Westerly winds are prevailing winds that blow from the west towards the east in the middle latitudes, specifically between 30 and 60 degrees latitude in both the Northern and Southern Hemispheres. They are a significant component of mid-latitude weather systems.
How Westerly Winds Form
Westerly winds primarily form due to Earth’s rotation and global pressure systems. Uneven solar heating drives atmospheric circulation, causing warm air to rise near the equator and cool air to sink at the poles. Warm air rising near the equator moves poleward at higher altitudes, then cools and descends around 30 degrees latitude, forming subtropical high-pressure zones.
Air moves from these high-pressure areas towards lower-pressure zones at higher latitudes. The Earth’s rotation significantly influences this movement through the Coriolis effect, deflecting air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection transforms poleward winds into winds blowing from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere, forming the westerlies.
Westerly winds are stronger during winter due to increased temperature gradients between polar and tropical air masses. Stronger low pressure near the poles intensifies the westerlies, bringing warmer air into mid-latitudes. Conversely, during summer, higher polar pressure weakens the westerlies and shifts their position. In the Southern Hemisphere, with fewer landmasses, westerlies are generally stronger and more consistent.
Westerly Winds and Global Weather
Westerly winds play a substantial role in shaping global weather patterns and climate. They steer weather systems, such as extratropical cyclones, across continents in the mid-latitudes. These systems bring varied conditions, including precipitation like rain or snow, as westerlies carry moisture-laden air.
These winds are closely connected to jet streams, narrow bands of strong winds high in the atmosphere. Jet streams move weather patterns around the world. Over the North Atlantic, for instance, the polar jet stream steers weather systems in a west-to-east direction.
Westerly winds also influence ocean currents, impacting regional climates. They drive surface currents, like the North Atlantic Drift, transporting warm equatorial waters poleward towards western continental coasts. This moderates the climate in affected regions. The interaction between wind and water also promotes upwelling, bringing nutrient-rich water to the surface and supporting marine life.
Place in Earth’s Wind Systems
Westerly winds are a component of Earth’s broader atmospheric circulation, a worldwide system transporting heat from tropical to polar latitudes. This global circulation is organized into three main cells in each hemisphere: the Hadley cell, the Ferrel cell, and the Polar cell. The westerlies are found within the Ferrel cell, situated between approximately 30 and 60 degrees latitude.
The Ferrel cell circulates air poleward near the surface and equatorward at higher altitudes. Unlike the Hadley and Polar cells, the Ferrel cell is weaker and more variable, acting like a gear driven by its neighboring cells.
Other major global wind patterns include the trade winds and the polar easterlies. Trade winds blow from the east towards the equator, originating from the Hadley cells. Polar easterlies, found near the poles, blow from the east as cold air moves away from high-pressure areas. These three prevailing wind belts distribute heat and moisture across the planet.