GEOG

• Hadley cell


  a system of vertical and horizontal air circulation that creates major weather patterns, predominantly in tropical and subtropical regions

  
• Ferrel cell


  air circulation cell found at midlatitudes (between 30° and 60°) between Hadley and Polar cells.

  
• Weather can be hazardous
• Global circulation system


  1. Oval movement of air between the Equator and the poles

  2. Air circulates between high and low pressure belts

  3. Winds move from areas of high pressure to areas of low pressure

  4. Winds are part of circulation loops called cells

  5. Cells have warm rising air which creates low pressure belts and cool falling air which creates high pressure belts
• There are three loops or cells in each hemisphere: the Hadley cell, the Ferrel cell, and the Polar cell
• How the global circulation system works

  1. At the Equator, the sun warms the Earth, transferring heat to the air above causing it to rise, creating a low pressure belt with rising air, clouds and rain

  2. The cooler air sinks at 30 degrees north and south of the Equator, creating a high pressure belt with cloudless skies and very low rainfall

  3. The cool air reaching the ground moves as surface winds back towards the Equator and the poles

  4. At 60 degrees north and south, the warmer surface winds meet colder air from the poles, causing the warmer air to rise, creating low pressure
• Climate zones


  • Polar climate zone
  • Temperate climate zone
  • Tropical climate zone
  • Subtropics
• Contrasting climates between the UK and Australia

  • Australia is warmer than the UK, with hotter summers and milder winters
  • Australia has much lower precipitation than the UK
  • Australia has more extreme winds than the UK, affected by tropical cyclones
• Tropical storms


  Intense low pressure weather systems bringing extremely strong winds and heavy rain
• Tropical storms develop when sea temperature is 27 degrees or higher, providing warm moist air to cause extreme precipitation
• The distribution and frequency of tropical storms is highest between 5 and 30 degrees north and south of the Equator, with most occurring in the northern hemisphere in late summer and autumn
• The number of tropical storms in the Atlantic has increased since 1984, but there is no overall trend over the last 130 years
• Drought


  Conditions drier than normal, where water supplies become depleted due to lack of rainfall and increased evaporation
• The frequency of droughts has not changed much since 1950, but the distribution has, with areas most at risk including Central and Southern Africa, the Middle East, Australia, East and South America, and parts of North America
• El Niño


  Climatic event in the Pacific Ocean where trade winds weaken or reverse, leading to drought in eastern Australia and flooding in South America
• La Niña


  Climatic event in the Pacific Ocean where trade winds blow more strongly west, leading to the opposite effects of El Niño
• The Earth's structure consists of a core, mantle, and crust, with the crust divided into tectonic plates
• Plate boundaries


  1. Constructive - plates moving apart, magma rises to form new crust

  2. Destructive - oceanic plate subducts under continental plate, forming volcanoes and deep ocean trenches

  3. Collision - continental plates crumple and fold to form mountains

  4. Conservative - plates move sideways past each other, causing severe earthquakes
• Earthquakes


  Caused by tension building and being released at plate boundaries, sending out shock waves felt as vibrations
• Volcanoes


  Found at destructive and constructive plate boundaries, erupting lava, ash, and gases
• Volcanic activity also occurs at hot spots, where a plume of hot magma from the mantle reaches the surface
• Types of volcanoes


  • Steep-sided composite volcanoes at destructive boundaries
  • Shallow-sided shield volcanoes at hot spots or constructive boundaries
• Technology can reduce the impact of tectonic hazards through early warning systems, monitoring, and building design