Cyclone#Structure

Henry Piddington published 40 papers dealing with tropical storms from Calcutta between 1836 and 1855 in The Journal of the Asiatic Society. He also coined the term cyclone, meaning the coil of a snake. In 1842, he published his landmark thesis, Laws of the Storms.{{cite web|url=http://www.mausam.gov.in/WEBIMD/modern_meteorology.jsp|title=Modern Meteorology|publisher=India Meteorological Department|access-date=2011-11-18}}{{dead link|date=August 2017 |bot=InternetArchiveBot |fix-attempted=yes }}

File:Post-Tropical Cyclone Nuri and Typhoon Haiyan surface analysis.png

There are a number of structural characteristics common to all cyclones. A cyclone is a low-pressure area.{{cite web|author=Chris Landsea and Sim Aberson|title=Subject: A11) What is the "eye"? How is it formed and maintained ? What is the "eyewall"? What are "spiral bands"?|url=http://www.aoml.noaa.gov/hrd/tcfaq/A11.html|date=August 13, 2004|publisher=Atlantic Oceanographic and Meteorological Laboratory|access-date=2009-12-28|archive-date=2006-06-14|archive-url=https://web.archive.org/web/20060614205417/http://www.aoml.noaa.gov/hrd/tcfaq/A11.html|url-status=live}} A cyclone's center (often known in a mature tropical cyclone as the eye), is the area of lowest atmospheric pressure in the region. 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 force from the Coriolis effect must be in an approximate balance, or the cyclone would collapse on itself as a result of the difference in pressure.{{cite web|url=http://homepages.abdn.ac.uk/wpe001/meteo/metoh8.pdf|title=The Atmosphere in Motion|publisher=University of Aberdeen|access-date=2011-09-11|url-status=dead|archive-url=https://web.archive.org/web/20121018224041/http://homepages.abdn.ac.uk/wpe001/meteo/metoh8.pdf|archive-date=2012-10-18}}

Because of the Coriolis effect, the wind flow around a large cyclone is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.{{cite web|author=Chris Landsea|date=2009-02-06|url=http://www.aoml.noaa.gov/hrd/tcfaq/D3.html|title=Subject: D3) Why do tropical cyclones' winds rotate counterclockwise (clockwise) in the Northern (Southern) Hemisphere?|access-date=2009-12-28|publisher=Atlantic Oceanographic and Meteorological Laboratory|author-link=Chris Landsea|archive-date=2009-01-06|archive-url=https://web.archive.org/web/20090106113522/http://www.aoml.noaa.gov/hrd/tcfaq/D3.html|url-status=live}} In the Northern Hemisphere, the fastest winds relative to the surface of the Earth therefore occur on the eastern side of a northward-moving cyclone and on the northern side of a westward-moving one; the opposite occurs in the Southern Hemisphere.{{cite web|url=https://www.usatoday.com/weather/resources/askjack/wfaqhur.htm|title=Are the winds on one side of a hurricane faster than on the other side?|series=Ask the Experts: Hurricanes|work=USA Today|date=November 11, 2007|access-date=September 9, 2011|archive-date=October 12, 2011|archive-url=https://web.archive.org/web/20111012204835/http://www.usatoday.com/weather/resources/askjack/wfaqhur.htm|url-status=dead}} In contrast to low-pressure systems, the wind flow around high-pressure systems are clockwise (anticyclonic) in the northern hemisphere, and counterclockwise in the southern hemisphere.

File:Baroclinicleafphasecyclogenesiscropped.gif is in light blue.]]

File:Hurricane profile.svg over warm ocean waters.{{cite web|author=Kerry Emanuel|url=http://wind.mit.edu/~emanuel/anthro2.htm|title=Anthropogenic Effects on Tropical Cyclone Activity|access-date=2008-02-25|date=January 2006|publisher=Massachusetts Institute of Technology|author-link=Kerry Emanuel|archive-date=2012-07-17|archive-url=https://web.archive.org/web/20120717074958/http://wind.mit.edu/~emanuel/anthro2.htm|url-status=live}}]]

{{main|Cyclogenesis|Tropical cyclogenesis}}

Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. Cyclogenesis is an umbrella term for several different processes that all result in the development of some sort of cyclone.{{cite web |title=Cyclogenesis {{!}} meteorology |url=https://www.britannica.com/science/cyclogenesis |website=Encyclopædia Britannica |access-date=13 January 2021 |archive-date=14 January 2021 |archive-url=https://web.archive.org/web/20210114004348/https://www.britannica.com/science/cyclogenesis |url-status=live }} It can occur at various scales, from the microscale to the synoptic scale.

