Wind belts

• Low pressure


  Air rises, lower pressure
• High pressure


  Air sinks, higher pressure
• Wind


  Air that blaws over the surface of the Earth
• Planetary winds


  The world's major winds that revolve from temperature differences
• How wind is created

  1. Air is heated, it expands and rises

  2. Air cools, it contracts and sinks

  3. Difference in pressure causes wind to blow from high to low pressure
• Air circulation


  Air rises at equator, flows to poles, cools and sinks at outer tropics, returns along surface to equator
• Doldrums


  Low-pressure region at equator where air is hot and rising
• Poles


  High-pressure region where air is cold and heavy, sinking and diverging towards equator
• Movement of winds in low pressure


  Winds deflected to the right in northern hemisphere (Ferrel's low)
• Movement of winds in high pressure

  Winds move outward from center (northern hemisphere)
• Air pressure or atmospheric pressure


  Caused by the weight of the air pressing on the Earth's surface
• The atmosphere exerts a pressure of about one kilogram on each square centimetre of the Earth's surface
• Air pressure


  Measured in millibars (mb)
• Average air pressure at sea level is about 1013.25 mb
• Atmospheric pressure


  Measured by an instrument called a barometer
• Types of barometers


  • Mercury barometer
  • Aneroid barometer
• Mercury barometer


  Consists of a graduated, straight glass tube or column, with one end sealed and filled with mercury, with the open end standing in a small vessel containing more mercury
• Height of the column of mercury

  Can be read against a vertical scale to indicate the pressure of the air
• Plotting data about atmospheric pressure on weather maps


  Using isobars, which are lines on the map that join all the places with the same atmospheric pressure
• Winds that blow frequently from one direction, such as the Trade Winds, are called prevailing winds
• The Trade Winds are confined to areas 5 to 30 degrees north and south of the equator
• The Trade Winds create pleasant temperatures that are popular with tourists, which is one reason why the Caribbean is such a popular and attractive tourist destination
• Where trade winds converge

  Along a line called the Inter-Tropical Convergence Zone (ITCZ), an area of low pressure lying along the equator
• Easterly waves


  Troughs of low pressure moving across the Atlantic and Caribbean on the southern fringes of the ITCZ, prevailing from May to November and associated with showers and thunderstorms
• Hurricanes


  Intense, tropical or cyclonic storms in which the winds move in a spiral fashion, with speeds of over 120 kilometres per hour
• Hurricanes develop in the Mid-Atlantic Ocean between latitudes 5°N and 20°N
• Hurricanes generally move in a north-westerly direction in the Caribbean
• Hurricanes are prevalent in the Caribbean and the Gulf of Mexico from June to November and are associated with torrential rainfall and thunderstorms
• Pressure in hurricanes


  Low, with winds blowing inwards in an anti-clockwise direction
• Eye of the hurricane


  An area of calm at the centre of the hurricane, with heavy rainfall occurring around it
• Hurricanes are very destructive, damaging lives, property and crops, and causing large tidal waves and flooding along coastal areas in the hurricane's path
• Tornado


  A small, violent, tropical storm prevalent in Florida and other parts of the USA
• Many people think hurricanes are connected to global warming, which is caused by the increased carbon dioxide in the atmosphere
• The theory of global warming is supported by the evidence of increased sea temperatures and rising sea levels, such as the erosion of beaches in the Dominican Republic