15. What are permanent winds and periodic winds ?

Permanent winds blow in the same direction throughout the year. The winds blowing approximately in the same direction between specific pressure belts permanently are called permanent winds.Trade winds, Westerly winds and Polar winds are Permanent winds. Permanent winds are also known as planetary winds.

Winds that result from the uneven heating and cooling of vast lands and water bodies are called periodic winds. Periodic winds are also known as seasonal winds.

16. What are trade winds ?

Trade winds are winds blowing from the subtropical high pressure belts to the equatorial low pressure belts. These winds blow as the north east winds in the northern hemisphere and the south east winds in the southern hemisphere. These are winds which blow in the same direction with the same velocity throughout the year, especially in the oceanic regions. Trade winds which carry water vapour from the oceans cause rainfall in the eastern coasts of the continents.

17. What are westerly winds ?

The winds blowing from the subtropical high pressure belts towards the sub-polar low pressure belts are called westerly winds. In the northern hemisphere the westerly winds blow from the south western direction to the north eastern direction. But in the southern hemisphere they blow from the north western direction to the south eastern direction. Since they blow from the western direction they are called the westerly winds.

18. What are polar winds ?

Polar winds are winds blowing from the polar high pressure belts to the subpolar low pressure belts.The polar winds are colder and stronger.These winds are also called easterly winds.

19. What are monsoon winds ?

The term monsoon has derived from the Arabic word 'Mausim' meaning seasons. Monsoonal winds blow over South Asia, South East Asia, Australia and East Africa. It was during the time when monsoonal winds became active that merchants used to travel by soil boats for trade purposes in the Indian Ocean.

20. What are South West monsoon winds ?

The winds which blow in a south east direction in the southern hemisphere when cross the equator, change their direction to the south west due to the coriolis effect.These are the south west monsoon winds.

21. What are the land breeze and the sea breeze ?

The winds that are formed in the coastal regions due to the uneven heating and cooling of the land and the oceans over shorter periods are called the land breeze and the sea breeze. The land and the sea do not get heat or cooled in the same manner. During the day time the land gets heated quickly and at night time it cools very fast.

22. What are cyclones?

The heating up of the atmospheric air of a region increasingly in relation to its surrounding regions causes sudden pressure changes. This pressure difference creates cyclones. Cyclones have low pressure at the central part and high pressure in the surrounding regions.

23. What are local winds ? What are the important local winds ?

The winds formed as a result of the local differences in atmosphere are known as local winds.Such winds blow locally. Local winds are known by different names in different places. The important local winds are the following :-

• Loo -  Hot dry winds that blow in the afternoons over the northern plains of India during the months of May and June.
  
  
• Chinook - The hot and dry winds that blow over the eastern slopes of the Rocky mountain chain of North America are called chinooks. This wind which blows during the winter time causes the melting of the snow in the prairies region.
  
  
• Mistral - The cold winds that blow in the southern slopes of the Alps mountains of Europe are called mistrals. The influence of mistral is considerable in Southern France.
  
  
• Foehn -  The hot dry winds that blow over the northern slopes of the Alps mountains are called Foehn.