Geography AQA

• The global atmospheric circulation can be described as a worldwide system of winds moving heat from the equator to the poles to reach a balance in temperature
• Wind formation


  Air always moves from high pressure to lower pressure, and this movement of air generates wind
• Winds are large scale movements of air due to differences in air pressure
• The pressure difference is because the Sun heats the Earth's surface unevenly
• Insolation


  The amount of solar radiation that reaches the Earth's surface
• Insolation that reaches the Earth's surface is greater at the equator than at the poles due to Earth's curvature and angle of the Earth's tilt
• The irregular heating of Earth's surface creates various pressure cells, each generating different weather patterns
• The movement of air within each cell is roughly circular and moves surplus heat from equatorial regions to other parts the Earth
• The three-cell model


  • Shows global circulation: the Hadley, Ferrel and Polar cells
• Climate


  What you expect a place to be over time (usually 30 years)
• The 3 atmospheric cells


  • Hadley cell
  • Ferrel cell
  • Polar cell
• Hadley cell


  • The largest cell and extends from the equator to between 30° and 40° north and south
  • Trade winds that blow from the tropical regions to the equator and travel in an easterly direction
  • Near the equator, the trade winds meet, and the hot air rises and form thunderstorms (tropical rainstorms)
  • From the top of these storms, air flows towards higher latitudes, where it becomes cooler and sinks over subtropical regions
  • This brings dry, cloudless air, which is warmed by the Sun as it descends - the climate is warm and dry (hot deserts are usually found here)
• Ferrel cell

  • The middle cell, and generally occurs from the edge of the Hadley cell to between 60° and 70° north and south of the equator
  • This is the most complicated cell as it moves in the opposite direction from the Hadley and Polar cells; similar to a cog in a machine
  • Air in this cell joins the sinking air of the Hadley cell and travels at low heights to mid-latitudes where it rises along the border with the cold air of the Polar cell
  • This occurs around the mid-latitudes and accounts for frequent unsettled weather (particularly the UK)
• Polar cell


  • The smallest and weakest of the atmospheric cells. It extends from the edge of the Ferrel cell to the poles at 90° north and south
  • Air in these cells is cold and sink creating high pressure over the highest latitudes
  • The cold air flows out towards the lower latitudes at the surface, where it is slightly warmed and rises to return at altitude to the poles
• Coriolis effect


  The appearance that global winds, and ocean currents curve as they move. The curve is due to the Earth's rotation on its axis, and this forces the winds to actually blow diagonally.
• The Coriolis effect influences wind direction around the world
• In the northern hemisphere it curves winds to the right, in the southern hemisphere it curves them left
• The exception is when there is a low-pressure system: in these systems, the winds flow in reverse (anti clockwise in the northern hemisphere and clockwise in the southern hemisphere)
• Global wind belts: Surface winds

  • The trade winds
  • The westerlies
  • The easterlies
• The combination of pressure cells, the Coriolis effect and the 3-cells

  Produce wind belts in each hemisphere
• Global atmospheric circulation affects the Earth's climate
• It causes some areas to have certain types of weather more frequently than other areas
• The UK has a lot of low-pressure weather systems that are blown in from the Atlantic Ocean on south-westerly winds, bringing wet and windy weather
• Explain the link between global air pressure and surface wind belts


  1. Sinking air causes high pressure, causing winds to move away/diverge to meet in areas of low pressure e.g. the Polar highs/easterlies meet the westerlies (low pressure) at 60 degrees N and S of the Equator

  2. Winds blow from high pressure areas to low pressure areas, such as the trade winds blowing from 30 degrees N and S towards the Equator
• Wind


  Movement of air from an area of high pressure to an area of low pressure due to pressure differences caused by uneven heating of the Earth's surface by the sun.
• Convection cell


  Circular motion of air caused by the rising and sinking of warm and cool air, respectively.
• Banbury


  Historic market town in the south-east of England, located within an hour's drive of London, Birmingham and Oxford
• Banbury


  • Influential to local and national trade since the medieval ages
  • Close proximity to three major UK cities
  • Prime location for businesses and commuting workers
• Banbury was destroyed during major flooding in 1998
• Date of Flooding


  Easter 1998
• Lives Lost = 0
• People forced to evacuate = 350
• Social benefits

  • House owners no longer worried about damage to their property
  • Uninsured houses especially at risk during flooding
  • New footpaths and parks surrounding the flood water storage
  • Improved quality of life for dog walkers and families
• Environmental costs

  • Biodiversity plan will increase vegetation to reduce risk of flooding
  • Heavy machinery damaged nearby vegetation during construction
  • Soil removed from areas surrounding Banbury to make embankments, disrupting habitats and wildlife
• Economic benefits


  • Construction work cost £18.5 million
  • Construction jobs created
  • Jobs to maintain the biodiversity plan
  • Estimated £100 million saved in avoiding damages
• The last ice age in the UK took place around 18,000 years ago. During this time, temperatures remained low throughout the year and ice sheets and glaciers covered the north of the UK and other parts of Europe.
• Glaciers


  • They shape the land through processes of erosion, weathering, transportation and deposition, creating distinct landforms
• Glacial abrasion


  A type of glacial erosion that occurs when rock fragments that are frozen into the bottom of a glacier scrape and erode the valley floor
• Glacial plucking


  A type of glacial erosion that occurs when ice freezes onto the landscape, ripping out rocks when it moves
• Freeze-thaw weathering


  The main type of weathering, where water in rocks freezes and expands, breaking the rock apart