XBT Products - Tropical Atlantic Currents

XBT temperature profiles combined with Argo absolute dynamic height at 800m depth, salinity from historical T-S relationships are used to produce volume transport, latitudinal location and maximum speed for the Atlantic off-equatorial currents, i.e., North Equatorial Countercurrent (NECC), North Equatorial Undercurrent (NEUC) and the South Equatorial Undercurrent (SEUC).

Altimetric sea level anomalies are combined with the in situ observations to derive synthetic estimates of the NECC Transport, Location, and Maximum velocity since 1993. This approach will be extended for the NEUC and SEUC in the near future.

AX08 XBT transect

The AX08 XBT transect crosses the Atlantic from Cape Town to New York four times a year since 2000. Approximately 300 XBTs are deployed during each transect realization.

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Definition of latitudinal bands of the off-equatorial currents

The currents were defined in certain latitudinal and depth bands:

  • NECC - between 3°N-10°N from the surface to σθ = 24.5
  • NEUC - between 3°N-6°N from σθ = 24.5 to σθ = 26.8
  • SEUC - between 3°S-6°S from σθ = 24.5 to σθ = 26.8

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NECC

Transport

(top) XBT-derived NECC Transport (red diamonds) overlaid on the synthetic NECC Transport (blue line) during 1993-2010. (middle) Synthetic NECC Transport residuals (seasonal cycle removed) during 1993-2010. (bottom) Monthly average synthetic NECC Transport during 1993-2010.


Location

(top) XBT-derived NECC Location (red diamonds) overlaid on the synthetic NECC Location (blue line) during 1993-2010. (middle) Synthetic NECC Location residuals (seasonal cycle removed) during 1993-2010. (bottom) Monthly average synthetic NECC Location during 1993-2010.


Maximum Velocity

(top) XBT-derived NECC maximum velocity (red diamonds) overlaid on the synthetic NECC maximum velocity (blue line) during 1993-2010. (middle) Synthetic NECC maximum velocity residuals (seasonal cycle removed) during 1993-2010. (bottom) Monthly average synthetic NECC maximum velocity during 1993-2010.


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NEUC

(top) XBT-derived NEUC Transport during 2001-2012. (middle) XBT-derived NEUC Location during 2001-2012. (bottom) XBT-derived NEUC Maximum velocity during 2001-2012.

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SEUC

(top) XBT-derived SEUC Transport during 2001-2012. (middle) XBT-derived SEUC Location during 2001-2012. (bottom) XBT-derived SEUC Maximum velocity during 2001-2012.

These products are updated on a yearly basis.

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References

Goes, M., G. Goni, V. Hormann, R. C. Perez: Variability of the Atlantic off-equatorial eastward currents during 1993-2010 using a synthetic method, accepted at J. Geophys. Res.-Oceans, doi: 10.1002/jgrc.20186.

Goni, G.J., and M.O. Baringer, 2002: Surface currents in the tropical Atlantic across high density XBT line AX08. Geophys. Res. Lett., 9(24):2218 ,doi:10.1029/2002GL015873 [PDF]

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