Extratropical cyclones begin as waves along weather fronts before occluding later in their life cycle as cold-core systems. However, some intense extratropical cyclones can become warm-core systems when a warm seclusion occurs.

Tropical cyclones form as a result of significant convective activity, and are warm core. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation. Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear.National Weather Service Key West [https://web.archive.org/web/20050211013703/http://www.srh.noaa.gov/eyw/HTML/spoutweb.htm summary of waterspout types] Cyclolysis is the opposite of cyclogenesis, and is the high-pressure system equivalent, which deals with the formation of high-pressure areas—anticyclogenesis.{{cite web|publisher = American Meteorological Society|author = Glossary of Meteorology|title = Cyclogenesis|date = June 2000|url = http://glossary.ametsoc.org/wiki/Cyclogenesis|access-date = 2009-12-28|archive-date = 2014-01-15|archive-url = https://web.archive.org/web/20140115065635/http://glossary.ametsoc.org/wiki/Cyclogenesis|url-status = live}}

A surface low can form in a variety of ways. Topography can create a surface low. Mesoscale convective systems can spawn surface lows that are initially warm-core.{{cite journal|author1=Raymond D. Menard |author2=J.M. Fritsch |title=A Mesoscale Convective Complex-Generated Inertially Stable Warm Core Vortex|date=June 1989|journal=Monthly Weather Review|pages=1237–1261|volume=117|issue=6|doi=10.1175/1520-0493(1989)117<1237:AMCCGI>2.0.CO;2|bibcode = 1989MWRv..117.1237M |doi-access=free}} The disturbance can grow into a wave-like formation along the front and the low is positioned at the crest. Around the low, the flow becomes cyclonic. This rotational flow moves polar air towards the equator on the west side of the low, while warm air move towards the pole on the east side. A cold front appears on the west side, while a warm front forms on the east side. Usually, the cold front moves at a quicker pace than the warm front and "catches up" with it due to the slow erosion of higher density air mass out ahead of the cyclone. In addition, the higher density air mass sweeping in behind the cyclone strengthens the higher pressure, denser cold air mass. The cold front over takes the warm front, and reduces the length of the warm front.{{cite web|author=Glenn Elert|year=2006|work=The Physics Factbook|url=http://hypertextbook.com/facts/2000/RachelChu.shtml|title=Density of Air|access-date=2010-01-01|archive-date=2010-01-02|archive-url=https://web.archive.org/web/20100102035928/http://hypertextbook.com/facts/2000/RachelChu.shtml|url-status=live}} 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.{{cite web|author=St. Louis University|url=http://www.eas.slu.edu/CIPS/Presentations/Conferences/NWA2002/Snow_NWA_02/tsld003.htm|publisher=National Weather Association|title=What is a trowal?|access-date=2010-01-01|date=2004-09-06|archive-url = https://web.archive.org/web/20080608235916/http://www.eas.slu.edu/CIPS/Presentations/Conferences/NWA2002/Snow_NWA_02/tsld003.htm |archive-date = June 8, 2008|url-status=dead}}

Tropical cyclogenesis is the development and strengthening of a tropical cyclone.{{cite web|author=Nina A. Zaitseva |year=2006 |url=http://nsidc.org/arcticmet/glossary/cyclogenesis.html |title=Definition for Cyclogenesis |publisher=National Snow and Ice Data Center |access-date=2006-10-20 |url-status=dead |archive-url=https://web.archive.org/web/20060830135741/http://www.nsidc.org/arcticmet/glossary/cyclogenesis.html |archive-date=2006-08-30 }} The mechanisms by which tropical cyclogenesis occurs are distinctly different from those that produce mid-latitude cyclones. Tropical cyclogenesis, the development of a warm-core cyclone, begins with significant convection in a favorable atmospheric environment. There are six main requirements for tropical cyclogenesis:

