Weather hazards

• Global Atmospheric circulation

  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

  
• Hadley cell

  • 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

  •  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

  • 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 Coriolis effect is 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 this way:
  • 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)
• The trade winds

   Blow from the subtropical high-pressure belts (30 degrees N and S) towards the Equator's low-pressure zones and are deflected by the Coriolis force
• The westerlies:


  Blow from the sub-tropical high-pressure belts to the mid-latitude low areas, but again, are deflected by the Coriolis force
• The easterlies

   Polar easterlies meet the westerlies at 60 degrees S