L1 - Global atmospheric circulation

• Global atmospheric circulation helps to explain the location of world climate zones and the distribution of weather hazards
• how air travels around the world determines the weather and the temperature
• the most important influence on worldwide variations in climate is latitude. because of the curved surface of the Earth, the equator receives a much higher insolation than the polar latitudes
• the parallel rays of sun are spread thinly when they strike the Earths surface at high latitudes, whereas at low latitudes the sunlight is more highly concentrated
• air at the equator is heated strongly, it becomes less dense and rises to a high altitude which creates a global climate zone of low pressure. after rising, the air spreads out and begins to flow towards the North and South poles
• the low insolation received at polar latitudes results in colder, dense air and high pressure. as the air sinks to ground level, it spreads out and flows towards the equator
• the low pressure belts at the equator and the high pressure belts provides the basis for a simple convection cell to operate
• as well as the pressure belts at the poles, there are areas of high pressure at the tropics of cancer and capricorn. air sinks towards the ground there, as it decends the air warms and the result is high pressure and hot, dry desert conditions. this is called the hadley cell
• seasons arise because the earth is tilted on its axis, each year as the planet journeys around the sun, insolation rises and falls at each latitude
• in high polar latitudes, the sun does not rise during the winter
• label diagram

  A) polar

  B) ferrel

  C) hadley

  D) hadley

  E) ferrel

  F) polar

  
• rainfall is high and constant throughout the year near the equator. as hot air rises, it cools slightly. water vapour is converted into droplets of convectional rain
• rainfall is often higher in coastal areas in western europe due to the movement of the jet stream over the atlantic. rain bearing weather systems called depressions follow the jet stream, often bringing stormy conditions to the uks west coast
• rainfall is often very low around the tropics of capricorn and cancer. dry air descends there as part of the hadley cell, resulting in arid (dry) conditions
• warm air rising =low air pressure
• cool air descending = high air pressure
• a convection cell is where hot and cold air moves around
• convection cell:

  1. the equator is heated
  2. the warm air rises to the poles
  3. the air cools and descends again
  4. it returns to the equator
• depression = low air pressire
• highest latitude = 90 degrees

  lowest latitude = 0 degrees (equator)
• 1. at the north pole, cold air sinks and creates a belt of high pressure and cold, dry climate
  2. at bout 60 degrees N and S, cold polar air mixes with warmer air and rises, creating a belt of low pressure
  3. at the tropic of cancer, cool air sinks which creates a belt of high pressure, as it sinks, it becomes warmer and drier
  4. at the equator, warm air rises, creating a belt of low pressure, as it rises it cools and clouds form and release precipitation. above, the air will eventually separate and move to higher latitudes