1. sufficiently warm sea surface temperatures,[http://www.thethermograpiclibrary.org/index.php?title=Fichier:Water_cooling.jpg Cyclon in a board] {{Webarchive|url=https://web.archive.org/web/20130614225446/http://www.thethermograpiclibrary.org/index.php?title=Fichier:Water_cooling.jpg |date=2013-06-14 }}. thethermograpiclibrary.org
2. atmospheric instability,
3. high humidity in the lower to middle levels of the troposphere
4. enough Coriolis force to develop a low-pressure center
5. a preexisting low-level focus or disturbance
6. low vertical wind shear.{{cite web|author=Chris Landsea |url=http://www.aoml.noaa.gov/hrd/tcfaq/A15.html |title=Subject: A15) How do tropical cyclones form ? |publisher=Atlantic Oceanographic and Meteorological Laboratory |access-date=2010-01-01 |date=2009-02-06 |url-status=dead |archive-url=https://web.archive.org/web/20090827030639/http://www.aoml.noaa.gov/hrd/tcfaq/A15.html |archive-date=2009-08-27 |author-link=Chris Landsea }}

An average of 86 tropical cyclones of tropical storm intensity form annually worldwide,{{cite journal |last1=Shultz |first1=James M. |last2=Russell |first2=Jill |last3=Espinel |first3=Zelde |title=Epidemiology of Tropical Cyclones: The Dynamics of Disaster, Disease, and Development |journal=Epidemiologic Reviews |date=July 2005 |volume=27 |issue=1 |pages=21–35 |doi=10.1093/epirev/mxi011 |pmid=15958424 }} with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones (at least Category 3 intensity on the Saffir–Simpson hurricane scale).{{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|date = 2000-01-04|access-date = 2006-10-19|author-link = Chris Landsea|archive-date = 2012-10-02|archive-url = https://web.archive.org/web/20121002045230/http://www.aoml.noaa.gov/hrd/Landsea/climvari/table.html|url-status = live}}

File:UK-Cyclone.gif indicate the direction of the wind, while the "L" symbol denotes the centre of the "low". Note the occluded, cold and warm frontal boundaries.]]

The following types of cyclones are identifiable in synoptic charts.

{{See also|Low-pressure area}}

There are three main types of surface-based cyclones: extratropical cyclones, subtropical cyclones and tropical cyclones.

{{main|Extratropical cyclone}}

An extratropical cyclone is a synoptic scale low-pressure weather system that does not have tropical characteristics,{{cite book |doi=10.1016/B978-0-444-53199-5.00027-0 |chapter=Precipitation |title=Treatise on Water Science |date=2011 |last1=Koutsoyiannis |first1=D. |last2=Langousis |first2=A. |pages=27–77 |isbn=978-0-444-53199-5 }} as it is connected with fronts and horizontal gradients (rather than vertical) in temperature and dew point otherwise known as "baroclinic zones".{{cite web

|title = ESCI 241 – Meteorology; Lesson 16 – Extratropical Cyclones

|author = DeCaria

|publisher = Department of Earth Sciences, Millersville University, Millersville, Pennsylvania

|date = 2005-12-07

|url = http://www.atmos.millersville.edu/~adecaria/ESCI241/esci241_lesson16_cyclones.html

|access-date = 2006-10-21 |archive-url = https://web.archive.org/web/20060903093420/http://www.atmos.millersville.edu/~adecaria/ESCI241/esci241_lesson16_cyclones.html |archive-date = September 3, 2006}}

"Extratropical" is applied to cyclones outside the tropics, in the middle latitudes. These systems may also be described as "mid-latitude cyclones" due to their area of formation, or "post-tropical cyclones" when a tropical cyclone has moved (extratropical transition) beyond the tropics.{{cite web

|title = Synoptic Composites of the Extratropical Transition Lifecycle of North Atlantic TCs as Defined Within Cyclone Phase Space

|author1 = Robert Hart

|author2 = Jenni Evans

|publisher = American Meteorological Society

|year = 2003

|url = http://ams.confex.com/ams/pdfpapers/70524.pdf

|access-date = 2006-10-03

|archive-date = 2011-06-09

|archive-url = https://web.archive.org/web/20110609164448/http://ams.confex.com/ams/pdfpapers/70524.pdf

|url-status = live

}} They are often described as "depressions" or "lows" by weather forecasters and the general public. These are the everyday phenomena that, along with anticyclones, drive 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 within the westerlies, they can sometimes become barotropic late in their life cycle when the temperature distribution around the cyclone becomes fairly uniform with radius.{{cite web|author=Ryan N. Maue|year=2008|url=http://www.coaps.fsu.edu/~maue/cyclone_ch3.html|title=Chapter 3: Cyclone Paradigms and Extratropical Transition Conceptualizations|access-date=2008-06-15|publisher=Florida State University|archive-url=https://web.archive.org/web/20080510210146/http://www.coaps.fsu.edu/~maue/cyclone_ch3.html |archive-date=2008-05-10}} An extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone, if it dwells over warm waters sufficient to warm its core, and as a result develops central convection.{{cite web|author = Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division|title = Frequently Asked Questions: What is an extra-tropical cyclone?|publisher = NOAA|access-date = 2006-07-25|url = http://www.aoml.noaa.gov/hrd/tcfaq/A7.html|archive-date = 2007-02-09|archive-url = https://web.archive.org/web/20070209121005/http://www.aoml.noaa.gov/hrd/tcfaq/A7.html|url-status = live}} A particularly intense type of extratropical cyclone that strikes during winter is known colloquially as a nor'easter.

