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For hundreds of years, maritime trade has revolved around trade winds. These winds have propelled commerce from when Columbus set sail to today's cargo voyages around the world. But exactly what (and where) are the trade winds?
Global Wind Patterns
Trade winds are global air currents that blow from east to west around the equator. The winds were especially helpful back when boats still relied on sails to travel. Ships that traveled from Europe and Africa to the Americas and from the Americas to Asia would use the trade winds to shorten their trips considerably. Without them, voyages would have taken much longer!
Modern ships still use the trade winds to hasten global journeys. Along with the winds come ocean currents that modern sailors refer to as “the trades.” Even though newer sea vessels don’t rely on sails anymore, the currents still propel them faster than they would move on their own. It works like a tailwind on a plane; as long as the current is going with you, you’ll move faster.
Where Are the Trade Winds?
If you’re thinking about sailing the high seas, you’ll be able to find the trade winds around the equator to about 30 degrees latitude in either direction. Since wind moves more efficiently over water than over land, the trade winds are more pronounced over the ocean than they would be over a continent — even if the continent lies right on the equator.
How the Trade Winds Are Formed
The trade winds are formed by circular wind patterns around the equator. The regions around the equator are typically hotter than other places around the world and the stretch of ocean along the equator is no different. The air along the equator is hot and rises high into the atmosphere where it travels north and south toward the poles. In the Northern Hemisphere, warm air travels north. In the Southern Hemisphere, it travels south. As the air travels toward the poles, it cools down and descends. The now-cooler air is attracted to the low-pressure system and blows back toward the equator.
The Coriolis Effect
Since a north-to-south wind pattern wouldn’t help global travelers, something needs to push the winds westward. That’s where the Coriolis effect comes in. The Coriolis effect has to do with the rotation of the Earth. Due to our planet's roundness, things along the equator spin much faster than things on the poles. To be more precise, things at the equator spin about 1,000 miles per hour, while the poles rotate only 0.00005 miles per hour.
Since wind isn’t connected to the ground, the Earth rotates under it. Within the subtropical regions, the easterly rotation of the Earth is so fast that it makes the wind seem like it’s blowing toward the west. The circular wind patterns coupled with the spinning of the Earth is what creates the easterly trade winds (that blow from east to west).
The Inter-Tropical Convergence Zone (ITCZ), which is also known as the doldrums, is located within five degrees of the equator in each direction. If you’re a sailor, it’s the place you don’t want to be. This is the region where the southern and northern trade winds collide, the air is heated, and starts to rise into the atmosphere, creating very calm wind conditions. Since rising air does little to propel seacraft, sailors would often get stuck in the doldrums for days or weeks on end. In addition to calm winds, rising heated air often causes rain and storms, which only makes being stuck in the doldrums even worse.