Cyclone 42806 224679304 2008-07-09T22:57:50Z Thegreatdr 825275 /* Weather fronts */ Adding ref for shear line {{otheruses1|the meteorological phenomenon}} [[Image:Polar low.jpg|thumb|250 px|Polar low over the [[Barents Sea]] on [[February 27]], [[1987]]]] In [[meteorology]], a '''cyclone''' is an area of [[atmospheric pressure|low atmospheric pressure]] characterized by inward [[spiral]]ling [[wind]]s that rotate [[counter clockwise]] in the [[northern hemisphere]] and [[clockwise]] in the [[southern hemisphere]] of the Earth.<ref name="BBCCycDef"> {{cite web | title = BBC Weather Glossary - 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 }} </ref><ref name="UCARCycDef"> {{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 }} </ref> The generic term covers a wide variety of low pressure areas. The largest of the systems are cold core polar cyclones and extratropical cyclones which lie on the [[synoptic scale]]. Warm core cyclones such as tropical cyclones, mesocyclones, and polar lows lie within the smaller mesoscale. Subtropical cyclones are of intermediate size.<ref name="AnlFcastHelp">{{cite web | title = Cyclone Phase Analysis and Forecast: Help Page | author = Robert Hart | publisher = [http://moe.met.fsu.edu Florida State University Department of Meteorology] | date = [[2003-02-18]] | url = http://moe.met.fsu.edu/cyclonephase/help.html | accessdate = 2006-10-03 }}</ref><ref>Orlanski, I., 1975. A rational subdivision of scales for atmospheric processes. Bulletin of the American Meteorological Society, 56(5), 527-530.</ref> Cyclones have also been seen on other planets outside of the [[Earth]], such as [[Mars]] and [[Neptune]].<ref name="Brand">David Brand. [http://www.news.cornell.edu/releases/May99/mars.cyclone.deb.html Colossal cyclone swirling near Martian north pole is observed by Cornell-led team on Hubble telescope.] Retrieved on [[2008-06-15]].</ref><ref name="WIZ">[[NASA]]. [http://solarsystem.nasa.gov/educ/themes/display.cfm?Item=hurricane Historic Hurricanes.] Retrieved on [[2008-06-14]].</ref> [[Cyclogenesis]] describes the process of development for extratropical cyclones.<ref name="Arc">Arctic Climatology and Meteorology. [http://nsidc.org/arcticmet/glossary/cyclogenesis.html Cyclogenesis.] Retrieved on 2006-[[December 4|12-04]].</ref> Extratropical cyclones form as waves along [[weather fronts]] before occluding later in their life cycle as cold core cyclones. Weather fronts separate two [[air mass|masses of air]] of different [[density|densities]], and are the principal cause of [[meteorological phenomenon|meteorological phenomena]]. The air masses separated by a front usually differ in [[temperature]] and [[humidity]]. Cold fronts may feature narrow bands of [[thunderstorm]]s and [[severe weather]], and may on occasion be preceded by [[squall line]]s or [[dry line]]s. [[Warm front]]s are usually preceded by [[stratiform]] [[Precipitation (meteorology)|precipitation]] and [[fog]]. Cold fronts and [[occluded front]]s generally move from west to east, while warm fronts move [[Geographical pole|poleward]]. [[Tropical cyclogenesis]] describes the process of development of tropical cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core.<ref name = "AOML FAQ A7">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is an extra-tropical cyclone? | publisher = [[NOAA]] | accessdate = 2007-03-23 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A7.html}}</ref> Cyclones can transition between extratropical, subtropical, and tropical phases under the right conditions. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation.<ref name="FoN">Forces of Nature. [http://library.thinkquest.org/C003603/english/tornadoes/themesocyclone.shtml Tornadoes : the mesocyclone.] Retrieved on [[2008-06-15]].</ref> [[Waterspout]]s can also form from mesocyclones, but more often develop from environments of high instability and low vertical [[wind shear]].