I have been writing this blog since mid-January now, from a student's persepective, and so this week I thought that I would try something slightly different. This week I have been helping out the Geography department at my secondary school and so I thought I would write about what I teach...............well, to be honest, it is more like what I observed being taught and then raise it to a slightly more academic level.
Most classes have been learning about hurricanes and the devastation caused by Hurricane Katrina. When asked questions, in reference to their formation, I had to refrain from going into any detail much more that the necessity for warm deep oceans and strong winds. So, after having to contain my enthusiasm all week I thought I would go into a bit more detail now (and anyway I am guessing it might come in handy when we do the climate module!). Hurricanes, tropical cyclones and typhoons are all tropical revolving storms and are named according to their location. There are a few common characteristics in the development and location of the development tropical revolving storms and they include:-- Very warm tropical oceans (temperatures need to exceed 26 degrees Celcius), where the ocean has been warmed to a depth of at least 50m. This is necessary to ensure sustained heating over a wide area which, in turn, provides a heat source to create a large mass of warm, unstable air.
- They occur most commonly in autumn as this is when sea temperatures are at their highest as temperatures have been built up over the summer.
- They are found within the trade wind belt as this is where the surface winds warm as they blow towards the equator.
- They are usually located between latitiudes 5-20 degrees north or south of the equator.
- They trael westwards on unpredicatble courses.
- On landfall they move towards the nearest poles and are another way in which surplus energy is tranferred away from the tropics with vertical displacement through the atmosphere.
- Away from their ocean heat source they rapidly lose power and eventually become storms before they are classified as depressions.Hurricanes in the Atlantic are often over 600km in diameter and are characterised by their relatively uniform temperatures, humidity and pressure. One of the main reasons that they most commonly form in late summer and autumn is because this is when the ITCZ has completed its move to the north of the equator and so large expanses of the ocean, to great depths, are heated and therefore so is the air above it. The convergence of air at low levels and uplift creates the very low pressure and strong winds that are required for the formation of a hurricane.
To develop from a depression into a tropical storm, the rising air currents must be maintained and that requires a constant supply of heat and moisture. As winds sweep over the ocean surface they increase the rate of evaporation and the latent heat needed to transform liquid to vapour is transferred to the rising air. Later, as the moist air rises it will conense to form clouds and heavy rainfall, releasing latent heat and further driving the storm. Once the storm has developed to a mature stage, a central eye develops with a diameter of 30-50km. This is an area of subsiding air, with light winds, clear skies and anomalous high temperatuers. The descending air increases instability by warming and serves to increase the intensity of the storm. wind speeds of 160-300km/hr are not uncommon, with larger hurricanes creating widespread damage and signinficant threat to life. Associated with the high winds are storm surges which are broad waves of water pushed ahead of the storm and excaberated by the rise in sea level allowed by intense low pressure beneath the hurricane. Intense rainfall leading to run-off on land feeds swollen rivers which may have their outlet to the sea impeded by the inundation of seawater driven by storm surges into estuaries and other low-lying land.
Once hurricanes reach land they rapidly decline in terms of energy. This is because the storm loses its source of heat and moisture over land and increased friction slows it down. If it carries on moving away from the tropics over the sea, the increasing cooler waters beneath restrict the amount of energy available and ultimately reduce the pressure difference. The average lifespan of a tropical cyclone is 7-14 days.
So, thats a brief look into hurricanes and their formation. I was going to look, in detail, into Hurricane Katrina but I might save that for another time. What did I learn during this week? Well, firstly that I am really bad at explaining things to others and at targetting what I say at specific year groups - something also proven by my attempt to research and write my EPQ!!!!! This week also made me realise just how much my geographical knowledge as improved and expanded since I first started learning geography in year 7 - even my old teacher (who taught me Geography for 5 years couldn't belive how much I know knew). My writing ability also seems to have flourished although my handwriting, compared to year 7, has shrunk considerably! It was really wierd to see some of my work from back then that my teacher has kept, and even my GCSE coursework. I honestly think that its since I started doing Geography at college that my level of understanding has so rapidly grown - along with my enthusiasm - and I know excatly who to thank for that!
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