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UDU Junior Geography Chapter 13
Chapter 13 - Air Masses, Fronts & Depressions
Air Mass - large body of air in which temperatures, pressure and humidity are fairly uniform (the same).
Front - The place where two different air masses meet. The fronts move as the air masses move. A front which is followed by a cold air mass is called a cold front. A front that is followed by a warm air mass is called a warm front.
Polar Fronts - usually occur between 50° and 60° N. & S. This is where cold polar air mass meets the warm tropical air mass.
In the N. Hemisphere the cold polar winds blow from a N.E. direction and they are dry winds. The warm tropical winds blow from a SW direction and are damp or wet winds.
Depressions - often occur along the polar front in the Northern Hemisphere. This front is over Ireland, and is the reason for our often wet and
changeable weather.
Formation:
1. The cold Polar air meets the warm tropical air at the polar front.
Diagram page 63:
2. These air masses push against each other and the warm air mass makes a dent into the cold air mass.
Diagram:
3. The cold air wraps itself around the back of the warm air mass until a large wedge of warm air is almost surrounded by the colder air. A depression has been formed.
Diagram.
Depressions and Irish weather:
Depressions develop over the Atlantic Ocean. They move in from the west and often reach Ireland, especially in winter.
Diagram:page 65
1. Cold Sector - temperature low, high cirrus cloud, dry, pressure falls slowly.
2.Warm Front - stratus clouds, continuous rainfall, pressure still falling.
3. Warm Sector - temperature rises, stratus cloud, drizzle or dry, pressure low.
4. Cold Front - temperature falls, cumulus cloud, blustery showers, pressure rises.
5. Cold Sector - temperature low, some cumulus cloud, becoming dry, pressure high.
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