Eye (cyclone)
4652664
223749691
2008-07-05T16:30:44Z
Chobot
259798
robot Modifying: [[zh:風眼]]
The '''eye''' is a region of mostly calm [[weather]] found at the center of strong [[tropical cyclone]]s. The eye of a [[storm]] is a roughly circular area and typically 30–65 km (20–40 [[statute mile|miles]]) in [[diameter]]. It is surrounded by the '''eyewall''', a ring of towering [[thunderstorm]]s where the most severe weather of a cyclone occurs. The cyclone's lowest [[barometric pressure]] occurs in the eye, and can be as much as 15% lower than the [[atmospheric pressure]] outside the storm.<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>
In strong tropical cyclones, the eye is characterized by light [[wind]]s and clear skies, surrounded on all sides by a towering, symmetric eyewall. In weaker tropical cyclones, the eye is less well-defined, and can be covered by the ''central dense overcast'', which is an area of high, thick [[cloud]]s which show up brightly on [[satellite imagery]]. Weaker or disorganized storms may also feature an eyewall which does not completely encircle the eye, or have an eye which features heavy [[rain]]. In all storms, however, the eye is the location of the storm's minimum barometric pressure: the area where the atmospheric pressure at sea level is the lowest.<ref name="FAQ eye"/><ref name="FAQ CDO">{{cite web | author=Landsea, Chris. | title=What is a "CDO"? | date=[[October 19]] [[2005]] | publisher=[[Atlantic Oceanographic and Meteorological Laboratory]] | accessdate=2006-06-14 | url = http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.html}}</ref>
{{tropical cyclone}}
==Structure==
[[Image:Eye structure.jpg|left|thumb|250px|A [[cross section (geometry)|cross section]] diagram of a mature tropical cyclone, with arrows indicating air flow in and around the eye]]
A typical tropical cyclone will have an eye approximately 30–65 km (20–40 mi) across, usually situated at the geometric center of the storm. The eye may be clear or have spotty low clouds (a ''clear eye''), it may be filled with [[Cloud#Middle clouds (Family B)|low- and mid-level clouds]] (a ''filled eye''), or it may be obscured by the central dense overcast. There is, however, very little wind and rain, especially near the center. This is in stark contrast to conditions in the eyewall, which contains the storm's strongest winds.<ref name="JetStream structure">{{cite web | url = http://www.srh.noaa.gov/jetstream/tropics/tc_structure.htm | author = [[National Weather Service]] | publisher = [[National Oceanic & Atmospheric Administration]] | title = Tropical Cyclone Structure | accessdate = 2006-12-14 | work = JetStream—An Online School for Weather | date = [[October 19]] [[2005]]}}</ref> Due to the [[Tropical cyclone#Mechanics|mechanics of a tropical cyclone]], the eye and the air directly above it are warmer than their surroundings.<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 = [[National Oceanic and Atmospheric Administration]] | accessdate = 2007-03-23 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A7.html}}</ref>
While normally quite symmetric, eyes can be oblong and irregular, especially in weakening storms. A large ''ragged eye'' is a non-circular eye which appears fragmented, and is an indicator of a weak or weakening tropical cyclone. An ''open eye'' is an eye which can be circular, but the eyewall does not completely encircle the eye, also indicating a weakening, moisture-deprived cyclone. Both of these observations are used to estimate the intensity of tropical cyclones via [[Dvorak technique|Dvorak analysis]].<ref name="ODT">{{cite web|title=Objective Dvorak Technique|url=http://cimss.ssec.wisc.edu/tropic/research/products/dvorak/odt.html|publisher=University of Wisconsin|accessdate=2006-05-29}}</ref> Eyewalls are typically circular; however, distinctly polygonal shapes ranging from triangles to [[hexagon]]s occasionally occur.<ref name="polygonal eyewalls">{{cite journal |last=Schubert |first=Wayne H. |authorlink=Wayne H. Schubert |coauthors=Michael T. Montgomery, Richard K. Taft, Thomas A. Guinn, Scott R. Fulton, James P. Kossin, and James P. Edwards |title=Polygonal Eyewalls, Asymmetric Eye Contraction, and Potential Vorticity Mixing in Hurricanes |journal=[[Journal of the Atmospheric Sciences]] |volume=59 |issue=9 |pages=1197–1223 |publisher=[[American Meteorological Society]] |date=May 1999 |url=http://ams.allenpress.com/perlserv/?request=get-abstract&issn=1520-0469&volume=056&issue=09&page=1197 |doi=10.1175/1520-0469(1999)056<1197:PEAECA>2.0.CO;2 |doilabel=10.1175/1520-0469(1999)056<1197:PEAECA>2.0.CO;2 |year=1999 }}</ref>
While typical mature storms have eyes that are a few dozen miles across, [[rapid deepening|rapidly intensifying]] storms can develop an extremely small, clear, and circular eye, sometimes referred to as a ''pinhole eye''. Storms with pinhole eyes are prone to large fluctuations in intensity, and provide difficulties and frustrations for forecasters.<ref>{{cite web | author=National Hurricane Center | title=Hurricane Wilma Discussion No. 14, 11:00 p.m. EDT | date=2005-10-08 | publisher=[[National Oceanic and Atmospheric Administration]] | accessdate=2006-06-12 | url = http://www.nhc.noaa.gov/archive/2005/dis/al242005.discus.014.shtml?}}</ref>
[[Image:Hurricane Nate Sept 6 05.jpg|thumb|250px|[[Hurricane Nate (2005)|Hurricane Nate]], as seen in this picture on [[September 6]] [[2005]], presents a cloud-filled eye.]]
