Cyclone

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image of a tropical cyclone in the northern hemisphere.In meteorology, a cyclone is an area of low pressure area characterized by inward spiraling winds that rotate counter clockwise in the northern hemisphere and clockwise in the southern hemisphere of the Earth. {{cite web | title = BBC Weather Gloassary - Cyclone | publisher= http://www.bbc.co.uk/weather/ BBC Weather | url = http://www.bbc.co.uk/weather/weatherwise/glossary/c.shtml | accessdate = 2006-10-24 --> {{cite web | title = UCAR Glossary - Cyclone | publisher= http://meted.ucar.edu/ University Corporation for Atmospheric Research | url = http://meted.ucar.edu/satmet/goeschan/glossary.htm#c | accessdate = 2006-10-24 --> Since the generic term covers a wide variety of [List of meteorological phenomena, such as [tropical cyclones, [extratropical cyclones, and [tornadoes, meteorologists rarely use it without additional qualification.

Etymology The word cyclones appears to have been coined by a Captain Henry Piddington, who used it to refer to the storm that blew a freighter in circles in Mauritius in February of 1845. Tropical cyclones are then circular wind storms that form in the tropics. It may have been derived from the Greek word kyklon, which means moving in a circle. {{cite web | title = The Weather Doctor: Cyclone Origin | author = Keith C. Heidorn, PhD | publisher= http://www.islandnet.com/~see/ Home Page of Keith C. Heidorn (The Weather Doctor) | date = [2003-10-01 | url = http://www.islandnet.com/~see/weather/history/cyclone-word.htm | accessdate = 2006-10-24 --> {{cite web | title = Banglapedia: Piddington, Henry | publisher= http://banglapedia.org/ Banglapedia | url = http://banglapedia.org/HT/P_0168.htm | accessdate = 2006-10-24 --> Some say that Piddington derived the word from the Greek word ''cyclos'', meaning "coils of a snake", in comparison with the tropical storms in the Bay of Bengal and in the Arabian Sea. {{cite web | title = Cyclone Related Disasters - What Are Cyclones? | publisher= http://www.imdmumbai.gov.in/main.htm India Meteorological department | url = http://www.imdmumbai.gov.in/cycdisasters.htm | accessdate = 2006-10-24 --> Others argue that the word was derived from ''[Cyclops'', a creature in Greek mythology with one eye, as it is 'turning wind with one eye'. {{cite web | title = ClearlyExplained.com - Cyclones | author = Richard Conan-Davies BSc Dip Ed | publisher= http://clearlyexplained.com Clearly Explained.com | date = [2003-05-14 | url = http://clearlyexplained.com/nature/earth/disasters/cyclones.html | accessdate = 2006-10-24 -->

Structure There are a number of structural characteristics common to all cyclones. Their center is the area of lowest atmospheric pressure, often known in mature tropical and subtropical cyclones as the eye. Near the center, the pressure gradient force (from the pressure in the center of the cyclone compared to the pressure outside the cyclone) and the Coriolis effect must be in an approximate balance, or the cyclone would collapse on itself as a result of the difference in pressure. The wind flow around a large cyclone is Clockwise and counterclockwise in the northern hemisphere and clockwise in the southern hemisphere as a result of the Coriolis effect.

Formation Cold-core cyclones (most cyclone varieties) form due to the nearby presence of an upper level trough, which increases divergence aloft over an area that induces upward motion and surface low pressure. Warm-core cyclones (such as tropical cyclones and many mesocyclones) can have their initial start due to a nearby upper trough, but after formation of the initial disturbance, depend upon a storm-relative upper level high to maintain or increase their strength.

Categorisation Each of the six main types of cyclone has further characteristics which define it as either a Polar cyclone, Polar low, Extratropical cyclone, Subtropical cyclone, Tropical cyclone, or Mesocyclone.

Polar cyclone Polar or Arctic cyclones are vast areas of low pressure. . A polar cyclone is a low pressure weather system, usually spanning 1,000–2,000 kilometers, in which the air circulates in a counterclockwise fashion in the northern hemisphere.

Polar low on February 27, 1987A polar low is a small-scale, short-lived atmospheric low pressure area (depression) that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. The systems usually have a horizontal length scale of less than 1,000 km and exist for no more than a couple of days. They are part of the larger class of mesoscale meteorology weather systems. Polar lows can be difficult to detect using conventional weather reports and are a hazard to high-latitude operations, such as shipping and gas and oil platforms.

Polar lows have been referred to by many other terms, such as polar mesoscale vortex, Arctic hurricane, Arctic low, and cold air depression. Today the term is usually reserved for the more vigorous systems that have near-surface winds of at least 17 m/s.