<ref name="NWS">[[National Weather Service]] [[Key West]] summary of waterspout types: http://www.srh.noaa.gov/eyw/HTML/spoutweb.htm</ref> ==Structure== There are a number of structural characteristics common to all cyclones. As they are [[low pressure area]]s, their center is the area of lowest atmospheric pressure in the region, often known in mature tropical cyclones as the [[eye (cyclone)|eye]].<ref name="FAQ eye">{{cite web | author=[[Chris Landsea|Landsea, Chris]] and Sim Aberson. | title=What is the "eye"? | date=[[August 13]] [[2004]] | publisher=[[Atlantic Oceanographic and Meteorological Laboratory]] | accessdate=2006-06-14 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A11.html}}</ref> 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|Coriolis force]] must be in an approximate balance, or the cyclone would collapse on itself as a result of the difference in pressure.<ref>[[University of Aberdeen]]. [http://www.abdn.ac.uk/physics/meteo/met8sum.pdf The Atmosphere in Motion.] Retrieved on [[2008-06-15]].</ref> The wind flow around a large cyclone is [[Clockwise and counterclockwise|counterclockwise]] in the northern hemisphere and clockwise in the southern hemisphere as a result of the Coriolis effect. (An [[anticyclone]], on the other hand, rotates clockwise in the northern hemisphere, and counterclockwise in the southern hemisphere.) ==Formation== [[Image:Baroclinicleafphasecyclogenesiscropped.gif|thumb|right|250px|The initial extratropical low pressure area forms at the location of the red dot on the image. It is usually perpendicular (at a right angle to) the leaf-like cloud formation seen on satellite during the early stage of cyclogenesis. The location of the axis of the upper level [[jet stream]] is in light blue.]] {{main|Cyclogenesis|Tropical cyclogenesis}} Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low pressure area).<ref name="Arc">Arctic Climatology and Meteorology. [http://nsidc.org/arcticmet/glossary/cyclogenesis.html Cyclogenesis.] Retrieved on 2006-[[December 4|12-04]].</ref> Cyclogenesis is an umbrella term for several different processes, all of which result in the development of some sort of cyclone. It can occur at various scales, from the microscale to the synoptic scale. Extratropical cyclones form as waves along [[weather fronts]] before occluding later in their life cycle as cold core cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core.<ref name = "AOML FAQ A7">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is an extra-tropical cyclone? | publisher = [[NOAA]] | accessdate = 2007-03-23 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A7.html}}</ref> Mesocyclones form as warm core cyclones over land, and can lead to tornado formation.<ref name="FoN">Forces of Nature. [http://library.thinkquest.org/C003603/english/tornadoes/themesocyclone.shtml Tornadoes : the mesocyclone.] Retrieved on [[2008-06-15]].</ref> [[Waterspout]]s can also form from mesocyclones, but more often develop from environments of high instability and low vertical [[wind shear]].<ref name="NWS">[[National Weather Service]] [[Key West]] summary of waterspout types: http://www.srh.noaa.gov/eyw/HTML/spoutweb.htm</ref> Cyclogenesis is the opposite of cyclolysis, and has an anticyclonic (high pressure system) equivalent which deals with the formation of [[high pressure area]]s—[[Anticyclogenesis]].<ref name="CyclogenesisDef"> {{cite web | title = American Meteorological Society Glossary - Cyclogenesis | publisher = [http://www.allenpress.com Allen Press Inc.] | date = [[2000-06]] | url = http://amsglossary.allenpress.com/glossary/search?p=1&query=cyclogenesis | accessdate = 2006-10-12 }}</ref> The surface low has a variety of ways of forming. Topography can force a surface low when dense low-level [[high pressure system]] ridges in east of a north-south mountain barrier.