Extreme weather

• What is the global pattern of air circulation?

  There are large-scale, circular movements of air over the Earth's surface.
• How do air circulations transport heat?

  They transport heat from the tropical regions at the Equator to the polar regions.
• What are lines of latitude?

  Imaginary lines that surround the Earth.
• Where is the Equator located in terms of latitude?

  The Equator is at the 0° latitude line.
• What are the 'low latitudes'?

  The region spanning the Equator.
• What are the 'high latitudes'?

  The polar regions towards 90° north and south of the Equator line.
• How is the world divided at the Equator?

  It creates the northern and southern hemispheres.
• What are the three specific 'cells' of air in each hemisphere?

  • Hadley cell
  • Ferrel cell
  • Polar cell
• What is the troposphere?

  It is the area of the atmosphere from the Earth's surface up to 10-15 km high.
• What role do the three cells of air play?

  They create the distinct climate zones that we experience on Earth.
• What is the Hadley cell?

  The largest cell which extends from the Equator to between 30° and 40° north and south.
• What are trade winds?

  Winds that blow from the tropical regions towards the Equator, usually from an easterly direction.
• What happens near the Equator with trade winds?

  They meet, and the warm air rises and forms thunderstorms.
• What occurs after warm air rises from thunderstorms?

  Air flows towards higher latitudes where it becomes cooler and sinks over subtropical regions.
• Where is the Ferrel cell located?

  The middle cell, which generally occurs from the edge of the Hadley cell to between 60° and 70°.
• How does the Ferrel cell move?

  It moves in the opposite direction from the Hadley and Polar cells.
• What happens to air in the Ferrel cell?

  Air 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.
• What weather is associated with the Ferrel cell?

  It accounts for frequently unsettled weather around the latitude of the UK.
• Where is the Polar cell located?

  The smallest and weakest cell, which extends from the edge of the Ferrel cell to the poles at 90°.
• What happens in the Polar cell?

  Air sinks over the highest latitudes at the poles and flows out towards the lower latitudes.
• What causes wind?

  Wind is air moving from high to low pressure.
• How is atmospheric air pressure measured?

  It is measured in millibars.
• What is the normal range of air pressure?

  980 millibars (low pressure) to 1050 millibars (high pressure).
• What creates low pressure at the Equator?

  Where the air in the Hadley cells rises.
• What happens where the Hadley and Ferrel cells meet?

  Air descends, creating high pressure on the ground below.
• What is a low-pressure system?

  It occurs when the atmospheric pressure is lower than that of the surrounding area.
• What is associated with low-pressure systems?

  High winds and warm, rising air.
• What happens as warm air rises in a low-pressure system?

  It cools and condenses, forming clouds.
• What is condensation?

  It is the process whereby rising vapor turns into a liquid.
• What is precipitation?

  Moisture that falls from the atmosphere as rain, sleet, snow, or hail.
• How does cloud cover affect daily temperature ranges in the UK?

  It reflects solar radiation during the day and traps heat during the night.
• What happens when air cools in a high-pressure system?

  It becomes denser and starts to fall towards the ground, increasing air pressure.
• What is associated with high-pressure systems at 30° north and south of the Equator?

  Clear skies and dry, calm weather.
• What is a tropical storm?

  A low-pressure system originating in the tropics that can develop into a tropical cyclone.
• What characterizes a tropical storm?

  It is a circular storm originating over warm water, characterized by high winds and heavy rain.
• What are the maximum wind speeds of a tropical storm?

  Ranging from 63 km per hour to 118 km per hour.
• When does a tropical storm become a tropical cyclone?

  When wind speeds exceed 119 km per hour.
• Where are tropical storms typically found?

  • Over tropical and sub-tropical waters typically between 5° and 15° north and south of the Equator.
  • Where the surface layer of ocean water is in excess of 27°C and at a depth of at least 50-60 m.
  • At least 500 km away from the Equator where the Coriolis effect is strong enough to make the weather system spin.
• How does the Coriolis effect influence tropical storms?

  It causes winds to take curved paths due to the Earth's rotation.
• What is necessary for a tropical storm to form?

  There needs to be movement in the air near the surface of the water and cooling temperatures in the troposphere.