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Link with CLIVAR GSOP through the CLIVAR/GODAE Global Ocean Synthesis Evaluation effort. Tony Lee, NASA JPL/CalTech. As a follow-up for the 1 st workshop for ocean reanalysis product intercomparison in the fall of 2006 at ECMWF, a 2 nd workshop was held in the fall of 2007 at MIT. - PowerPoint PPT Presentation
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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.
Comparison of Atlantic Meridional Overturning Circulation (MOC) for 7 assimilation products
Thank the following groups for providing MOC fields:
ECCO (MIT/AER, U. Hamburg/G-ECCO, & JPL), K-7, Mercator, & ECMWF
Picture from http://www.noc.soton.ac.uk
Tony Lee, NASA JPL/CalTech
Bryden et al. (2005)
Maximum strength of Atlantic MOC at 25N
from the ECMWF meeting in 2006, plot generated by Armin Koehl
MOC strength at 900 m (near the depth of MAX MOC strength)
26N 48N
Seasonal & non-seasonal MOC at 900 m
26N 48N
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).
(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
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
Summary
• 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.
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