Use of recent geoid models to estimate mean dynamic topography and geostrophic currents in South Atlantic and Brazil Malvinas confluence

The use of geoid models to estimate the Mean Dynamic Topography was stimulated with the launching of the GRACE satellite system, since its models present unprecedented precision and space-time resolution. In the present study, besides the DNSC08 mean sea level model, the following geoid models were used with the objective of computing the MDTs: EGM96, EIGEN-5C and EGM2008. In the method adopted, geostrophic currents for the South Atlantic were computed based on the MDTs. In this study it was found that the degree and order of the geoid models affect the determination of TDM and currents directly. The presence of noise in the MDT requires the use of efficient filtering techniques, such as the filter based on Singular Spectrum Analysis, which presents significant advantages in relation to conventional filters. Geostrophic currents resulting from geoid models were compared with the HYCOM hydrodynamic numerical model. In conclusion, results show that MDTs and respective geostrophic currents calculated with EIGEN-5C and EGM2008 models are similar to the results of the numerical model, especially regarding the main large scale features such as boundary currents and the retroflection at the Brazil-Malvinas Confluence.

Use of recent geoid models to estimate mean dynamic topography and geostrophic currents in South Atlantic and Brazil Malvinas confluence

The use of geoid models to estimate the Mean Dynamic Topography was stimulated with the launching of the GRACE satellite system, since its models present unprecedented precision and space-time resolution. In the present study, besides the DNSC08 mean sea level model, the following geoid models were used with the objective of computing the MDTs: EGM96, EIGEN-5C and EGM2008. In the method adopted, geostrophic currents for the South Atlantic were computed based on the MDTs. In this study it was found that the degree and order of the geoid models affect the determination of TDM and currents directly. The presence of noise in the MDT requires the use of efficient filtering techniques, such as the filter based on Singular Spectrum Analysis, which presents significant advantages in relation to conventional filters. Geostrophic currents resulting from geoid models were compared with the HYCOM hydrodynamic numerical model. In conclusion, results show that MDTs and respective geostrophic currents calculated with EIGEN-5C and EGM2008 models are similar to the results of the numerical model, especially regarding the main large scale features such as boundary currents and the retroflection at the Brazil-Malvinas Confluence.

Decadal Variabilities and Trends in the Southwest Atlantic in a model forced with NCEP Reanalysis from 1960 to 2012

Analysis of the NCAR/NCEP Reanalysis show changes in the atmospheric circulation in the Southern hemisphere, with a strengthening and poleward displacement of the westerlies. Because the wind is one of the main sources of the ocean's kinetic energy, a numerical experiment with the Hybrid Coordinate Ocean Model (HYCOM) was forced with monthly means of the NCAR/NCEP Reanalysis products to investigate the effects of the changes in the wind on the ocean circulation in a geographical domain defined by 98W – 114E; 65S – 60N. The results show good agreement with other models and with available satellite data. In the western sector of the South Atlantic there are several indications of changes such as a poleward displacement of the Brazil-Malvinas Confluence and positive trends in temperature and salinity of the southwestern region of the subtropical gyre

Decadal Variabilities and Trends in the Southwest Atlantic in a model forced with NCEP Reanalysis from 1960 to 2012

Analysis of the NCAR/NCEP Reanalysis show changes in the atmospheric circulation in the Southern hemisphere, with a strengthening and poleward displacement of the westerlies. Because the wind is one of the main sources of the ocean's kinetic energy, a numerical experiment with the Hybrid Coordinate Ocean Model (HYCOM) was forced with monthly means of the NCAR/NCEP Reanalysis products to investigate the effects of the changes in the wind on the ocean circulation in a geographical domain defined by 98W – 114E; 65S – 60N. The results show good agreement with other models and with available satellite data. In the western sector of the South Atlantic there are several indications of changes such as a poleward displacement of the Brazil-Malvinas Confluence and positive trends in temperature and salinity of the southwestern region of the subtropical gyre.