<ref>COMET Program [http://meted.ucar.edu/mesoprim/flowtopo/print.htm Flow Interaction With Topography]</ref> [[Mesoscale Convective System|Mesoscale convective systems]] can spawn surface lows which are initially warm core.<ref> Raymond D. Menard1, and J.M. Fritsch [http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0493(1989)117%3C1237:AMCCGI%3E2.0.CO%3B2 A Mesoscale Convective Complex-Generated Inertially Stable Warm Core Vortex]</ref> The disturbance can grow into a wave-like formation along the [[Surface weather analysis|front]] and the low will be positioned at the crest. Around the low, flow will become cyclonic, by definition. This rotational flow will push polar air equatorward west of the low via its trailing [[cold front]], and warmer air with push poleward low via the [[warm front]]. Usually the cold front will move at a quicker pace than the warm front and “catch up” with it due to the slow erosion of higher density airmass located out ahead of the cyclone and the higher density airmass sweeping in behind the cyclone, usually resulting in a narrowing warm sector.<ref>The Physics Factbook [http://hypertextbook.com/facts/2000/RachelChu.shtml Density of Air]</ref> At this point an [[occluded front]] forms where the warm air mass is pushed upwards into a trough of warm air aloft, which is also known as a trowal.<ref>St. Louis University [http://www.eas.slu.edu/CIPS/Presentations/Conferences/NWA2002/Snow_NWA_02/tsld003.htm What is a trowal?]</ref> [[Image:Hurricane profile.svg|thumb|250px|right|Tropical cyclones form when the energy released by the condensation of moisture in rising air causes a [[positive feedback loop]] over warm ocean waters.<ref>[[Kerry Emanuel]]. [http://wind.mit.edu/~emanuel/anthro2.htm Anthropogenic Effects on Tropical Cyclone Activity.] Retrieved on [[2008-02-25]].</ref>]] Tropical cyclogenesis is the technical term describing the development and strengthening of a [[tropical cyclone]] in the [[atmosphere]].<ref name="CYCDEF">{{cite web | author = Arctic Climatology and Meteorology | url = http://nsidc.org/arcticmet/glossary/cyclogenesis.html | title = Definition for Cyclogenesis | publisher = National Snow and Ice Data Center | accessdate = 2006-10-20}}</ref> The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-[[latitude]] cyclogenesis occurs. Tropical cyclogenesis involves the development of a [[Tropical cyclone#Mechanics_of_tropical_cyclones|warm-core]] cyclone, due to significant [[convection]] in a favorable atmospheric environment. There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high [[humidity]] in the lower to middle levels of the [[troposphere]], enough [[Coriolis force]] to develop a low pressure center, a preexisting low level focus or disturbance, and low vertical [[wind shear]].<ref name="A15">[[Chris Landsea]]. [http://www.aoml.noaa.gov/hrd/tcfaq/A15.html Subject: A15) How do tropical cyclones form ?] Retrieved on [[2008-06-08]].</ref> An average of 86 tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones (at least Category 3 intensity on the [[Saffir-Simpson Hurricane Scale]]).<ref>{{cite web | author = [[Chris Landsea]] | url = http://www.aoml.noaa.gov/hrd/Landsea/climvari/table.html | title = Climate Variability table - Tropical Cyclones | publisher = [[Atlantic Oceanographic and Meteorological Laboratory]], [[National Oceanic and Atmospheric Administration]] | accessdate =2006-10-19}}</ref> Mesocyclones are believed to form when strong changes of wind speed and/or direction with height ("[[wind shear]]") sets parts of the lower part of the atmosphere spinning in invisible tube-like rolls. The convective updraft of a thunderstorm is then thought to draw up this spinning air, tilting the rolls' orientation upward (from parallel to the ground to perpendicular) and causing the entire updraft to rotate as a vertical column. Mesocyclones are normally relatively localized: they lie between the [[Synoptic scale meteorology|synoptic scale]] (hundreds of kilometers) and microscale (hundreds of meters). Radar imagery is used to identify these features.