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The relationship between MVT & MHT of AMOC:

The relationship between MVT & MHT of AMOC: a comparison between observations & ocean state estimation products Tong Lee, Jet Propulsion Laboratory Bill Johns, University of Miami. Picture from http://www.noc.soton.ac.uk. MVT: Meridional Volume Transport MHT: Meridional Heat Transport.

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The relationship between MVT & MHT of AMOC:

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  1. The relationship between MVT & MHT of AMOC: a comparison between observations & ocean state estimation products Tong Lee, Jet Propulsion Laboratory Bill Johns, University of Miami Picture from http://www.noc.soton.ac.uk MVT: Meridional Volume Transport MHT: Meridional Heat Transport

  2. Motivation • Trans-oceanic arrays such as RAPID/MOCHA are designed to monitor MVT. • MHT is more climate relevant but more difficult to measure. • MVT-MHT empirical relation (linear regression) was inferred from RAPID-MOCHA & auxiliary data (Baringer et al. 2010). • Comparison with ocean state estimation (OSE) products. Coordination with GFDL & NCAR for similar analysis. Related to Monday’s talk by Rym Msadek.

  3. OSE products used for comparison • ECCO-JPL (1993-present) • Near-global, 1°x(0.3°x1°), 46 levels, MITgcm. • Prior NCEP forcing. • Assimilates anomalies of SSH and vertical T profiles. • ECCO2 (1993-2008) • Global, 18x18 km, 50 levels, MITgcm cubed-sphere. • Prior ECMWF analysis forcing. • Assimilate observed SSH anomaly and T/S profiles. • GECCO (1950-2000) • Near global, 1°x1°, 23 levels, MITgcm • Prior NCEP forcing • Assimilate a large suite of data

  4. Time mean for Apr. 2004- Sept. 2007 at 26.5N: MVT (max MOC): RAPID (18.5 Sv), ECCO-JPL (15.8), ECCO2 (17.9) MHT: RAPID (1.3 PW), ECCO-JPL (0.9), ECCO2 (1.0) MVT anomaly

  5. Comparison of averaged seasonal MVT anomaly

  6. Comparison of MVT-MHT linear regression & correlation Slope: change of MHT per unit MVT Intercept: physical meaning problematic Larger scatter due to eddies?

  7. Little dependence of MVT-MHT relation on time period (GECCO)

  8. Relatively large dependence of MVT-MHT relation on time scale MHT MVT MHT Smaller slope for longer time scales: geostrophic shear flow advecting smaller vertical T gradient (than Ekman)

  9. Dependence of MVT-MHT relation on latitude: Relatively high regression & correlation coeff. in subtropics & 15N due to dominant overturning contribution & minor gyre contribution

  10. Summary • Time mean MVT and MHT in 3 ECCO products are some what too weak • Seasonal variation reasonably well reproduced. • MVT-MHT regression slope and correlation: • Low-resolution model closer to RAPID/MOCHA estimate; effect of eddies? • Little variation in different decades. • Relatively large dependence on time scales (monthly from interannual). • Subtropical N. & S. Alt. and near 15N have relatively large regression and correlation coefficients between MVT & MHT. • STILL NEED TO UNDERSTAND HOW MVT & MHT ARE FORCED DIFFERENTLY, ESP. ON LONGER TIME SCALES!

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