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TROPICAL CYCLONES (Defined as: (KEY CHARACTERISTICS to be classified as…
TROPICAL CYCLONES
Defined as:
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Characterised by winds, clouds and thunderstorms that spiral inwards
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DISTRIBUTION
SPATIAL
Generally formed over western sections of the Atlantic, Indian and Pacific Oceans (5 to 25 deg N/S of equator)
More frequent in the northern hemisphere than in the Southern Hemisphere due to differing annual frequencies.
Each individual cyclone normally lasts from two to three days, sometimes more.
Cyclones depend on an initial supply of heat and moisture for development, and are sustained by further release of latent heat through massive condensation
TEMPORAL
Occurs normally during Northern/Southern summers from December-May in there Southern Hemisphere and June-October in Northern Hemisphere.
Formation of cyclones
Pre-requisites
Intense surface heating create warm ocean waters therefore, tropical cyclones only occurs in summer
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Thunderstorm activity which allows latent heat stored in ocean waters to be released for tropical cyclone development following condensation of water vapour in rising air parcels.
Thus tropical cyclones formed between 5-25 degrees N and S due to warmer ocean waters at this region
Warm waters must be about 60m deep, as cyclones stir up the ocean, bringing up cold water from below
Minimum distance of about 500km from equator as some Coriolis force is needed to maintain low pressure rotation of the systems.
For mass thunderstorms to organise into hurricane, there must be some mechanism that triggers the formation such as preexisting atmospheric disturbance like Tropical wave which is a type of atmospheric trough, an elongated area of relatively low air pressure, orientated from North to South.
1) Near the surface, moist tropical air flows in toward the tropical cyclone's low pressure centre.
2) Adjacent to The Eye, this air rises and condenses into tall cumulonimbus clouds within the eyewall. The vigorous convective clouds produce heavy rainfall. Hence, the air warms due to the release of large quantities of latent heat during condensation. The release of heat energy fuels the heat engine of the tropical cyclone.
3) Near the top of the clouds, the release of latent heat mentioned in (2) leaves the air cooler and hence denser, and having lost much of its moisture, drier. It now has two paths to take.
A. Begins to flow outwards away from the centre. This diverging air aloft actually produces a clockwise flow of air several hundred kilometres away from The Eye. As this outflow reaches the storm's periphery, it begins to sink and warm adiabatically, inducing clear skies.
B. Travels downwards back into The Eye. The release of latent heat leaves air parcels that has risen cooler and denser and this induces higher pressures in the upper atmosphere, which initiate downward air motion within The Eye. Once again, the air sinks and warms adiabatically, inducing clear skies.
4) This process helps to account for the warm air and absence of convective clouds in the eye of the storm
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IMPACTS
Primary
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Storm surges produced by high winds and extreme low pressure. Storm tides will reach areas that might have otherwise been safe, such that in low lying areas there is increased rate of flooding and thus causing deaths by drowning
Secondary
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Negative effect on tourism, EG Hurricane Irma affected the Caribbean and Florida which are places that traditionally depended upon tourism for sources of income.
Blockage of road and rail transport by floodwaters, with electricity cut off.
Contamination of water may occur from dead animals or rotting food, resulting in diseases amongst the people.