CoAuthors

Sabine Arnault (LOCEAN, IRD, Paris, France)

The intra-annual variability of the tropical Atlantic Ocean is investigated with satellite altimetry Absolute Dynamic Topography data. Three regions of high variability are found. The first region, between 3°N and 11°N, is characterized by the presence of westward propagating eddies linked to the North Equatorial Counter Current (NECC) retroflection in the vicinity of the Brazilian coast. In the second region, we observed the presence of westward propagating instability waves centered at 5°N between 30°W and 10°W. The third region, around the Equator, is characterized by the presence of eastward propagating Kelvin waves at the Equator, and westward propagating Rossby waves centered at 5°S and 5°N.
The eddies linked to the NECC show a strong annual cycle: their number varies from ~4 per year in October to ~9 per year in March. The more powerful eddies occur in October around 40°W. Their diameter varies from 5° of longitude at 40°W to 2.5° at 60°W, and their speed is 18 cm/s. The instability waves also shows a strong seasonal cycle with maximum amplitude around August. They are generated by meridional winds at the African coast and by zonal winds at the Equator.
The Kelvin waves at the Equator are generated by zonal wind anomalies at the Equator at 30°W with a 2.6 weeks delay, and their speed is 175 cm/s (2nd order baroclinic). The speed of the Rossby waves is 50 cm/s at 5°N, and 49 cm/s at 5°S.