Validation of a global finite element sea ice-ocean model
Ralph Timmermann, Sergey Danilov, Jens Schröter
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven
Finite-Element Sea-ice Ocean Model1. Introduction
Results from a global Finite Element Sea ice–Ocean Model (FESOM; Timmermann et al., 2009) are evaluated using eulerian and lagrangian datasets We demonstrate that the model captures many of
2. Model Description: Finite Element Sea Ice Ocean Model (FESOM; Timmermann et al. 2009)
• hydrostatic, free-surface, primitive-equation Finite Element Ocean Model (grown up from FENA model ofDanilov et al 2004)
• dynamic-thermodynamic Finite-Element Sea-Ice Model (FESIM)
• Heat storage in ice/snow neglected evaluated using eulerian and lagrangian datasets. We demonstrate that the model captures many of
the typical features of sea ice distribution and global ocean circulation, but also shows a couple of weaknesses. Local refinement of the grid is expected to improve results further.
(grown up from FENA model of Danilov et al., 2004)
• tetrahedral mesh, P1-P1 discretization
• global domain, 1.5° horizontal resolution, 26 layers, shaved cells
• Heat storage in ice/snow neglected
• EVP rheology
• atmospheric forcing from NCEP reanalysis 1948-2007
3. Results: Ocean circulation, meridional overturning and bottom water formation
4. Results: Sea ice cover 5. Results: Estimating net freezing rates
Annual mean net growth rateg
Equatorial currents
Sea ice net freezing rates 4
FESOM Eisbildungsrate
Fig. 5: Simulated and observed minimum and maximum sea ice extents
Antarctic Circumpolar Current (ACC)
-2 -1 0 1 2 3
[cm/d]
FESOM Seal
cm/Tag
Daten
m/yr Charassin et al., PNAS (2008)
Fig. 8: Comparison of FESOM freezing rates to estimates derived from repeated salinity profiles obtained from Southern Elephant Seals (Charrassin et al PNAS 2008) Similar agreement for other positions g
ACC: 145 Sv, Gulf Stream: 30 Sv, Kurushio: 30 Sv : -2.6 %/decade
0 100 200 300
days of year 2004 -3
Tag des Jahres 2004
Fig. 2: 16 yrs of simulated trajectories (200 m depth) Fig. 1: Annual mean velocity at 150 m depth after 10 years of integration (displayed on 3°x3° grid)
Uta Menzel
(Charrassin et al., PNAS 2008). Similar agreement for other positions.
Global meridional overturning circulation (MOC)
−5 15
20 −15−30−25−20 2025
25 0 25
1000
FESOM (after 50 yrs of integration) North Atlantic Deep Water Antarctic Bottom Water formation:
Propagation of a ventilation tracer (constantly restored to 1 in surface layer) in FESOM bottom layer
7. New “Weddell Sea grid”: global with local refinements
FESOM
−30
−30
−25
−25
−20
−20
−15
−15
−10
−10
−5
−5
−5
−10
−10 −15
5 10
−20 5
−25 1510
−5 −30
−10
latitude [°]
depth [m]
−80 −60 −40 −20 0 20 40 60 80
1000 2000 3000 4000 5000 6000
Antarctic Bottom Water (AABW) : -6.5 %/decade
Antarctic Bottom Water (AABW)
−1 −1
13
−5−3 0
Meridional overturning circulation in the North Atlantic
FESOM (after 50 yrs of integration) North Atlantic Deep Water
Fig. 6: Time series of simulated ice extents and volume
Timmermann et al., 2009 Compares well to CFC‐11
bottom concentration map of Orsi et al. (1999)
−5
−5
−3
−3
−1
−1 1
3 5 97
−1 11
−1
−3
−5
13
latitude [o]
depth [m]
−80 −60 −40 −20 0 20 40 60 80
1000 2000 3000 4000 5000
6000 FESOM
Fig. 7: FESOM ice thickness validation:
North Atlantic Weddell Sea Verena Haid
Fig. 3: Meridional overturning circulation (global mean and North Atlantic) Fig. 4: Bottom spreading of a numerical tracer released at the surface
6. Conclusions
latitude [o] Antarctic Bottom Water (AABW)
ice thickness validation:
comparison to upward looking sonars (ULS)
6. Conclusions
- good representation of ocean general circulation; subsurface velocities on the small side. Strong AABW cell, ventilation at correct locations.
- summer ice extent too small, winter ice extent excellent. Realistic trends. Ice thickness comparison for Weddell Sea very good, except for northwestern corner.
Fig. 9: Surface grid to be used for study of ice-ocean-atmosphere interaction in the Weddell Sea. 106959 surface nodes, resolution varies from 0.25° to 2.5°.
Further reading:
Charrassin, J-B., et al.: Southern Ocean frontal structure and sea ice formation rates revealed by elephant seals, Proceedings of the National Academy of Sciences, 105(33), 11634-11639, doi: 10.1073/pnas.0800790105, 2008.
Rollenhagen, K., R. Timmermann, T. Janjic, J. Schröter, and S. Danilov: Assimilation of sea ice motion in a Finite Element Sea Ice Model. Journal of Geophysical Resarch (in press)
7. Outlook
• Local refinements in the Weddell Sea
• Implementation of ice shelf-ocean interaction
Contact:
Ralph Timmermann (Ralph.Timmermann@awi.de), Alfred Wegener Institute for Polar and Marine Research, Bussestraße 24, 27570 Bremerhaven, Germany
Timmermann, R., Danilov, S., Schröter, J., Böning, C., Sidorenko, D., Rollenhagen, K.(2009): Ocean circulation and sea ice distribution in a finite element global sea ice -- ocean model, Ocean Modelling, doi:10.1016/j.ocemod.2008.10.009.
• Coupling to COSMO (coop. with D. Schröder / G. Heinemann, Uni Trier)
