Hurricanes

This is a satellite picture of Hurricane Katrina that hit the USA in August 2005, affecting in particular New Orleans. This is a great case study of both physical and human geography and how they can be interlinked in study.







I am going to focus on the physical aspects as one of the points of this sequence of blogs is to develop my knowledge of my' weaker' subject which generally relate to physical elements.

• Typhoon, cyclone or hurricane?

Really it just depends where they occur in the world. The map shows where they can originate and the appropriate name.

How do they develop?

They all start from a basic thunderstorm over the ocean. A source of moist warm air derived from tropical oceans, the temperature generally has to be over 27 centigrade. The winds blowing in different directions converge and cause the air to rise and from storm clouds. The winds are known as low wind sheer and this allows the storm clouds to rise vertically to a high level. The clouds then start to spin having been induced by the earths rotation.

The storm becomes allocated a typhoon or a hurricane if the speeds of the winds exceed 74mph and then they are given a name such as Katrina. In additional they are also given gradings depending on the speeds of the wind, so Katrina for example was a category 5 hurricane with speeds of over 155mph. This the top category.

The damage that is caused by these massive storms can be utterly devastating. Katrina hit land fall at New Orleans and caused massive flooding and devastation of much of the lower lying land occupied by the poorer residents mainly black Afro-Americans. Support from the Bush government was perceived as slow, leading to accusations of a lack of care by the administration for the poorer, black community.

The physical development of typhoons or hurricanes occurs over oceans in the tropical belt, they gather speed and power whilst moving across the sea and dramatically lose power when they hit land. Then the physical geography interacts with the human world. The physical development and the impact on the human geography will make a good case study.

Resources for this could include, weather activities, watching videos of the development and its' consequences. I have found various web sites with fantastic resources including the Met Office, The Geographical Association, Enchanting Teaching to name just 3. These can be differentiated depending on ability of the student.

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.