What Are The Westerlies?

The westerly winds occur from December to February in the northern hemisphere.
The westerly winds occur from December to February in the northern hemisphere.

The westerly winds, also known as the westerlies, occur at two regions on Earth: between 30 and 60 degrees latitude in the northern hemisphere and between 30 and 60 degrees latitude in the southern hemisphere. The name of these unique winds comes from the direction of their origin; the westerlies run west to east while other winds run east to west. Essentially, the air around the equator rises as it heats up. This upward motion causes the cooler air at higher altitudes to be moved to the previously mentioned latitudes. This circulating air causes the air at lower altitudes in this higher latitudinal range to also move. The difference in speed between these two types of air is what is felt on the surface of the earth.

Meteorologists report that the westerlies have higher speeds and more force during the winter season, which in the northern hemisphere is from December to February and in the southern hemisphere is from June to August. This distinction is due to the air pressure over the poles during the winter. Lower pressure means stronger westerly winds. When these winds move over land areas, the direction is changed and moves in more of a north-south pattern. This directional change means the westerlies are slowed down significantly over land. The opposite is true over water, where the westerlies may reach higher speeds. This action means that the westerly winds tend to move at greater speeds in the southern hemisphere, where there is less land area than the northern hemisphere.

The Ocean and the Westerlies

Like the wind, the ocean moves constantly and this movement is affected by the wind. All winds, including the westerlies, pull across the surface of the ocean, causing the current to move in the same direction as the wind. Because the westerlies move in the opposite direction of the trade winds and land masses obstruct the flow of ocean water, a circular pattern of ocean current occurs.

The difference in speed and strength of the westerly winds in the northern and southern hemispheres corresponds to the speed and strength of the ocean currents as well. This correlation means that the ocean current in the southern hemisphere is much stronger than that found in the northern hemisphere. Another factor that contributes to the strength of the current is known as western intensification, which occurs as a result of the previously mentioned circular pattern of the Earth’s oceans. The result of this intensification is that the current along the western boundary of the ocean is stronger than along the eastern border. These western waters carry warmer temperatures toward both the north and south poles. One example of this is the Gulf Stream, which is located at the western edge of the Atlantic Ocean. The Gulf Stream is stronger than the California Current, which is located on the eastern edge of the Pacific Ocean. The Gulf Stream continues in a northeastern direction, but is stopped by the westerly winds before it can reach the islands of Antigua and Barbuda. The same behavior is seen in the northwestern region of the Pacific Ocean.

The Westerlies and Trade Winds

As the dominant winds in the middle latitude regions, the westerly winds have had a significant impact on trade routes throughout history. This importance to trade is particularly true of the “Roaring Forties”, some of the strongest westerly winds in the southern hemisphere between 40 and 50 degrees latitude. These winds facilitated the Brouwer Route, which was used during the 1600’s to travel from the Cape of Good Hope in southern Africa to the island of Java in Indonesia. Not only did the westerly winds help direct sailors along the correct path, but they also made the journey faster than previous methods had been. According to some sources, the time it took to get between these two places by using the westerly winds was cut in half. Hendrick Brouwer, a Dutch explorer, is credited with discovering the route. The significance of the westerly winds helped shape the face of trade for roughly two centuries. Additionally, using these winds led to the European discovery of Australia (which was inhabited by indigenous peoples prior to this discovery).

Although the Age of Sail ended in the middle of the 1800’s, with the advent steamships, the westerly winds are still an important navigation tool for modern-day ships. In fact, sailboats often continue to follow the westerly winds route, particularly those participating in racing competitions.

Impacts of Climate Change on the Westerlies

Researchers have recently made a connection between the westerly blowing winds and global climate change. Human activity has led to a change in the temperatures and climate patterns in certain areas of the world. This change is particularly noticeable over the Antarctic, where temperatures tend to be cooler than historic trends indicate, and in the southern hemisphere in general, where temperatures are heating up. The human activity believed to be responsible for this is ozone depletion and CFC pollution.

The area between the pole and the westerly winds (in the southern hemisphere) is experiencing increased temperatures as a result of the combination of these two weather patterns. In turn, this warmer temperature causes the westerly winds to grow in strength and speed. As these winds become stronger, they prevent the warm air from making its way to the south pole. Therefore, the Antarctic coastal zones are more affected by the increased temperatures. The westerlies in the northern hemisphere are experiencing the opposite effect, largely because the ozone in this area has not been quite as depleted as in the south. These weakened westerly winds mean that the Arctic polar jet stream is not as strong as in previous years. As this jet stream moves at a slower pace, it tends to change its course in more extreme patterns than it once did. This changing course combines with the cooler temperatures to produce extreme weather conditions in the northern hemisphere. Other scientists have claimed a correlation between these changes in both the northern and southern westerlies patterns and increasing instances of drought, in countries of both hemispheres. These same scientists predict that these weather changes will continue in the future, increasing wildfires, decreasing agricultural output, and depleting marine resources.


More in Environment