Small eyes—those less than 10 [[nautical mile|nmi]] (19 km, 12 [[statute mile|mi]]) across—often trigger [[#Eyewall replacement cycles|eyewall replacement cycles]], where a new eyewall begins to form outside the original eyewall. This can take place anywhere from ten to a few hundred miles (fifteen to hundreds of kilometers) outside the inner eye. The storm develops two ''concentric eyewalls'', or an "eye within an eye". In most cases, the outer eyewall begins to contract soon after its formation, which chokes off the inner eye and leaves a much larger but more stable eye. While the replacement cycle tends to weaken storms as it occurs, the new eyewall can contract fairly quickly after the old eyewall dissipates, allowing the storm to re-strengthen. This may trigger another cycle of eyewall replacement.<ref name="AOML FAQ D8"/>
Eyes can range in size from 320 km (200 miles) ([[1960 Pacific typhoon season#Typhoon Carmen|Typhoon Carmen]]) to a mere 3 km (2 mi) ([[Hurricane Wilma]]) across.<ref name="Very Large Eye">{{cite web | author=Lander, Mark A. | title=A Tropical Cyclone with a Very Large Eye | date= 1998 | publisher=Monthly Weather Review: Vol. 127, pp. 137–142 | accessdate=2006-06-14 | url = http://ams.allenpress.com/amsonline/?request=get-document&doi=10.1175%2F1520-0493(1999)127%3C0137:ATCWAV%3E2.0.CO%3B2}}</ref> While it is uncommon for storms with large eyes to become very intense, it does occur, especially in [[annular hurricane]]s. [[Hurricane Isabel]] was the eleventh most powerful [[Atlantic hurricane]] in recorded history, and sustained a large, 65–80 km (40–50 mi)-wide eye for a period of several days.<ref name="Isabel TCR">{{cite web|author=Beven, Jack and Hugh Cobb|year=2003|title=Hurricane Isabel Tropical Cyclone Report|publisher=[[National Hurricane Center]]|accessdate=2006-03-26|url=http://www.nhc.noaa.gov/2003isabel.shtml?}}</ref>
== Formation and detection==
{{seealso|Tropical cyclogenesis}}
[[Image:Hurricane-profile-en.svg|thumb|250px|Tropical cyclones form when the energy released by the condensation of moisture in rising air causes a [[positive feedback loop]] over warm ocean waters.]]
[[Image:HurricaneAndrewFLRADAR.png|thumb|250px|Typically, eyes are easy to spot using [[weather radar]]. This radar image of [[Hurricane Andrew]] clearly shows the eye over southern [[Florida]].]]
