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
- Equatorial Air Mass
(a) Originate from equatorial oceans.
(b) It’s hot and unstable.
- Sub-tropical Air Mass
(a) Forms near sub-tropical high pressure belt.
- Polar Air Mass
(a) Forms near the poles or temperate low pressure zone.
(b) It’s cool.
- Arctic and Antarctic air Masses
(a) Forms over the ice sheets of Greenland and Antarctica respectively.
- Effect of air masses on Weather
(a) When warm moist air mass and cool air mass meet cyclonic rainfall is formed e.g. tropical maritime and polar maritime.
(b) Cool air masses take cooling effect to the areas they move to e.g. polar continental.
(c) If they are warm they take warming influence to the area they move to e.g. tropical continental.
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