South Atlantic subtropical high

South Atlantic subtropical high
Name	South Atlantic subtropical high
Location	South Atlantic Ocean
Type	Atmospheric high-pressure system

South Atlantic subtropical high The South Atlantic subtropical high is a semi-permanent anticyclonic pressure center over the South Atlantic Ocean that influences weather across South America, Southern Africa, and adjacent ocean basins. It modulates trade winds, subtropical jet streams, and ocean circulation features such as the Benguela Current, Brazil Current, and the South Atlantic Gyre. The feature interacts with large-scale modes like the El Niño–Southern Oscillation, the Southern Annular Mode, and the Madden–Julian Oscillation, affecting precipitation, heat fluxes, and marine ecosystems.

Overview

The South Atlantic subtropical high acts as a dominant node of the Hadley cell in the Southern Hemisphere and is linked to the position of the Intertropical Convergence Zone. It typically resides between the latitudes of the Tropic of Capricorn and the South Atlantic Ocean midlatitudes, anchoring the western flank of the South Pacific High and the eastern edge of the South Indian Ocean High. Its anticyclonic circulation reinforces the Southeast Trade Winds off the coast of Brazil and the South Atlantic Convergence Zone location, while its western extension influences the climate of the Southeastern Brazil and the Rio de la Plata basin. The high’s variability ties into teleconnections with the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation.

Formation and Dynamics

The high forms through subsidence associated with the descending branch of the Hadley circulation and radiative cooling over subtropical latitudes modulated by sea surface temperature patterns such as the South Atlantic sea surface temperature gradient. Baroclinic interactions with storm tracks near the Drake Passage and the Roaring Forties provide transient eddy forcing. Atmospheric angular momentum considerations and Rossby wave propagation from disturbances near Africa and South America can shift the high’s center. Ocean-atmosphere coupling with the Benguela upwelling system and the Brazil–Malvinas Confluence alters surface pressure via latent and sensible heat fluxes, while stratosphere–troposphere interactions related to the Antarctic Oscillation modulate the high’s intensity.

Climatic and Oceanic Impacts

Position and strength of the high determine wind stress curl over the South Atlantic Gyre, driving gyre circulation changes and influencing the Agulhas Current retroflection teleconnections. The high’s control of the trade winds affects coastal upwelling off Namibia and Uruguay, altering primary productivity in regions linked to the Benguela Current Large Marine Ecosystem and the Patagonian Shelf. Variations in moisture advection associated with the high influence summer precipitation extremes in Southeastern Brazil, the Cerrado biome, and the Cape Floristic Region. The high modulates the pathway of extratropical cyclones that impact ports such as Cape Town, Montevideo, and Port Elizabeth.

Seasonal and Interannual Variability

Seasonal migration of the high follows insolation patterns tied to the Southern Hemisphere summer and winter, typically moving poleward during austral summer and equatorward in austral winter. Interannual shifts correlate with El Niño and La Niña phases of the El Niño–Southern Oscillation and with the Atlantic Meridional Mode, altering the likelihood of drought in the Northeastern Brazil and flood events in the La Plata Basin. Decadal modulation by the Atlantic Multidecadal Oscillation and abrupt episodes linked to volcanic forcing observed in datasets tied to the International Geophysical Year produce multi-year anomalies in the high’s intensity. Sudden stratospheric warming events and changes in the Southern Annular Mode create transient departures from climatology.

Observational and Modeling Studies

Observationally, the high is characterized using reanalysis products from organizations including the European Centre for Medium-Range Weather Forecasts, National Oceanic and Atmospheric Administration, and satellite missions such as TOPEX/Poseidon, Jason-1, and Aqua (satellite). Field campaigns involving institutes like the South African Weather Service and the Instituto Nacional de Pesquisas Espaciais have deployed drifters, buoys, and radiosondes to resolve boundary layer structure. Climate models from the Coupled Model Intercomparison Project and regional downscaling by centers such as the Hadley Centre simulate responses to greenhouse gas forcing and ozone recovery scenarios. Model intercomparison highlights biases in representing the western extension of the high and its coupling to the Brazil Current, prompting process studies using the Community Earth System Model and the European Regional Reanalysis.

Regional Effects and Human Implications

The high influences maritime navigation, fisheries off Namibia and South Africa, and coastal storm frequency affecting cities like Rio de Janeiro and Port Elizabeth. Agricultural productivity in regions such as the Pampas and the Cerrado depends on the high’s control of dry spells and humid incursions linked to the South Atlantic Convergence Zone and the La Plata Basin hydrology. Changes in storm tracks impact energy infrastructure including coastal Porto Alegre and Cape Town power and shipping logistics, while altered upwelling affects commercial fisheries managed by bodies like the South Atlantic Fisheries Commission. Adaptation planning by national agencies including the Ministry of Environment (Brazil) and the Department of Environmental Affairs (South Africa) increasingly incorporates projections of high-induced climate shifts.

Category:Atmospheric circulation