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Climate Dynamics

, Volume 51, Issue 9–10, pp 3251–3273 | Cite as

Decadal change of the south Atlantic ocean Angola–Benguela frontal zone since 1980

  • Edward K. VizyEmail author
  • Kerry H. Cook
  • Xiaoming Sun
Article

Abstract

High-resolution simulations with a regional atmospheric model coupled to an intermediate-level mixed layer ocean model along with multiple atmospheric and oceanic reanalyses are analyzed to understand how and why the Angola–Benguela frontal Zone (ABFZ) has changed since 1980. A southward shift of 0.05°–0.55° latitude decade−1 in the annual mean ABFZ position accompanied by an intensification of + 0.05 to + 0.13 K/100-km decade−1 has occurred as ocean mixed layer temperatures have warmed (cooled) equatorward (poleward) of the front over the 1980–2014 period. These changes are captured in a 35-year model integration. The oceanic warming north of the ABFZ is associated with a weakening of vertical entrainment, reduced cooling associated with vertical diffusion, and a deepening of the mixed layer along the Angola coast. These changes coincide with a steady weakening of the onshore atmospheric flow as the zonal pressure gradient between the eastern equatorial Atlantic and the Congo Basin weakens. Oceanic cooling poleward of the ABFZ is primarily due to enhanced advection of cooler water from the south and east, increased cooling by vertical diffusion, and shoaling of the mixed layer depth. In the atmosphere, these changes are related to an intensification and poleward shift of the South Atlantic sub-tropical anticyclone as surface winds, hence the westward mixed layer ocean currents, intensify in the Benguela upwelling region along the Namibian coast. With a few caveats, these findings demonstrate that air/sea interactions play a prominent role in influencing the observed decadal variability of the ABFZ over the southeastern Atlantic since 1980.

Keywords

Angola–Benguela frontal zone Air–sea interactions South Atlantic sub-tropical high Ocean mixed-layer Benguela upwelling region Angola South Atlantic climate variability Coupled regional climate model 

Notes

Acknowledgements

This research was supported by award NNX13AQ76G from NASA’s Physical Oceanography Program. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NASA. The Texas Advanced Computing Center (TACC) at the University of Texas at Austin provided the high performance computing and database resources. We also gratefully acknowledge the Climate Prediction Division of the Japan Meteorological Agency for the dissemination of JRA-55. ECMWF ERA-Interim data used in this study were obtained from the ECMWF data server.

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© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Geological SciencesJackson School of Geosciences, The University of Texas at AustinAustinUSA

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