Model sensitivity experiments on data assimilation, downscaling and tides for the representation of the Cape São Tomé Eddies
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.
KeywordsCape São Tomé Eddy Data assimilation Tides Downscaling
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.
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).
- Campos EJD (2006) Equatorward translation of the Vitoria Eddy in a numerical simulation. Geophys Res Lett 33:L22607. https://doi.org/10.1029/2006GL026997
- Daher VB, Costa PRCJ (2014) Regional altimetry product to the area of interests of the oceanographic modeling and observation network (REMO). In: Revista Pesquisa Naval, Brasília - DF, n. 26, 2014, p., pp 22–33Google Scholar
- Dorfschafer GS (2017) Nova Abordagem para Estimar a Salinidade no Atlântico Sudoeste e sua Aplicação em um Experimento com Assimilação de Dados. Thesis, Universidade Federal da Bahia. Available at: http://www.pggeofisica.ufba.br/media/uploads/publicacoes/348.pdf . Accessed on 16 Nov 2018.
- Gabioux MG, Costa VS, Souza JMAC, Oliveira BF, Paiva AM (2013) Modeling the South Atlantic Ocean from medium to high-resolution. Braz J Geophys 31:229–242Google Scholar
- Intergovernmental Oceanographic Commission (IOC) (1990) GTSPP REAL-TIME Quality Control Manual. Unesco, p 128Google Scholar
- Lima LN (2018) Estudo das Incertezas na Simulação por Conjuntos e no uso da Assimilação de Dados no Oceano Atlântico Sudoeste Dissertation, Instituto Nacional de Pesquisas Espaciais. Available at: http://urlib.net/8JMKD3MGP3W34R/3QMBU45. Accessed on 16 Nov 2018.
- Lima LN, Tanajura CAS (2013) Assimilation of sea surface height anomalies into HYCOM with an optimal interpolation scheme over the Atlantic ocean METAREA V. Braz J Geophys 31(2):271–288Google Scholar
- Lima JAM, Martins RP, Tanajura CA, Paiva AM, Cirano M, Campos EJD, Soares ID, Franca GB, Obino RS, Alvarenga JBR (2013) Design and implementation of an oceanographic modeling and observation network (REMO) for operational oceanography and ocean forecasting. Braz J Geophys 31:209–228Google Scholar
- Mascarenhas AS, Miranda LB, Rock NJ (1971) A study of oceanographic conditions in the region of Cabo Frio. In: Costlow D Jr (ed) Fertility of the Sea, pp 285–308Google Scholar
- Moon I-J (2005) Impact of a coupled ocean wave-tide-circulation system on coastal modelling. Ocean Model 6:31–49Google Scholar
- Moore AM, Arango HG, Broquet G, Powell BS, Weaver AT, Zavala-Garay J (2011) The Regional Ocean Modeling System (ROMS) 4-dimensional variational data assimilation systems: Part I-System overview and formulation. Prog Oceanogr 91:34–49. https://doi.org/10.1016/j.pocean.2011.05.004 CrossRefGoogle Scholar
- Oke PR, Larnicol G, Fujii Y, Smith GC, Lea DJ, Guine-hut S, Remy E, Alonso Balmaseda M, Rykova T, Surcel-Colan D, Martin MJ, Sellar AA, Mulet S, Turpin V (2015) Assessing the impact of observations on ocean forecasts and re-analyses: Part 1, Global studies. J Oper Oceanogr 8:s49–s62. https://doi.org/10.1080/1755876X.2015.1022067 CrossRefGoogle Scholar
- Silveira ICA, Calado L, Castro BM, Cirano M, Lima JAM, Mascarenhas AS (2004) On the baroclinic structure of the Brazil Current-Intermediate Western Boundary Current system at 22°– 23°S. Geophys Res Lett 31Google Scholar
- Tanajura CAS, Mignac D, Santana AN, Costa FB, Lima LN, Belyaev K, Zhu J (2018) Observing system experiments over the Atlantic ocean with the REMO Ocean Data Assimilation System (RODAS) into HYCOM. Ocean Dyn submitted to this issueGoogle Scholar