AOML
NOAA

SAMOC Altimetry

Draft - Work in Progress

Methods

Version 1

The methodology for version 1 can be found in Dong et al. (2015). A short description is given here:

A. Contruction of full depth T-S profiles

Hydrographic data and satellite altimeter measurements indicate that the isothermal depths and sea height anomalies (SHA) are significantly correlated in the subtropical South Atlantic. Those correlations allow to derive temperature profiles from SHA, referred to as synthetic temperature profiles. Salinity profile for each synathethic temperature profile is drived using statistical relationship between temperature and salinity. The T-S relationship is based on Thacker (2008).

Full depth temperature/salinity profiles are contructed through a combination of synthetic profiles, motnhly climatologies from Argo floats and world ocean atlas 2013 (WOA13): synthetic temperature profiles are used for upper 800m water column, monthly climatologies from Argo are used from 800m to 2000m depth, the profiles are completed by adding WOA13 below 2000m depth. Synthetic temperature and salinty sections are contructed along 4 latitudes: 20°S, 25°S, 30°S and 34.5°S.

B. Computation of geostrohpic and Ekman transports

Geostrophic velocity is computed for each section from geostrophy with a reference velocity at 1000 m depth from Argo drifting velocity. These reference velocities are constant in time due to the limited available data. Geostrophic velocity is adjust to satisfy zero mass transport across the section.

The zonal wind stress from the NCEP/NCAR Reanalysis is used to compute the Ekman transport.

C. Estimates of the Meridional Overturning Circulation (MOC)

The strength of the MOC is estimated as the maximum northward transport in the upper ocean: sum of transport from surface to the depth where the flow reversed from northward to southward.

Version 2

The only difference from version 1 is that the salinity profiles are derived from a newly developed T-S relationship (Goes et al. 2016).

References

Dong, S ., G. Goni , and F. Bringas (2015): Temporal variability of the Meridional Overturning Circulation in the South Atlantic between 20S and 35S. Geophys. Res. Lett., 42, 7655-7662, (doi:10.1002/2015GL065603).