Tropical cyclones typically form from large, disorganized areas of disturbed weather in [[tropics|tropical regions]]. As more thunderstorms form and gather, the storm develops [[Tropical cyclone#Physical structure|rainbands]] which start rotating around a common center. As the storm gains strength, a ring of stronger [[Convection#Atmospheric convection|convection]] forms at a certain distance from the rotational center of the developing storm. Since stronger thunderstorms and heavier rain mark areas of stronger [[updraft]]s, the barometric pressure at the surface begins to drop, and air begins to build up in the upper levels of the cyclone.<ref name="eye formation"/> This results in the formation of an upper level [[anticyclone]], or an area of high atmospheric pressure above the central dense overcast. Consequentially, most of this built up air flows outward anticyclonically above the tropical cyclone. Outside the forming eye, the anticyclone at the upper levels of the atmosphere enhances the flow towards the center of the cyclone, pushing air towards the eyewall and causing a [[positive feedback loop]].<ref name="eye formation"/>
However, a small portion of the built-up air, instead of flowing outward, flows inward towards the center of the storm. This causes air pressure to build even further, to the point where the weight of the air counteracts the strength of the updrafts in the center of the storm. Air begins to descend in the center of the storm, creating a mostly rain-free area; a newly-formed eye.<ref name="eye formation">{{cite web | author = Vigh, Jonathan | date = 2006 | url = http://ams.confex.com/ams/pdfpapers/108319.pdf | title = Formation of the Hurricane Eye | publisher = Department of Atmospheric Science, [[Colorado State University]] | location = Fort Collins, Colorado | accessdate = 2006-03-26 | format = PDF}}</ref>
There are many aspects of this process which remain a mystery. Scientists do not know why a ring of convection forms around the center of circulation instead of on top of it, or why the upper-level anticyclone only ejects a portion of the excess air above the storm. Hundreds of theories exist as to the exact process by which the eye forms: all that is known for sure is that the eye is necessary for tropical cyclones to achieve high wind speeds.<ref name="eye formation"/>
The formation of an eye is almost always an indicator of increasing tropical cyclone organisation and strength. Because of this, forecasters watch developing storms closely for signs of eye formation.
For storms with a clear eye, detection of the eye is as simple as looking at pictures from a [[weather satellite]]. However, for storms with a filled eye, or an eye completely covered by the central dense overcast, other detection methods must be used. Observations from ships and [[Hurricane Hunters]] can pinpoint an eye visually, by looking for a drop in wind speed or lack of rainfall in the storm's center. In the [[United States]], [[South Korea]], and a few other countries, a network of [[NEXRAD]] [[Doppler weather radar]] stations can detect eyes near the coast. Weather satellites also carry equipment for measuring atmospheric [[Water vapor#Radar and satellite imaging|water vapor]] and cloud temperatures, which can be used to spot a forming eye. In addition, scientists have recently discovered that the amount of [[ozone]] in the eye is much higher than the amount in the eyewall, due to air sinking from the ozone-rich stratosphere. Instruments sensitive to ozone perform measurements, which are used to observe rising and sinking columns of air, and provide indication of the formation of an eye, even before [[satellite imagery]] can determine its formation.<ref>{{cite news | url = http://www1.nasa.gov/vision/earth/environment/ozone_drop.html | date = [[June 8]], [[2005]] | title = Ozone Levels Drop When Hurricanes Are Strengthening | publisher = [[NASA]] | accessdate = 2006-05-09}}</ref>
== Associated phenomena ==
=== Eyewall replacement cycles ===
[[Image:Typhoon amber concentric eyewalls.gif|thumb|250px|A satellite photo of Typhoon Amber of the [[1997 Pacific typhoon season]], exhibiting an outer and inner eyewall while undergoing an ''eyewall replacement cycle''.]]
''Eyewall replacement cycles'', also called ''concentric eyewall cycles'', naturally occur in intense [[tropical cyclone]]s, generally with winds greater than 185 km/h (115 mph), or major hurricanes ([[Saffir-Simpson Hurricane Scale|Category 3]] or above). When tropical cyclones reach this threshold of intensity, and the eyewall contracts or is already sufficiently small (see [[#Structure|above]]), some of the outer rainbands may strengthen and organize into a ring of thunderstorms—an outer eyewall—that slowly moves inward and robs the inner eyewall of its needed moisture and [[angular momentum]]. Since the strongest winds are located in a cyclone's eyewall, the tropical cyclone usually weakens during this phase, as the inner wall is "choked" by the outer wall. Eventually the outer eyewall replaces the inner one completely, and the storm can re-intensify.
