weather hazards

• Atmospheric Circulation


  The movement of air around the globe which influences temperature and humidity
• Atmosphere


  • Layer of air surrounding the Earth's surface which extends hundreds of kilometres high
  • Contains different gases, water droplets and particles
• Atmospheric Circulation


  1. Air moving in different directions due to sun's energy, differences in pressure, and Earth's rotation

  2. Following generally quite predictable movements
• The Global Atmospheric Circulation Model can be seen in the diagram
• Cells in the Global Atmospheric Circulation Model

  • Hadley Cell
  • Ferrel Cell
  • Polar Cell
• Hadley Cell


  At the equator, hot, moist air rises, moves to higher latitudes (30°) and sinks
• Ferrel Cell


  At around 60° either side of the equator, moist air rises, and travels to lower latitudes at around 30° where it sinks, along with air travelling from the equator
• Polar Cell

  At 60° north or south of the equator, moist air rises, and travels to the poles (90°), where it sinks
• Pressure Belts


  Areas of high and low pressure created by air circulation
• • When air rises, it creates an area of low pressure underneath
  • When air sinks, it creates an area of high pressure
• Diagram of the global pressure belts
• Wind


  Air particles moving from an area of high pressure to an area of low pressure
• Winds are deflected due to the Coriolis Effect
• This website allows you to look at the global surface winds in real time
• Climate at the Equator


  Hot, moist air rises creating an area of low pressure and very rainy conditions
• Climate at the Subtropics


  Dry air sinks creating an area of high pressure and very dry conditions
• Climate at Subpolar latitudes

  Low pressure belt causing cloudy and wet conditions
• Tropical Storm

  Very large, spinning storm that forms in the tropics with high winds and torrential rain
• Different names for tropical storms in different regions

  • Hurricane: USA and Latin America/The Caribbean
  • Cyclone: Australia (Oceania) and Madagascar
  • Typhoon: India, Japan and the Philippines
• Conditions for tropical storm formation

  • Ocean temperature around 26-27°C and at least 50 metres deep
  • Unstable air pressure with areas of high and low pressure meeting
  • Presence of wind but not too strong
  • Formation between 5-30° north or south of the equator
• Tropical Storm Formation


  1. Warm, moist air rises, leaving an area of low pressure below

  2. Warm air from surroundings moves into low pressure area and rises too

  3. Warm air constantly rising and accumulating in the atmosphere

  4. Warm air cools as it rises, causing moisture to condense and form clouds
• Warm air rises because it is less dense than cold air
• Warm, moist air rises, leaving an area of low pressure below
• Tropical Storm Formation


  1. Warm, moist air rises

  2. Warm air from surroundings moves into low pressure area and rises

  3. Warm air constantly rising and accumulating in atmosphere
• Cloud Formation


  1. Warm air rises and cools

  2. Moist air condenses and forms thunderstorm clouds
• The whole system is spinning due to the Coriolis effect
• In the southern hemisphere, the storms spin clockwise; in the northern, anticlockwise
• Tropical Storm Development


  1. Constant additions of energy from warm air causes storm to spin faster and generate higher wind speeds

  2. Storm reaches category 1 tropical storm
• Eye


  Area of extremely low pressure where cool, dry air descends; relatively calm and cloud free
• Eyewall


  Most intense and powerful area of the storm; warm, moist air rapidly rises with extremely high winds and torrential rain
• Storm reaches coast


  Low pressure and high winds cause storm surge
• Storm reaches land


  Storm loses energy and dissipates
• Heavy rain can persist for days after the storm dissipates
• Protecting


  • Increasing the resistance of a population to the tropical storm by physically designing things that will withstand the effects
• Planning


  Having systems in place, such as evacuation routes, so that if a tropical storm does occur, the population is prepared in advance
• Monitoring


  1. Tracking cloud formations and movements using satellite technology

  2. Monitoring the areas where tropical storms usually form to see if one is on the way

  3. Monitoring the route a tropical storm is taking, to see if there is potential for the tropical storm to make landfall
• Hurricane Igor forming off the coast of the Caribbean, 2010
• Predicting


  1. Using monitoring and computer modelling, it is possible to predict the route a tropical storm is going to take as well as its intensity up to days in advance

  2. Informing the population of the estimated time that the tropical storm will hit them, so they can take action accordingly
• Predictions become more reliable as the storm gets closer
• Projected path of Hurricane Florence

  • Tropical depression
  • Tropical storm
  • Cat. 1 (74-95 mph)
  • Cat. 2 (96-110 mph)
  • Cat. 3 (111-129 mph)
  • Cat. 4 (130-156 mph)
  • Cat. 5 (157+ mph)