The distribution of pressure is not equal on the earth’ surface. It changes from palace to place and time to time on the basis of air temperature and rotation of the earth. Any area in the atmosphere where air pressure is higher than in the surrounding areas is called “ High pressure”/ Thee are 4 high pressure belts and 3 low pressure belts on the earth’ surface.
Equatorial Low pressure belt: This belt *** between latitudes 5° N and 5° . The Sun’* rays are almost vertical on the equator throughout the year. As a result, the temperature is uniformly high and pressure is low throughout the year. It is also known as “Doldrums”. The air gets warm and rises upward. Horizontal movement of air is absent and convectional currents occur. This is the zone of convergence of the trade winds.
Sub tropical high pressure belts: The air ascended in the form of convectional currents from the equatorial region partly descends in the between 30 to 40’ latitudes in both the hemispheres. The descending air has thus formed two high pressure zones known as subtropics high pressure belts. It is the zone from which trade and anti-trade winds originate. This belt is also known as “ horse altitudes’. It is dry and quite stable. The name horse latitude is given by the ancient sailors who used to transport horses on ships. Due to absence of strong winds, some times the ship could not move with horses. Hence sailors used to dump horses to make the ship move forward.
Sub Polar low pressure belts: In between polar high pressure knd sub-tropical high pressure belt, the sum-tropical low pressure belts are situated. They **** in between 60’ to 70’ latitudes in both the hemispheres. They are formed with spinning action of rotation of the earth and also uprising air as an effect of incoming cold polar winds.
Polar high pressure belts: The Polar Regions are characterized with low temperature. The air raised at the equator descends around the poles causing high pressure belts. The cold polar winds **** outward from this zone.
