South Atlantic Anticyclone

South Atlantic Anticyclone
Name	South Atlantic Anticyclone
Caption	Schematic of subtropical high over the South Atlantic
Type	subtropical anticyclone
Location	South Atlantic Ocean

South Atlantic Anticyclone The South Atlantic Anticyclone is a persistent subtropical high-pressure cell centered over the South Atlantic Ocean that influences weather across South America, Africa, and the Southern Hemisphere midlatitudes. It is a component of the general circulation described by the Hadley cell, Ferrel cell, and Ekman transport and interacts with systems such as the Benguela Current, Brazil Current, and the Intertropical Convergence Zone. The feature modulates precipitation, trade winds, and storm tracks affecting regions from the Patagonian Desert to the Namib Desert and is monitored by agencies including the National Oceanic and Atmospheric Administration, the European Centre for Medium-Range Weather Forecasts, and the South African Weather Service.

Overview

The anticyclone sits roughly between 20°S and 40°S and is linked to the subtropical ridge that also includes the South Pacific High and the Azores High. It establishes the climatological zonal flow that shapes the Southeast Pacific, South Atlantic Gyre, and adjacent coastal climates such as Rio de Janeiro, Cape Town, and Montevideo. Its position and strength are governed by planetary-scale waves like the Rossby wave train and baroclinic interactions with the Antarctic Circumpolar Current and subtropical jets including the South Atlantic jet stream. Satellite missions such as TOPEX/Poseidon, Jason-3, and instruments like scatterometers and altimeters provide crucial data for mapping the anticyclonic circulation.

Formation and Dynamics

Formation arises from radiative cooling, subsidence in the descending branch of the Hadley circulation, and conservation of angular momentum near the subtropics, interacting with sea surface temperature gradients produced by the Benguela Current and South Equatorial Current. Rossby wave breaking, baroclinic instability along the Polar front, and mechanisms described by Ekman pumping and the thermal wind relation modulate its dynamics. The anticyclone’s western flank generates the southeast trade winds that feed into the Amazon Basin moisture transport and fuel systems like the South Atlantic Convergence Zone. Synoptic interactions with transient cyclones from the South Pacific Convergence Zone and extratropical cyclones affecting Falkland Islands airflows further complicate its evolution.

Seasonal and Interannual Variability

Seasonal migration follows the solar declination, shifting poleward during austral summer and equatorward during austral winter, influencing seasonal rainfall over Brazil, Uruguay, and Namibia. Interannual variability links to modes like the El Niño–Southern Oscillation, the Madden–Julian Oscillation, and the Southern Annular Mode, as well as teleconnections from the North Atlantic Oscillation and Pacific Decadal Oscillation. Large volcanic eruptions recorded in the Mount Pinatubo and Mount Tambora eruptions have had transient effects on radiative forcing and circulation, while anthropogenic forcing from Intergovernmental Panel on Climate Change assessed greenhouse gas increases modulates the subtropical ridge response.

Impacts on Weather and Climate

The anticyclone enforces persistent subsidence that suppresses convection, contributing to the aridity of the Atacama Desert and Patagonian steppe and promoting marine stratocumulus decks off the coasts of Chile and Angola. It steers midlatitude cyclones that affect ports such as Buenos Aires and Lagos and influences coastal upwelling regimes critical to fisheries managed by organizations like the Food and Agriculture Organization. By modifying low-level wind stress, it affects sea surface temperature patterns that feedback on regional climates including the Pantanal wetlands and the Cape Floristic Region. The ridge also shapes the climatology of tropical cyclone formation near the South Atlantic Ocean basin where rare storms have impacted Santa Catarina and Abrolhos Islands.

Interactions with Ocean and Atmospheric Systems

The anticyclone interacts with the South Atlantic Gyre, influencing the strength and position of the Brazil Current and the Malvinas Current confluence off the Rio de la Plata and the Brazil–Malvinas Confluence Zone. Surface wind patterns drive upwelling along the Benguela upwelling system and affect biogeochemical cycles including primary productivity linked to the Sargasso Sea analogs. Teleconnections with the Antarctic Oscillation alter storm tracks and sea ice extent around Antarctica, while coupled ocean–atmosphere phenomena studied in the World Climate Research Programme frameworks mediate longer-term shifts.

Observational Studies and Modeling

Observational programs using platforms like Argo, NOAA satellites, European Space Agency missions, and research cruises from institutions such as Woods Hole Oceanographic Institution and CSIRO have characterized the anticyclone’s structure. Reanalysis datasets like ERA-Interim, ERA5, and NCEP/NCAR Reanalysis inform model validation, while global climate models from the Coupled Model Intercomparison Project and high-resolution regional models developed by Met Office and INMET simulate its responses to forcing. Studies published in journals like Nature Climate Change, Journal of Climate, and Geophysical Research Letters use diagnostics including potential vorticity, streamfunction, and sea level pressure composites.

Historical and Societal Effects

Historically, the anticyclone influenced Age of Sail navigation used by Portuguese Empire and Dutch East India Company shipping routes, shaping trade patterns between Lisbon, Cape Town, and Rio de Janeiro. Its control over winds affected early exploration by figures such as Ferdinand Magellan and colonization of South America and Southern Africa. Contemporary societal impacts include effects on agriculture in Sudan and Argentina, fisheries along the Namibian coast, wind energy potential off Brazil and South Africa, and hazard mitigation efforts coordinated by national meteorological services and international agencies after events with socioeconomic consequences.

Category:Atmospheric circulation