South Atlantic Meridional Mode

South Atlantic Meridional Mode
Name	South Atlantic Meridional Mode
Location	South Atlantic Ocean
Period	interannual to decadal

South Atlantic Meridional Mode is a leading mode of coupled ocean–atmosphere variability in the South Atlantic basin characterized by meridional sea surface temperature and wind anomalies that influence regional climate. It interacts with basin-scale features such as the South Atlantic Convergence Zone, the Benguela upwelling system, and the Brazil–Malvinas Confluence, linking processes across the coasts of Brazil, Argentina, Uruguay, South Africa, and Namibia. Research on the mode connects work from institutions like National Oceanic and Atmospheric Administration, Woods Hole Oceanographic Institution, University of São Paulo, and South African Weather Service.

Overview

The South Atlantic Meridional Mode (SAMM) is analogous to the Atlantic meridional mode concept applied to the northern basin and is framed within studies of the Intertropical Convergence Zone, South Atlantic Subtropical High, and the Antarctic Circumpolar Current. Descriptions emphasize meridional gradients of sea surface temperature (SST) and surface wind anomalies spanning the subtropical and tropical South Atlantic, with connections to phenomena documented by researchers at Scripps Institution of Oceanography, Lamont–Doherty Earth Observatory, and Plymouth Marine Laboratory. The SAMM is diagnosed in observational analyses produced by centers such as European Centre for Medium-Range Weather Forecasts and Met Office.

Physical Mechanisms

Mechanisms include wind–evaporation–SST (WES) feedbacks implicated in studies from Geophysical Fluid Dynamics Laboratory and air–sea coupling described in literature from Princeton University and MIT. The SAMM arises where anomalies in the South Atlantic High and trade-like wind fields modify latent heat flux, driving SST anomalies that further modify the low-level flow. Interactions with the Benguela Current, the Brazil Current, and the South Equatorial Current alter ocean advection and mixed-layer depth; processes examined in work by NOAA Atlantic Oceanographic and Meteorological Laboratory and CSIC clarify roles of upwelling and eddy fluxes. Teleconnections involve modulation by the El Niño–Southern Oscillation, Southern Annular Mode, and fluctuations of the Atlantic Meridional Overturning Circulation investigated by teams at Euro-Mediterranean Center on Climate Change and Max Planck Institute for Meteorology.

Observational Evidence and Indices

Indices for the SAMM have been constructed using SST gradients, sea level pressure anomalies, and surface wind stress datasets from ERS-1, TOA, and reanalyses like NCEP/NCAR Reanalysis and ERA-Interim. Studies by researchers affiliated with NOAA NCEI, CSIRO, and INPE present empirical orthogonal function analyses and regression maps identifying the meridional pattern. Satellite missions such as AVHRR, TOPEX/Poseidon, and SeaWiFS have provided continuity for SST and radiative flux diagnostics used in index development, while buoy networks coordinated by Global Drifter Program and ARGO supply in situ validation.

Climate Impacts and Teleconnections

The SAMM modulates regional rainfall patterns including variability of the South Atlantic Convergence Zone, the austral summer precipitation over Southeastern Brazil, and drought episodes affecting Northeastern Brazil and Uruguay. Impacts extend to marine ecosystems in the Benguela upwelling system and fisheries off Namibia and South Africa, with implications studied by Plymouth Marine Laboratory and University of Cape Town. Teleconnections reach into the Southern Ocean climate, influence extratropical storm tracks analyzed by European Space Agency collaborations, and interact with variability in the Amazon River basin and the La Plata Basin observed by hydrology groups at Instituto Nacional de Pesquisas Espaciais.

Variability and Trends

The SAMM exhibits interannual to decadal variability influenced by modes such as the Pacific Decadal Oscillation and the Atlantic Multidecadal Variability. Long-term analyses using datasets from Hadley Centre and NOAA indicate decadal modulation possibly linked to anthropogenic forcing assessed by Intergovernmental Panel on Climate Change reports and climate assessments at IPCC. Paleoclimate proxies from Brazilian Highlands speleothems and marine sediment cores retrieved by cruises organized by RV Meteor and RV Knorr provide longer context for SAMM-like variability.

Modeling and Predictability

Global and regional climate models from CMIP6 ensembles, configurations at NOAA GFDL, UK Met Office Hadley Centre, and high-resolution regional models developed at Instituto Nacional de Pesquisas Espaciais are used to assess SAMM representation. Predictability studies examine initialization strategies used by Subseasonal to Seasonal (S2S) Prediction Project and seasonal forecasting systems run by CONMEBOL-linked research centers, with skill dependent on model physics of air–sea fluxes, representation of the Brazil–Malvinas Confluence, and coupled ocean dynamics documented by National Center for Atmospheric Research.

Regional and Socioeconomic Implications

SAMM-related climate variability affects agriculture in Brazil, Argentina, and Uruguay through impacts on soybean, maize, and sugarcane yields analyzed by institutes like EMBRAPA and INTA. Water resource management for urban centers such as São Paulo and Buenos Aires is sensitive to SAMM-influenced precipitation anomalies noted by municipal agencies and research at University of Buenos Aires and University of São Paulo. Marine fisheries authorities in Namibia and South Africa monitor SAMM-associated SST shifts due to effects on fish stocks tracked by Food and Agriculture Organization collaborations. Adaptation planning has been considered in reports from World Bank and regional bodies including Mercosur.

Category:Climate oscillations