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
Refer to Rym’s talk
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 ( )
Global, 18x18 km, 50 levels, MITgcm cubed-sphere.
Prior ECMWF analysis forcing.
Assimilate observed SSH anomaly and T/S profiles.
GECCO ( )
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
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!