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Extreme cold makes the polar air extremely cold and dense. So this heavy air of the region tends to settle near the ground. Apart from that, a part of the air rising from the sub polar lows that moves mainly polewards, also gradually colder and heavier, and comes down. Slowly, the cold surface winds creep towards the equator as the polar winds.
In other words, emanating from the polar highs, the areas of high pressure around the North and South Poles, the polar winds or polar easterlies flow to the low-pressure areas in sub-polar regions. As they blow from the cold deserts, which are extremely cold and dry, these cold winds sink to the ground level, form very high pressure over the poles and blow to the sub polar low pressure belts.
The polar winds are also deflected, and due to deflection they blow from the north-east in the northern hemisphere and from the south-east in the southern hemisphere. They are also called the polar easterlies, from the direction in which they blow.
This belt of low pressure is more persistent in the summer season and generally disappears in the winter season. However, the Icelandic and Aleutian low pressure belts persist throughout the year. Due to the northward shifting of pressure belts at the time of summer solstice in the northern hemisphere, the region of polar winds shrinks, but it is extended up to 60°N latitude during the winter solstice.
Although the polar easterlies are one of the five primary wind zones, known as wind belts that make up our atmosphere's circulatory system, they are often weak. Unlike the westerlies in the middle latitudes and trade winds in the tropics, the polar winds are the most irregular among the planetary winds.
