Geography Theme 2 Key Ideas

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Frontal Rainfall

(1) A cold polar air mass meets a tropical air mass and form fronts.

(2) The colder air mass is heavier than the warm air so the lighter warm air mass rises over the top of the heaiver, colder air. 

(3) As the warm air is forced to rise, it cools. It also cools because the warm air is in contact with the cold air. 

(4) Condensation occurs and clouds form.

(5) Rain occurs along the front.


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Relief Rainfall

(1) Prevailing winds bring warm, moist air to the western British isles.

(2) Air is forced to rise over high areas causing the air to cool and condense, which forms clouds and results in rain.

(3) The air descends down other side of high area, the air warms up while descending and therefore it is dry the other side of the high area. 


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Convectional Rainfall

(1) The ground warms up, due to the sun, meaning the the air above the ground is also heated up. 

(2) This causes th air to rise.

(3) As this happens, the air cools and condenses to form clouds resulting in rain. 


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Low pressure systems

Depressions = Low Pressure 

Despressions happen in winter & summer:  Rain, snow & ice (winter only). Windy. Moist. Very cloudy. Moderate temperatures.

(1) It is slightly warmer in the winter as clouds keep the heat in. However, it is slightly cooler in the summers as clouds keep the sunlight out. 

(2) Warm air is light and unstable so there is wind. 

(3) Warm air rises (anticlockwise), evaporating water as it rises. This air cools and condenses creating clouds.

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High pressure systems

Anticyclones = High Pressure

Anticyclone weather in winter: fog, forst, cold, clear skies, and little wind. Anticyclone weather in summer: clear skies, little wind, very hot and hazy.

(1) Cool air condenses (clockise) stops clouds forming so skies are clear.

(2) Because air is sinking slowly there is little wind. 

(3) No clouds mean the sun's ray's create hot temperatures in summer. However, no clouds, in winter, means that all the heat escapes. 

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Typhoons, Hurricanes & Cyclones

(1) The oceans needs to be 26C or more, this can be found near the equator.

(2) The hot air from the ocean rises very quickly (convectional rainfall), the air rising evaporates ocean water with it. 

(3) As the air, it cools and condenses forming huge rain storms. The heat energy gives the storms lots of power so there are high winds.

(4) When winds winds reach up to or more than 70mph, huricanes/typhoons/cyclones occur. 


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