regional ocean modelling in southern africa sea surface temperature [ o c] acknowledgements: n....
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Regional Ocean Modelling in Southern Africa
Sea Surface Temperature [oC]
Acknowledgements:
N. Chang, UCT; L. Debreu, IMAG; P. Florenchie, BCLME; J. Lefevre, IRD; J.R.E. Lutjeharms, UCT; E. Machu, IRD;
P. Marchesiello, IRD; F. Shillington, UCT, J. Veitch, UCT.
1 - Some modelling tools used at IRD (Institut de Recherche pour le Developpement)
1.1 - ROMS_AGRIF: ROMS with embedding
1.2 - ROMSTOOLS: A Series of Tools for the Pre- and Post-
processing of Oceanic Regional ROMS Simulations.
2 - SAfE (Southern Africa Experiments)
2.1 - Climatology experiment (Process studies).
2.2 - Inter-annual experiment.
2.3 - Nested models.
Regional Ocean Modelling in Southern Africa
ROMS_AGRIF: Embedding capabilities
"from the large scale to the coastal applications"ROMS_AGRIF:
- Arbitrary number of embedded grids.
- Parent/child exchanges during run time.
- OpenMP/MPI compliant.
- Enforcement of mass conservation in
agreement with ROMS time stepping.
- Biology.
- 2way nesting in progress.
After Penven, P., L. Debreu, P. Marchesiello and J.C. McWilliams, Application of the ROMS embedding procedure for the Central California Upwelling System, 2006, Ocean Modelling, 12, 157-187.
ROMS_TOOLS: A toolbox for ROMS pre- and post-processinghttp://www.brest.ird.fr/Roms_tools/index.html
Goal: to simplify the design and analysis of ROMS model configurations
An observation: Similarities for the choices in different ROMS applications.
Possibility to use a systematic approach
Strategy:
Global datasets:
etopo2, WOA2001, TPX06,
DASILVA Climatology
ROMS input netcdf files:
roms_grd.nc, roms_frc.nc, roms_blk.nc,
roms_ini.nc, roms_clm.nc, roms_bry.ncROMS_AGRIF
ROMS output netcdf files: roms_his.nc, roms_avg.nc
ROMS_GUI
VisualizationDiagnostic tools
Analysis
OPENDAP servers:
NCEP, GFS, ECCO, SODA
ROMSTOOLS
roms_gui: visualization.
Inter-annual simulations
~/Roms_tools/Run/run_roms_inter.csh
make_OGCM.m , make_NCEP.m
Use of OPENDAP to get automatically the necessary data over the web
(OGCMs: ECCO, SODA, surface forcing: NCEP).
Real-time coastal system
~/Roms_tools/Run/run_roms_forecast.csh
make_forecast.m
Hypothesis:
Large scale: slow.
On the shelf: winds
http://sea.uct.ac.za/penven/RealTime/index.html
Real Time ROMS Ocean Simulations in the Southern Benguela
Model grid: 1/9 degree resolution (i.e. 10 km); 72 X 94 X 32 grid points.
Lateral boundary conditions: ECCO.
Surface forcing: GFS.
One model run every day:
1 day hindcast + 8 days forecast.
2 - SAfE (Southern Africa Experiments)
image source: J. Lutjeharms, 2006.
Upwelling
Agulhas Current
Benguela upwelling system: influence of the Agulhas Current ?
Agulhas Current:
- Velocities up to 2 m.s-1
- 70 Sverdrups.
- Sources: South-Western Indian Ocean.image source: J. Lutjeharms, 2006.
SAfE strategy:
- Parent model which resolves both the Agulhas (from its sources to the spawning of Agulhas Rings) and the Benguela.
- Coastal zooms depending on the scientific interest.
Large region: intermediate resolution (20-25 km) for the parent model.
easy to test new ideas or parameters
¼o resolution (i.e. 20-25 km)
244 X 192 X 32 grid points
Bottom topography: GEBCO
Boundary conditions (climatology run): WOA 2001
Surface forcing (climatology run): COADS
SAfE parent configuration
SAfEAVISO
Annual mean SSH [cm]:
RMS SSH [cm]:
Upstream of the Agulhas Retroflection: - spurious recirculation. - spurious high level of variability.
AVISO SAfE
Problem: High variability upstream of the Agulhas Retroflection.
Surface layer eddy kinetic energy [log (m2/s2)] (adapted from Wallcraft et al., 2002).
NLOM: Global layered ocean model at 1/32°resolution (Wallcraft et al., 2003).