{{Main|Polar low}}

File:Sea of Japan polar low 2009-12-20 0213Z.jpg in December 2009]]

A polar low is a small-scale, short-lived atmospheric low-pressure system (depression) that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. Polar lows were first identified on the meteorological satellite imagery that became available in the 1960s, which revealed many small-scale cloud vortices at high latitudes. The most active polar lows are found over certain ice-free maritime areas in or near the Arctic during the winter, such as the Norwegian Sea, Barents Sea, Labrador Sea and Gulf of Alaska. Polar lows dissipate rapidly when they make landfall. Antarctic systems tend to be weaker than their northern counterparts since the air-sea temperature differences around the continent are generally smaller {{citation needed|reason=As far as I know, the Arctic and Antarctic oceans are both warmer than the air above, at about the freezing point, and the air over the ocean is generally colder in the Antarctic due to the katabatic winds sweeping off the continent|date=July 2015}}. However, vigorous polar lows can be found over the Southern Ocean. During winter, when cold-core lows with temperatures in the mid-levels of the troposphere reach {{convert|-45|C|F}} move over open waters, deep convection forms, which allows polar low development to become possible.{{cite book|url=https://books.google.com/books?id=-tBa1DWYoDIC&pg=PA227|title=Polar lows: mesoscale weather systems in the polar regions|page=224|author1=Erik A. Rasmussen |author2=John Turner |year=2003|publisher=Cambridge University Press|access-date=2011-01-27|isbn=978-0-521-62430-5}} 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 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.{{cite book|author1=E. A. Rasmussen |author2=J. Turner |year=2003|title=Polar Lows: Mesoscale Weather Systems in the Polar Regions|publisher=Cambridge University Press|page=612|isbn=978-0-521-62430-5}}

File:Alex 2016-01-13 1530Z.jpg in the north Atlantic Ocean in January 2016]]

{{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. 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.{{cite journal |doi=10.1175/1520-0493(1973)101<0380:R>2.3.CO;2 |title=Reply |date=1973 |last1=Spiegler |first1=David B. |journal=Monthly Weather Review |volume=101 |issue=4 |page=380 |bibcode=1973MWRv..101..380S |doi-access=free }} By 1972, the National Hurricane Center officially recognized this cyclone category.{{cite journal |doi=10.1175/1520-0493(1973)101<0323:AHSO>2.3.CO;2 |title=Atlantic Hurricane Season of 1972 |date=1973 |last1=Simpson |first1=R. H. |last2=Hebert |first2=Paul J. |journal=Monthly Weather Review |volume=101 |issue=4 |pages=323–333 |bibcode=1973MWRv..101..323S |doi-access=free }} Subtropical cyclones began to receive names off the official tropical cyclone list in the Atlantic Basin in 2002. 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.{{cite web|author=Chris Landsea|url=http://www.aoml.noaa.gov/hrd/tcfaq/A6.html|title=Subject: A6) What is a sub-tropical cyclone?|access-date=2009-12-27|date=2009-02-06|publisher=Atlantic Oceanographic and Meteorological Laboratory|author-link=Chris Landsea|archive-date=2011-10-11|archive-url=https://web.archive.org/web/20111011042947/http://www.aoml.noaa.gov/hrd/tcfaq/A6.html|url-status=live}}