The discovery of this process was partially responsible for the end of the U.S. government's hurricane modification experiment [[Project Stormfury]]. This project set out to [[cloud seeding|seed clouds]] outside the eyewall, causing a new eyewall to form and weakening the storm. When it was discovered that this was a natural process due to hurricane dynamics, the project was quickly abandoned.<ref name = "AOML FAQ D8">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What are "concentric eyewall cycles" (or "eyewall replacement cycles") and why do they cause a hurricane's maximum winds to weaken? | publisher = [[NOAA]] | accessdate = 2006-12-14 | url = http://www.aoml.noaa.gov/hrd/tcfaq/D8.html}}</ref>
Almost every intense hurricane undergoes at least one of these cycles during its existence. [[Hurricane Allen]] in 1980 went through repeated eyewall replacement cycles, fluctuating between Category 5 and Category 3 status on the [[Saffir-Simpson Scale]] several times. [[Hurricane Juliette (2001)|Hurricane Juliette]] was a rare documented case of triple eyewalls.<ref name="Triple Eyewalls">{{cite web | author=McNoldy, Brian D. | title=Triple Eyewall in Hurricane Juliette | date= 2004 | publisher=Bulletin of the American Meteorological Society: Vol. 85, pp. 1663–1666 | url = http://ams.allenpress.com/archive/1520-0477/85/11/pdf/i1520-0477-85-11-1663.pdf}}</ref>
=== Moats ===
A ''moat'' in a tropical cyclone is a clear ring outside the eyewall, or between concentric eyewalls, characterized by slowly sinking air, little or no precipitation, and [[strain (materials science)|strain]]-dominated flow.<ref name="Rapid Filamentation">{{cite web | author=Rozoff, C. M., W. H. Schubert, B. D. McNoldy, and J. P. Kossin | title=Rapid filamentation zones in intense tropical cyclones | date= 2006 | publisher=Journal of the Atmospheric Sciences: Vol. 63, pp. 325–340 | url = http://www.ssec.wisc.edu/~kossin/articles/Rozoffetal2006.pdf | format = PDF | accessdate = 2007-11-16}}</ref> The moat between eyewalls is just one example of a ''rapid filamentation zone'', or an area in the storm where the rotational speed of the air changes greatly in proportion to the distance from the storm's center. Such strain-dominated regions can potentially be found near any [[vortex]] of sufficient strength, but are most pronounced in strong tropical cyclones.
=== Eyewall mesovortices ===
''Eyewall mesovortices'' are small scale rotational features found in the eyewalls of intense tropical cyclones. They are similar, in principle, to small "suction vortices" often observed in [[Multiple vortex tornado|multiple-vortex tornadoes]]. In these vortices, wind speed can be up to 10% higher than in the rest of the eyewall. Eyewall mesovortices are most common during periods of intensification in tropical cyclones.
Eyewall mesovortices often exhibit unusual behavior in tropical cyclones. They usually rotate around the low pressure center, but sometimes they remain stationary. Eyewall mesovortices have even been documented to cross the eye of a storm. These phenomena have been documented observationally,<ref name="Vortical Swirls">{{cite web | author=Kossin, J. P., B. D. McNoldy, and W. H. Schubert | title=Vortical swirls in hurricane eye clouds | date= 2002 | publisher=Monthly Weather Review: Vol. 130, pp. 3144–3149 | url = http://www.ssec.wisc.edu/~kossin/articles/kossin_etal_2002.pdf | format=PDF | accessdate=2007-11-16}}</ref> experimentally,<ref name="Experimental Study">{{cite web | author=Montgomery, M. T., V. A. Vladimirov, and P. V. Denissenko | title=An experimental study on hurricane mesovortices | date= 2002 | publisher=Journal of Fluid Mechanics: Vol. 471, pp. 1–32 | url = http://journals.cambridge.org/action/displayFulltext?type=1&fid=128928&jid=FLM&volumeId=471&issueId=-1&aid=128927}}</ref> and theoretically.<ref name="Mesovortices">{{cite web | author=Kossin, J. P., and W. H. Schubert | title=Mesovortices, polygonal flow patterns, and rapid pressure falls in hurricane-like vortices | date= 2001 | publisher=Journal of the Atmospheric Sciences: Vol. 58, pp. 2196–2209 | url = http://www.ssec.wisc.edu/~kossin/articles/kos_sch2001.pdf | format = PDF | accessdate = 2007-11-16}}</ref>
Eyewall mesovortices are a significant factor in the formation of [[tornado]]es after tropical cyclone landfall. Mesovortices can spawn rotation in individual thunderstorms (a [[mesocyclone]]), which leads to tornadic activity. At landfall, friction is generated between the circulation of the tropical cyclone and land. This can allow the mesovortices to descend to the surface, causing large outbreaks of tornadoes.
