Tropical cyclone

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Tropical cycloneFrom Wikipedia, the free encyclopedia"Hurricane" redirects here. For other uses, seeHurricane (disambiguation).

Hurricane Isabel(2003) as seen from orbit duringExpedition 7of theInternational Space Station. Theeye, eyewall and surroundingrainbandsthat are characteristics of tropical cyclones are clearly visible in this view from space.Part of theNatureseries onWeather

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Atropical cycloneis astorm systemcharacterized by a largelow-pressurecenter and numerousthunderstormsthat produce strong winds and heavy rain. Tropicalcyclonesstrengthen when water evaporated from the ocean is released as the saturatedairrises, resulting incondensationofwater vaporcontained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such asnor'easters,European windstorms, andpolar lows. The characteristic that separates tropical cyclones from other cyclonic systems is that at any height in the atmosphere, the center of a tropical cyclone will be warmer than its surroundings; a phenomenon called "warm core" storm systems.The term "tropical" refers both to the geographical origin of these systems, which usually form intropicalregions of the globe, and to their formation inmaritime tropical air masses. The term "cyclone" refers to such storms' cyclonic nature, withcounterclockwisewind flow in theNorthern Hemisphereand clockwise wind flow in theSouthern Hemisphere. The opposite direction of the wind flow is a result of theCoriolis force. Depending on its location and strength, a tropical cyclone is referred to by names such ashurricane(/hrken/,/hrkn/),typhoon,tropical storm,cyclonic storm,tropical depression, and simplycyclone.While tropical cyclones can produce extremely powerful winds and torrentialrain, they are also able to produce high waves and damagingstorm surgeas well as spawningtornadoes. They develop over large bodies of warm water, and lose their strength if they move over land due to increased surface friction and loss of the warm ocean as an energy source. This is why 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 coastalfloodingup to 40 kilometres (25mi) from the coastline. Although their effects on human populations can be devastating, tropical cyclones can relievedroughtconditions. They also carry heat energy away from the tropics and transport it towardtemperatelatitudes, which makes them an important part of the globalatmospheric circulationmechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth'stroposphere, and to maintain a relatively stable and warm temperature worldwide.Many tropical cyclonesdevelopwhen the atmospheric conditions around a weak disturbance in the atmosphere are favorable. The background environment is modulated by climatological cycles and patterns such as theMadden-Julian oscillation,El Nio-Southern Oscillation, and theAtlantic multidecadal oscillation. Others form whenother types of cyclonesacquire tropical characteristics. Tropical systems are then moved bysteering windsin thetroposphere; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop aneye. 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. It is not possible to artificially induce the dissipation of these systems with current technology.Part of a series on

Tropical cyclones

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Contents[hide] 1Physical structure 1.1Eye and center 1.2Size 2Mechanics 3Major basins and related warning centers 4Formation 4.1Times 4.2Factors 4.3Locations 5Movement and track 5.1Steering winds 5.2Coriolis effect 5.3Interaction with the mid-latitude westerlies 5.4Landfall 5.5Multiple storm interaction 6Dissipation 6.1Factors 6.2Artificial dissipation 7Effects 8Observation and forecasting 8.1Observation 8.2Forecasting 9Classifications, terminology, and naming 9.1Intensity classifications 9.1.1Tropical depression 9.1.2Tropical storm 9.1.3Hurricane or typhoon 9.2Origin of storm terms 9.3Naming 10Notable tropical cyclones 11Changes caused by El Nio-Southern Oscillation 12Long-term activity trends 13Global warming 14Related cyclone types 15Tropical cyclones in popular culture 16See also 17References 18External links

[edit]Physical structureSee also:Eye (cyclone)All tropical cyclones are areas oflowatmospheric pressurein the Earth's atmosphere. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface atsea level.[1]Tropical cyclones are characterized and driven by the release of large amounts of latentheat of condensation, which occurs when moist air is carried upwards and itswater vaporcondenses. This heat is distributed vertically around the center of the storm. Thus, at any given altitude (except close to the surface, where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.[2][edit]Eye and centerA strong tropical cyclone will harbor an area of sinking air at the center of circulation. If this area is strong enough, it can develop into a large "eye". Weather in the eye is normally calm and free of clouds, although the sea may be extremely violent.[3]The eye is normally circular in shape, and is typically 3065 km (1940 miles) indiameter, though eyes as small as 3 kilometres (1.9mi) and as large as 370 kilometres (230mi) have been observed.[4][5]Intense, mature tropical cyclones can sometimes exhibit an outward curving of the eyewall's top, making it resemble an arena football stadium; this phenomenon is thus sometimes referred to as thestadium effect.[6]It is usually coldest in the center.There are other features that either surround the eye, or cover it. Thecentral dense overcastis the concentrated area of strong thunderstorm activity near the center of a tropical cyclone;[7]in weaker tropical cyclones, the CDO may cover the center completely.[8]Theeyewallis a circle of strong thunderstorms that surrounds the eye; here is where the greatest wind speeds are found, where clouds reach the highest, and precipitation is the heaviest. The heaviest wind damage occurs where a tropical cyclone's eyewall passes over land.[3]Eyewall replacement cyclesoccur naturally in intense tropical cyclones. When cyclones reach peak intensity they usually have an eyewall andradius of maximum windsthat contract to a very small size, around 10 to 25 kilometres (6.2 to 16 mi). Outer rainbands can organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture andangular momentum. When the inner eyewall weakens, the tropical cyclone weakens (in other words, the maximum sustained winds weaken and the central pressure rises.) The outer eyewall replaces the inner one completely at the end of the cycle. The storm can be of the same intensity as it was previously or even stronger after the eyewall replacement cycle finishes. The storm may strengthen again as it builds a new outer ring for the next eyewall replacement.[9]Size descriptions of tropical cyclones


Less than 2degrees latitudeVery small/midget

2 to 3degrees of latitudeSmall

3 to 6degrees of latitudeMedium/Average

6 to 8degrees of latitudeLarge

Over 8degrees of latitudeVery large[10]

[edit]SizeOne measure of the size of a tropical cyclone is determined by measuring the distance from its center of circulation to its outermost closedisobar, also known as itsROCI. If the radius is less than twodegrees of latitudeor 222 kilometres (138mi), then the cyclone is "very small" or a "midget". A radius between 3 and 6latitude degrees or 333 to 670 kilometres (207 to 420 mi) are considered "average-sized". "Very large" tropical cyclones have a radius of greater than 8degrees or 888 kilometres (552mi).[10]Use of this measure has objectively determined that tropical cyclones in the northwest Pacific Ocean are the largest on earth on average, withAtlantic tropical cyclonesroughly half their size.[11]Other methods of determining a tropical cyclone's size include measuring the radius of gale force winds and measuring the radius at which its relativevorticityfield decreases to 1105s1from its center.[12][13][edit]Mechanics

Tropical cyclones form when the energy released by the condensation of moisture in rising air causes apositive feedback loopover warm ocean waters.[14]A tropical cyclone's primary energy source is the release of theheat of condensationfrom water vaporcondensing, withsolar heatingbeing the initial source for evaporation. Therefore, a tropical cyclone can be visualized as a giant verticalheat enginesupported by mechanics driven by physical forces such as therotationandgravityof the Earth.[15]In another way, tropical cyclones could be viewed as a special type ofmesoscale convective complex, which continues to develop over a vast source of relative warmth and moisture. While an initial warm core system, such as an organized thunderstorm complex, is necessa