Ocean Dynamics

, Volume 64, Issue 8, pp 1121–1136 | Cite as

Assimilating along-track SLA data using the EnOI in an eddy resolving model of the Agulhas system

  • Björn C. Backeberg
  • François Counillon
  • Johnny A. Johannessen
  • Marie–Isabelle Pujol
Article
Part of the following topical collections:
  1. Topical Collection on the 5th International Workshop on Modelling the Ocean (IWMO) in Bergen, Norway 17-20 June 2013

Abstract

The greater Agulhas Current is one of the most energetic current systems in the global ocean. It plays a fundamental role in determining the mean state and variability of the regional marine environment, affecting its resources and ecosystem, the regional weather and the global climate on a broad range of temporal and spatial scales. In the absence of a coherent in-situ and satellite-based observing system in the region, modelling and data assimilation techniques play a crucial role in both furthering the quantitative understanding and providing better forecasts of this complicated western boundary current system. In this study, we use a regional implementation of the Hybrid Coordinate Ocean Model and assimilate along-track satellite sea level anomaly (SLA) data using the Ensemble Optimal Interpolation (EnOI) data assimilation scheme. This study lays the foundation towards the development of a regional prediction system for the greater Agulhas Current system. Comparisons to independent in-situ drifter observations show that data assimilation reduces the error compared to a free model run over a 2-year period. Mesoscale features are placed in more consistent agreement with the drifter trajectories and surface velocity errors are reduced. While the model-based forecasts of surface velocities are not as accurate as persistence forecasts derived from satellite altimeter observations, the error calculated from the drifter measurements for eddy kinetic energy is significantly lower in the assimilation system compared to the persistence forecast. While the assimilation of along-track SLA data introduces a small bias in sea surface temperatures, the representation of water mass properties and deep current velocities in the Agulhas system is improved.

Keywords

Agulhas current Data assimilaiton Hybrid coordinate Ocean model Ensemble optimal interpolation Along–track sea level anomaly 

Notes

Acknowledgments

This work has been jointly supported by the Nansen-Tutu Centre for Marine Environmental Research, Cape Town, South Africa, the South African National Research Foundation through the Grant 87698, the Nansen Environmental and Remote Sensing Center, Bergen, Norway, and through the EU FP7 Marie Curie International Research Staff Exchange Scheme (IRSES) Fellowship SOCCLI “The role of Southern Ocean Carbon cycle under CLImate change”, which received funding from the European Commission’s Seventh Framework Programme under grant agreement number 317699. This work has also received a grant for computer time from the Norwegian Program for supercomputing (NOTUR project number nn2993k). The altimeter products used in this study was produced by Ssalto/Duacs and distributed by Aviso, with the support from CNES (http://www.aviso.oceanobs.com/duacs/), and the surface drifter data were made available through the Data Assembly Center of the NOAA AOML Physical Oceanography Division. The Argo data were collected and made freely available by the Coriolis project and programmes that contribute to it (http://www.coriolis.eu.org).

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Björn C. Backeberg
    • 1
  • François Counillon
    • 2
  • Johnny A. Johannessen
    • 2
  • Marie–Isabelle Pujol
    • 3
  1. 1.Nansen-Tutu Centre for Marine Environmental Research, Department of OceanographyMarine Research Institute, University of Cape TownCape TownSouth Africa
  2. 2.Nansen Environmental and Remote Sensing CenterBergenNorway
  3. 3.Collecte Localisation Satellites (CLS)Ramonville Saint-AgneFrance

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