Since they form from extratropical cyclones, which have colder temperatures aloft than normally found in the tropics, the sea surface temperatures required is around 23 degrees Celsius (73 °F) for their formation, which is three degrees Celsius (5 °F) lower than for tropical cyclones.{{cite web

|title = A Fifty year History of Subtropical Cyclones

|author = David Mark Roth

|publisher = Hydrometeorological Prediction Center

|date = 2002-02-15

|url = http://www.wpc.ncep.noaa.gov/research/roth/Subpreprint.pdf

|access-date = 2006-10-04

|archive-date = 2021-04-17

|archive-url = https://web.archive.org/web/20210417020816/https://www.wpc.ncep.noaa.gov/research/roth/Subpreprint.pdf

|url-status = live

}} 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.{{cite web|author = Chris Landsea|publisher = NOAA|title = Frequently Asked Questions: What is a sub-tropical cyclone?|access-date = 2009-12-27|date = 2009-02-06|url = http://www.aoml.noaa.gov/hrd/tcfaq/A6.html|author-link = Chris Landsea|archive-date = 2011-10-11|archive-url = https://web.archive.org/web/20111011042947/http://www.aoml.noaa.gov/hrd/tcfaq/A6.html|url-status = live}}

{{main|Tropical cyclone}}

File:Dramatic Views of Hurricane Florence from the International Space Station From 9 12 (42828603210) (cropped).jpg viewed from the International Space Station]]

A tropical cyclone is a storm system characterized by a low-pressure center and numerous thunderstorms that produce strong winds and flooding rain.{{cite web |title=StackPath |url=https://www.laserfocusworld.com/home/article/14192224/tropical-cyclone#:~:text=View%20Image%20Gallery-,A%20tropical%20cyclone%20is%20a%20storm%20system%20characterized%20by%20a,contained%20in%20the%20moist%20air. |website=www.laserfocusworld.com | date=10 August 2011 |access-date=13 January 2021 |archive-date=14 April 2021 |archive-url=https://web.archive.org/web/20210414230334/https://www.laserfocusworld.com/home/article/14192224/tropical-cyclone#:~:text=View%20Image%20Gallery-,A%20tropical%20cyclone%20is%20a%20storm%20system%20characterized%20by%20a,contained%20in%20the%20moist%20air. |url-status=live }} 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'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems.

The term "tropical" refers to both the geographic origin of these systems, which form almost exclusively in tropical regions of the globe,{{cite web |title=StackPath |url=https://www.laserfocusworld.com/home/article/14192224/tropical-cyclone#:~:text=View%20Image%20Gallery-,A%20tropical%20cyclone%20is%20a%20storm%20system%20characterized%20by%20a,contained%20in%20the%20moist%20air |website=www.laserfocusworld.com | date=10 August 2011 |access-date=14 January 2021 |archive-date=14 April 2021 |archive-url=https://web.archive.org/web/20210414230334/https://www.laserfocusworld.com/home/article/14192224/tropical-cyclone#:~:text=View%20Image%20Gallery-,A%20tropical%20cyclone%20is%20a%20storm%20system%20characterized%20by%20a,contained%20in%20the%20moist%20air |url-status=live }} and their dependence on Maritime Tropical air masses for their formation. The term "cyclone" refers to the storms' cyclonic nature, with 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.

While tropical cyclones can produce extremely powerful winds and torrential rain, they are also able to produce high waves and a damaging storm surge.{{cite journal |last1=Shultz |first1=James M. |last2=Russell |first2=Jill |last3=Espinel |first3=Zelde |title=Epidemiology of Tropical Cyclones: The Dynamics of Disaster, Disease, and Development |journal=Epidemiologic Reviews |date=July 2005 |volume=27 |issue=1 |pages=21–35 |doi=10.1093/epirev/mxi011 |pmid=15958424 }} Their winds increase the wave size, and in so doing they draw more heat and moisture into their system, thereby increasing their strength. They develop over large bodies of warm water,{{cite web|author=Chris Landsea |title=Frequently Asked Questions: How do tropical cyclones form? |date=2009-02-06 |publisher=NOAA |access-date=2006-07-26 |url=http://www.aoml.noaa.gov/hrd/tcfaq/A15.html |url-status=dead |archive-url=https://web.archive.org/web/20090827030639/http://www.aoml.noaa.gov/hrd/tcfaq/A15.html |archive-date=2009-08-27 |author-link=Chris Landsea }} and hence lose their strength if they move over land.{{cite web|author=Sim Aberson|publisher=National Hurricane Center|url=http://www.aoml.noaa.gov/hrd/tcfaq/C2.html|title=Subject : C2) Doesn't the friction over land kill tropical cyclones?|access-date=2008-02-25|date=2009-02-06|archive-date=2012-07-31|archive-url=https://web.archive.org/web/20120731202853/http://www.aoml.noaa.gov/hrd/tcfaq/C2.html|url-status=live}} This is the reason coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from strong winds. Heavy rains, however, can produce significant flooding inland. Storm surges are rises in sea level caused by the reduced pressure of the core that in effect "sucks" the water upward and from winds that in effect "pile" the water up. Storm surges can produce extensive coastal flooding 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.National Oceanic and Atmospheric Administration. [http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html 2005 Tropical Eastern North Pacific Hurricane Outlook.] {{Webarchive|url=https://web.archive.org/web/20090614024616/http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html |date=2009-06-14 }} Retrieved on 2006-05-02. 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.

