Storms

Storms

Hurricanes
1. cyclonic tropical storms
  1. found in the tropics between 30degreesN and 30degreesS
  2. develop over oceans and lose energy over land
  3. develop where the trade winds are sucked towards the equator because of the hot air rising there.
    1. sea temp must be above 26degrees celcius for atleast 60m below surface. Humidity 75-80% this gives the right amount of heat and water vapour to sustain the storm once started
2. wind speed must be above 120km/ph
3. Forms: rising warm air creates a low pressure zone, sucks in more air, lots of moisture due to evaporation, air rises and cools condensing into clouds, latent heat energy released due to the transformation of vapour into droplets heating the air even more.
  1. Then, air rises even higher upto 10,000 m - this is the eye of the storm. The spiralling rising air causes a huge column of cumulonimbus clouds. When the air inside the hurricane reaches the highest level it flows out of the eye a forms a broad canopy of cirrus clouds.
    1. The air cools and falls back down to sea level and is sucked back into the centre. The Coriolis force cause the sucked in air at the bottom to spin into the storm clockwise and the escaping air spins out anticlockwise (opposite in the southern hem)
  2. the formation of them is much rarer then the opportunities. 10% of falling pressure centres give rise to them. In a year of high incidence perhaps a max of 50 will develop but not all may cause disaster.
    1. However, 2005 was a significant year for hurricanes in the north atlantic with 20 forming and five reaching category 4 or 5. Including hurricane Katrina , New Orleans USA.
4. size can vary from 100-1500km can form over a few days of 6-12 hours can last two-three days and take four to five to die out.
5. Destructive due to high winds and intense rainfall.
Tornadoes
1. A violent rotating column of air. Cone shaped cloud formation.
2. similar to tornadoes - whirl-winds, dust-devils(weaker appearing over dry lands) and water spouts (tornado over water)
3. numerous and devastating E.g. USA central, E and NE where an average five a day are reported in May.
  1. Also common in Aus 15 a year but most fatalities in USA where between 1950-78 689 t's where classed as deadly.
4. Can be viewed as miniature hurricanes, more common overland.
5. Form = warm moist air near the ground and dry air above. E.g. Late spring early summer over the Great Plains, USA. Intense heating of the ground make warm moist air rise as it does it cools and makes large cumulonimbus clouds.
  1. The strength of the updraft (rising air) determines how much air is sucked into the bottom.
  2. 2 things help rotation:1) Coriolis force 2)high-level jet stream passing across the top of the storm which gives an extra twist. Because of the conditions required they can easily occur under thunderstorms and hurricanes.
6. strength defined using 2 diff methods Fujita (speed) and Pearson (length and width of path) scale. Using these two you can predict are affected and potential damage.
Ice, wind, hail and snow storms
1. associated with either a polar front or high mountainous regions. They are worse in winter. In northern hem common over N. America, Europe, Asia and Japan.
2. associated with depressions and violent mixing of warm and cold air masses.
3. SNOW = temp between the base of the cloud and ground must be below 4 degrees Celsius.
4. HAIL = Top of the storm must be very cold. In the reduced pressure high up in the atmosphere, droplets supercooled to less than zero degrees Celcius. They collide to form ice. 2mm to 20cm. The size is dependent on the updraft strength as this determines how long they stay up in the atmosphere.
5. BLIZZARDS = worst storm conditions. They combine strong winds, driving snow, ice and hail with temps as low as 12 degrees Celsius and visibility less than 150 m.

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	Created by Sharondeep about 10 years ago