<ref>Roger Edwards. [http://www.spc.ncep.noaa.gov/faq/tornado/ The Online Tornado FAQ: Frequently Asked Questions About Tornadoes.] Retrieved on [[2008-06-14]].</ref> ==Categorization== There are six main types of cyclones: [[Polar cyclone]]s, [[Polar low]]s, [[Extratropical cyclone]]s, [[Subtropical cyclone]]s, [[Tropical cyclone]]s, and [[Mesocyclone]]s. ===Polar cyclone=== {{main|Polar cyclone}} Polar, sub-polar, or Arctic cyclones (also known as the polar vortex)<ref name="glossvortex">Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=polar-vortex1 Polar vortex.] Retrieved on [[2008-06-15]].</ref> are vast areas of low pressure which stengthen in the winter and weaken in the summer.<ref>Halldór Björnsson. [http://andvari.vedur.is/~halldor/HB/Met210old/GlobCirc.html Global circulation.] Retrieved on [[2008-06-15]].</ref> A polar cyclone is a low pressure [[weather system]], usually spanning {{convert|1000|km|mi}} to {{convert|2000|km|mi}}, in which the air circulates in a counterclockwise direction in the northern hemisphere, and a clockwise direction in the southern hemisphere. In the Northern Hemisphere, the polar cyclone has two centers on average. One center lies near Baffin Island and the other over northeast Siberia.<ref name="glossvortex">Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=polar-vortex1 Polar vortex.] Retrieved on [[2008-06-15]].</ref> In the southern hemisphere, it tends to be located near the edge of the [[Ross ice shelf]] near 160 west longitude.<ref>Rui-Rong Chen, Don L. Boyer, and Lijun Tao. [http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0469(1993)050%3C4058%3ALSOAMI%3E2.0.CO%3B2&ct=1 Laboratory Simulation of Atmospheric Motions in the Vicinity of Antarctica.] Retrieved on [[2008-06-15]].</ref> When the polar vortex is strong, westerly flow descends to the earth's surface. When the polar cyclone is weak, significant cold outbreaks occur.<ref>James E. Kloeppel. [http://www.news.uiuc.edu/scitips/01/12weather.html Stratosheric polar vortex influences winter cold, researchers say.] Retrieved on [[2008-06-15]].</ref> ===Polar low=== {{main|Polar low}} A polar low is a small-scale, short-lived atmospheric [[low pressure area|low pressure system]] (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 {{convert|1000|km|mi}} and exist for no more than a couple of days. They are part of the larger class of [[mesoscale meteorology|mesoscale]] 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.<ref>Rasmussen,E.A. and Turner, J.(2003). Polar Lows: Mesoscale Weather Systems in the Polar Regions, Cambridge University Press, Cambridge, pp 612.</ref> ===Extratropical=== [[Image:UK-Cyclone.gif|thumb|right|250px|A fictitious synoptic chart of an extratropical cyclone affecting the UK and Ireland. The blue arrows between [[isobars]] 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|frontal boundaries]].]] {{main|Extratropical cyclone}} An extratropical cyclone is a [[Synoptic scale meteorology|synoptic scale]] [[Low pressure area|low pressure]] weather system that has neither [[tropical cyclone|tropical]] nor [[polar cyclone|polar]] characteristics, being connected with [[Surface weather analysis|fronts]] and horizontal [[gradients]] in [[temperature]] and [[dew point]] otherwise known as "baroclinic zones".