Many tropical cyclones develop when the atmospheric conditions around a weak disturbance in the atmosphere are favorable. Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved by steering winds in the troposphere; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an 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. A tropical cyclone is usually not considered to become subtropical during its extratropical transition.{{cite web|author = Padgett, Gary|url = http://australiasevereweather.com/cyclones/2001/summ0012.htm|title = Monthly Global Tropical Cyclone Summary for December 2000|year = 2001|access-date = 2006-03-31|archive-date = 2014-11-29|archive-url = https://web.archive.org/web/20141129070208/http://www.australiasevereweather.com/cyclones/2001/summ0012.htm|url-status = live}}

{{main|Polar cyclone}}

A polar, sub-polar, or Arctic cyclone (also known as a polar vortex) is a vast area of low pressure that strengthens in the winter and weakens in the summer.{{cite web|author=Halldór Björnsson |date=2005-01-19 |url=http://andvari.vedur.is/~halldor/HB/Met210old/GlobCirc.html |title=Global circulation |publisher=Veðurstofa Íslands |access-date=2008-06-15 |url-status=dead |archive-url=https://web.archive.org/web/20110807132251/http://andvari.vedur.is/~halldor/HB/Met210old/GlobCirc.html |archive-date=2011-08-07 }} A polar cyclone is a low-pressure weather system, usually spanning {{convert|1000|km|mi}} to {{convert|2000|km|mi}},{{cite web |last1=Garima |first1=Khera |title=A vortex of winds-Cyclones – Geography and You |url=https://geographyandyou.com/a-vortex-of-winds-cyclones/ |access-date=14 January 2021 |archive-date=2 March 2021 |archive-url=https://web.archive.org/web/20210302232449/https://geographyandyou.com/a-vortex-of-winds-cyclones/ |url-status=live }} in which the air circulates in a counterclockwise direction in the northern hemisphere, and a clockwise direction in the southern hemisphere. The Coriolis acceleration acting on the air masses moving poleward at high altitude, causes a counterclockwise circulation at high altitude. The poleward movement of air originates from the air circulation of the Polar cell. The polar low is not driven by convection as are tropical cyclones, nor the cold and warm air mass interactions as are extratropical cyclones, but is an artifact of the global air movement of the Polar cell. The base of the polar low is in the mid to upper troposphere. In the Northern Hemisphere, the polar cyclone has two centers on average. One center lies near Baffin Island and the other over northeast Siberia.{{cite web|author=Glossary of Meteorology|date=June 2000|url=http://glossary.ametsoc.org/wiki/Polar_vortex|title=Polar vortex|access-date=2008-06-15|publisher=American Meteorological Society|archive-date=2019-07-18|archive-url=https://web.archive.org/web/20190718200838/http://glossary.ametsoc.org/wiki/Polar_vortex|url-status=live}} In the southern hemisphere, it tends to be located near the edge of the Ross ice shelf near 160 west longitude.{{cite journal |last1=Chen |first1=Rui-Rong |last2=Boyer |first2=Don L. |last3=Tao |first3=Lijun |title=Laboratory Simulation of Atmospheric Motions in the Vicinity of Antarctica |journal=Journal of the Atmospheric Sciences |date=December 1993 |volume=50 |issue=24 |pages=4058–4079 |doi=10.1175/1520-0469(1993)050<4058:LSOAMI>2.0.CO;2 |bibcode=1993JAtS...50.4058C |doi-access=free }} When the polar vortex is strong, its effect can be felt at the surface as a westerly wind (toward the east). When the polar cyclone is weak, significant cold outbreaks occur.{{cite web|author=James E. Kloeppel|url=http://www.news.uiuc.edu/scitips/01/12weather.html |date=2001-12-01|publisher=University of Illinois at Urbana–Champaign via the Internet Wayback Machine|title=Stratospheric polar vortex influences winter freezing, researchers say|access-date=2009-12-27 |archive-url = https://web.archive.org/web/20011224094138/http://www.news.uiuc.edu/scitips/01/12weather.html |archive-date=2001-12-24}}

