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 \tA large volume of air. \tCovers an extensive area. \tHas uniform temperature and humidity. \tDistinct from the surrounding air. \tRetains its characteristics when it moves away. Types of Air Masses \tEquatorial Air Mass \tOriginate from equatorial oceans. \tIt’s hot and unstable. \t Sub-tropical Air Mass \tForms near sub-tropical high pressure belt. \t Polar Air Mass \tForms near the poles or temperate low pressure zone. \tIt’s cool. \t Arctic and Antarctic air Masses \tForms over the ice sheets of Greenland and Antarctica respectively. \t Effect of air masses on Weather \tWhen warm moist air mass and cool air mass meet cyclonic rainfall is formed e.g. tropical maritime and polar maritime. \tCool air masses take cooling effect to the areas they move to e.g. polar continental. \tIf they are warm they take warming influence to the area they move to e.g. tropical continental.