What Are Trade Winds?

Trade winds are the easterly winds in oceanic regions just above and below the equator. They were named by sailors who relied upon these winds to propel their ships across the seas. It was essential for sailors to know global circulation patterns, because some regions with little to no wind were important to avoid.

Identification

Because sailors needed wind to travel the oceans until steam power was harnessed in the 1800s, they depended on the very reliable easterly winds in the tropics to sail westward, then returned eastward by the westerly winds that are further afield.

The trade winds occur between about 5 degrees latitude to 30 degrees latitude above and below the equator, blowing to the northeast and southeast at an angle toward the equator at a steady 11 to 13 mph. The westerlies are located between 30 and 60 degrees north and south. They blow toward the poles.

Geography

Sailors tried to avoid two specific regions because of the weak wind patterns there. One was an area they called the doldrums, a low-pressure region within 5 degrees of either side of the equator. The other they called the horse latitudes, a dry high-pressure subtropical area between about 30 to 35 degrees south and north of the equator. In these regions, a ship could stall for weeks.

Folklore says that the horse latitudes were so named because if a ship was stranded in these waters long enough, sailors tossed provisions overboard to lighten the ship in the hope that weak winds could send it forward. Horses were among the last items to go. There seems to be no explanation as to why the sailors did not eat the horses instead.

Considerations

Sailors relied on these winds to travel the Pacific and Indian oceans as well as the north Atlantic, but the south Atlantic was problematic. It has a tendency toward winds of over 100 mph and frequent storms. Shifting winds can create waves over 50 feet high. In addition, powerful intersecting ocean currents could cause significant problems for sailors.

Significance

The Portuguese were eventually to gain success as world explorers in the late 1400s. However, sailors such as Christopher Columbus and Ferdinand Magellan trailed Leif Erikson and his Viking crew by nearly 500 years in reaching the New World. Even traveling from as far away as Scandinavia, the Vikings were able to reach Canada by traveling north of the westerly winds and staying within a day or two's sighting of land. Portuguese explorers had to deal with westerly winds blowing their ships in the wrong direction, forcing them to travel down the coast until they could pick up the northeasterly trade winds.

Time Frame

In early sea travel, sailors used the stars for navigation and stayed as close to land as possible. Once the compass was invented in the 11th century, sailors had a much easier time staying on course when the skies were obscured by clouds. Today, large ships use computers and satellite technology to navigate.

With the advent of steam power in the 1800s, business travel by wind-powered sailing ships became a thing of the past, but the global winds retain their traditional names to this day.

Resources

• Atmospheric explanation of the global winds