=== Stadium effect ===
[[Image:Hurricane Wilma eye.jpg|thumb|250px|A picture of [[Hurricane Wilma]]'s eye taken at 08:22 [[Central Time Zone (North America)|CDT]] (13:22 [[Coordinated Universal Time|UTC]]) [[October 19]], [[2005]], by the crew aboard the [[International Space Station]]. At the time, Wilma was the strongest Atlantic hurricane in history, with a minimum central pressure of only 882 [[Bar (unit)|mbar]] (26.06 [[inHg]]).<ref name="Wilma TCR">{{cite web | author= Richard J. Pasch, Eric S. Blake, Hugh D. Cobb III, and David P. Roberts | title= Tropical Cyclone Report: Hurricane Wilma | date= 2006-01-12 | publisher= National Hurricane Center | url = http://www.nhc.noaa.gov/pdf/TCR-AL252005_Wilma.pdf}}</ref> Not only is this a classic example of a ''pinhole eye'', but also of the ''stadium effect'', where the eyewall slopes out and up.]]
The ''stadium effect'' is a phenomenon observed in strong tropical cyclones. It is a fairly common event, where the clouds of the eyewall curve outward from the surface with height. This gives the eye an appearance resembling an open dome from the air, akin to a [[Stadium|sports stadium]]. An eye is always larger at the top of the storm, and smallest at the bottom of the storm because the rising air in the eyewall follows [[Contour line|isolines]] of equal [[angular momentum]], which also slope outward with height.<ref name="ang_mom_0">{{cite web | author=Hawkins, H. F., and D. T. Rubsam | title=Hurricane Hilda, 1964: II. Structure and budgets of the hurricane on October 1, 1964 | date= 1968 | publisher=Monthly Weather Review: Vol. 96, pp. 617–636 | url = http://docs.lib.noaa.gov/rescue/mwr/096/mwr-096-09-0617.pdf}}</ref><ref name="ang_mom_1">{{cite web | author=Gray, W. M., and D. J. Shea | title=The hurricane's inner core region: II. Thermal stability and dynamic characteristics | date= 1973 | publisher=Journal of the Atmospheric Sciences: Vol. 30, pp. 1565–1576 | url = http://ams.allenpress.com/perlserv/?request=get-document&doi=10.1175%2F1520-0469(1973)030%3C1565%3ATHICRI%3E2.0.CO%3B2}}</ref><ref name="ang_mom_2">{{cite web | author=Hawkins, H. F., and S. M. Imbembo | title=The structure of a small, intense hurricane—Inez 1966 | date= 1976 | publisher=Monthly Weather Review: Vol. 104, pp. 418–442 | url = http://ams.allenpress.com/archive/1520-0493/104/4/pdf/i1520-0493-104-4-418.pdf | format = PDF }}</ref> This phenomenon refers to the characteristics of tropical cyclones with very small eyes, where the sloping phenomenon is much more pronounced.
=== Eye-like features ===
An eye-like structure is often found in intensifying tropical cyclones. Similar to the eye seen in hurricanes or typhoons, it is a circular area at the circulation center of the [[storm]] in which [[convection]] is absent. These eye-like features are most normally found in intensifying tropical storms and hurricanes of category 1 strength on the [[Saffir-Simpson Scale]]. For example, an eye-like feature was found in [[Hurricane Beta]] when the storm had maximum [[wind speed]]s of 50 [[mph]].<ref>John L. Beven. [http://www.nhc.noaa.gov/archive/2005/dis/al262005.discus.003.shtml? TROPICAL STORM BETA DISCUSSION NUMBER 3.] Retrieved on [[2008-01-08]].</ref> These eye-like features are typically not visible on [[visible light|visible wavelengths]] or [[infrared light|infrared wavelengths]] from space, however, they are easily seen on [[microwave]] satellite imagery.<ref name="TRMM">Frank Marks and Stacy Stewart. [http://sciencepolicy.colorado.edu/about_us/meet_us/roger_pielke/workshops/trmm/presentations/marks.pdf TRMM Satellite Data - Applications to Tropical Cyclone Analysis and Forecasting.] Retrieved on [[2008-01-10]].</ref> The development of this feature at mid level is similar to the formation of the complete eye but its position might be different due to the vertical wind shear<ref>{{Cite web
