Extreme weather events

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temperate storms are weather systems with strong winds and heavy rainfall. they're caused by extreme low pressure systems called depressions

  • Warm air constantly moves out of tropical areas, towards the poles. A warm front is the leading edge of a warm air mass
  • Cold air moves out of polar regions, towards the tropics. A cold front is the leading edge of a cold air mass
  • Where the air masses meet in the temperate zone, the warm air heading towards the pole rises above the cold air heading towards the tropics
  • the rising warm air means there's less air at ground level
  • strong winds blow into the area of low pressure in a spiral fashion
  • the cold front catches up with the warm front and when this happens the warm air behind the warm front is undercut by the incoming cold front and is lifted away from the ground entirely. It now sits above the cold air (this is the occluded front). The warm air rises into the upper atmosphere
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  •  A tornado is a rotating column of air that is in contact with the ground surface and the clounds above.
  • Tornadoes have wind speeds of up to 480kph and can travel over land for many kilometres.
  • They form when rotating air high in the atmosphere gets turned on its side into a vertical column and is dragged down to the surface by descending air. This happens in large storms
  • This means tornadoes occur anywhere there are temperate storms- they're most common in the USA
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Tropical Cyclones

  • tropical cyclones are huge spinning storms with strong winds and torrential rain that develop over water
  • The conditions needed include a disturbance near the sea surface that triggers the cyclone, sea water above 26.5 degrees and the coriolis effect (making the winds spin)
  • tropical cyclones form around the tropics because the water there is warm
  • they don't perform below the 5 degrees latitude because the coriolis effect isn't strongg enough
  • tropical cyclones dissipate over land 
  • they move away from the equator because of the coriolis effect
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  • flooding is when an area of land that isn't usually covered in water becomes submerged
  • river flooding: rivers flood when the water level becomes so high that the river spills over its banks onto the flood plain. This can be caused by constant rainfall over a long period of time or a massive input of water over a short period of time. Any low lying area near to a river channel is at risk from river flooding
  • costal flooding: costal areas can flood when the sea surges onto the land. This can happen when temperate storms or cyclones cause a storm surge. Strong onshore winds associated with storms can also force water to higher levels along the cost. Any low lying area near the coast is potentially at risk from costal flooding. 
  • Flooding can be particularly severe when several factors are combined e.g. melting ice and snow in the Himalayas. 
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  • long periods where precipitation is constistently below average
  • droughts are different for each country
  • Areas of high pressure cause droughts in subtropical and temperate zones.
  • When air sinks an area of high pressure called an anticyclone is formed. They stop air rising meaning the sky is clear and there is no precipitation. 
  • A heatwave is a long period during which the temperature is much higher than normal. 
  • They are also caused by anticyclones

Droughts and heat waves can cause wildfires. They are uncontrolled fires that usually start in the natural environment and can spread into human environments.Vegetation can be easily ignited and they spread quickly. 

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