<ref name="ExtraLessonMillUni"> {{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 }} </ref> 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|extratropical transition]] has occurred,<ref name="ExtraLessonMillUni">ExtraLessonMillUni</ref><ref name="ExtratropicalPhases">{{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 }}</ref> and are often described as "depressions" or "lows" by weather forecasters and the general public. These are the everyday phenomena which along with [[anti-cyclone]]s, 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.<ref>Ryan N. Maue. [http://www.coaps.fsu.edu/~maue/cyclone_ch3.html CHAPTER 3: CYCLONE PARADIGMS AND EXTRATROPICAL TRANSITION CONCEPTUALIZATIONS.] Retrieved on [[2008-06-15]].</ref> An extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone, if it dwells over warm waters and develops central convection, which warms its core.<ref name = "AOML FAQ A7">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is an extra-tropical cyclone?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A7.html}}</ref> ====Weather fronts==== {{Main article|Weather front}} [[Image:Airmassesorigin.gif|300px|thumb|right|Different air masses which affect North America, as well as other continents, tend to be separated by frontal boundaries. In this illustration, the Arctic front separates Arctic from Polar air masses, while the Polar front separates Polar air from warm air masses.]] Weather fronts separate two [[air mass|masses of air]] of different [[density|densities]], and is the principal cause of [[meteorological phenomenon|meteorological phenomena]]. In [[surface weather analysis|surface weather analyses]], fronts are depicted using various colored lines and symbols, depending on the type of front. The air masses separated by a front usually differ in [[temperature]] and [[humidity]]. Cold fronts may feature narrow bands of [[thunderstorm]]s and [[severe weather]], and may on occasion be preceded by [[squall line]]s or [[dry line]]s. [[Warm front]]s are usually preceded by [[stratiform]] [[Precipitation (meteorology)|precipitation]] and [[fog]]. The weather usually clears quickly after a front's passage. Some fronts produce no precipitation and little cloudiness, although there is invariably a wind shift.<ref name=stm>{{cite web|author=Author unknown|title=Lesson 7: Clouds and Precipitation|year=|accessdate=2007-04-29|url=http://www.ccrc.sr.unh.edu/~stm/AS/Teaching/STEC521/STEC521_7.html|publisher=Self-published}}</ref> Cold fronts and [[occluded front]]s generally move from west to east, while warm fronts move [[Geographical pole|poleward]]. Because of the greater density of air in their wake, cold fronts and cold occlusions move faster than warm fronts and warm occlusions. [[Mountain]]s and warm bodies of water can slow the movement of fronts.<ref name="DR">{{cite web|author=David Roth|title=Unified Surface Analysis Manual|year=|accessdate=2006-10-22|publisher=[[Hydrometeorological Prediction Center]]|url= http://www.hpc.ncep.noaa.gov/sfc/UASfcManualVersion1.pdf}}</ref> When a front becomes [[stationary front|stationary]], and the density contrast across the frontal boundary vanishes, the front can degenerate into a line which separates regions of differing wind velocity, known as a shearline.<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?p=1&query=shear+line Shear Line.] Retrieved on 2006-10-22.</ref> This is most common over the open ocean. ===Subtropical=== [[Image:Subtropical_Storm_Andrea_2007.jpg|thumb|200px|right|[[Subtropical Storm Andrea (2007)|Subtropical Storm Andrea]] in [[2007 Atlantic hurricane season|2007]]]] {{main|Subtropical cyclone}} A subtropical cyclone is a [[weather]] system that has some characteristics of a [[tropical cyclone]] and some characteristics of an [[extratropical cyclone]]. They can form between the equator and the 50th parallel.<ref name="A6">[[Chris Landsea]]. [http://www.aoml.noaa.gov/hrd/tcfaq/A6.html Subject: A6) What is a sub-tropical cyclone?] Retrieved on [[2008-06-14]].