|author=Jacksonville Weather Forecast Office
|title=STORM project
|url=http://www.srh.noaa.gov/jax/storm/storm.shtml
|accessdate=2008-03-12
|publisher=[[NOAA]]}}</ref><ref>{{Cite web
|author=Daniel Brown and Lt. Dave Roberts
|work=[[National Hurricane Center]]
|title=Interpretation of passive microwave imagery
|url=http://www.srh.noaa.gov/jax/storm/presentations/displayable/2007_NHC_microwave/player.html
|accessdate=2008-03-12
|publisher=[[NOAA]]}}</ref>
== Hazards ==
Though the eye is by far the calmest part of the storm, with no wind at the center and typically clear skies, over the ocean it is possibly the most hazardous area. In the eyewall, wind-driven waves are all traveling in the same direction. In the center of the eye, however, waves from all directions converge, creating erratic crests which can build on each other, creating [[Freak wave|rogue waves]]. The maximum height of hurricane waves is unknown, but measurements of [[Hurricane Ivan]], when it was a category four hurricane, estimated that waves near the eyewall were in excess of 40 meters (130 ft) from peak to trough.<ref>{{cite journal
| author= David W. Wang, Douglas A. Mitchell, William J. Teague, Ewa Jarosz, Mark S. Hulbert
| title= Extreme Waves Under Hurricane Ivan
| journal = Science
| url = http://www.sciencemag.org/cgi/content/full/309/5736/896
| volume = 309
| issue = 5736
| pages = 896
| pmid= 16081728
| doi= 10.1126/science.1112509
| year= 2005
}}</ref> This is in addition to any [[storm surge]] which may occur, as storm surges often extend into the eye.
A common mistake, especially in areas where hurricanes are uncommon, is for residents to wander outside to inspect the damage while the eye passes over, thinking the storm is over. They are then caught completely by surprise by the violent winds in the opposite eyewall. The [[National Weather Service]] strongly discourages leaving shelter while the eye passes over.<ref>{{cite web | author=National Weather Service Southern Region Headquarters | title=Tropical Cyclone Safety | date=[[January 6]], [[2005]] | publisher=[[National Weather Service]] | accessdate=2006-08-06 | url = http://www.srh.noaa.gov/srh/jetstream/tropics/tc_safety.htm}}</ref>
== Other storms ==
{{main|Cyclone}}
Though only tropical cyclones have structures which are officially called "eyes", there are other storms which can exhibit eye-like structures:
=== Polar lows ===
[[Polar low]]s are [[mesoscale meteorology|mesoscale]] weather systems (typically smaller than 1,000 km or {{convert|600|mi|km}} across) found near the [[Geographical pole|poles]]. Like tropical cyclones, they form over relatively warm water, can feature deep convection (thunderstorms), and feature winds of [[Beaufort scale|gale force]] (51 km/h, 32 mph) or greater. Unlike storms of tropical nature, however, they thrive in much colder temperatures and at much higher [[latitude]]s. They are also smaller and last for shorter durations (few last longer than a day or so). Despite these differences, they can be very similar in structure to tropical cyclones, featuring a clear eye surrounded by an eyewall and rain/snow bands.<ref>{{cite web| url = http://nsidc.org/arcticmet/patterns/polar_low.html| title = Polar Lows| accessdate = 2007-01-24 | author = [[National Snow and Ice Data Center]]}}</ref>
=== Extratropical storms ===
[[Image:GreatBlizzardof2006.jpg|thumb|250px|The [[North American blizzard of 2006]], an extratropical storm, showed an eye-like structure at its peak intensity (here seen just to the east of the [[Delmarva Peninsula]]).]]
