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| Anticyclone of the South Pacific | |
|---|---|
| Name | Anticyclone of the South Pacific |
| Other name | South Pacific High |
| Type | Subtropical high-pressure system |
| Region | South Pacific Ocean |
| Coordinates | Southern Hemisphere |
| Area km2 | Variable |
Anticyclone of the South Pacific The Anticyclone of the South Pacific, commonly called the South Pacific High, is a persistent subtropical high-pressure system centered over the southeastern Pacific Ocean that influences weather across Oceania, South America, and the Southern Hemisphere. It modulates trade winds, the position of the South Pacific Convergence Zone, and oceanic features such as the Peru Current and the South Pacific Gyre, thereby affecting climatological phenomena including El Niño–Southern Oscillation, Pacific Decadal Oscillation, and Southern Hemisphere storm tracks. The feature is monitored by national meteorological services such as MetService (New Zealand), Meteorological Service of Chile, and the Bureau of Meteorology (Australia) and studied in atmospheric dynamics research at institutions like the National Oceanic and Atmospheric Administration, Scripps Institution of Oceanography, and CSIRO.
The South Pacific High is a semi-permanent anticyclone that typically occupies a broad region between latitudes approximately 25°S and 40°S and longitudes from the western coastline of South America toward the vicinity of Easter Island and the waters north of New Zealand. Its core is characterized by subsiding air, clear skies, and relatively low precipitation, influencing climate patterns across the South Pacific, Fiji, Tonga, Samoa, and the western coasts of Chile and Peru. Variations in its central pressure and geographic extent are linked to large-scale modes of climate variability such as Southern Annular Mode and Madden–Julian Oscillation. Operational forecasting and paleoclimate reconstruction of the High draw on data from observing networks including Argo (oceanography), TAO/TRITON, and satellite missions like ERS-2 and Jason-3.
The anticyclone arises from poleward transport of air in the subtropical Hadley circulation and Rossby wave dynamics associated with the mid-latitude jet stream, influenced by thermal contrasts between the Andes–Patagonia region and the open ocean. Typical sea level pressure in the High exceeds 1020 hPa at the center during austral winter; core pressure and size vary with episodes of strengthened subtropical ridging and blocking influenced by interactions with the Aleutian Low and the Amundsen Sea Low. The system exhibits clockwise circulation in the Southern Hemisphere that reinforces the southeast trade winds and contributes to Ekman transport, upwelling along the Peru–Chile Trench, and surface current structures within the South Pacific Gyre. The anticyclone's subsidence suppresses convective cloud formation, producing persistent marine stratocumulus decks similar to those studied near California Current systems and the Canary Current.
Seasonal shifts move the anticyclone poleward and equatorward with the austral winter–summer cycle, altering its influence on regions such as New South Wales, North Island, and the Juan Fernández Islands. In austral winter, the High typically intensifies and expands due to stronger subtropical ridging, affecting extratropical cyclone pathways related to the Roaring Forties and storm activity near Tasman Sea. During austral summer, the High weakens and migrates equatorward, modulating monsoonal and intertropical influences associated with Papua New Guinea and the Australian Monsoon. Interannual variability is tied to El Niño and La Niña phases, with notable teleconnections to the Indian Ocean Dipole and North Pacific Gyre Oscillation.
The anticyclone governs precipitation regimes across the southeastern Pacific and adjacent landmasses, contributing to aridity in coastal Peru and Chile through persistent subsidence and offshore flow that enhances coastal upwelling and sea surface temperature gradients. It influences tropical cyclone steering in the South Pacific basin, affecting tracks of systems that impact Vanuatu, Fiji, and New Caledonia. The High modulates regional sea level pressure gradients and wind-driven coastal processes tied to fisheries and marine ecosystems, including impacts on the Humboldt Current and associated productivity. Its role in climate variability links to extreme events such as prolonged droughts in Argentina and flood events in New Zealand when displaced ridging interacts with mid-latitude troughs.
The South Pacific High interacts dynamically with the South Pacific Convergence Zone (SPCZ), altering its location and intensity, and with the Pacific South American pattern (PSA) which mediates teleconnections between tropical Pacific SST anomalies and mid-latitude circulation. Coupling with the Southern Ocean storm track and the Antarctic Oscillation can produce blocking patterns that redirect extratropical cyclones toward the subtropics. During strong El Niño events, changes in the Walker circulation and equatorial convection shift the High eastward, while La Niña tends to strengthen the High westward, altering moisture transports to island nations and the runoff regimes of river systems such as the Maule River and Santa Cruz River.
Observational studies leverage in situ buoy arrays, radiosonde records from stations like Auckland and Valparaíso, reanalysis datasets including ERA5 and NCEP/NCAR, and satellite remote sensing from platforms such as MODIS and ASCAT to characterize pressure, wind, and cloud fields. Climate models in the Coupled Model Intercomparison Project (CMIP) ensembles simulate shifts in the anticyclone under greenhouse gas forcing, with research groups at NOAA Geophysical Fluid Dynamics Laboratory, Met Office Hadley Centre, and Max Planck Institute for Meteorology assessing projected changes in intensity and latitudinal position. Paleoclimate reconstructions using tree rings from Chile, coral records from Raratonga and Fiji, and marine sediments from the Peru Basin provide multi-century context for variability and extremes linked to the High. Continued integration of observations and high-resolution models is critical for improving seasonal forecasts used by agencies such as World Meteorological Organization and national services for hazard mitigation in the South Pacific region.