Discriminating the Dynamical Nature of the Multi-Scale SSH Variability Over Three Transatlantic Sections at 11°5S, 24°S and 34.5°S

Previous analysis of the South Atlantic Meridional Overturning Circulation (SAMOC) at 34.5°S shows mechanical energy spread in scales from days to years. Our main objective is to understand what physics are associated to these variations. For that, satellite altimetry yields 25 years of precise estimates of a vertically integrated view of the internal dynamics.

Part of the height variability can be described as a general positive trend caused by heat, freshwater and mass accumulation. Part of the variance can be associated with the annual cycle, another to planetary waves, and the rest can be tentatively described as transient mesoscale turbulence. A set of zonal-temporal filters is constructed from a-priori theoretical knowledge of the constraints regarding wavelengths and periods that characterize the dispersion diagram of the phenomena above.

Near 11°S, 24°S and 34.5°S our analysis shows that:

• The inter annual signal explains 44%, 31% and 17%, respectively, with cumulative increases approximately in 1998, 2000 and 2002;
• Conversely, the transient residuals explain 17%, 28% and 56% of the variance, however 24°S and 34.5°S have larger amplitudes in the E and
  W O[1000km] borders compared to the ocean interior;
• Transient residuals are not so transient after all: in 24°S (Figure 1) and 34.5°S the clear signature of solitary, westward propagating vortices is detected with speeds
  similar to those of long baroclinic Rossby waves;
• Long baroclinic Rossby waves explain 6%, 20%, and 14%, with no difference between border and interior.

This detailed analysis allow us to show that, for example, the peak in SAMOC transport observed at 34.5°S by Meinen et al. (GRL, 2018) in 2015 that is associated to the western side bottom pressure coincides with the arrival of long Rossby waves and local eddies.