Extratropical indicate the direction of the wind, while the "L" symbol denotes the centre of the "low". Note the occluded, cold and warm Surface weather analysis.An extratropical cyclone, sometimes inaccurately called a cyclone, is a Synoptic scale meteorology Low pressure area weather system that has neither tropical cyclone nor polar cyclone characteristics, being connected with Surface weather analysis and horizontal gradients in temperature and dew point otherwise known as "baroclinic zones". {{cite web | title = ESCI 241 – Meteorology; Lesson 16 – Extratropical Cyclones | author = Dr. DeCaria | publisher = http://muweb.millersville.edu/~esci/ Department of Earth Sciences, Millersville University, Millersville, Pennsylvania | date = [2005-12-07 | url = http://www.atmos.millersville.edu/~adecaria/ESCI241/esci241_lesson16_cyclones.html | accessdate = 2006-10-21 -->

The descriptor "extratropical" refers to the fact that this type of cyclone generally occurs outside of the tropics, in the middle latitudes of the planet. These systems may also be described as "mid-latitude cyclones" due to their area of formation, or "post-tropical cyclones" where Extratropical cyclone#Extratropical transition has occurred,ExtraLessonMillUni{{cite web | title = Synoptic Composites of the Extratropical Transition Lifecycle of North Atlantic TCs as Defined Within Cyclone Phase Space | author = Robert Hart and Jenni Evans | publisher = http://ams.confex.com/ American Meteorological Society | date = 2003 | url = http://ams.confex.com/ams/pdfpapers/70524.pdf | accessdate = 2006-10-03 --> and are often described as "depressions" or "lows" by weather forecasters and the general public. These are the everyday phenomena which along with [anti-cyclones, drive the weather over much of the Earth.

Although extratropical cyclones are almost always classified as baroclinic since they form along zones of temperature and dewpoint gradient, they can sometimes become barotropic late in their life cycle when the temperature distribution around the cyclone becomes fairly uniform with radius.

Subtropical A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. It can form in a wide band of latitude, from the equator to 50°.

Tropical , a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26 2004

A tropical cyclone is a storm system fueled by the heat released when moist air rises and the water vapor in it condensation. The term describes the storm's origin in the tropics and its cyclonic nature, which means that its circulation is counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. Tropical cyclones are distinguished from other cyclonic windstorms such as nor'easters, European windstorms, and polar lows by the heat mechanism that fuels them, which makes them "warm core" storm systems.

Depending on their location and strength, there are various terms by which tropical cyclones are known, such as hurricane, typhoon, tropical storm, cyclonic storm and tropical depression.

Tropical cyclones can produce extremely strong winds, tornadoes, torrential rain, high waves, and storm surges. The heavy rains and storm surges can produce extensive flooding. Although their effects on human populations can be devastating, tropical cyclones also can have beneficial effects by relieving drought conditions. They carry heat away from the tropics, an important mechanism of the global atmospheric circulation that maintains equilibrium in the Earth's troposphere.

Mesoscale A mesocyclone is a cyclonic vortex of air, between approximately 2 and 10 km diameter within a convective storm. They can often be found in association with updrafts in supercells, where tornadoes may form. The term refers only to mesoscale cyclones found within convective storms, and does not apply to other cyclones on the mesoscale. {{cite web] | date = 2000-06 | url = http://amsglossary.allenpress.com/glossary/search?id=mesocyclone1 | accessdate = 2006-12-07 --> Storms with mesocyclones can feature strong surface winds and severe [hail.

Extraterrestrial cyclones

Cyclones are not unique to Earth. Cyclonic storms are common on Jovian planets, like the Small Dark Spot on Neptune. Mars has also exhibited cyclonic storms. Jovian storms like the Great Red Spot are usually mistakenly named as giant hurricanes or cyclonic storms. This is wrong, as they are the total opposite, anticyclones.

See also

Anticyclone
Cyclogenesis
Eye (cyclone)
List of environment topics
Meteorology
Mesocyclone
Polar cyclone
Polar low
Extratropical cyclone
Subtropical cyclone
Tropical cyclone
Tropical cyclogenesis

References

External links

Fundamental of Physical Geography: The Mid-Latitude Cyclone - Dr. Michael Pidwirny, University of British Columbia, Okanagan
Glossary Definition: Cyclogenesis - The National Snow and Ice Data Center
Glossary Definition: Cyclolysis - The National Snow and Ice Data Center
Weather Facts: The Polar Low - Weather Online UK
NOAA FAQ
Cyclones 'ClearlyExplained'
Kent Cyclone - Listen to 'Cyclone What?' here

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International overnight and UK courier services, based in London's West End.

BBC NEWS | World | South Asia | Bangladesh cyclone kills hundreds
The death toll from a cyclone that hit the southern coast of Bangladesh reportedly reaches more than 600.

BBC NEWS | South Asia | Bangladesh cyclone kills hundreds
The death toll from a cyclone that hit the southern coast of Bangladesh reportedly reaches more than 600.

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Cyclone - Wikipedia, the free encyclopedia
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