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.

Everyone knows that the hurricane hit Darwin, but what else did it go? Well it started of in the Arafura Sea, about 370km north-east of Darwin. The United States found the first traces of Tracy with there ESSA-8 satellite. At that time it was just a large cloud. It was monitored for a while and them an alert was made. Since the cyclone was small and wasn’t heading towards Darwin there was no need for panache.

The small islands above Darwin were damaged on the 23rd of September during the morning but there weren’t a lot of people living there and because the cyclone was only small and undeveloped the damage was little.

The storm then continued down the coast of Bathurst Island. When the coast ended the tropical cyclone made a 90° turn toward Darwin. It was now the 24th of December. Early that morning an alert was let out and Darwin officials began passing the word and planning evacuation.

The final approach began on Christmas Eve. Evacuation began to stop and the city was nearly at its goal of 10500 people. The people that were in the city started to find somewhere they could be protected from the storm. Some of the children were evacuated before there parents with there school, some of those parents didn’t know were there children were. Around 20 people are already dead.

Early Christmas morning the category 5 tropical cyclone made landfall with wind speeds over 220km/h. everyone leaving was now out and 10638 people were left in the city, 138 more then there target. Now no one was allowed in the city without special permission. Nearby towns were finishing there evacuation and following the same procedure as Darwin did.

The cyclone then slowly collapsed after traveling over Darwin. Members of the city were still not allowed back in to try and stop a big rush of people returning. A lot of information about the cyclone was kept conferential. Rescue teams, soldiers, police and reconstruction people were let in.

The city then slowly opened it self back up to the public and word began to pass about what happened to the rest of the country. Since communication wasn’t as good as it is today a lot of the country still didn’t know that there was even a cyclone near Darwin.

Over $800000 worth of property was damaged and 65 people were declared dead as a direct result of the cyclone. Alice Springs citizens raised over $105000 to help rebuild there neighboring city. Back then that was an amazing achievement.

To rebuild the city Gough Whitlam created Darwin Reconstruction Commission. Its task was to rebuild the city within 5 years. Some people suggested moving the entire city to a new location since the damage was so big but the government didn’t like this idea. A lot of the next 9 months was spent making temp accommodation; this included the ocean liner MV Patris.

Then in September 1975 permerment housing started to replace temporarily ones. This time with stricter housing codes and rules.

By 1978 most Darwin was back in full operation but a lot of its old residendants never returned.

This cyclone highlighted a problem in the political system. NT did not have enough governmental responsibilities or powers. After Tracy NT was given extra powers to self-govern.

Up until 2005 government responses to Tracy were kept conferential. When the Australia Freedom of Information act was passed people were given a better understanding to what happened as conferential information was released.

To learn more about Tropical cyclone Tracy visit http://en.wikipedia.org/wiki/Cyclone_Tracy or to find out more about tropical cyclones in general visit http://en.wikipedia.org/wiki/Tropical_cyclone.