Propagating Modes of Variability and Their Impact on the Western Boundary Current in the South Atlantic

Abstract

Studies have suggested that the South Atlantic Ocean plays an important role in modulating climate at global and regional scales and thus could serve as a potential predictor of extreme rainfall and temperature events globally. To understand how propagating modes of variability influence the circulation of the subtropical gyre and the southward flowing Brazil Current (BC) at interannual frequencies, a Complex Empirical Orthogonal Function (CEOF) analysis was performed on the satellite‐derived sea surface height (SSH). The first three CEOF modes explain about 23%, 16%, and 11% of the total interannual variability and show clear westward propagation with phase speeds comparable to that of theoretical baroclinic mode 1 Rossby waves. Results suggest that there is a change in the way energy is distributed among the modes before and after 2005. Before 2005, the SSH variability in the western boundary in the South Atlantic and the volume transport of the BC are more closely linked to the first and the second modes, while the third mode dominates after 2005. This change in energy distribution around 2005 is associated with the recent El Niño‐Southern Oscillation (ENSO) regime shift in the Pacific Ocean via atmospheric teleconnections. We found that the first CEOF mode is strongly correlated with eastern Pacific (i.e., canonical) ENSO events and the Pacific Decadal Oscillation, whereas the third CEOF is correlated to central Pacific (i.e., Modoki) ENSO. These results are useful to understand the overall dynamics of the South Atlantic and to potentially improve predictability of Meridional Overturning Circulation and monsoon pattern changes around the world.

Long‐Term Monitoring of the Brazil Current Transport at 22°S From XBT and Altimetry Data: Seasonal, Interannual, and Extreme Variability

“…As the BC flows southward, more intense contributions of central and intermediate waters increase considerably its total transport. To quantify this contribution, we estimate the BC transport using the data from the AX18 XBT transect across the nominal latitude of 34.5°S (not shown; see companion paper Majumder et al, ). We apply the same methodology described in section for inner shelf extrapolation and Argo absolute dynamic height referencing at a 1,000 m. The mean BC transport across 34.5°S in the upper 1,000 m is 12.4 ± 3.5 Sv along 34.5°S, which is similar to the values calculated using other data and methods (Schmid & Majumder, ), which implies that the BC gains approximately 7–8 Sv of central and intermediate waters between 22°S and 34.5°S.…”

“…These results suggest that the increased heat transport along the BC and its propagation timescales during this event were mostly driven by velocity anomalies rather than temperature anomalies. Effects of planetary Rossby wave propagation at different latitudes (Majumder et al, 2019;Polito & Liu, 2003) and convergence associated with the meridional overturning circulation (Lopez et al, 2016) may also play an important role for the increased heat anomaly within the subtropical gyre, but this is beyond the scope of this study.…”

More Than 50 Years of Successful Continuous Temperature Section Measurements by the Global Expendable Bathythermograph Network, Its Integrability, Societal Benefits, and Future

“…AX97 transects have resolved the high mesoscale variability associated with the BC that can manifest in inshore or offshore states, depending on transient eddies and the semi-permanent Cape of São Tomé eddy (Mill et al, 2015). During the summer of 2009-2010, an extreme warm SST event (>3 • C) was identified near 22 • S off the coast of Brazil, which was associated with atmospheric teleconnections from a Central Niño event in the Pacific (Majumder et al, 2019). During the warm SST event, the XBT-derived geostrophic BC transport (12 Sv) was three times larger than average.…”

Description and Dynamics of the Santos Bifurcation

“…Some secular, but also meaningfully, aspect that is interesting to point out here is the presence of propagating mesoscale waves coming from the east as described by Majumder et al (2018).…”

“…days ω, thus a phase speed of 0.42 ms −1 . This signal resemble the signals described at upper depths by Majumder et al (2018), however our analyzes were short and need more robustness that can be regarded in future works. On the other hand, for the AI Section we obtained mainly a dual regime, divided exactly at the SB region, as we presented in Figure 3.17.…”