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Model sensitivity experiments on data assimilation, downscaling and tides for the representation of the Cape São Tomé Eddies

  • Rafael SantanaEmail author
  • Filipe B. Costa
  • Davi Mignac
  • Alex N. Santana
  • Vitor F. da S. Vidal
  • Jiang Zhu
  • Clemente A. S. Tanajura
Article
Part of the following topical collections:
  1. Topical Collection on the 10th International Workshop on Modeling the Ocean (IWMO), Santos, Brazil, 25-28 June 2018

Abstract

The impacts of data assimilation, downscaling, and tidal forcing were investigated with focus on the representation of the Cape São Tomé Eddy (CSTE). Sea level anomaly (SLA), sea surface temperature (SST), and temperature and salinity (TS) profiles were assimilated into a HYCOM nested grid system composed by three grids with horizontal resolutions from 1/4° to 1/24°. Tides were included in the highest resolution domain, which covers the Brazil Current (BC) northern region. Sensitivity experiments were conducted using the high-resolution domain when each observation type was assimilated alone and all together. In addition, the non-tidal and mid-resolution (1/12°) assimilative models were used in the comparison to evaluate the impacts of tides and downscaling. All assimilated observations positively contributed to reducing the temperature errors in the upper 500 m. However, the salinity was degraded in these depths by the assimilation of SST and SLA alone. Assimilation of all observations together decreased T and S errors by 34% and 17%, respectively, as well as raised (and reduced) in 77% (60%) the correlation (deviation) of SLA (SST) between remotely sensed observations when compared to the control run without assimilation. Six observed eddies were objectively compared against the simulated eddies using an eddy tracking algorithm. Downscaling to the higher resolution model was crucial to better represent the observed eddies, as well to increase the simulated energetic levels in the studied region. The inclusion of tides improved the turbulent kinetic energy levels and the CSTE SLA amplitude simulation. SLA data assimilation is of utmost importance for the representation of the CSTE. However, the assimilation of SST and mostly TS was also relevant for correcting the thermohaline field and enabling the correct eddy translation. Finally, possible mechanisms were discussed to explain the CSTE northward migration, against the BC main flow.

Keywords

Cape São Tomé Eddy Data assimilation Tides Downscaling 

Notes

Acknowledgments

We thank Steve Penny for the advice to include the HYCOM 1/12° simulation in the analysis and for the general comments that helped improve the research quality. Thanks are also extended to the anonymous reviewers for their extensive suggestions that strengthened the analyses and writing.

Funding information

This work received financial support from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the research grant (446528/2014-5). This work was also supported by PETROBRAS and the Brazilian oil regulatory agency ANP (Agência Nacional de Petróleo, Gás Natural e Biocombustíveis), within the special participation research project Oceanographic Modeling and Observation Network (REMO).

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Oceanographic Modeling and Observation Network (REMO)Federal University of BahiaSalvadorBrazil
  2. 2.Physics Institute, Federal University of BahiaSalvadorBrazil
  3. 3.Department of Meteorology, University of ReadingReadingUK
  4. 4.IUNICS, University of the BalearicPalma de MallorcaSpain
  5. 5.LAPC, Institute of Atmospheric PhysicsChinese Academy of SciencesBeijingChina

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