{{Main|Upper tropospheric cyclonic vortex}}

Under specific circumstances, upper level cold lows can break off from the base of the tropical upper tropospheric trough (TUTT), which is located mid-ocean in the Northern Hemisphere during the summer months. These upper tropospheric cyclonic vortices, also known as TUTT cells or TUTT lows, usually move slowly from east-northeast to west-southwest, and their bases generally do not extend below {{convert|20,000|ft|m}} in altitude. A weak inverted surface trough within the trade wind is generally found underneath them, and they may also be associated with broad areas of high-level clouds. Downward development results in an increase of cumulus clouds and the appearance of a surface vortex. In rare cases, they become warm-core tropical cyclones. Upper cyclones and the upper troughs that trail tropical cyclones can cause additional outflow channels and aid in their intensification. Developing tropical disturbances can help create or deepen upper troughs or upper lows in their wake due to the outflow jet emanating from the developing tropical disturbance/cyclone.{{cite web|author = Clark Evans|url = http://flhurricane.com/cyclone/showflat.php?Cat=0&Number=64429&an=0&page=0|title = Favorable trough interactions on tropical cyclones|publisher = Flhurricane.com|date = January 5, 2006|access-date = 2006-10-20|archive-url = https://web.archive.org/web/20061017001243/http://flhurricane.com/cyclone/showflat.php?Cat=0&Number=64429&an=0&page=0|archive-date = October 17, 2006|url-status = dead}}{{cite journal|author1=Deborah Hanley |author2=John Molinari |author3=Daniel Keyser |title = A Composite Study of the Interactions between Tropical Cyclones and Upper-Tropospheric Troughs|date=October 2001|journal = Monthly Weather Review|publisher = American Meteorological Society|volume = 129|issue = 10|pages = 2570–84|doi = 10.1175/1520-0493(2001)129<2570:ACSOTI>2.0.CO;2|bibcode = 2001MWRv..129.2570H |doi-access = free}}

The following types of cyclones are not identifiable in synoptic charts.

{{Main|Mesocyclone}}

A mesocyclone is a vortex of air, {{convert|2.0|km|mi}} to {{convert|10|km|mi}} in diameter (the mesoscale of meteorology), within a convective storm.{{cite web|title=Mesocyclone|author=Glossary of Meteorology|publisher=American Meteorological Society|date=June 2000|url=http://glossary.ametsoc.org/wiki/Mesocyclone|access-date=2006-12-07|archive-date=2014-05-17|archive-url=https://web.archive.org/web/20140517225409/http://glossary.ametsoc.org/wiki/Mesocyclone|url-status=live}} Air rises and rotates around a vertical axis, usually in the same direction as low-pressure systems{{cite web |title=Mesocyclone – SKYbrary Aviation Safety |url=https://www.skybrary.aero/index.php/Mesocyclone |website=www.skybrary.aero |access-date=13 January 2021 |archive-date=14 January 2021 |archive-url=https://web.archive.org/web/20210114104249/https://www.skybrary.aero/index.php/Mesocyclone |url-status=live }} in both northern and southern hemisphere. They are most often cyclonic, that is, associated with a localized low-pressure region within a supercell.{{cite web|author=National Weather Service Forecast Office State College, Pennsylvania|url=http://www.erh.noaa.gov/ctp/features/2006/07_10/|title=Splitting Storm and Anti-cyclonic Rotating Mesocyclone in a Thunderstorm over Elk County July 10th, 2006|date=2006-07-16|access-date=2008-06-15|archive-date=2009-01-14|archive-url=https://web.archive.org/web/20090114220647/http://www.erh.noaa.gov/ctp/features/2006/07_10/|url-status=live}} Such storms can feature strong surface winds and severe hail. Mesocyclones often occur together with updrafts in supercells, where tornadoes may form. About 1,700 mesocyclones form annually across the United States, but only half produce tornadoes.Forces of Nature. [http://library.thinkquest.org/C003603/english/tornadoes/themesocyclone.shtml Tornadoes : the mesocyclone.] {{webarchive|url=https://web.archive.org/web/20080616154710/http://library.thinkquest.org/C003603/english/tornadoes/themesocyclone.shtml|date=2008-06-16}} Retrieved on 2008-06-15.

