Cyclones in General
The word cyclone has two possible origins. The first one being from the mid 19th century when captain Henry Piddington referred to a storm as a cyclone. It is thought the Piddington got this word from the Greek word cyclos which means coils of a snake. The other possible origin is the word Cyclops. A Cyclops is a mythical Greek creature with only one eye. A cyclone also has one eye.
A cyclone is defined as an area of low atmospheric pressure with inward spiraling wind. In the northern hemisphere the wind rotates counter-clockwise but in the southern hemisphere the wind rotates clockwise. The word covers a wide variety of winds and should not be used by itself very often. Words like tropical or extratropical should be used with it.
All cyclones have a few common characteristics. The centre is the area of lowest atmospheric pressure, often called the eye. Also they all rotate clockwise in the southern hemisphere and anti-clockwise in the northern hemisphere. All cyclones can only be formed when the pressure in the centre of the cyclone compared to the pressure outside the cyclone is balanced with the Coriolis force.
Cyclones spin in different direction in different hemispheres because of the Coriolis Effect. The equator cannot have a cyclone on it as the coriolis parameter is exactly zero, therefore the cyclones perimeter would also be exactly zero therefore no cyclone has ever turned its rotating direction.
Tropical Cyclones
There are 6 main types of cyclones. One type is the tropical cyclone. It is fueled by the heat released when moist air rises and the water vapor in it condenses. These types of cyclones only exist near the equator. Most of them appear only near the Pacific Ocean, Indian Ocean and there are a lot of tropical cyclones in the north parts of the Atlantic Ocean.
Although tropical cyclones are very deadly and devastating, they play an important part in keeping the Earth wet. The areas that the cyclones hit are usually in need of rain or are in drought; therefore the water that a cyclone provides helps the native ecosystems.
Cyclones vary in sizes. A small cyclone has a radius of about 200km, but this doesn't make them weak, some of the strongest cyclones have been midgets. Between 350 and 650 are average and a huge cyclone has a radius of over 900km, that's more then 8 degrees of latitude!
Often people are afraid of when a cyclone reaches landfall, when it crosses land, but in most cases cyclones to the most damage to settlements before landfall. If a tropical cyclone has its strongest winds over land then it is said that it made a direct hit. For a cyclone to make a direct hit it doesn't need to make landfall at all.
Since tropical cyclones are powered by water. Normally, when a cyclone hits land it losses power and eventually stops. Other ways of cyclones stopping is if it stays in the one area too long and uses all the warm water and if the cyclone hits mountains then it can loose its structure and collapse. When a cyclone collapse on mountain terrain it can release deadly winds and rain which can cause mudslides and be very fatal. There have been attempts by US military to stop tropical cyclones but there have been no successful results.
Australia has a category 1-5 system. Category 1 is a strong gale with winds averaging 63-88km/h. Category 2 measures 10-11 on the Beaufort scale and has maximum winds of 170km/h. Category 3-5 all measure 12 on the Beaufort scale. Category 4 cyclones have average winds of up to 200km/h and the extremely dangerous category 5 cyclone is any cyclone stronger then a category 4.
Cyclone Tracy
Cyclone Tracy was Australia's worst tropical cyclone. It directly killed 71 people, ruined thousands of people's lives and has costs over $4.73 billion USD at last count in 2005.
The cyclone was mainly a category 4 but during landfall it was a category 5 tropical cyclone. Although it was an extremely dangerous and strong cyclone, it is the smallest tropical cyclone on record. It was only 100km wide.
Of the 71 deaths, 22 were at sea, long before the cyclone hit Darwin. There were defiantly 49 deaths on land but of the 22 deaths at sea 6 of them were only considered "perished at sea" when in 2005 the coroner decided that it wasn't probable that the missing men were alive. There is also no evidence that the men died at sea. We only assume that they died at sea as that was the last place they made contact.
One of the major problems with this disaster is that it struck a part of the country which still didn't have major telephone or computer communication systems. And getting the word out fast was made even harder as most of the media were on holidays for Christmas.
