A vocabulary of landscape — a landscape of words
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horse latitudes
The horse latitudes are the belts near 30 degrees north and south where air descending from the tropics produces persistent high pressure, light and variable winds, clear skies, and very little rain. They sit between the trade winds and the westerlies, and a sailing ship crossing them could be becalmed for weeks. The same descending air is the reason most of the world’s great deserts sit at that latitude.
Etymology
The name is old and the explanation for it is not settled. The most repeated account holds that ships carrying horses to the Americas ran short of water while becalmed and put the animals over the side, which is widely printed and thinly documented. A better-supported explanation involves a sailors’ term for working off the dead horse, meaning the period of a voyage already covered by wages paid in advance, with a straw horse thrown overboard to mark the end of it.
Notes
Whatever the origin, the meteorology is exact. The descending branch of the Hadley circulation lands in these belts, and air warming as it sinks cannot form cloud, so the Sahara, the Arabian, the Chihuahuan, the Kalahari, and the Australian deserts all sit under it. The corresponding calm at the equator is the doldrums.