</ref> As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical cyclones or extratropical cyclones, and used terms such as quasi-tropical and semi-tropical to describe the cyclone hybrids.<ref>David B. Spiegler. [http://docs.lib.noaa.gov/rescue/mwr/101/mwr-101-04-0380.pdf Reply.] Retrieved on [[2008-04-20]].</ref> By 1972, the [[National Hurricane Center]] officially recognized this cyclone category.<ref>R. H. Simpson and Paul J. Hebert. [http://www.aoml.noaa.gov/general/lib/lib1/nhclib/mwreviews/1972.pdf Atlantic Hurricane Season of 1972.] Retrieved on [[2008-06-14]].</ref> Subtropical cyclones began to receive names off the official tropical cyclone list in the Atlantic Basin in 2002.<ref name="A6">[[Chris Landsea]]. [http://www.aoml.noaa.gov/hrd/tcfaq/A6.html Subject: A6) What is a sub-tropical cyclone?] Retrieved on [[2008-06-14]].</ref> They have broad wind patterns with maximum sustained winds located farther from the center than typical tropical cyclones, and exist in areas of weak to moderate temperature gradient.<ref name="A6">[[Chris Landsea]]. [http://www.aoml.noaa.gov/hrd/tcfaq/A6.html Subject: A6) What is a sub-tropical cyclone?] Retrieved on [[2008-06-14]].</ref> Since they form from initially extratropical cyclones which have colder temperatures aloft than normally found in the tropics, the sea surface temperatures required for their formation are lower than the tropical cyclone threshold by three degrees [[Celsius]], or five degrees [[Fahrenheit]], lying around 23&nbsp;degrees Celsius.<ref name="HistSubTropCyclones">{{cite web | title = A Fifty year History of Subtropical Cyclones | author = David Mark Roth | publisher = [http://www.hpc.ncep.noaa.gov/ Hydrometeorological Prediction Center] | date = 2002-02-15 | url = http://www.hpc.ncep.noaa.gov/research/roth/Subpreprint.pdf | accessdate = 2006-10-04 }}</ref> This means that subtropical cyclones are more likely to form outside the traditional bounds of the hurricane season. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm.<ref name = "AOML FAQ A6">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is a sub-tropical cyclone?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A6.html}}</ref> ===Tropical=== [[Image:Cyclone Catarina from the ISS on March 26 2004.JPG|thumb|250px|[[Cyclone Catarina]], a rare [[South Atlantic tropical cyclone]] viewed from the [[International Space Station]] on [[March 26]] [[2004]]]] {{main|Tropical cyclone}} A tropical cyclone is a [[storm|storm system]] characterized by a [[low pressure system|low pressure]] center and numerous [[thunderstorms]] that produce strong winds and [[flood]]ing [[rain]]. A tropical cyclone feeds on heat released when moist [[air]] rises, resulting in [[condensation]] of [[water vapour]] contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as [[nor'easter]]s, [[European windstorm]]s, and [[polar low]]s, leading to their classification as "warm core" storm systems.<ref name = "AOML FAQ A7">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is an extra-tropical cyclone? | publisher = [[NOAA]] | accessdate = 2007-03-23 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A7.html}}</ref> The term "tropical" refers to both the geographic origin of these systems, which form almost exclusively in [[tropics|tropical]] regions of the globe, and their formation in [[Air mass#Classification|Maritime Tropical air masses]]. The term "cyclone" refers to such storms' cyclonic nature, with [[Clockwise and counterclockwise|counterclockwise]] rotation in the [[Northern Hemisphere]] and clockwise rotation in the [[Southern Hemisphere]]. Depending on their location and strength, tropical cyclones are referred to by other names, such as hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply as a cyclone.