Unit 1A - the challenge of natural hazards (3. weather hazards) Flashcards
what is global atmospheric circulation
how air currents in the atmosphere move. The global atmospheric circulation model is based around cells. These cells are regions where the air moves from low pressure to high pressure.
how does global air circulation work
Air rises at the equator, leading to low pressure and rainfall. When the air reaches the edge of the atmosphere, it cannot go any further and so it travels to the north and south. The air becomes colder and denser, and falls, creating high pressure and dry conditions at around 30° north and south of the equator. Large cells of air are created in this way.
what are the 3 types of cells
polar ferrel hadley
what is the hadley cell
The first cell is called the Hadley cell. At the equator, the ground is intensely heated by the sun. This causes the air to rise which creates a low-pressure zone on the Earth’s surface. As the air rises, it cools and forms thick cumulonimbus (storm) clouds. The air continues to rise up to the upper atmosphere
what is the ferrel cell
Air on the surface is pulled towards the poles, forming the warm south-westerly winds in the northern hemisphere and north-westerly winds in the southern hemisphere.
These winds pick up moisture as they travel over the oceans. At around 60 degrees N and 60 degrees S, they meet cold air, which has drifted from the poles.
The warmer air from the tropics is lighter than the dense, cold polar air and so it rises as the two air masses meet.
This uplift of air causes low pressure at the surface and the unstable weather conditions that are associated with the mid-latitude depressions. Much of our wet and windy weather in the UK is determined by this
what is the polar cell
At the poles, air is cooled and sinks towards the ground forming high pressure, this known as the Polar high. It then flows towards the lower latitudes. At about 60 degrees N and S, the cold polar air mixes with warmer tropical air and rises upwards, creating a zone of low pressure called the subpolar low. The boundary between the warm and cold air is called the polar front. It accounts for a great deal of the unstable weather experienced in these latitudes.
what is a tropical storm
huge storm that develops in the tropics. tropical storm causes devestation to small islands and regions due to the cost of repair and the lives that are lost.
where do tropical storms form
over warm ocean above 27 degrees Celsius
form in summer and autumn
most tropical storms form 5-15 degrees north and south of the equator
how do tropical storms form
1) strong upward movement of air draws water vapour up from the warm ocean surface
2) evaporated air cools as it rises and condenses to form towering thunder clouds
3) as the air condenses releases heat which powers the storm and draws up more and more water
4) several small thunderstorms join together to form a giant spinning storm. When surface winds reach an average of 120km per hr the storm officially becomes a tropical storm.
5) the storm now develops an eye at its centre where the air descends rapidly. the outer edge of the eye is the eyeball where the most intense weather conditions are felt.
6) storm is carried across the ocean by the prevailing winds.
7) On land the storm’s energy supply is cut off.
maximum length and height of a tropical storm
go up to 480km across and up to 14km tall
how are hurricanes measured
saffir simpson scale
what does the saffir simpson scale go up to
category 1-5 (1 is the lowest ,119km, and 5 is the highest , 252km)
when did typhoon haiyan happen
nov 2013
what was typhoon haiyan on the saffir Simpson scale
category 5
primary effects of typhoon haiyan
6300 killed
600000 people displaced, 40000 homes damaged
90% of tacloban destroyed
400mm of rain caused widespread flooding
