Atlantic subtropical high

Atlantic subtropical high
Name	Atlantic subtropical high
Type	subtropical ridge
Location	North Atlantic Ocean
Coordinates	25–35°N, 30–80°W
Period	year-round, strongest in summer
Aliases	Bermuda High, Azores High (regional)

Atlantic subtropical high

The Atlantic subtropical high is a persistent semipermanent ridge of high atmospheric pressure over the North Atlantic Ocean that strongly influences weather and climate across the Americas, Europe, and Africa. It is central to the seasonal evolution of the North Atlantic Oscillation, the steering of tropical cyclones, and the modulation of trade winds, connecting with patterns observed in the Hadley Cell, the Intertropical Convergence Zone, and midlatitude jet streams. Its variations affect precipitation, temperature extremes, and ocean circulation through links to the Gulf Stream, the Azores, and the Caribbean Basin.

Overview

The Atlantic subtropical high manifests as a radiating anticyclonic circulation centered near the Azores and the Bermuda region and is closely associated with the climatological centers identified in the World Meteorological Organization reports and synoptic charts used by the National Hurricane Center, the Met Office, and the European Centre for Medium-Range Weather Forecasts. Its presence organizes the summer monsoon progression for the West African monsoon and shapes the storm tracks that impact the United Kingdom, Iberian Peninsula, and the eastern seaboard of the United States. Observational campaigns by the NOAA Atlantic Oceanographic and Meteorological Laboratory, the National Oceanic and Atmospheric Administration, and research programs at institutions such as Woods Hole Oceanographic Institution have characterized its mean state and variability.

Formation and Dynamics

The anticyclonic ridge forms through the subsidence branch of the Hadley Cell and radiative-convective equilibrium influenced by sea surface temperature gradients set by the Gulf Stream and the North Atlantic Drift. Rossby wave interactions originating from tropospheric disturbances over the Rocky Mountains, the Sierra Madre, and the Great Plains can amplify or displace the ridge, while baroclinic eddies associated with the Icelandic Low and the Azores High modulate its intensity. Dynamical coupling with the subtropical jet stream, variations in the Atlantic Meridional Overturning Circulation, and stratosphere–troposphere exchange processes observed during Sudden stratospheric warming events also alter vertical structure and vorticity of the high.

Seasonal Variability and Position

Seasonally the high migrates and intensifies, typically retreating poleward in boreal summer toward the vicinity of the Bermuda–Azores corridor and expanding equatorward in boreal winter under influence from the North Atlantic Oscillation phase and teleconnections with the El Niño–Southern Oscillation and the Madden–Julian Oscillation. During summer the ridge reinforces the subtropical dry belt affecting the Mediterranean Basin, Sahel region, and the Caribbean, while winter displacements alter storm trajectories that strike the British Isles and the Iberian Peninsula. Paleoclimate records from Greenland ice cores and marine sediment cores near the Cape Verde islands document long-term shifts tied to orbital forcing documented in the Milankovitch cycles.

Climatic and Weather Impacts

The high is instrumental in steering Atlantic tropical cyclones toward the Gulf of Mexico, the Florida peninsula, and the Yucatán Peninsula or conversely out to sea toward the Azores and Iberia depending on its position, thereby affecting seasonal hurricane forecasts by the National Hurricane Center and the Florida State University hurricane research community. It suppresses convection inland, contributing to heatwaves in the Southeastern United States, droughts in the Maghreb and the Iberian Peninsula, and coastal upwelling off West Africa that influences fisheries managed by authorities such as the European Union and the African Union. The ridge also modulates trade wind strength that affects transatlantic shipping routes linking ports like Miami, Lisbon, and Lisbon Port and influences aerosol transport pathways between Saharan Air Layer events and the Amazon rainforest.

Interactions with Oceanic Processes

Sea surface temperature anomalies in the North Atlantic, including the Atlantic Multidecadal Variability and the Atlantic Multidecadal Oscillation, interact with the high to alter heat fluxes, salinity distributions, and the position of the Gulf Stream and the North Atlantic Current. These ocean–atmosphere feedbacks impact the strength of the Atlantic Meridional Overturning Circulation and modulate marine heatwaves that affect ecosystems studied by NOAA Fisheries and initiatives like the Global Ocean Observing System. Exchanges across the air–sea interface influence the formation of subtropical gyres and link to teleconnections with the Pacific Decadal Oscillation and basin-scale phenomena documented in the Intergovernmental Panel on Climate Change assessments.

Historical Trends and Climate Change Influence

Instrumental records from the National Centers for Environmental Prediction reanalyses and long-term station networks show century-scale shifts in the average position and intensity of the ridge, with attribution studies by the IPCC and research groups at Columbia University and MIT indicating influences from anthropogenic greenhouse gas forcing, aerosol emissions from industrial regions like the United States and Europe, and land-use changes across the Sahel. Projections from coupled climate models used in CMIP6 ensembles suggest potential poleward expansion and altered seasonal behavior, with implications for hurricane genesis regions, European summer drought frequency, and North Atlantic storm-track variability critical to policy discussions in forums such as the United Nations Framework Convention on Climate Change.

Category:Atmospheric circulation