Horse Latitudes

Any of the two subtropical atmospheric high-pressure belts that are present around the Earth, around the latitudes 30° N - 35° N and 30° S - 35° S that can generate light winds and clear skies are known as Horse Latitudes. The significance of the horse latitudes is that they contain the dry subsiding air, they are responsible for the arid climates below them. The best example is the Sahara, which is situated below a horse latitude. The southern hemisphere has a more continuous belt of subsiding air as compared to the northern hemisphere, as there is more water content in the southern hemisphere. These belts are known to contain several separate high-pressure centres.

The Naming of the Horse Latitudes

Horse latitude meaning is literally derived from three specific conditions that have revolved around the actual animal. These three interesting conditions are mentioned below:

• One of the origins of the meaning is from the term ‘dead horse’ which was a ritual performed by the seamen. In this ritual, the seamen paraded a straw-stuffed effigy of the animal around the deck and then threw it overboard. According to the story, the seamen were partly paid in advance before leaving for the voyage, which they usually spent all at once. This would result in a time period without any income for approximately a month or two. When they got advances from the ship’s paymaster, they would be under debt and for that period of one or two months, which came to be known as the “dead horse” period, they would be doing extra chores or any work asked of them on the ship. At the end of such a period, the seamen ceremoniously celebrated having worked off the “dead horse” debt. For westbound ships from Europe, the time such debt was worked off came around the specific latitudes of 30° N - 35° N. Hence, such a latitude came to be known as a dead horse latitude. 

• Another theory arising from the folklore is of the incidents of throwing an actual horse overboard on lengthy voyages by Spanish ships. The story follows the Spanish voyages that included the transportation of horses by ship to their distant colonies present in the West Indies and the Americas. The ships on reaching the specific latitudes are becalmed in the mid-ocean which prolonged the voyage. Hence, any water shortage arising from the prolonging of the journey required the crew to throw away dead or dying animals overboard. 

• The third incident that provides the answer for what is horse latitude is the maritime terminology that was acquired over time and can explain both the north and south horse latitudes definition as they do not depend on the length of the journey or the port from which they sailed. Technically, a ship was said to be horsed, which was typically in these latitudes, because even though there wasn't enough wind for sail, the vessel could make good progress as it latched onto the strong current. It is explained by Edward Taube in his article, “The Sense of ‘Horse’ in Horse Latitudes”. The argument is put forward from the reasoning that in maritime terminology, as the ship was carried more because of the power of the current rather than the wind and the sail, it was as the same manner of a rider on a horseback. This acceptance of the horse latitude meaning has been in use since the seventeenth century. 

These fascinating stories are the reason why specific latitudes are known as horse latitudes. 

Formation and Weather Conditions of Horse Latitudes

An image is given below showing the north and south horse latitudes:

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There is a large amount of convection air current around the intertropical convergence zone because of the heating of the surface from the solar radiation at the thermal equator. This air mass because of low density rises above and then diverges and moves away from the equator in both the northerly and southerly directions. When the air starts moving towards the mid-latitudes present on both sides of the Equator it cools and sinks.  Because of this, a high-pressure ridge is created around the 30th degree parallel in both hemispheres. At the surface level, the sinking air diverges again and some of it returns to the equator creating the Hadley cell. Such climatological high-pressure areas are the reason for many of the deserts in the world. 

The location as per the horse latitudes definition also explains the reason for its association with the subtropical cyclone. The northern hemisphere belt is sometimes referred to as “calms of Cancer” and the one in the southern hemisphere is known as “calms of Capricorn”. The consistently warm, dry and sunny conditions of the horse latitudes are one of the main reasons for the major non-polar deserts like the Sahara, Arabian desert, Syrian desert in the Middle East, the Mojave and Sonoran deserts in the southwestern US and northern Mexico, present in the northern hemisphere, and the Atacama desert, Kalahari desert, and the Australian desert in the southern hemisphere.  

These horse latitudes are responsible for some of the weather conditions around the world. The subtropical ridge in the northwest Pacific when stronger than normal leads to a wet monsoon season for Asia. This subtropical ridge is also responsible for the extension of thunderstorms into the United States and brings rainfall in the Desert southwest of North America from July to September. Thus, as much interesting, the horse latitude meaning is, the wind current arising due to conditions mentioned in the horse latitudes definition is of significance in rainfall and also in affecting large areas of the land and the sea and their climate and vegetation.