What are horse latitudes and doldrums?

Answer 1

The doldrums is a colloquial expression derived from historical maritime usage, in which it refers to those parts of the Atlantic Ocean and the Pacific Ocean affected by the Intertropical Convergence Zone, a low-pressure area around the equator where the prevailing winds are calm. The low pressure is caused by the heat at the equator, which makes the air rise and travel north and south high in the atmosphere, until it subsides again in the horse latitudes. Some of that air returns to the doldrums through the trade winds. This process can lead to light or variable winds and more severe weather, in the form of squalls, thunderstorms and hurricanes. The doldrums are also noted for calm periods when the winds disappear altogether, trapping sail-powered boats for periods of days or weeks. The term appears to have arisen in the 18th century - when cross-Equator sailing voyages became more common. Horse Latitudes or Subtropical High are subtropical latitudes between 30 and 35 degrees both north and south. This region, under a ridge of high pressure called the subtropical high, is an area which receives little precipitation and has variable winds mixed with calm. The horse latitudes are associated with the subtropical anticyclone and the large-scale descent of air from high-altitude currents moving toward the poles. After reaching the earth's surface, this air spreads toward the equator as part of the prevailing trade winds or toward the poles as part of the westerlies. The belt in the Northern Hemisphere is sometimes called the "calms of Cancer" and that in the Southern Hemisphere the "calms of Capricorn".