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Winds originating from subtropical high pressure belts

and blowing towards sub polar low pressure belt generally
originate from the western direction are called Westerlies.
Winds that blow from the polar high pressure belt to the sub-
polar low pressure belt are called Polar Winds. The winds
blow in both northern and southern Hemispheres.

2. sEasoNal WiNds

The winds blow in a particular direction during a period of
time is called periodic or seasonal wind. Monsoon winds
are seasonal winds. The word ‘monsoon’ has been derived Different types of Winds
from the Arabic word ‘Mousin’, which means ‘season’. For six months they blow from land
to sea and for the other six months from sea to land. These winds change their direction in
different seasons. For example, monsoons in India.

3. local WiNds
Some winds blow in local area with specific characteristics. These blow only during a
particular period of the day or year in a small area. The hot and dry local wind of northern
plains of India is called loo. For example, land and sea breeze.

moisturE

When our body becomes too hot, it naturally starts
sweating. Sweating is an inbuilt natural mechanism for
cooling itself down. As the sweat of your body turns into
vapour, it carries the excess heat with it into the air. The
same happens with the surface of the earth. As water
evaporates, heat is carried from the earth’s surface into
the atmosphere in form of water vapour. Moisture in the
Clouds form because of Moisture in the air atmosphere prevails in solid, liquid and gaseous states.
The amount of moisture available in the air varies time to time and place to place.

Moisture in the air at any time is known as humidity. Moisture (water) in the atmosphere
causes clouds to form, fog to cover the landscape, and humidity to thicken the air. It also
causes rain, snow, hail and sleet to form.
And when the droplets of water vapour become too heavy and it becomes difficult for
clouds to hold it any longer they fall down on the earth surface in form of rain. Some other
forms of precipitation are snow, sleet and hail. Rainfall is very important for the survival
of plants and animals. It brings fresh water to the earth’s surface.

rainfall
Rainfall itself is of three types.

(i) rEliEf raiNfall

It occurs when moist bearing winds are forced to rise over a hill or mountain and shed its
moisture in the form of rainfall. It is also called the orographic rainfall.
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