{{main|Tornado}}

A tornado is a violently rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or,{{cite web |title=Tornado Basics |url=https://www.nssl.noaa.gov/education/svrwx101/tornadoes/ |website=NOAA National Severe Storms Laboratory |access-date=13 January 2021 |language=EN-US |archive-date=31 August 2018 |archive-url=https://web.archive.org/web/20180831211732/https://www.nssl.noaa.gov/education/svrwx101/tornadoes/ |url-status=live }} in rare cases, the base of a cumulus cloud. Also referred to as twisters, a colloquial term in America, or cyclones, although the word cyclone is used in meteorology, in a wider sense, to name any closed low-pressure circulation.

{{main|Dust devil}}

A dust devil is a strong, well-formed, and relatively long-lived whirlwind,{{cite web |title=Dust Devils |url=https://www.crystalinks.com/dustdevils.html |website=www.crystalinks.com |access-date=13 January 2021 |archive-date=25 January 2021 |archive-url=https://web.archive.org/web/20210125094338/https://www.crystalinks.com/dustdevils.html |url-status=live }} ranging from small (half a metre wide and a few metres tall) to large (more than 10 metres wide and more than 1000 metres tall). The primary vertical motion is upward. Dust devils are usually harmless, but can on rare occasions grow large enough to pose a threat to both people and property.

{{main|Waterspout}}

A waterspout is a columnar vortex forming over water that is, in its most common form, a non-supercell tornado over water that is connected to a cumuliform cloud. While it is often weaker than most of its land counterparts, stronger versions spawned by mesocyclones do occur.

{{main|Steam devil}}

A gentle vortex over calm water or wet land made visible by rising water vapour.

{{main|Fire whirl}}

A fire whirl – also colloquially known as a fire devil, fire tornado, firenado, or fire twister – is a whirlwind induced by a fire and often made up of flame or ash.

{{Main|Extraterrestrial vortex}}

File:Mars cyclone.jpg]]

File:Jupiter North Pole - PJ28-12 - Detail (50199724973).png, imaged by Juno]]

Cyclones are not unique to Earth. Cyclonic storms are common on giant planets, such as the Small Dark Spot on Neptune.{{cite web |title=TCFAQ H6) Are there hurricanes on other planets ? |url=https://www.aoml.noaa.gov/hrd/tcfaq/H6.html#:~:text=Subject%3A%20H6)%20Are%20there%20hurricanes%20on%20other%20planets%20%3F&text=There%20are%20no%20other%20planets,and%20Saturn%20exhibits%20such%20storms. |website=www.aoml.noaa.gov |access-date=13 January 2021 |archive-date=19 March 2021 |archive-url=https://web.archive.org/web/20210319065453/https://www.aoml.noaa.gov/hrd/tcfaq/H6.html#:~:text=Subject%3A%20H6)%20Are%20there%20hurricanes%20on%20other%20planets%20%3F&text=There%20are%20no%20other%20planets,and%20Saturn%20exhibits%20such%20storms. |url-status=live }} It is about one third the diameter of the Great Dark Spot and received the nickname "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. Mars has also exhibited cyclonic storms.{{cite web|author=David Brand|url=http://www.news.cornell.edu/releases/May99/mars.cyclone.deb.html|title=Colossal cyclone swirling near Martian north pole is observed by Cornell-led team on Hubble telescope|access-date=2008-06-15|date=1999-05-19|publisher=Cornell University|archive-url = https://web.archive.org/web/20070613133949/http://www.news.cornell.edu/releases/May99/mars.cyclone.deb.html |archive-date = June 13, 2007|url-status=dead}} 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.{{cite web

|title = Jupiter's Great Red Spot

|year = 2009

|author = Ellen Cohen

|publisher = Hayden Planetarium

|url = http://haydenplanetarium.org/resources/ava/page/index.php?file=P0413jupispot

|access-date = 2007-11-16

|url-status = dead

|archive-url = https://web.archive.org/web/20070808130633/http://haydenplanetarium.org/resources/ava/page/index.php?file=P0413jupispot

|archive-date = 2007-08-08

}}

{{stack|{{Portal|Weather|Tropical cyclones|Tornadoes}}}}

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• Tropical cyclone
• Subtropical cyclone
• Extratropical cyclone
• Tornado
• Storm
• Atlantic hurricane
• Australian region tropical cyclone
• Space hurricane
• Space tornado

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{{Reflist|30em}}

{{commons category|Cyclones}}

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{{Wikivoyage|Cyclones}}

• [https://earth.nullschool.net/#current/wind/surface/level/overlay=mean_sea_level_pressure/winkel3 Current map of global mean sea-level pressure]

{{Cyclones}}

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Category:Meteorological phenomena

Category:Tropical cyclone meteorology

Cyclone

Category:Weather hazards

Category:Vortices