cims.nyu.edu/˜uotila/
20
25
30
35
8
Results: Salinity at -400 m
01/1948, Salinity at −400 m
34
34.5
35
P. Uotila, http://cims.nyu.edu/˜uotila/
01/2003, Salinity at −400 m
34
34.5
35
9
Results: Ocean circulation at -400 m
01/1953, Ocean velocity field at −400 m
0
0.05
0.1
0.15
P. Uotila, http://cims.nyu.edu/˜uotila/
0.2
01/2003, Ocean velocity field at −400 m
0
0.05
0.1
0.15
0.2
10
Concluding Remarks
• Data can be found from AOMIP-LAS
• Freshening due to the lacking salt input from the Pacific and due to the too weak advection of
fresh water from the Arctic ?
• Freshening of the surface layer increases stratification and separates deeper layers from the
surface layer.
• Atlantic layer circulation becomes non-dependent on the surface conditions.
• Deeper layers become more fresh as well
• Mixed layer thinning when there’s no restoring → Gaspar et al. -scheme, mixing, shear ?
• Thin mixed layer cools/warms fast and affects ice conditions and causes excessive seasonal ice
variability
P. Uotila, http://cims.nyu.edu/˜uotila/
11
Maximum Ice extent in 03/1989
03/1989, Ice Concentration
0.5 0.6 0.7 0.8 0.9
1
11 million sq km
P. Uotila, http://cims.nyu.edu/˜uotila/
12
Minimum Ice extent in 08/1995
08/1995, Ice Concentration
0.5 0.6 0.7 0.8 0.9
1
3.2 million sq km
P. Uotila, http://cims.nyu.edu/˜uotila/
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