AIR MASSES 

Distinct large parcels of air moving in one direction

– Originate from areas of uniform weather and topography from where they derive their characteristics e.g. flat areas, forests, deserts, and snow covered areas.

Characteristics of Air Masses

• A large volume of air.
• Covers an extensive area.
• Has uniform temperature and humidity.
• Distinct from the surrounding air.
• Retains its characteristics when it moves away.

Types of Air Masses

1. Equatorial Air Mass

• Originate from equatorial oceans.
• It’s hot and unstable.

1. Sub-tropical Air Mass

• Forms near sub-tropical high pressure belt.

2. Polar Air Mass

• Forms near the poles or temperate low pressure zone.
• It’s cool.

3. Arctic and Antarctic air Masses

• Forms over the ice sheets of Greenland and Antarctica respectively.

4. Effect of air masses on Weather

• When warm moist air mass and cool air mass meet cyclonic rainfall is formed e.g. tropical maritime and polar maritime.
• Cool air masses take cooling effect to the areas they move to e.g. polar continental.
• If they are warm they take warming influence to the area they move to e.g. tropical continental.