HORSE LATITUDES
The Horse Latitudes are located at approximately 30° north and south of the equator. In these regions, winds either diverge toward the poles (forming westerlies) or flow back toward the equator (forming trade winds).
Characteristics:
- The horse latitudes are characterized by high-pressure zones that result in calm winds, clear skies, and little to no precipitation.
- Historically, these latitudes were named by sailors who, when their ships were becalmed in these areas, sometimes threw horses overboard to conserve water.
Formation:
- Air in Upper Atmosphere Becomes Dry: As the air moves away from the equatorial low-pressure zone (ITCZ), it loses moisture and becomes dry and cold. This process occurs in the upper troposphere.
- High-Pressure Belt at 30°: As this dry air subsides, it creates a high-pressure belt at around 30° north and south, leading to the calm, dry conditions typical of the Horse Latitudes.
Features of the Horse Latitudes:
- High Pressure: Areas of high pressure are marked by calm, subsiding air that heats during descent. Reasons for high pressure:
- Subsidence of air from the equatorial region, which becomes heavier as it descends.
- Blocking effect of air at upper levels due to the Coriolis force, preventing further upward movement of air.
- Less Rainfall: The horse latitudes receive little precipitation and are characterized by variable winds mixed with calm conditions.
- Disturbances: These regions are frequently invaded by tropical and extratropical disturbances, although they remain primarily dry and calm.
- Temperate Deserts: The subsiding air is warm and dry, leading to the formation of deserts along this belt. Examples include:
- Northern Hemisphere: Sahara Desert (Africa), southwestern United States, northern Mexico, and parts of the Middle East.
- Southern Hemisphere: Atacama Desert (Chile), Kalahari Desert (southern Africa), and the Australian Desert.
Challenges in the Horse Latitudes:
- Widening of Tropical Belts: Since 1979, the tropical belt has widened by several degrees latitude, suggesting a poleward shift of the jet streams and storm tracks.
- Climate Change: Areas that used to be in temperate zones may now shift into desertification zones, while previously arid regions may receive more precipitation. Examples include:
- Sydney, Australia (34° S): Poleward of the southern horse latitude.
- Upper Colorado River Basin (37° N): Poleward of the northern horse latitude.