Fre2010c

Fre2010c
Deriving ocean surface currents
from remote sensing techniques
Grit Freiwald, Martin Losch (AWI)
Silvia Becker, Wolf-Dieter Schuh (IGG - TG)
Hamburg, 12.06.2010
SR3 section
o
140 O
oO
150oO
160 oO
130
o
30 S
170 o
O
EAC
COUN
o
40 S
Assimilation:
SAF
o
50 S
PF
oS
60
o
70 S
◮
temperature
◮
salt
◮
velocities
Ocean model result
0
0.4
−500
0.3
−1000
0.2
depth (m)
−1500
0.1
−2000
0
−2500
−0.1
−3000
−0.2
−3500
−0.3
−4000
−4500
45
50
55
latitude (°S)
60
65
Transport across section: 159 ± 64 Sv
Formal errors: Inverse of the Hessian of the cost function.
−0.4
Mean dynamic topography
◮
geostrophic balance:
◮
η = h−N
∂η
∂x
= gf v => reference surface velocity
satellite orbit
sea surface
η
geoid
reference ellipsoid
Problems with the geoid!
◮
geoid models describe short scales not sufficiently for
oceanography
◮
omission error is generally neglected
=> underestimation of the geoid model error
◮
“higher” accuracy => larger formal error
◮
considering omission error => “complete” geoid models
Is it possible to improve the ocean models
by assimilating MDT?
Principle for omission error problems
Homogeneous, isotropic covariance function for geoid model
Ocean model parameters
Free to choose:
◮
discretization method
◮
number of iterations
◮
bottom (reference) velocities
◮
roughness parameters
for salinity, temperature, horizontal velocities
◮
prior error estimations
Transport across section: 174 ± 48 Sv
Transport error estimates
Sv
80
60
40
20
0
No
MDT
Omission Omission
Full
error
error
omission
neglected partly
error
considered
Stationary 3D model: IFEOM
Inverse box model for the Southern Ocean
e.g. Sloyan and Rintoul (2001),
Losch, Sloyan, Schröter and Sneeuw (2002)
Ice drift algorithm
c¯u
c¯v
=
Ū
V̄
−F ·
cos θ − sin θ
sin θ
cos θ
ū
v̄
P ′ ′ P ′ ′ uV − vU
Turning angle: θ = arctan P ′ ′ P ′ ′
uU + vV
Speed reduction factor:
P
P
P
P
cos θ u ′ U ′ + sin θ v ′ U ′ − sin θ u ′ V ′ + cos θ v ′ V ′
P
P
,
F =
u ′2 + v ′2
u ′ = u − ū
etc.
(N. Kimura: Sea Ice Motion in Response to Surface Wind and
Ocean Current in the Southern Ocean, JMSJ 2004.)
Ice drift and wind data
o
140 E
oE
130
o
30 S
o
40 S
o
150 E
160 oE
170 o
E
o
140 E
oE
130
o
30 S
o
40 S
o
50 S
o
50 S
o
60 S
5~cm/s
o
70 S
o
60 S
5~m/s
o
70 S
o
150 E
160 oE
170 o
E
Resulting ocean surface currents
o
140 E
oE
130
oS
30
150oE
160 oE
170 o
E
o
40 S
Mass transport across section:
o
50 S
173 ± 46 Sv
oS
60
5~cm/s
o
70 S
Summary
Mass transport across section for the 3 cases:
Ocean model only:
159 ± 64 Sv
Ocean with dynamic topography:
174 ± 48 Sv
Ocean with drifting sea ice:
173 ± 46 Sv
Thank you for your attention!
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