Subtropical HighEdit
Subtropical High refers to the belt of persistent high atmospheric pressure that typically sits around 20 to 35 degrees latitude in both the Northern and Southern Hemispheres. This feature arises from the world’s general circulation, where air cools and subsides in the subtropics after rising near the equator, producing clear skies, light winds, and warm, dry conditions. The resulting high-pressure cells strongly influence regional climates, oceanic circulation, and the global wind patterns that power trade winds and mid-latitude westerlies. The best-known manifestations are the Azores High over the North Atlantic and the Pacific High over the North Pacific, along with analogous high-pressure zones in the southern hemisphere. These systems are not fixed in place; they shift with the seasons and with fluctuations in ocean temperatures, producing a dynamic pattern that interacts with monsoons, storms, and droughts.
A core concept in understanding the subtropical high is the Hadley cell, the large-scale circulation pattern that transports heat from the equator toward the subtropics. In the Hadley circulation, air rises near the equator, moves poleward aloft, cools and sinks in the subtropics, and then returns toward the equator at the surface. The sinking branch creates a layer of high pressure that forms the subtropical high. This mechanism explains why these high-pressure systems are strongest over warm ocean basins and tend to produce large, stable desert regions at the edges of the tropics. The subtropical ridges—long, broad zones of high pressure—wrap around the globe, shaping the climate of adjacent continents and the pathways of weather systems.
Major centers of the subtropical high and their regional expressions are well known. In the North Atlantic, the Azores High contributes to the steady easterly trade winds and can influence winter storm tracks toward Europe. In the North Pacific, the Pacific High guides the trade winds across the equatorial Pacific and interacts with the subtropical jet stream as conditions change with the seasons. In the Southern Hemisphere, a similar belt forms over the southern oceans and around the Indian Ocean, contributing to aridity in subtropical land areas and to the steering of mid-latitude weather systems. The term Bermuda High is often used to describe the western Atlantic extension of the subtropical high and its influence on Atlantic hurricane activity and maritime weather. The behavior of these highs is interlinked with other large-scale patterns, including the El Niño–Southern Oscillation and its phases, which can modulate their position and strength from year to year.
Structure and origins
The Hadley cell and subsidence: The high-pressure zones of the subtropics emerge where air descends from the upper branches of the Hadley circulation. This subsidence suppresses convection, yielding clear skies and dry conditions that help define the subtropical climate belt. For a detailed look at this large-scale circulation, see Hadley cell.
The subtropical ridge: The broad arc of high pressure that encircles each hemisphere at subtropical latitudes is often referred to as the subtropical ridge. It functions as a semi-permanent cap on the atmosphere in these latitudes and modulates regional precipitation and wind patterns. For regional examples, see Azores High and Pacific High.
Major centers and regional expressions: While there is not a single global “subtropical high,” there are several prominent systems that together form the subtropical high belt. These include the Azores High in the North Atlantic, the Bermuda High as an extension into the western Atlantic, the North Pacific High, and corresponding high-pressure zones in the southern oceans. See Azores High and Bermuda High for connected discussions.
Seasonal cycle and interannual variability
Seasonal migration: The subtropical highs tend to migrate toward the pole in summer and retreat toward lower latitudes in winter, reflecting the shifting temperature contrasts between land and sea and the response of the Hadley circulation to solar heating. This movement helps drive seasonal rainfall patterns, desert expansion or retreat, and variations in storm tracks.
Interannual influences: The position and intensity of subtropical highs are modulated by ocean-atmosphere interactions, including the El Niño–Southern Oscillation. For example, El Niño events typically alter atmospheric pressure patterns across the Pacific, which can shift the Pacific High’s position and affect rainfall and storm activity far from the equator. La Niña tends to have the opposite effect.
Impacts on weather, climate, and human activity
Regional climates: The dry, stable air associated with the subtropical high supports arid and semi-arid climates around the world, such as parts of the southwestern United States, North Africa, the Middle East, and parts of Australia. This belt also shapes the timing and intensity of monsoon systems by interacting with the moisture-laden air from adjacent regions.
Winds and storm tracks: The subtropical high influences the global wind field, strengthening trade winds on their equatorward flank and guiding mid-latitude westerlies on their poleward edge. The resulting wind patterns help drive ocean surface currents, which in turn affect marine ecosystems and commerce.
Tropical cyclones and weather systems: While high pressure generally suppresses tropical convection, the outer edges of the subtropical high can steer tropical cyclones and influence their tracks. In some basins, the position of the subtropical ridge can determine whether storms curve toward land or recurve into open seas.
Climate change context: Warming trends and shifting ocean temperatures are expected to affect the intensity and location of subtropical highs in complex ways. Some studies project a poleward expansion or a shift in the subtropical ridge that could alter precipitation regimes and drought risks in various regions. Because the atmosphere–ocean system is highly interconnected, precise regional outcomes remain a topic of active research, with ongoing debates about the magnitude and seasonality of any changes. See Climate model discussions and reviews for more detail.
See also