[[Extratropical cyclone|Extratropical storms]] are areas of low pressure which exist at the boundary of different [[air mass]]es. Almost all storms found at mid-latitudes are extratropical in nature, including classic North American [[nor'easter]]s and [[European windstorms]]. The most severe of these can have a clear "eye" at the site of lowest barometric pressure, though it is usually surrounded by lower, non-convective clouds and is found near the back end of the storm.<ref name="WarmSeclusionCycMet"> {{cite web
| title = Warm seclusion cyclone climatology | author = Maue, Ryan N. | publisher = [http://ams.confex.com/ American Meteorological Society Conference] | date = [[2006-04-25]] | url = http://ams.confex.com/ams/27Hurricanes/techprogram/paper_108776.htm | accessdate = 2006-10-06 }}</ref>
=== Subtropical storms ===
[[Subtropical cyclone|Subtropical storms]] are cyclones which have some extratropical characteristics and some tropical characteristics. As such, they may have an eye, but are not true tropical storms. Subtropical storms can be very hazardous, with high winds and seas, and often evolve into true tropical storms. As such, the [[National Hurricane Center]] began including subtropical storms in their naming scheme in 2002.<ref name="subtrop 1">{{cite web| url = http://www.usatoday.com/weather/hurricane/2003-04-22-subtropical-storms_x.htm| title = Weather Basics: Subtropical storms| accessdate = 2006-09-15| last = Cappella| first = Chris| date = [[April 22]], [[2003]]| work = [[USA Today]]}}</ref>
=== Tornadoes ===
[[Tornado]]es are destructive, small-scale storms, which produce the fastest winds on earth. There are two main types—single-vortex tornadoes, which consist of a single spinning column of air, and multiple-vortex tornadoes, which consist of small ''suction vortices'', resembling mini-tornadoes themselves, all rotating around a common center. Both of these types of tornadoes are theorized to have calm centers, referred to by some meteorologists as "eyes". These theories are supported by doppler velocity observations by weather radar<ref name="tornado 1">{{cite web| url = http://www.sciencenews.org/pages/sn_arc99/5_15_99/fob1.htm| title = Oklahoma Tornado Sets Wind Record| accessdate = 2006-09-15| last = Monastersky| first = R.| date = [[May 15]], [[1999]]| work = [[Science News]]}}</ref> and eyewitness accounts.<ref name="tornado 2">{{cite web| url = http://docs.lib.noaa.gov/rescue/mwr/058/mwr-058-05-0205.pdf| title = Seeing the Inside of a Tornado| accessdate = 2006-09-15| author = Justice, Alonzo A.| year = 1930| month = May| format = [[Portable Document Format|PDF]]| work = [[Monthly Weather Review]]| pages = 205–206}}</ref>
===Extraterrestrial storms===
[[Image:PIA08333 Saturn storm.jpg|thumb|left|A hurricane-like storm on the south pole of Saturn displaying an eyewall tens of kilometers high]]
[[NASA]] reported in November 2006 that the Cassini spacecraft observed a '[[tropical cyclone|hurricane]]-like' storm locked to the south pole of [[Saturn (planet)|Saturn]] that had a clearly defined eyewall. This observation is particularly notable because eyewall clouds have not been seen on any planet other than Earth (including a failure to observe an eyewall in the [[Great Red Spot]] of Jupiter by the [[Galileo (spacecraft)|Galileo]] spacecraft).<ref>{{cite web|url=http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=703|title=NASA Sees into the Eye of a Monster Storm on Saturn|publisher=[[NASA]]|date=[[2006-11-09]]|accessdate=November 10|accessyear=2006}}</ref> In 2007, very large vortices[http://www.esa.int/esa-mmg/mmg.pl?b=b&type=I&mission=Venus%20Express&single=y&start=5] on both poles of [[Venus]] are observed by the [[Venus Express]] mission of the [[European Space Agency]] to have a dipole eye structure.<ref name="Venus Express">{{cite journal |last=Piccioni |first=G. |coauthors=et al |title=South-polar features on Venus similar to those near the north pole |journal=[[Nature (journal)|Nature]] |volume= |issue=450 |pages=637–40 |date=[[2007-11-29]] |url=http://www.nature.com/nature/journal/v450/n7170/abs/nature06209.html |doi=10.1038/nature06209 }}</ref>
== See also ==
{{tcportal}}
* [[List of tropical cyclones]]
* [[Radius of maximum wind]]
* [[Storm surge]]
* [[Tropical cyclone]]
== References ==
{{reflist|2}}
== External links ==
* [http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.html Atlantic Oceanographic and Meteorological Laboratory]
* [http://www.atl.ec.gc.ca/weather/hurricane/hurricanes9.html#eye Canadian Hurricane Centre: Glossary of Hurricane Terms]
{{Featured article}}
[[Category:Tropical cyclone meteorology]]
[[Category:Vortices]]
{{link FA|pt}}
[[de:Auge (Meteorologie)]]
[[es:Ojo (ciclón)]]
[[fr:Œil (cyclone)]]
[[ko:태풍의 눈]]
[[ja:台風の目]]
[[pl:Oko cyklonu]]
[[pt:Olho (ciclone)]]
[[simple:Eye (cyclone)]]
[[fi:Myrskyn silmä]]
[[sv:Orkanens öga]]
[[vi:Mắt bão]]
[[zh:風眼]]