Polar easterlies
Encyclopedia
The polar easterlies are the dry, cold prevailing winds
Prevailing winds
Prevailing winds are winds that blow predominantly from a single general direction over a particular point on Earth's surface. The dominant winds are the trends in direction of wind with the highest speed over a particular point on the Earth's surface. A region's prevailing and dominant winds...

 that blow from the high-pressure areas of the polar high
Polar high
The polar highs are areas of high atmospheric pressure around the north and south poles, south polar high being the stronger one because land gains and loses heat more effectively than sea...

s at the north
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...

 and south pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...

s towards low-pressure areas within the Westerlies
Westerlies
The Westerlies, anti-trades, or Prevailing Westerlies, are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. These prevailing winds blow from the west to the east, and steer extratropical...

 at high latitudes. Cold
Cold
Cold describes the condition of low temperature.Cold may also refer to:*Common cold, a contagious viral infectious disease of the upper respiratory system*Chronic obstructive pulmonary disease...

 air subsides at the pole creating the high pressure, forcing a southerly (northward in the southern hemisphere) outflow of air towards the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

; that outflow is then deflected westward by the Coriolis effect
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

. Unlike the westerlies
Westerlies
The Westerlies, anti-trades, or Prevailing Westerlies, are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. These prevailing winds blow from the west to the east, and steer extratropical...

 in the middle latitudes
Middle latitudes
The middle latitudes are between 23°26'22" North and 66°33'39" North, and between 23°26'22" South and 66°33'39" South latitude, or, the Earth's temperate zones between the tropics and the Arctic and Antarctic. The prevailing winds in the middle latitudes are often very strong...

, the polar easterlies are often weak and irregular. These prevailing winds blow from the east
East
East is a noun, adjective, or adverb indicating direction or geography.East is one of the four cardinal directions or compass points. It is the opposite of west and is perpendicular to north and south.By convention, the right side of a map is east....

 to the west
West
West is a noun, adjective, or adverb indicating direction or geography.West is one of the four cardinal directions or compass points. It is the opposite of east and is perpendicular to north and south.By convention, the left side of a map is west....

.

The polar easterlies are one of the five primary wind zones, known as wind belts, that make up our atmosphere's circulatory system. This particular belt of wind begins at approximately 60 degrees north and south latitude and reaches to the poles. When air moves near the poles, cold temperatures shrink the air. This promotes air from warmer latitudes to flow into the area, causing a polar high-pressure zone. Air from this high-pressure zone then rushes toward the low-pressure zone surrounding the sub-polar region. This flow of air is altered by the Earth's rotation and deflected east, hence the name easterlies.

The other four primary wind zones are known as the doldrums, trade winds, prevailing westerlies and horse latitudes. The sun heats the Earth in an uneven fashion, causing variations in pressure in the atmosphere. As air moves between high- and low-pressure zones, its path is deflected -- to the east or west, depending on the hemisphere, as we saw with the polar easterlies -- thanks to the rotation of the Earth. All of this unequal heat, rushing air and spinning Earth combine to form global currents such as the polar easterlies.

Another example of the phenomenon would be the trade winds, which reach from where the doldrums (the area that gets the biggest blast of heat from the sun) leave off at about 5 degrees north and south latitude to as far as 30 degrees north and south. They are caused by air moving into the area from the subtropics to fill the void left by the doldrums' rising air. The trade winds blow steadily westward out of the northeast in the Northern Hemisphere and out of the southeast in the Southern Hemisphere. Sailors in earlier times, traveling by wind current and sail only, counted upon the reliability of the trade winds to help them along on their voyages. Similarly, they sought to avoid the doldrums, where the wind was so scant they risked coming to a complete stop
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