Page 139 - SST Class 07

Where the tempera- particular direction throughout the year.
ture is low, the air is Winds which blow from subtropical high-
cold and therefore pressure belts to equatorial low-pressure
heavy. This heavy belts are called Trade Winds.
air sinks and creates Winds originating from subtropical high-
a high-pressure area. pressure belts and blowing towards sub-
High pressure is polar low-pressure belt generally originate
associated with clear from the western direction are called
and sunny sky. Barometer Westerlies.

The movement of air is always from areas of high Winds that blow from the polar high-pressure
pressure to areas of low pressure. belt to the sub-polar low-pressure belt are
Barometer is used to measure atmospheric called polar winds. The winds blow in both
pressure. Northern and Southern Hemispheres.
Wind Pole
Polar
Air in motion is called wind. Difference in atmo- L Easterlies 60°N
sphere pressure helps wind to blow. Wind direc- Prevailing
H Westerlies
tion is measured by an instrument known as the 30°N
Northeast
wind vane and its speed is measured by ane- Trade Winds
L 0°
mometer. Doldrums
Wind plays a very important role in our lives. It
H 30°S
forms and carries clouds. It influences air and
oceanic transport and communications. It con-
L 60°S
tains a form of energy called kinetic energy.
Pole
Planetary Winds
2. Seasonal or Periodic Winds
These are winds which change their direc-
tion in different seasons during the year.
They blow during a specific season. The
monsoon winds in India blow during a
particular season and bring rain to the
whole country. They change their direction
with the change of seasons.

Wind Vane and Anemometer 3. Local Winds
There are broadly three types of winds : Blowing only during a particular period of a
day or year, these winds have some specific
1. Permanent or Planetary Winds
characteristics and blow over a small area,
2. Seasonal or Periodic Winds
e.g., ‘Land’ and ‘Sea breeze’. They are
3. Local Winds
known by local names, e.g., ‘Loo’ which are
1. Permanent or Planetary Winds hot and dry local winds blowing in northern

These are winds which constantly blow in a India in summer season. Sea Winds are also

Social Science-7 139