<ref name="NHC glossary">{{cite web | author = [[National Hurricane Center]] | url = http://www.nhc.noaa.gov/aboutgloss.shtml | year = 2005 | title = Glossary of NHC/TPC Terms | accessdate= 2006-11-29 | publisher = [[National Oceanic and Atmospheric Administration]]}}</ref> While tropical cyclones can produce extremely powerful winds and torrential [[rain]], they are also able to produce high waves and damaging [[storm surge]].<ref name="oxfo">{{cite web|author=James M. Shultz, Jill Russell and Zelde Espinel|year=2005|title=Epidemiology of Tropical Cyclones: The Dynamics of Disaster, Disease, and Development|publisher=Oxford Journal|accessdate=2007-02-24|url=http://epirev.oxfordjournals.org/cgi/content/full/27/1/21}}</ref> They develop over large bodies of warm water,<ref name = "AOML FAQ A15">{{ cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: How do tropical cyclones form? | publisher = [[NOAA]] | accessdate = 2006-07-26 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A15.html}}</ref> and lose their strength if they move over land.<ref>[[National Hurricane Center]]. [http://www.aoml.noaa.gov/hrd/tcfaq/C2.html Subject : C2) Doesn't the friction over land kill tropical cyclones?] Retrieved on [[2008-02-25]].</ref> This is the reason coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal [[flood]]ing up to {{convert|40|km|mi}} from the coastline. Although their effects on human populations can be devastating, tropical cyclones can also relieve [[drought]] conditions.<ref name="2005 EPac outlook">[[National Oceanic and Atmospheric Administration]]. [http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html 2005 Tropical Eastern North Pacific Hurricane Outlook.] Retrieved on [[2006-05-02]].</ref> They also carry heat and energy away from the tropics and transport it toward [[temperate]] [[latitudes]], which makes them an important part of the global [[atmospheric circulation]] mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's [[troposphere]], and to maintain a relatively stable and warm temperature worldwide. Many tropical cyclones [[tropical cyclogenesis|develop]] when the atmospheric conditions around a weak disturbance in the atmosphere are favorable. Others form when [[#Related cyclone types|other types of cyclones]] acquire tropical characteristics. Tropical systems are then moved by [[#Steering winds|steering winds]] in the [[troposphere]]; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an [[eye (cyclone)|eye]]. On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses;<ref name = "AOML FAQ A7">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is an extra-tropical cyclone?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A7.html}}</ref> From an operational standpoint, a tropical cyclone is usually not considered to become subtropical during its extratropical transition.<ref name=PadgetDecember2000>{{cite web | author = Padgett, Gary | url = http://australiasevereweather.com/cyclones/2001/summ0012.htm | title = Monthly Global Tropical Cyclone Summary for December 2000 | year = 2001 | accessdate = 2006-03-31}}</ref> ===Mesoscale=== [[Image:Greensburg3 small.gif|thumb|A mesocyclone from the [[May 2007 Tornado Outbreak|Greensburg, Kansas tornado]] indicated on [[Doppler effect|Doppler]] [[weather radar]].]] {{main|Mesocyclone}} A mesocyclone is a [[vortex]] of air, approximately {{convert|2|km|mi}} to {{convert|10|km|mi}} in diameter (the [[mesoscale]] of meteorology), within a [[convection|convective]] [[storm]].<ref name="MesocyloneDef"> {{cite web| title = American Meteorological Society Glossary - Mesocyclone | publisher = [http://www.allenpress.com Allen Press Inc.] | date = 2000-06 | url = http://amsglossary.allenpress.com/glossary/search?id=mesocyclone1 | accessdate = 2006-12-07 }}</ref> Air rises and rotates around a vertical axis, usually in the same direction as low pressure systems in a given hemisphere. They are most often cyclonic, that is, associated with a localized low-pressure region within a [[severe thunderstorm]].