AOML
NOAA

Argo & Altimetry

Methods

Transports of the Atlantic Meridional Overturning Circulation
from Argo and Altimetry

Methods


Deriving fields of horizontal velocity

Details on the methodology can be found in Schmid (2014) and Majumder et al. (2016).

1. Generating synthetic dynamic height profiles

Temperature and salinity profiles from Argo floats are used to derive dynamic height profiles.

The relationship between sea surface height and in situ dynamic height is used to generate synthetic dynamic height profiles on a regular grid.

2. Computation of velocity

Geostrophic velocity is computed for each section from the synthetic dynamic height profiles. The reference velocity is derived from the climatological subsurface velocity derived from Argo and other float trajectories.

The wind stress from various wind products (NCEP/NCAR Reanalysis II, ERA interim) are used to compute the Ekman velocities and transport.

3. Estimates of the Meridional Overturning Circulation (MOC)

The strength of the Meridional Overturning Circulation is estimated as the northward transport in the upper ocean assuming mass balance while allowing for a Bering Strait throughflow.

The meridional heat transport (MHT) and fresh water budget (MOV) assiciated with the Meridional Overturning Circulation are derived as well. Temperature, salinity and density fields needed for this are derived from Argo profiles.

Near 26° N the transport of the Florida Current is based on the cable data collected in the Florida Straits.

Gaps in the data are padded with profiles from the World Ocean Atlas to achieve basin-wide coverage from top to bottom.

4. Estimation of the transport in the Brazil Current and Benguela Current

Transport time series for the eastern and western boundaries in the subtropical South Atlantic are derived from the three-dimensional velocity field.

The methods are described in schmid and Majumder (2017) for the Brazil Current and Majumder and schmid (2017) for the Benguela Current.

References

Schmid, C. (2014): Mean vertical and horizontal structure of the subtropical circulation in the South Atlantic from three-dimensional observed velocity fields. Deep Sea Research I, 91 (9), 50-71, doi: 10.1016/j.dsr.2014.04.015 [PDF]

Majumder, S., C. Schmid, G. Halliwell (2016): An Observations and Model Based Analysis of Meridional Transports in the South Atlantic. Journal of Geophysical Research, doi: 10.1002/2016JC011693 [PDF]

Schmid, C. and S. Majumder (2017): An Observations and Model-based Analysis of the Temporal Variability of the Brazil Current. Ocean sciences, doi:10.5194/os-2017-59

Majumder, S. and Claudia Schmid (2017): A Study of the Variability of the Benguela Current. Ocean sciences, doi:10.5194/os-2017-63