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. In this study, assimilation of Jason-1 and Jason-2 along-track sea level anomaly (SLA) data was conducted in a region of the tropical and South Atlantic (7◦N-36◦S, 20◦W up to the Brazilian coast) using an optimal interpolation method and the HYCOM (Hybrid Coordinate Ocean Model). Four 24 h-forecast experiments were performed daily from January 1 until March 31, 2011 considering different SLA assimilation data windows (1 day and 2 days) and different coefficients in the parameterization of the SLA covariance matrix model. The model horizontal resolution was 1/12◦ and the number of vertical layers was 21. The SLA analyses added to the mean sea surface height were projected to the subsurface with the Cooper & Haines (1996) scheme. The results showed that the experiment with 2-day window of along-track data and with specific parameterizations of the model SLA covariance error for sub-regions of the METAREA V was the most accurate. It completely reconstructed the model sea surface height and important improvements in the circulation were produced. For instance, there was a substantial improvement in the representation of the Brazil Current and North Brazil Undercurrent. However, since no assimilation of vertical profiles of temperature and salinity and of sea surface temperature was performed, the methodology employed here should be considered only as a step towards a high quality analysis for operational forecasting systems. Keywords : data assimilation, optimal interpolation, Cooper & Haines scheme, altimetry data. RESUMO . Neste estudo, a assimilacao de dados de anomalia da altura da superficie do mar (AASM) ao longo da trilha dos satelites Jason-1 e Jason-2 foi conduzida em uma regiao do Atlântico tropical e Sul (7◦N-36◦S, 20◦W ate a costa do Brasil) com o metodo de interpolacao otima e o modelo oceânico HYCOM (Hybrid Coordinate Ocean Model). Foram realizados quatro experimentos de previsao de 24 h entre 1 de janeiro e 31 de marco de 2011, considerando diferentes janelas de assimilacao de AASM (1 dia e 2 dias) e diferentes coeficientes na parametrizacao da matriz de covariância dos erros de AASM do modelo. A resolucao horizontal empregada no HYCOM foi 1/12◦ para 21 camadas verticais. As correcoes de altura da superficie do mar devido a assimilacao de AASM foram projetadas abaixo da camada de mistura atraves da tecnica de Cooper & Haines (1996). Os resultados mostraram que o experimento com assimilacao de dados ao longo da trilha dos satelites com a janela de 2 dias e com parametrizacoes da matriz de covariância especificas para sub-regioes da METAREA V foi o mais acurado. Ele reconstruiu completamente a altura da superficie do mar e tambem proporcionou melhorias na circulacao oceânica reproduzida pelo modelo. Por exemplo, houve substancial melhoria da representacao nos campos da Corrente do Brasil e Subcorrente Norte do Brasil. Entretanto, tendo em vista que nao foi realizada a assimilacao de perfis verticais de temperatura e de salinidade e da temperatura da superficie do mar, a metodologia apresentada deve ser considerada apenas como um passo na conquista de uma analise oceânica e de um sistema previsor de qualidade para fins operacionais. Palavras-chave: assimilacao de dados, interpolacao otima, tecnica de Cooper & Haines, dados de altimetria.

brazilian journal of geophysics

A STUDY OF THE IMPACT OF ALTIMETRY DATA ASSIMILATION ON SHORT-TERM PREDICTABILITY OF THE HYCOM OCEAN MODEL IN REGIONS OF THE TROPICAL AND SOUTH ATLANTIC OCEAN