Down in the Doldrums (and the Horse Latitudes)

If you’re feeling stuck in the doldrums today, it’s likely that the last thing on your mind is just how such a quaint expression came into the English language in the first place. The condition of being stuck in a mundane, listless rut may seem as though it has little to do with wind convergence as it related to intercontinental sailing in the 18th century, but that’s exactly where the term comes from.

The doldrums are a very real geographic phenomenon. Though they have no precise boundary, the doldrums generally refer to the area encircling the Earth in the immediate vicinity of the Equator between 5°N and 5°S. In modern formal terminology, it’s known as the Intertropical Convergence Zone (ITCZ); the place where winds from the both the Northern and Southern hemispheres converge on one another and move upward due to the warm temperatures at the Equator. The rising air creates a band of low pressure which produces hot, humid, and very wet weather (which is why equatorial climes across the globe are covered in tropical rainforests) and – most importantly for sailors in the days before steamships – light, variable winds that alternate wildly between severe and serene.

Indeed, conditions could be so serene that sail-powered vessels travelling from the Northern Hemisphere into the Southern Hemisphere or vice versa could get trapped for days on end with little or no movement.  As traffic in equatorial waters increased during the mid-18th century, English-speaking sailors took to calling the area of these latitudes the ‘doldrums’, combining the archaic dold (‘stupid’, as in ‘dolt’ or ‘dull’) with the plural suffix –rum, reflecting their opinions of the region.  Standard use of the word ‘doldrums’ occurred as early as 1811and perhaps as early as 1795.

500px-Atmospheric_circulation.svg

Source: Burschlk, http://commons.wikimedia.org/wiki/File:Atmospheric_circulation.svg.   Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported licence.

The doldrums are hardly static, as their position changes with the seasons based upon the Earth’s position relative to the sun.  As well, the positioning of Earth’s landmasses disrupts atmospheric airflow because of the higher variation in temperatures over land compared to water, meaning the doldrums do not occur at a uniform latitude.  For example, during January when the Southern Hemisphere is closest to the sun and experiences summer, the doldrums are pushed a handful of degrees further south.  On the other hand, during the Northern summer in July the doldrums typically roam much farther away from 0° as there is more land in the Northern Hemisphere.  At that point, the doldrums lie at an average position of 5 to 12°N. Across much of Africa and especially Asia, the doldrums can move well into the thirties and even as high as 45°N in extreme cases. In any case, the further away from the Equator the doldrums get, the narrower they become.

640px-ITCZ_january-july

The maximal positions of the Intertropical Convergence Zone, nicknamed ‘the doldrums’.

So, the next time you’re ‘stuck in the doldrums’, be thankful that those doldrums are merely a metaphoric location and that you’re not actually marooned at sea in the middle of the tropics.

The doldrums are hardly the only atmospheric convergence zone with a quirky name.  Take the horse latitudes (more formally the subtropical ridges), which lie at approximately 30°N and 30°S.  The high-pressure horse latitudes are where the air pushed up from the doldrums comes back toward the Earth’s surface.  Half of the air then moves back toward the low-pressure doldrums from either the northeast or southeast direction, depending upon the hemisphere, in the form of the fast-moving trade winds; the other half travels toward the poles in the form of the westerlies.  As shown in the first diagram, these circulations are known as the Hadley cell and the Ferrel cell, repectively. In contrast to the doldrums, air in the horse latitudes is drier, giving rise to desert conditions across most of the landmasses which lie at the latitudes.   As with the doldrums, however, winds here are weak.  Also like the doldrums, the horse latitudes move closer to or away from the Equator based upon the time of year.

North_Atlantic_Gyre

The infamously still waters of the Sargasso Sea, where many a boat has become trapped for days or weeks on end without movement, lie in the horse latitudes in the western portion of the North Atlantic Gyre, the great rotating system of ocean currents that represents the interaction between the doldrums, trade winds, horse latitude, and westerlies in the North Atlantic.

The term ‘horse latitudes’ dates to approximately the same age as the word ‘doldrums’; Merriam-Webster places the first recorded use of the word in 1777.  Rather than lending itself to a metaphor like the doldrums, the term ‘horse latitudes’ itself comes from a metaphor, though exactly which metaphor is up for debate.  One story connects the phrase with the sailor’s ritual of ‘working off a dead horse’. Seamen were often partially paid in advance for working on ships, and as a result often incurred debt that would take a month or two of sailing to pay off.  The often difficult task of getting sailors to work for no money during this time was akin to ‘flogging a dead horse into activity’.  By the time the seamen had worked enough to pay off their advance, they were usually in the subtropical regions of the ocean – the ‘horse’ latitudes.  A ceremonial straw horse would often be cast adrift at this point to commemorate the occasion.

The other story states that when ships became stuck in these latitudes for substantial lengths of time traveling back and forth between Europe and the New World, fresh water supplies and other provisions on these ships would become strained.  Any animals that were on board, usually horses, thus had to be sacrificed to ensure the sailors had enough water and nourishment for themselves.  As such, the horses would be killed and thrown overboard, leaving the waters strewn with horse carcasses, or simply eaten.

Further Reading

Ahrens, C.D. (2007).  Three-Cell Model.  In Meteorology Today: An Introduction to Weather, Climate, and the Environment, 257-258.  Belmont, CA: Thomson Brooks/Cole.

HowStuffWorks.com (2009).  Wind.  16 September 2009.  Available at http://science.howstuffworks.com/dictionary/meteorological-terms/wind-info.htm.  Accessed 14 September 2012.

Jeans, P.D. (2004).  Seafaring Lore and Legend.  New York: McGraw-Hill.

NASA Earth Observatory (2000).  The Intertropical Convergence Zone.  12 July 2000.  Available at http://earthobservatory.nasa.gov/IOTD/view.php?id=703.  Accessed 14 September 2012.

Rosenberg, M. (n.d.).  Trade Winds, Horse Latitudes, and the Doldrums: Global Atmospheric Circulation and its Related Effects.  About.com: Geography.  Available at http://geography.about.com/od/physicalgeography/a/tradewinds.htm.  Accessed 14 September 2012.

Rosenberg, M. (2005).  ITCZ: The Intertropical Convergence Zone or ITCZ Brings Convectional Precipitation.  About.com: Geography, 1 March 2005.  Available at http://geography.about.com/od/climate/a/itcz.htm.  Accessed 14 September 2012.

Vigor, J. (2004).  The Practical Encyclopedia of Boating.  New York: McGraw-Hill.

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