Westerlies (Detailed)

In the intricate ballet of Earth’s atmospheric circulation, the westerlies play a crucial role. Often referred to as the “westerly winds,” these prevailing winds blow from the west to the east in the middle latitudes of both hemispheres. While they might seem like mere meteorological features, the westerlies have a significant impact on weather patterns, climate, and even global trade routes.

The Mechanics Behind Westerlies

The westerlies are part of the Earth’s atmospheric circulation cells, particularly the Ferrel cells, nestled between the polar and subtropical cells. They owe their existence to the Coriolis effect – the apparent deflection of moving air due to the Earth’s rotation. In the Northern Hemisphere, air is deflected to the right, while in the Southern Hemisphere, it’s deflected to the left. This deflection sets the stage for the westerlies to emerge as powerful, persistent winds.

Two Belts of Westerlies

The westerlies manifest as two distinct belts in each hemisphere: the Subtropical Westerlies and the Polar Westerlies.

• Subtropical Westerlies: These winds are found between 30 and 60 degrees latitude in both hemispheres. They are responsible for the movement of weather systems from west to east across continents and oceans. In the Northern Hemisphere, these winds are dominant over the United States and Europe. The jet stream, a narrow ribbon of strong westerly winds high in the atmosphere, is a product of the subtropical westerlies and greatly influences weather patterns and aviation routes.
• Polar Westerlies: Located between 50 and 70 degrees latitude, these winds are especially influential in the Southern Hemisphere due to the vast expanse of unobstructed ocean. They have a significant impact on the Southern Ocean’s currents, affecting marine life and climate patterns. In the Northern Hemisphere, these winds are more fragmented due to the presence of more landmasses.

Influence on Climate and Weather

The westerlies play a pivotal role in shaping regional climates and weather phenomena.

• Temperature Regulation: The westerlies help distribute heat from the equator towards the poles, contributing to the moderation of temperature extremes. Coastal areas affected by the westerlies tend to have milder climates than their inland counterparts.
• Storm Tracks: The movement of weather systems from west to east is facilitated by the westerlies, leading to the formation of storm tracks. These are the preferred paths for cyclones, anticyclones, and other weather systems.
• Rainfall Patterns: The westerlies influence precipitation patterns. As moist air from oceans encounters landmasses, it is forced to ascend due to the westerlies, leading to rainfall on the windward side of mountains (orographic rainfall), creating distinct rain shadows on the leeward side.

Impact on Trade and Travel

The westerlies have significantly impacted historical trade routes and travel patterns, both on sea and in the air.

• Historical Maritime Trade: The westerlies have been vital for maritime trade, especially during the Age of Exploration. Sailing ships utilized the predictable westerly winds to navigate between continents, most notably the trade routes connecting Europe to the Americas.
• Modern Air Travel: The jet stream, a product of the westerlies, greatly affects air travel times and fuel efficiency. Aircraft flying from west to east can benefit from tailwinds provided by the jet stream, reducing flight times, while the opposite is true for eastbound flights.

Westerlies Comparison

The westerlies, those steadfast winds that traverse the globe, are much more than meteorological curiosities. Their influence extends from shaping climate and weather patterns to revolutionizing historical trade routes and modern air travel.