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					Towards eddy permitting estimates of the global-ocean and sea-ice circulations
Presenter: Dimitris Menemenlis (JPL/Caltech) Collaborators: A. Adcroft, J.-M. Campin, P. Heimbach, C. Hill, J. Marshall, and C. Wunsch (MIT) B. Cheng, I. Fukumori, T. Lee, B. Tang, and O. Wang (JPL/Caltech) M. Steele and J. Zhang (APL/UW) C. Henze and J. Taft (NAS/AMES) Web site: http://ecco.jpl.nasa.gov/cube_sphere Computing resources: NASA’s Project Columbia

The ECCO project: Ocean state estimation
based on a state-of-the-art general circulation model (the MIT GCM), a vast complement of observations (altimeter, scatterometer, SST, XBT, hydrographic sections, PALACE/ARGO, drifter, SSS, surface fluxes, etc.), and rigorous assimilation methods (Green’s functions, Kalman filter/RTS smoother, and adjoint-model).

•ECCO results and applications:
•Over 60 publications have originated from ECCO (http://www.ecco-group.org/publications.html): •- ocean circulation, e.g., Gebbie et al. (2004), •- ocean biogeochemical/carbon cycle, e.g., McKinley et al. (2004), •- air-sea fluxes, e.g., Stammer et al. (2004), •- subgridscale parameterizations, e.g., Ferreira et al. (2004), •- earth rotation and polar motion, e.g., Gross et al. (2004), •- etc.

ASOR: Arctic Sea ice – Ocean Reanalysis
Co-I’s: Ron Lindsay, Drew Rothrock, Axel Schweiger, Jinlun Zhang Dimitris Menemenlis (JPL)
(a) Model only
ice velocity: Jan 1, 1993

PI: Michael Steele (Univ. of

WA)
(Univ. of WA)

(b) Observations

(a) + (b)

Assimilation:

(a) reduces bias (b) increases correlation
…with respect to: * submarine ice thickness obs. * independent ice velocity obs.
J. Zhang et al., J. Geophys. Res., 108(C6), 2003.

New thrusts for 2004 – 2006:  Assimilation of ice concentration
& SST

 Validation of model surface temperatures (SST/IST)
 Rigorous estimation: adjoint model & Green functions

Recent advances that bring rigorous eddypermitting estimates of the global ocean and sea-ice circulations within reach:
1. the configuration of an efficient eddy-permitting global-ocean and sea-ice model,
2. the demonstration that boundary conditions estimated at coarse resolution have skill when applied to an eddy-permitting model, and

3. the development and deployment of a hierarchy of methods for assimilating observations in a mathematically rigorous way.

Recent advances that bring rigorous eddypermitting estimates of the global ocean and sea-ice circulations within reach:
1. the configuration of an efficient eddy-permitting global-ocean and sea-ice model,

2. the demonstration that boundary conditions estimated at coarse resolution have skill when applied to an eddy-permitting model, and
3. the development and deployment of a hierarchy of methods for assimilating observations in a mathematically rigorous way.

Normalized components of ECCO cost function, which includes the quadratic model-data difference for various ocean and surface flux components and a measure of model drift.

NCEP high-resolution

ECCO high-resolution

NCEP low-resolution

ECCO low-resolution

Recent advances that bring rigorous eddypermitting estimates of the global ocean and sea-ice circulations within reach:
1. the configuration of an efficient eddy-permitting global-ocean and sea-ice model, 2. the demonstration that boundary conditions estimated at coarse resolution have skill when applied to an eddy-permitting model, and

3. the development and deployment of a hierarchy of methods for assimilating observations in a mathematically rigorous way.

Green’s Function Approach
The Green function approach involves the computation of GCM sensitivity experiments followed by a recipe for constructing a solution that is the best linear combination of these sensitivity experiments.

Effective sea-ice thickness (m) around Antarctica on August 1996 for six sensitivity experiments.

(Menemenlis et al., 2005)

Coarse grid configuration for Agulha cell.

Partitioned Kalman Filter & Smoother
The state error covariance matrix is approximated by a sum of smaller independent elements that are evaluated separately.
Amplitude of 1st baroclinic displacement after a 3-day integration.

(Fukumori, 2002)

1992-2001 WOCE synthesis.

Adjoint-model method

The adjoint model is used to produce the partial derivatives of a cost function with respect to control parameters, which permits a relatively rapid optimization.

Mean and standard deviation of adjustment in net surface heat (top) and freshwater (bottom) fluxes.

(Stammer et al., 2003, 2004)

Concluding Remarks
Key ingredients for eddy-permitting estimates of global-ocean and seaice circulations are now in place. This includes the computational and modelling infrastructure as well as a range of rigorous estimation methodologies. The focus of ocean state estimation during the past five years has been to demonstrate the feasibility and utility of rigorous, sustained estimates, with considerable success for upper-ocean and for equatorial processes. The scientific challenges during the next five years, e.g., ocean carbon cycle, polar-subpolar interactions, time-evolving term balances within and between different components of the Earth system, require much improved accuracy in the estimation of water mass formation and transformation rates, mixed layer depths, and high-latitude ocean and sea-ice processes.

Simulated and observed Arctic Ocean mass change

cm of seawater

Year


				
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