An easterly wind travels from the east toward the west, named for its direction of origin. Easterlies are a fundamental component of the Earth’s general atmospheric circulation, a predictable, planet-wide system driven by the uneven distribution of solar energy. This large-scale circulation ensures that heat and moisture are constantly redistributed, creating the major climate zones and weather patterns. These prevailing patterns result in two major, consistent easterly wind belts found near the poles and in the tropical regions.
The Mechanics of Easterly Flow
The reason winds flow from east to west lies in the physics of a rotating sphere combined with the movement of air between pressure zones. Air naturally moves from areas of high atmospheric pressure, where air is sinking and dense, toward areas of low pressure, where air is rising and less dense. This movement is not a straight line because of the planet’s continuous rotation.
The Earth’s spin introduces the Coriolis Effect, which deflects any moving object, including air masses, relative to the planet’s surface. In the Northern Hemisphere, this deflection pushes moving air to the right of its intended path, while in the Southern Hemisphere, the deflection is to the left. The strength of this effect increases with latitude. When air flows outward from a high-pressure zone, the Coriolis deflection acts on the moving mass. For winds traveling toward the equator or the poles, this deflection turns the pole-to-equator flow into a sideways, east-to-west motion, creating the planetary easterly wind belts.
Polar Easterlies
The Polar Easterlies are cold, dry prevailing winds that flow across the highest latitudes, generally positioned poleward of the 60-degree latitude lines in both hemispheres. These winds originate from the frigid, dense air masses that form the Polar High pressure zone directly over the poles. Because the air here is extremely cold, it sinks, creating a stable area of high pressure near the surface. Air moving outward from this Polar High flows toward the warmer, lower-pressure Subpolar Lows, situated near 60 degrees latitude. As this equatorward-moving air is deflected by the Coriolis effect, it gains an easterly component, creating the Polar Easterlies. This wind system is the surface component of the Polar Cell.
Compared to other global wind systems, the Polar Easterlies are often weaker and more erratic in their direction and strength. They transport cold, dry air from the poles toward the mid-latitudes, where they meet the warmer prevailing westerly winds. This convergence zone is frequently a site of intense storms and is connected to the movement and intensity of the polar jet stream.
Tropical Easterlies (Trade Winds)
The Tropical Easterlies, commonly known as the Trade Winds, dominate the latitudes between the equator and about 30 degrees north and south. These winds are the surface manifestation of the Hadley Cell, an atmospheric circulation loop driven by intense solar heating near the equator. Warm air rises at the equator, travels poleward high in the atmosphere, and then sinks back toward the surface around the 30-degree latitudes.
This sinking air creates a belt of high pressure called the subtropical high, or the Horse Latitudes. Air flows along the surface from these high-pressure zones back toward the equatorial low-pressure zone, known as the Inter-Tropical Convergence Zone (ITCZ). As this air moves toward the equator, the Coriolis effect deflects it to the west, resulting in the northeast Trade Winds in the Northern Hemisphere and the southeast Trade Winds in the Southern Hemisphere.
The Trade Winds are remarkably stable and reliable, historically relied upon by sailing vessels for trans-oceanic voyages. They are a powerful driver of both atmospheric and oceanic circulation. By continuously pushing surface water westward across the tropical oceans, these winds generate major ocean currents, such as the Equatorial Current, which influences the distribution of global heat. These easterlies also play a defining role in tropical weather, acting as the steering mechanism for tropical storms, cyclones, and hurricanes. The persistent flow of these winds influences the distribution of rainfall, bringing precipitation to many tropical islands and coastlines.