Friday, March 23, 2007

WINDS - that blow.....

Air has weight - cold air weighs in more than warmer air. Therefore, cold air has more pressure. When the sun warms the air, the air expands - becomes lighter and rises. This movement causes a wind - the air to move. The speed of air movement is determined by how close the cold air and warm air mass together and their pressure or temp difference. The bigger the difference, the faster the wind blows...

Winds do not blow in striaght lines due to the Coriolis force - a result of the Earth's rotation - In the Northern Hemisphere the winds blow clockwise around areas of high pressure - counterclockwise around areas of low pressure.

The Beaufort Wind Force Scale was developed in 1805 by Admiral Sir Francis Beaufort of the British Navy to measure sea winds. This is the common way of estimating wind speed.

Hurricanes - June through November - develop over warm tropical waters (80F or higher), getting their energy from the warm moist air rising from the ocean's surface. To getclassified as a Hurricane, the storm must have winds of 74 milesPH or greater. Some sustained winds can reach 150mph plus with gusts up to 190mph. Such storms are called Typhoons in the Western Pacific and Cyclones in the Indian Ocean.

Tornadoes are violently rotating colums of air known as the Vortex. These require high humidity, extreme atmospheric instability and falling pressure. A Vortex is often created as part of a thunderstorm when swift winds in the upper atmostphere and slower winds near the ground set are into a spinning motion. Those high winds in a Tornado are due to the extreme low pressure forming at the centre of the spinning column of air. Air speads up as it converges toward the low pressure.

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