The movement of air which is caused by the non-uniform heating of Earth by Sun is called as Wind
- Sometimes wind blows gently, refreshingly us. At other times, it blows strongly creating storms that cause widespread damages.
- We need measurements of two quantities : direction and speed, to give a description of the wind.
- They move from the Subtropical High pressure Belt to the Equatorial Low Pressure Belt in the tropics lying between 30° North and 30°South Latitudes.
- They blow as the N.E Trades in the Northern Hemisphere and as the S.E Trades in the Southern Hemisphere.
- The name “Trade” is derived from a nautical expression ”to blow tread” meaning o blow along a regular path or “tread”.
- They move from the Sub-tropical High Pressure Belt to the Sub-polar Low Pressure Belt in the temperate latitudes lying between 30° and 60°, on either side of the Equator.
- They are more constant and stronger in the southern Hemisphere because there are no large landmasses to interrupt them.
- In places they become so strong that these winds are known as the Roaring Forties or the Brave West Winds and the Furious Fifties.
- The belts of the Westerlies move north and south following the sun’s movement. These are known as Westerlies because they blow out of the west.
- They blow from the Polar High Pressure Belt to the Sub-polar Low Pressure Belt lying between latitudes 60° and the poles on both sides of the Equator.
- These winds blow from the east to form the Polar Easterlies.
- They are more regular in the Southern Hemisphere.
- Polar winds are extremely cold and dry because they come from the ice-cap region.
Climate Winds or Periodic Winds
These winds change their direction along with change in time or change in climate. Typical examples are the sea breezes & Monsoon winds.
- Monsoon winds are seasonal winds which is distinguished by their direction completely reversal from one season to another.
- They blow from the sea to the land in summer.
- They blow from the land to the sea in winter.
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