1. Link with CLIVAR GSOP through the CLIVAR/GODAE Global Ocean Synthesis Evaluation effort
Tony Lee, NASA JPL/CalTech
As a follow-up for the 1st workshop for ocean reanalysis product intercomparison in the fall of 2006 at ECMWF, a 2nd workshop was held in the fall of 2007 at MIT.
More focused analysis and intercomparison: (1) Atlantic Meridional Overturning Circulation (AMOC); (2) water-mass characteristics.
Synthesis application: global sea level.
Status of coupled approach.
Uncertainty in surface fluxes.
Data errors.
Error covariance.

2. Comparison of Atlantic Meridional Overturning Circulation (MOC) for 7 assimilation products
Tony Lee, NASA JPL/CalTech
Thank the following groups for providing MOC fields:
ECCO (MIT/AER, U. Hamburg/G-ECCO, & JPL), K-7, Mercator, & ECMWF
Picture from

3. Maximum strength of Atlantic MOC at 25N
from the ECMWF meeting in 2006, plot generated by Armin Koehl
Bryden et al. (2005)

4. MOC strength at 900 m (near the depth of MAX MOC strength)

5. Seasonal & non-seasonal MOC at 900 m

6. Also presented a decomposition of AMOC into 3 dynamical components that are directly related to observations of density, sea level, and wind stress. Will not discuss here.
See the following references for more info: Lee & Marotzke (1998), Baehr, Hirschi, Beismann, & Marotzke (2004), Cabanes, Lee, & Fu (2007).

7. Summary statistics for MOC strength at 900 m
Black column: r.m.s. difference of MOC anomaly among products
Red column: r.m.s. difference of time-mean MOC among products
Blue column: r.m.s. variability of MOC itself, averaged over 6 products
(Unit: Sv)
26N
48N
Total
1.02, 2.57, 2.50
0.72, 2.15, 2.29
Seasonal
0.53
0.37
Non-seasonal
0.87
0.62

8. Summary Take home messages:
Good consistency for the temporal variability of 900-m MOC strength at 26N (48N) for the 7 products.
The r.m.s. difference among the products (overall <= 1 Sv) is smaller than the variability of the MOC itself (~ 2.5 Sv).
The consistency is better for seasonal (<= 0.5 Sv) than for non-seasonal anomalies.
The consistency of the time mean is much poorer than that for the anomaly.
Take home messages:
Uncertainty of observational estimates need to be smaller than 1 Sv to effectively constrain/distinguish these products.
Need to understand why these products agree so well in estimated MOC variability?
Hypothesis - consistency in wind forcing
Cabanes, Lee, and Fu (2008): interannual variability of AMOC in subtropical North Atlantic is largely controlled by Ekman pumping near the western boundary; most wind products consistently show much larger Ekman pumping near the western boundary.