Calms of Capricorn

The Calms of Capricorn refer to a belt of light winds and high atmospheric pressure situated around 30° South latitude in the Southern Hemisphere. This region forms part of the broader system known as the Horse Latitudes, where air descending from higher levels of the atmosphere produces calm and dry weather conditions. The Calms of Capricorn are a defining feature of the global wind and pressure system, influencing both climatic and oceanic conditions in the subtropical southern regions.

Background and Formation

The Earth’s atmosphere circulates in large convection cells known as Hadley Cells, which play a central role in the formation of the Calms of Capricorn. Warm, moist air near the equator rises due to intense solar heating within the Intertropical Convergence Zone (ITCZ). As it ascends and moves poleward, it cools and descends near the subtropical latitudes, around 30° N and 30° S.
In the Southern Hemisphere, this descending air forms a belt of subtropical high pressure, creating the Calms of Capricorn. The air that descends here is dry and stable, suppressing convection and cloud formation. The result is a region characterised by calm or variable winds and consistently clear skies.
The name “calms” reflects the lack of prevailing winds, as subsiding air discourages the horizontal movement necessary for strong wind systems. Historically, sailors encountered long periods of stillness and found their ships becalmed in this region, giving rise to the term Horse Latitudes for both hemispheric counterparts—the northern one near the Tropic of Cancer and the southern one near the Tropic of Capricorn.

Characteristics

• Wind Conditions: Winds are light, variable, and often calm. The large-scale circulation patterns diverge horizontally, reducing surface wind speeds.
• Atmospheric Pressure: High and stable pressure dominates the region, forming part of the global subtropical high-pressure belt.
• Weather: The descending air inhibits vertical cloud development, resulting in clear skies and low precipitation.
• Temperature: Warm days and cool nights are common due to high insolation and limited moisture.

Climatic Effects

The Calms of Capricorn exert a major influence on the climate of adjacent landmasses. The persistent descending air and lack of precipitation contribute to the development of subtropical deserts. Notable examples include:

• The Atacama Desert in Chile and Peru.
• The Namib and Kalahari Deserts in southern Africa.
• The Great Victoria and Simpson Deserts in Australia.

In these areas, stable atmospheric conditions and minimal cloud cover lead to aridity and low humidity. Furthermore, the high-pressure system associated with the Calms of Capricorn can deflect or suppress tropical rainfall systems, influencing seasonal climate variations and monsoon activity.

Geographic Extent and Variation

The Calms of Capricorn generally occupy the zone between 25° S and 35° S latitude, though their exact position shifts seasonally due to the migration of the thermal equator and changes in solar heating. During the Southern Hemisphere’s summer, the belt moves slightly southward, while in winter it retreats northward.
The phenomenon is most pronounced over the oceans, particularly in the South Atlantic, South Pacific, and Indian Ocean basins, but its effects also extend over adjacent continental margins.

Associated Oceanic and Atmospheric Features

The Calms of Capricorn are closely linked to cold ocean currents that flow along western continental margins, such as:

• The Benguela Current (off the coast of southern Africa).
• The Peru or Humboldt Current (off the coast of South America).
• The West Australian Current (off western Australia).

These currents enhance the cooling of the overlying air and reinforce the stability of the subtropical high-pressure zones. As a result, fog formation and low-level temperature inversions are common near coastal areas.

Meteorological Significance

The Calms of Capricorn form part of the global circulation pattern that includes the Hadley Cell, Ferrel Cell, and Polar Cell systems. They represent the descending limb of the Hadley Cell, balancing the rising air of the equatorial regions. The high-pressure belt also contributes to the generation of trade winds on its equatorward side and westerlies on its poleward side.
In modern meteorology, this region is also referred to as the subtropical ridge or anticyclonic belt. It plays a critical role in determining storm tracks, influencing tropical cyclone formation, and shaping seasonal rainfall patterns in subtropical regions.

Historical and Navigational Importance

For early sailors navigating by wind power, the Calms of Capricorn posed significant challenges. Ships often became becalmed for days or weeks, unable to move due to the absence of wind. This stillness, coupled with limited water supplies, gave rise to maritime legends associated with the Horse Latitudes.
Although modern navigation no longer depends on wind patterns, understanding these zones remains vital for maritime meteorology, aviation, and climate modelling.