Weather Hazards

• describe the global atmospheric circulation model

  3 cells - Hadley (0-30 degrees N/S), Ferrell (30-60 degrees N/S), Polar (60-90 degrees N/S)
• How does global atmospheric circulation work?

  1) Air rises at equator - creates low pressure belt with rising air, clouds and rain.

  2) As the air rises it cools, moving 30 degree N + S of equator

  3) Cool air sinks - high pressure - cloudless skies, very low rainfall

  4) Surface winds blow the cool air back to equator or towards the poles
• What is the weather like at deserts and why?

  Hot and dry because of the intense sun from the equator which cause all the water to evaporate and warm air to rise
• what is the weather like in rainforests and why?


  Hot and sweaty because of the low pressure areas in the hadley cells
• What happens in a Hadley cell?

  Hot, wet air rises and expands and cools as it rises, forming clouds where water condenses and causes precipitation. It tries to equilibrate by going to the poles as there is less energy there on average. As it goes, it will begin to cool, and descend as cool, dry air.
• What is weather like in the UK?

  - Cold and wet
• What cell is the UK in

  - Ferrel cell
• What cells are desert and rainforest found in?

  - Hadley cells
• What happens in a ferrel cell?

  - 30°- 60° N/S

  
  

  - winds pulled towards the poles pick up moisture as they travel over oceans

  
  

  - warm moist air meets cold air at 60°

  
  

  - warm air from tropics = light

  
  

  - cold air from poles = dense

  
  

  - warm air rises above the cold air

  
  

  - causes low pressure = unstable weather conditions

  
  

  - UK weather caused by this
• Describe the distribution of tropical storms

  • Found over oceans with sea temperatures of 27'C

  • Found 30' North and South of the Equator

  • Florida in the USA,
• How do tropical storms form?


  - A strong upward movement of air draws water vapour up from the warm ocean suface (27 degrees +)

  
  

  - This evaporated air cool as it rises and forms thunderstorm clouds

  
  

  - As the air condenses it releases heat which powers the storm and draws up more water

  
  

  - Several smaller thunderstorms join together to form a giant spiralling storm

  
  

  - when surface winds reach an average of 120km the storm becomes a tropical storm

  
  

  - the storm now develops an eye at its centre where air descends rapidly. the outer edge of the eye is the eyewall which has the most intense weather conditions

  
  

  - the storm gathers strength as it is carried across the ocean

  
  

  - upon reaching land the storm's energy supply (evaporated water) is cut off.

  friction slows it down and it begins to weaken
• How may tropical storms be affected by global warming

  - More ocean above 27.C - more places experience tropical storms

  
  

  - Oceans stay at 27.C or higher for more of the year - tropical storms each year could increase

  
  

  - Higher temps - stronger storms
• How can monitoring reduce the effects of tropical storms?

  satellite tracking allows prediction maps to be prepared and warning issues
• How does prediction reduce the effects of tropical storms?

  Satellites

  People can evacuate + protect their homes in advance
• How does protection reduce the effects of tropical storms

  - Buildings designed to withstand storms - flood defences built (e.g) houses on stilts

  - these reduce number of buildings destroyed
• What weather hazards does the UK experience?

  strong winds, heavy rainfall, snow and ice, drought, thunderstorms, heat waves
• Is UK Weather becoming more extreme?

  - Temperatures more extreme - April 2011 warmest April on record

  - Flooding - somerset levels
• When does rainfall occur

  When warm, moist air rises, cools, and condenses
• how can extreme weather events be managed to reduce the impacts

  Flooding - prevent building on sites where flood risk is high

  
  

  Strong winds - Met Office issue weather warnings

  
  

  Droughts + heatwaves - hosepipe bans

  
  

  Extreme cold - Gritters salt roads during cold winter months