Mid-latitude depressions

A depression is an area of low pressure accompanied by a front. They commonly affect the weather in the UK.

There is a great experiment to help us to understand the differences in air pressure, that can easily be set up in a class room:

• Blow up a balloon to just beyond the width of a large jar, and tie the end to keep the air in


• Place pieces of paper in the jar and set them alight, therefore heating the air.


• Blow out the flames and place the balloon on the top of the jar.
  
  Outcome: The balloon will be sucked into the jar. this is called precipitation, generating low pressure and therefore sucking the balloon into the jar, due to a difference in air pressure. This is just an experiment in a class room, which is dramatic can you imagine what it is like when 2 massive air masses, come together creating a mid-latitude depression!

The Bergen School Model was devised to assist in the understanding of the formation of Mid-latitude depressions. It comes in 4 stages:

• Origin and infancy: warm air front meets cold air front, generally warm coming from the south of the UK and cold from the north.
  
  
• Maturity: the warm air spirals over the cold anticlockwise as the cold air sinks. Then a warm area exists between the cold and warm fronts.
  
• Occlusion: the warm sector disappears as the cold front moves faster. Cold air is denser, so it forces the warm air upwards. It is harder for the warm lighter air to move and this causes the cold air to sink. The cold air moves at about 40/50 mph whereas the warm travel travels at about 20/30 mph.
• 
  Death: the frontal system dies as the warm air is forced upwards and cools and the cold air remains underneath. the difference in temperatures have level out and therefore there is no longer an occluded front.
  
  

The result of this is a cold period and depending on the energy in the front, it can cause a wide variety of precipitation. in the UK an example of this occurred in 2002 when a storm hit. according to the BBC reporting at the time, 7 people died and repairs to property were expected to total over £50 million according to the insurance industry. Wind speeds reached 90mph and rainfall caused wide spread flooding. This was due to the existence of a mid-latitude depression or a low. The storm was wide spread hitting many parts of the UK from Aberdeen to London.

This would be a great case study as the storm will probably be in the living memory of the children's parents and other family members. Research can be undertaken to not only look at the physical geography but also the human element by looking at the effects of the storm on individuals and communities.