måndag 19 december 2011

Why is it more windy during winter?


The difference in air pressure between the Equator and North Pole is at its highest during midwinter. Then the air over the North Pole is at its coldest and heaviest, while it is still summer warm over the Equator. When the air in the north is at the coldest and heaviest, the kinetic energy towards the high pressure in the south is the greatest and we get stronger winds than during our summer half year when the differences in temperature are smaller.

Wind occurs because of pressure differences in the air. These pressure differences are created by air temperature differences. We get temperature differences in the atmosphere because the earth is spherical and therefore the solar radiation has different approach to the Earth's surface. In the northern hemisphere, the angle between the sun and the earth's surface reduces the further north one travels. Therefore, it is warmer at the equator and colder at the poles.

In the atmosphere there is high pressure and low pressure created by the difference in temperature of the air masses in different areas. When air masses move from areas of high pressure to areas of low pressure winds occurs. The greater the pressure difference is the harder it blows.

Solar heating is unevenly distributed over the earth and the wind is trying to smooth out these differences in temperature. Therefore, the wind blows more in the fall and winter in our part of the world, when very cold air has formed at the North Pole, while air masses in the south are still summer warm.

There are different types of high pressure. Stationary high pressures are warm and created over large sea areas while the seasonal high pressures are cold and occur during winter over the northern continents. Variable high-pressures occur in connection with the migratory lows. It is the seasonal high pressure that creates cold winds from north to south.

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