Summary AQA geography last minute revision - Global hazard
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Course
Geography
Institution
GCSE
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Global pattern of air circulation Topic 1: Global Hazards Distribution of Tropical Storms.
Atmospheric circulation is the large- Causes of Drought: El Nino effect They are known by many names, including hurricanes
scale movement of air by which heat is (North America), cyclones (India) and typhoons (Japan and
distributed on the surface of the Earth. The El Nino effect is also associated with creating dry conditions. East Asia). They all occur in a band that lies roughly
In an El Niño year (every 2-7 years) Normally, warm ocean currents off between the tropics of Cancer and Capricorn.
Hadley Largest cell which extends
cell from the Equator to the cycle reverses. Cooler water off the coast of Australia cause moist
the coast of Australia reverses the warm air to rise and condense Distribution of Droughts
between 30° to 40° north &
south. wind direction leading to dry, sinking causing storms and rain over Drought can occur anywhere throughout the world but
air over Australia causing hot weather Australia. they are more frequent between the tropics of Cancer and
Ferrel Middle cell where air flows and a lack of rainfall. Capricorn. Many countries in Africa suffer from severe
cell polewards between 60° & drought, such as Ethiopia but Australia also suffer.
70° latitude. Types of precipitation
Polar Smallest & weakness cell Convectional Rainfall When the land warms up, it heats the air enough to Formation of Tropical Storms
cell that occurs from the poles expand and rise. As the air rises it cools and condenses. 1
The sun’s heats large areas of ocean in the summer
to the Ferrel cell. If this process continues then rain will fall.
and autumn. This causes warm, moist air to rise
Frontal Rainfall When warm air meets cool air an front is formed. As the over the particular spots
High and Low Pressure warm air rises over the cool air, clouds are produced. 2
Once the temperature is 27⁰, the rising warm moist
High Pressure Low Pressure Eventually steady rain is produced. air leads to a low pressure. This eventually turns
Relief Rainfall When wind meets mountains, the warm air is forced to into a thunderstorm. This causes air to be sucked in
Caused by cold Caused by hot air
rise quickly and cool. This leads condensation and from the trade winds.
air sinking. rising. Causes
Causes clear and stormy, cloudy eventually rainfall. When the air descend however, little 3
With trade winds blowing in the opposite direction
calm weather weather. very rainfall falls, creating a rain shadow. and the rotation of earth involved (Coriolis effect),
the thunderstorm will eventually start to spin.
Types of wind Changing pattern of these Hazards 4
When the storm begins to spin faster than 74mph,
Katabatic Winds that carry air from the high Tropical Storms Scientist believe that global warming is a tropical storm (such as a hurricane) is officially
Winds ground down a slope due to gravity. having an impact on the frequency and born.
e.g. Antarctic. strength of tropical storms. This may be due 5
With the tropical storm growing in power, more
to an increase in ocean temperatures. cool air sinks in the centre of the storm, creating
Trade Winds Wind that blow from high pressure
belts to low pressure belts. calm, clear condition called the eye of the storm.
Droughts The severity of droughts have increase since
6
Jet Streams These are winds that are high in the the 1940s. This may be due to changing When the tropical storm hit land, it loses its energy
atmosphere travelling at speeds of rainfall and evaporation patterns related to source (the warm ocean) and it begins to lose
225km/h. gradual climate change. strength. Eventually it will ‘blow itself out’.
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