Weather hazards

• What is global atmospheric circulation

  It is when wind is caused by differences in the atmospheric pressure. When there is a difference, air moves from a area of high pressure to an area of low pressure, resulting in winds
• What are the three cells

  called

  Hadley

  ferrel

  polar
• Wind


  Caused by differences in atmospheric pressure, air moves from high pressure to low pressure areas
• Difference in air pressure

  Stronger the winds
• Towards the poles

  • Sun's energy spreads over a large area, resulting in low temperatures and high pressure
• At the Equator


  • Sun's energy is concentrated over a small area, resulting in high temperatures and low pressure
• Global Atmospheric Circulation Model


  Difference in air pressure on Earth's surface causes global patterns of air circulations (cells) from high to low pressure areas
• Convection cells in each hemisphere

  • Hadley
  • Ferrel
  • Polar
• Hadley cell


  1. Warm air rises from Equator, creating low pressure belt

  2. Air cools as it rises, resulting in clouds and rain north and south of Equator

  3. At 30° north and south, cold dry air sinks, creating high pressure and clear skies

  4. Sinking air moves back to Equator or towards poles
• Ferrel cell


  1. At 60° north and south, surface air meets colder air from poles, causing it to rise, creating low pressure belt

  2. Rising air cools and moves back to Equator or towards poles
• Polar cell

  1. At poles, cool air sinks, creating high pressure

  2. Sinking air moves back towards Equator
• Tropical Storms


  Extreme low-pressure weather systems that cause severe winds and torrential rain
• Conditions required for Tropical Storms


  • Ocean Temperature: >26°C
  • Water Depth: 60-70 m
  • Location: Between 5 and 30° north and south of the Equator
• Tropical storms cannot form more than 30° north or south of the Equator as the water is not warm enough and the Coriolis force (spin) not great enough
• Hurricanes


  Tropical storms in the Atlantic and Eastern Pacific Oceans
• Cyclones

  Tropical storms in the Indian and South Pacific Oceans
• Typhoons

  Tropical storms in the west of the North Pacific Ocean
• Formation of Tropical Storms

  1. Warm, moist, unstable air above the ocean rises, creating an area of low pressure below

  2. Surrounding cooler air is drawn into the area of low pressure, causing winds

  3. The cool drawn-in air now warms up and takes on moisture, causing it to rise

  4. The large mass of rising, warm air cools and condenses, forming large cumulonimbus clouds and heavy rain

  5. Latent heat released during condensation helps to power the storm

  6. As more air is drawn into the area of low pressure, the Earth's rotation causes wind to spiral into the storm's centre, or eye

  7. Colder, drier air sinks into the centre (eye) of the storm, creating calm conditions. Prevailing winds then push the storm towards land

  8. The storm continues to get bigger and stronger until it reaches land or colder seas. Landfall and friction slow the storm down
• Climate change


  • This has increased the frequency and intensity of tropical storms
• Distribution of Tropical Storms


  • Tropical storms are most common in late summer and early autumn
• Storms move

  1. From east to west

  2. Due to the direction in which the Earth spins
• The Coriolis Force


  Due to the Earth's curved surface and rotation, the Coriolis force causes winds to bend and cyclones to spin
• In the northern hemisphere


  The winds curve to the right, causing storms to swirl in an anticlockwise direction
• In the southern hemisphere

  The winds curve to the left, causing storms to swirl in a clockwise direction
• Climate change is heating the world's oceans and causing sea levels to rise
• As sea temperatures rise


  More of the world's oceans will heat to above 27°C, so tropical storms may be able to develop in areas further north or south of the Equator
• As sea temperatures rise


  Storms will become more intense, with higher rainfall and stronger winds
• Rising sea levels


  Place coastal areas at greater risk of flooding from tropical storms
• The frequency of tropical storms

  May remain the same or decrease as the Earth gets warmer, but more storms will be classed as severe (category 4 or 5) and last for a longer time