Wallcraft, A. J., Hurlburt, H. E., Rhodes, R. C. and J. F. Shriver, 1/32o global ocean modeling and prediction, Intern. report, 2002.
Wallcraft, A. J., Kara, A. B., Hurlburt, H. E. and P. A. Rochford, The NRL Layered Global Ocean Model(NLOM) with an embedded
mixed layer submodel: formulation and tuning, J. Atmos. Ocean. Tech., 2003, 20, 1601-1615.
1/16° NLOM (1980-1989) 1/32° NLOM (1980-1989)
Topex/Poseidon (1993-2001)
POP: Global z-coordinate ocean model at 1/10°resolution (Maltrud and McClean, 2005).
Maltrud, M. E. and J. L. McClean, An eddy resolving 1/10o ocean simulation, Ocean Modelling, 2005, 8, 31-34.
Surface height variability [cm] (adapted from Maltrud and McClean, 2005).
1/10° POP (1991- 1993) 0.28° POP (1995- 1996) TOPEX/ERS (1993- 1997)
OFES: Global z-coordinate ocean model at 1/10°resolution (Sasaki et al., 2005).
Figures adapted from Sasaki et al., 2005.
Sasaki, H., Komori, N., Takahashi, K., Masumoto, Y. and H. Sakuma, Fifty years Time-integration of Global Eddy-
resolving Simulation, Intern. Report, 2005.
RMS SSH [cm] (years 46 - 50) mean SSH [cm]
Snapshot of sea surface height
[cm] and velocity vectors at 100m.
RMS sea surface elevation [cm]:
SAfE – Smagorinsky
(a=0.1)
SAfE– Smagorinsky
(a=0.05)
SAfE – Smagorinsky
(a=0.025)
SAfE – Smagorinsky
(a=0.0125)
SAfEAVISO
Smoother topography +
Parametrisation of shear induced horizontal turbulent mixing (Smagorinski, 1963):
New SAfE simulations
Final SAfE climatology experiment:
Penven, P., J. Lutjeharms and P. Florenchie, Madagascar: a pacemaker for the Agulhas Current system ? Geophys. Res. Lett., 2006, 33, L17609, doi:10.1029/2006GL026854.
image source: J. Lutjeharms, 2006.
SAfE annual mean transport (1500m - surface)
Madagascar: a pacemaker for the Agulhas Current System ?
Penven, P., J. Lutjeharms and P. Florenchie, Madagascar: a pacemaker for the Agulhas Current system ? Geophys. Res. Lett., 2006, 33, L17609, doi:10.1029/2006GL026854.
SAfE Inter-annual simulation Boundary conditions: SODA (Carton et al., 2005)
Surface forcing: NCEP/NCAR (bulk formula).
Time period: 1958-2001 (+ 2 years spin-up).
SST [oC] in St Helena Bay [33oS-31oS; 17oE-19oE]:
1 - Annual mean:
SAfE ~ SODA: 17.4oC (0.5 higher than OI-SST).
2 - Seasonal cycle:
SAfE: winter warm bias (no summer bias).
3 - Non seasonal anomalies:
RMS(OI-SST - SODA) = 0.56oC
RMS(OI-SST - SAfE) = 0.45oC
Correlation Coefficients:
OI-SST/SODA: 0.62; OI-SST/SAfE: 0.58
4 - Annual anomalies:
RMS(OI-SST - SODA) = 0.29oC
RMS(OI-SST - SAfE) = 0.2oC
Correlation Coefficients:
OI-SST/SODA: 0.61; OI-SST/SAfE: 0.65
SODA
SAfE
OI-SST
Without data assimilation, in the Benguela, SAfE perform at least as well as SODA.
Nested model for the Agulhas Bank (N. Chang, UCT PhD student)
• Zoom in SAfE.
• Resolution: 1/12o (i.e. ~ 8 km).
• Analysis of the dynamics of the
cool ridge, the seasonal cycle, the
effects of the wind.
Nested model for the West Coast (J. Veitch, UCT PhD student)
• Zoom in SAfE.
• Resolution: 1/12o (i.e. ~ 8 km).
• Comparisons between the South
Benguela (seasonal upwelling) and
the North Benguela (perennial
upwelling).
Biological application (collaboration with V. Kone & E. Machu, IRD)
Conclusion
• ROMS: • Generic and robust regional oceanic model.
• ROMSTOOLS:
• Systematic approach.
• Climatological, long term inter-annual and quasi real time
applications.
• SAfE:
• Spurious recirculation upstream of the Agulhas Retroflection.
• Role of Madagascar.
• Dynamics of the cool ridge.
• Dynamics of the Benguela upwelling system.
• Applications to fisheries.