<ref>[[National Weather Service]] Forecast Office State College, Pennsylvania. [http://www.erh.noaa.gov/ctp/features/2006/07_10/ Splitting Storm and Anti-cyclonic Rotating Mesocyclone in a Thunderstorm over Elk County July 10th, 2006.] Retrieved on [[2008-06-15]].</ref> Such storms can feature strong surface winds and severe [[hail]]. Mesocyclones often occur together with updrafts in [[supercell]]s, where [[tornado]]es may form. About 1700 mesocyclones form annually across the [[United States]], but only half produce tornadoes.<ref name="FoN">Forces of Nature. [http://library.thinkquest.org/C003603/english/tornadoes/themesocyclone.shtml Tornadoes : the mesocyclone.] Retrieved on [[2008-06-15]].</ref> ==Extraterrestrial cyclones== {{main|Extraterrestrial cyclone}} [[Image:Mars cyclone.jpg|thumb|right|Cyclone on Mars, imaged by the [[Hubble Space Telescope]]]] Cyclones are not unique to Earth. Cyclonic storms are common on [[gas giant|Jovian planets]], like the [[Small Dark Spot]] on [[Neptune]]. Also known as the [[Wizard's Eye]], it is about one third the diameter of the Great Dark Spot. It received the name "Wizard's Eye" because it looks like an eye. This appearance is caused by a white cloud in the middle of the Wizard's Eye.<ref>[[NASA]]. [http://solarsystem.nasa.gov/educ/themes/display.cfm?Item=hurricane Historic Hurricanes.] Retrieved on [[2008-06-14]].</ref> [[Mars]] has also exhibited cyclonic storms.<ref name="Brand">David Brand. [http://www.news.cornell.edu/releases/May99/mars.cyclone.deb.html Colossal cyclone swirling near Martian north pole is observed by Cornell-led team on Hubble telescope.] Retrieved on [[2008-06-15]].</ref> Jovian storms like the [[Great Red Spot]] are usually mistakenly named as giant hurricanes or cyclonic storms. However, this is inaccurate, as the Great Red Spot is, in fact, the inverse phenomenon, an [[anticyclone]].<ref name="HaydPlan"> {{cite web | title = Jupiter's Great Red Spot | author = Ellen Cohen | publisher= [http://haydenplanetarium.org/ Hayden Planetarium] | url = http://haydenplanetarium.org/resources/ava/page/index.php?file=P0413jupispot | accessdate = 2007-11-16 }} </ref> ==See also== {{tcportal}} *[[Gyre]] *[[List of environment topics]] *[[Meteorology]] {{Cyclones}} ==References== {{reflist|2}} ==External links== *[http://www.physicalgeography.net/fundamentals/7s.html Fundamental of Physical Geography: The Mid-Latitude Cyclone] - Dr. Michael Pidwirny, University of British Columbia, Okanagan *[http://nsidc.org/arcticmet/glossary/cyclogenesis.html Glossary Definition: Cyclogenesis] - The National Snow and Ice Data Center *[http://nsidc.org/arcticmet/glossary/cyclolysis.html Glossary Definition: Cyclolysis] - The National Snow and Ice Data Center *[http://www.weatheronline.co.uk/feature/wf261103.htm Weather Facts: The Polar Low] - Weather Online UK *[http://www.aoml.noaa.gov/hrd/tcfaq/A1.html NOAA FAQ] *[http://clearlyexplained.com/nature/earth/disasters/cyclones.html Cyclones 'ClearlyExplained'] *[http://emdat.be The EM-DAT International Disaster Database] by the [[Centre for Research on the Epidemiology of Disasters]] [[Category:Basic meteorological concepts and phenomena]] [[Category:Tropical cyclone meteorology]] [[Category:Types of cyclone|*]] [[Category:Weather hazards]] [[Category:Vortices]] <!-- interwiki --> [[af:Sikloon]] [[ar:زوبعة]] [[bn:ঘূর্ণিঝড়]] [[cs:Cyklóna]] [[da:Cyklon]] [[de:Zyklon]] [[el:Πεδίο χαμηλού βαρομετρικού]] [[et:Tsüklon]] [[es:Ciclón]] [[eo:Ciklono]] [[fa:چرخند]] [[fr:Cyclone]] [[ko:사이클론 (열대저기압)]] [[id:Siklon]] [[it:Ciclone]] [[he:ציקלון]] [[sw:Tufani]] [[lt:Ciklonas]] [[hu:Ciklon]] [[ja:サイクロン]] [[no:Syklon]] [[nn:Syklon]] [[pl:Cyklon]] [[pt:Ciclone]] [[ru:Циклон]] [[simple:Cyclone]] [[sk:Tlaková níž]] [[sr:Циклон]] [[fi:Sykloni]] [[tr:Siklon]] [[uk:Циклон (атмосферний вихор)]] [[zh:气旋]]