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Cyclones ClearlyExplained.com

Tropical Cyclone Bonnie
Image Courtesy of NASA

 

What are cyclones? Cyclones ( or more properly called Tropical Cyclones) are a type of severe spinning(rotating) storm that occurs over the ocean near the tropics. The word "Cyclone" just means 'turning wind with one eye. It relates to the word "Cyclops" that one eyed creature in an Ancient Greek story.   Tropical Cyclones have a number of characteristics like: They must have a wind speed greater than 119km/h They start in the tropics. more...

Image: Courtesy of NOAA Did you know that cyclones are actually the release of stored solar energy that rotates. The sun heats the ocean up and this creates the condition for a tropical cyclone to develop. Cyclones spin because the Earth is spinning. It's due to something called the coriolis effect. The direction they spin depends on which hemisphere they are in. In the Southern hemisphere they spin in a clockwise direction and Northern hemisphere they spin in an anti-clockwise direction. Did you know... cyclones are also called hurricanes around the US. Cyclones are called typhoons near the South China sea (from the chinese word meaning 'big wind' )

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Why are cyclones important ? There are some obvious reasons for knowing about cyclones, these include: Environmentally cyclones can be important to local ecosystems. eg reefs and the distribution of plants and sand have adapted to them. Cyclones can have a economic and emotional effect on people and property directly affected. thousands of people have died or been displaced by them. Hundreds of homes could be destroyed causing millions of dollars damage. Having a better understanding of cyclones can help you better prepare and perhaps minimise or prevent cyclcone damage.

Cyclones and Culture Cyclones, like other natural disasters, have an impact on our culture, inspiring films and stories and even names of sporting teams. Extra info: The impact that cyclones have on the Earth's surface

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News about cyclones. Google News Headline search about Tropical Cyclone ABC News Online search Tropical Cyclone Current Official Cyclone Warnings for Australia from BoM Australia, Brisbane QLD From BoM, Northern Territory From BoM, Western Australia (for northern parts) Radar image of Darwin Region in Australia showing rainfall for Cyclone Ingrid 13 March 2005 . Notice that there is not much heavy rain at the centre of the cyclone.

Here are some useful links to resources and general information about cyclones Australian Resources Modelling Tropical Cyclones from the Bureau of Meteorology(BOM) Tropical Cyclone Vance 1999(excellent info) from BOM Tropical Cyclone introduction from the NT US Resources NASA Hurricane Guide National Oceanic and Atmospheric Admininstration (NOAA) Hurricane FAQ and National Hurricane Centre Hurricane information from University of Illinois

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How do cyclones occur or form? The formation of a cyclone has a number of stages Stage 0 (Zero)- The right place and the right sea temperature is needed. The place is usually within + or - 5° to °15 Lattitude from the equator over the ocean. The surface temperature of the ocean/sea needs to be 26.5°C or above. A low airpressure system (depression) with convection currents starts to gather clouds/stormy Stage 0 is basically continuous cloud build up even during the night time. The sun sun helps to heat the ocean and produces water vapour that forms couds.   Stage I is linked with a low air pressure system that starts to pull clouds in and rotate. It's not quite a cyclone but pretty likely.   Stage II is at the stage when the clouds start to really rotate but there is sometimes a chance that it may not develop in to a full cyclone. After stage II the cyclone is mature and developed, it may increase in size or decrease. It can be in it's full maturity stage. (image of TC Bonnie /NASA) BOM Reference   The cyclone seasons The northern hemisphere is: June - November The southern hemisphere is: November -May

How do cyclones progress? Often once the cyclone starts out small and starts to grow larger as it moves towards the north or south. Destructive Cyclones don't last more than a few days as their energy runs out. Although it can pick up energy as it travels across warm water. The low air pressure tends to 'drag' material around, eg clouds and moisture from the ocean. Predicting the direction of a cyclone is very difficult for more than a few hours ahead in time. They can sometimes change direction very quickly(doing a hair pin turn) or just move in fairly straight line.   When a cyclone moves overland they usually lose most of their energy but can cause floods.   How are cyclones classified? The more common scale is the one for measuring typical likely damage. This is based on the Saffir-Simpson Hurricane Scale Category Wind gust speed/ Swell Damage 1 less than 125km/h 1.2-1.6m mild damage 2 126-169km/h 1.7-2.5m significant damage to trees 3 170 - 224km/h 2.6 -3.7 structural damage, power failures likely 4 225 - 279 km/h 3.8-5.4 most roofing lost 5 more than 280 km/h more than 5.4m almost total destruction Cyclones are classified based on information from satellite images and uses a scale called the Dvorak Number going from 0 to 8. References: BoM Cyclone Survival Handbook Other wind scales including beaufort and Dvorak A great diagram/animation of the type of damage cyclones cause.

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What is the history of cyclones? Cyclones have existed for as long as the history of the Earth with water. So it is hard to say when the first hurricane or cyclone was recorded. It is likely that if you looked at some Ships logs from a few hundred years ago it is likely that they recorded cyclone conditions, although many simply would not have survived. "The Bathurst Bay Hurricane occurred in March 1899. Over 300 people were killed. It was the worst ever cyclone-related disaster in Australia's history" From BOM

Historic Cyclones The most famous Australian historic Cyclone was Cyclone Tracy, December 1974, where around 49 people died in Darwin, Northern Territory. There were another 16 who died at sea more... (from ABC news) but this has been revised with another 6 more lost at sea...more... making total of 71. The US has a long history of Hurricanes that are documented because they often affected populated areas. Historic Hurricane Hunters Historical Hurricane Information from the US/NOAA The first Hurricane hunter or person who flew an aircraft into a hurricane , may have been by a man called Joe Duckwork. More...

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The future of cyclones. Cyclones will continue to play a part of the natural cycles on Earth. The future of cyclones is really about the ability to better predict their intensity and direction. It is about being able to prevent future injury to people affect by them.

Perhaps a future prospect is to be able to disrupt a cyclone, or change its' direction to avoid populated areas, but this would require technologies we have not yet developed. satellite technology and computer modelling of weather is likely to be a key in helping to provide early detection of cyclones. SeaStar Satellite NASA/Oceans

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