Geoscience Reference
In-Depth Information
Table 1 Characterization of the three coupled sea ice-ocean models used for inter-comparison to the
GOCE-derived MDT and mean surface geostrophic current
Model
run
Region
Spatial
resolution
Period
Vertical grid, # of
layers, forcing
ATL12
Atlantic Ocean north of 33S
including the Nordic Seas and
the Arctic Ocean. Uses
ETOPO 2-min resolution
bathymetry
*8 km
1948-2009
Hindcast
z-coordinates,
50 levels,
NCEP—6 h
MICOM
North of 30S with Nordic Seas
and Arctic Ocean included.
Uses ETOPO 1 5-min
resolution bathymetry
*15 km
1948-2007
Hindcast
Isopycnal,
35 layers,
NCEP—6 h
HYCOM
Hybrid
coordinates,
28 layers,
ERA Interim—
6h
ETOPO 2-min Earth's relief data set with a grid size of 2 0 by 2 0 , from NOAA Geophysical Data Center
NCEP relates to US National Centers for Environmental Prediction
GEBCO 1-min Earth's relief data set with a grid size of 1 0 by 1 0 , from UNESCO and IOC
ERA relates to European Center for Medium-Range Weather Forecasting Reanalyses
High latitude- Arctic Ocean.
Uses GEBCO 1-min
resolution bathymetry
*12-16 km
1993-2010
Hindcast
3 Surface Circulation
With access to the new GOCE-based MDT with unprecedented accuracy, the uncertainties
in mean ocean circulation and transport estimation are expected to improve. The mean
surface geostrophic velocities are computed from the MDT, under the assumption of
geostrophic balance;
u s ¼ g
f
: oMDT
oy
ð 1 Þ
v s ¼ g
f
: o MDT
ox
ð 2 Þ
where u s and v s are components of the surface geostrophic velocity, g is the acceleration
due to gravity, f is the Coriolis parameter, and x and y are the longitudinal and latitudinal
coordinates. The corresponding surface geostrophic current derived from the GOCE MDT
for the Nordic Seas over the period 1993-2009 is shown in Fig. 7 and compared to the
independently derived CNES_CLS09 MDT Rio et al. 2011 and Maximenko et al. 2009
(which both are using a GRACE-based geoid model together with in situ Argo floats and
surface drifter data integrated over the 17-year period from 1992 to 2009), as well as the
climatological mean surface velocities (predominantly based on drifters in the Nordic Seas
from 1991 to 2010) from the surface drifter data ( http://www.aoml.noaa.gov/phod/dac/
drifter_climatology.html ) .
The large-scale cyclonic surface circulation regime is well-reproduced in all three fields.
However, while the strongest mean surface currents of the inflowing Atlantic Water to the
Norwegian Sea reaching nearly 0.20 m/s are derived from the GOCE MDT, the inflow in the
other two surface current fields is clearly weaker with maximum speed not much more than
0.10 m/s. Moreover, it is only the GOCE-based surface geostrophic current that reveals distinct
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