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A tropical cyclone is a meteorological term for a Storm System characterized by a Low Pressure center and Thunderstorms that produces strong wind and flooding rain. A tropical cyclone feeds on the heat released when moist air rises and the water vapor it contains Condenses . 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. The adjective "tropical" refers to both the geographic origin of these systems, which form almost exclusively in Tropical regions of the globe, and their formation in Maritime Tropical Air Masses . The noun "cyclone" refers to such 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 various other names, such as hurricane, '''typhoon''', '''tropical storm''', '''cyclonic storm''', and '''tropical depression'''. While tropical cyclones can produce extremely powerful winds and torrential Rain , they are also able to produce high waves and damaging Storm Surge . They develop over large bodies of warm water, and lose their strength if they move over land. 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 25 Mi (40 Km ) from the coastline. Although their effects on human populations can be devastating, tropical cyclones can also relieve Drought conditions. They also carry heat and energy away from the tropics and transport it towards 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 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. PHYSICAL STRUCTURE See Also: Eye (cyclone) All tropical cyclones are areas of Low Atmospheric Pressure near the Earth's surface. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface at Sea Level .1 Tropical cyclones are characterized and driven by the release of large amounts of latent Heat Of Condensation , which occurs when moist air is carried upwards and its water vapor condenses. 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 Banding Rainbands are bands of showers and thunderstorms that spiral cyclonically toward the storm center. High wind gusts and heavy downpours often occur in individual rainbands, with relatively calm weather between bands. Tornadoes often form in the rainbands of landfalling tropical cyclones.3 Intense Annular Tropical Cyclones are distinctive for their lack of rainbands; instead, they possess a thick circular area of disturbed weather around their low pressure center.4 While all surface low pressure areas require divergence aloft to continue deepening, the divergence over tropical cyclones is in all directions away from the center. The upper levels of a tropical cyclone feature winds directed away from the center of the storm with an Anticyclonic rotation, due to the Coriolis Effect . Wind s at the surface are strongly cyclonic, weaken with height, and eventually reverse themselves. Tropical cyclones owe this unique characteristic to requiring a relative lack of vertical Wind Shear to maintain the warm core at the center of the storm. Eye and inner core A 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 an Eye . Weather in the eye is normally calm and free of clouds, though the sea may be extremely violent. The eye is normally circular in shape, and may range in size from 3 to 370 km (2–230 miles) in diameter.56 Intense, mature hurricanes can sometimes exhibit an inward curving of the eyewall's top, making it resemble a football stadium; this phenomenon is thus sometimes referred to as the '' Stadium Effect ''.7 There are other features that either surround the eye, or cover it. The Central Dense Overcast is the concentrated area of strong thunderstorm activity near the center of a tropical cyclone;8 in weaker tropical cyclones, the CDO may cover the center completely.9 The Eyewall is 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 hurricane's eyewall passes over land. Associated with eyewalls are Eyewall Replacement Cycles , which occur naturally in intense tropical cyclones. When cyclones reach peak intensity they usually—but not always—have an eyewall and Radius Of Maximum Wind s that contract to a very small size, around 10–25 km (5 to 15 miles). At this point, some of the outer rainbands may organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and Angular Momentum . During this phase, the tropical cyclone weakens (i.e., the maximum winds die off somewhat and the central pressure goes up), but eventually the outer eyewall replaces the inner one completely. The storm can be of the same intensity as it was previously or, in some cases, it can be even stronger after the eyewall replacement cycle. Even if the cyclone is weaker at the end of the cycle, the storm may strengthen again as it builds a new outer ring for the next eyewall replacement.10 Size The size of a tropical cyclone is determined by measuring the distance from its center of circulation to its outermost closed . Other methods of determining a tropical cyclone's size include measuring the radius of gale force winds and measuring the radius of the central dense overcast. MECHANICS over warm ocean waters.]] A tropical cyclone's primary Energy source is the release of the Heat Of Condensation from water vapor Condensing at high altitudes, with Solar Heating being the initial source for evaporation. Therefore, a tropical cyclone can be visualized as a giant vertical Heat Engine supported by mechanics driven by physical forces such as the Rotation and Gravity of the Earth .11 In another way, tropical cyclones could be viewed as a special type of Mesoscale Convective Complex , which continues to develop over a vast source of relative warmth and moisture. Condensation leads to higher wind speeds, as a tiny fraction of the released energy is converted into mechanical energy; the faster winds and lower pressure associated with them in turn cause increased surface evaporation and thus even more condensation. Much of the released energy drives Updrafts that increase the height of the storm clouds, speeding up condensation.12 This provides the system with enough energy to be self-sufficient and causes a Positive Feedback Loop that continues as long as the tropical cyclone can draw energy from its Thermal Reservoir , the warm water at the surface of the ocean. Factors such as a continued lack of equilibrium in air mass distribution would also give supporting energy to the cyclone. The rotation of the Earth causes the system to spin, an effect known as the Coriolis Effect , giving it a cyclonic characteristic and affecting the trajectory of the storm. What primarily distinguishes tropical cyclones from other meteorological phenomena is deep Convection as a driving force.13 Because convection is strongest in a Tropical Climate , it defines the initial domain of the tropical cyclone. By contrast, Mid-latitude Cyclone s draw their energy mostly from pre-existing horizontal temperature Gradient s in the atmosphere. To continue to drive its heat engine, a tropical cyclone must remain over warm water, which provides the needed atmospheric moisture to maintain the positive feedback loop running. As a result, when a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly. as Hurricanes Katrina and Rita passed over]] The passage of a tropical cyclone over the ocean can cause the upper layers of the ocean to cool substantially, which can influence subsequent cyclone development. Cooling is primarily caused by upwelling of cold water from deeper in the ocean due to the wind stresses the storm itself induces upon the sea surface. Additional cooling may come in the form of cold water from falling raindrops. Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days.14 Scientists at the National Center For Atmospheric Research estimate that a tropical cyclone releases heat energy at the rate of 50 to 200 Trillion Joule s per day. For comparison, this rate of energy release is equivalent to 200 times the world-wide electrical generating capacity, or to exploding a 10- Megaton Nuclear Bomb every 20 minutes. University Corporation For Atmospheric Research Hurricanes: Keeping an eye on weather's biggest bullies accessed March 31, 2006 While the most obvious motion of clouds is toward the center, tropical cyclones also develop an upper-level (high-altitude) outward flow of clouds. These originate from air that has released its moisture and is expelled at high altitude through the "chimney" of the storm engine. This outflow produces high, thin Cirrus Cloud s that spiral away from the center. These high cirrus clouds may be the first signs of an approaching tropical cyclone when seen from dry land. MAJOR BASINS AND RELATED WARNING CENTERS See Also: Tropical cyclone basins Regional Specialized Meteorological Centre Tropical Cyclone Warning Centre
The word ''hurricane'', used in the North Atlantic and Northeast Pacific, is derived from the name of a native Caribbean Amerindian storm God , Huracan , via Spanish ''huracán''.59 (Huracan is also the source of the word ''Orcan'', another word for the European Windstorm . These events should not be confused.) Naming See Also: Tropical cyclone naming Lists of tropical cyclone names Storms reaching tropical storm strength were initially given names to eliminate confusion when there are multiple systems in any individual basin at the same time which assists in warning people of the coming storm.National Hurricane Center. Worldwide Tropical Cyclone Names. Retrieved on 2006-12-28 . In most cases, a tropical cyclone retains its name throughout its life; however, under Special Circumstances , tropical cyclones may be renamed while active. These names are taken from lists which vary from region to region and are drafted a few years ahead of time. The lists are decided upon, depending on the regions, either by committees of the World Meteorological Organization (called primarily to discuss many other issues), or by national weather offices involved in the forecasting of the storms. Each year, the names of particularly destructive storms (if there are any) are "retired" and new names are chosen to take their place. NOTABLE TROPICAL CYCLONES See Also: List of notable tropical cyclones List of notable Atlantic hurricanes List of notable Pacific hurricanes Tropical cyclones that cause extreme destruction are rare, though when they occur, they can cause great amounts of damage or thousands of fatalities. The 1970 Bhola Cyclone is the deadliest tropical cyclone on record, killing over 300,000 people60 and potentially as many as 1 million61 after striking the densely populated Ganges Delta region of Bangladesh on November 13 , 1970 . Its powerful storm surge was responsible for the high death toll. The North Indian Cyclone Basin has historically been the deadliest basin, with several cyclones since 1900 killing over 100,000 people, all in Bangladesh.6263 Elsewhere, Typhoon Nina killed 29,000 in China due to a 2000-year Flood which caused 62 dams including the Banqiao Dam to fail; another 145,000 died during the subsequent famine and epidemic.64 The Great Hurricane Of 1780 is the deadliest Atlantic Hurricane on record, killing about 22,000 people in the Lesser Antilles .65 A tropical cyclone does need not be particularly strong to cause memorable damage, primarily if the deaths are from rainfall or mudslides. Tropical Storm Thelma in November 1991 killed thousands in the Philippines ,66 while in 1982, the unnamed tropical depression that eventually became Hurricane Paul killed around 1,000 people in Central America .67 Hurricane Katrina is estimated as the costliest tropical cyclone worldwide,68 causing $81.2 billion in property damage (2005 USD)69 with overall damage estimates exceeding $100 billion (2005 USD). Katrina killed at least 1,836 people after striking Louisiana and Mississippi as a Major Hurricane in August 2005. The Galveston Hurricane Of 1900 is the deadliest natural disaster in the United States , killing an estimated 6,000 to 12,000 people in Galveston, Texas . Hurricane Iniki in 1992 was the most powerful storm to strike Hawaii in recorded history, hitting Kauai as a Category 4 hurricane, killing six people, and causing U.S. $3 billion in damage.70 Other destructive Eastern Pacific Hurricane s include Pauline and Kenna , both causing severe damage after striking Mexico as major hurricanes.7172 In March 2004, Cyclone Gafilo struck northeastern Madagascar as a powerful cyclone, killing 74, affecting more than 200,000, and becoming the worst cyclone to affect the nation for over 20 years.73 , Cyclone Tracy , and the United States.]] The most intense storm on record was Typhoon Tip in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of 870 Mbar (25.69 InHg ) and maximum sustained wind speeds of 165 knots (190 mph, 305 km/h).74 Tip, however, does not solely hold the record for fastest sustained winds in a cyclone. Typhoon Keith in the Pacific and Hurricanes Camille and Allen in the North Atlantic currently share this record with Tip.75 Camille was the only storm to actually strike land while at that intensity, making it, with 165 knots (190 mph, 305 km/h) sustained winds and 210 mph (335 km/h) gusts, the strongest tropical cyclone on record at landfall.76 Typhoon Nancy in 1961 had recorded wind speeds of 185 knots (215 mph, 345 km/h), but recent research indicates that wind speeds from the 1940s to the 1960s were gauged too high, and this is no longer considered the storm with the highest wind speeds on record.77 Similarly, a surface-level gust caused by Typhoon Paka on Guam was recorded at 205 knots (235 mph, 380 km/h). Had it been confirmed, it would be the strongest non- Tornadic wind ever recorded on the Earth 's surface, but the reading had to be discarded since the Anemometer was damaged by the storm.78 In addition to being the most intense tropical cyclone on record, Tip was the largest cyclone on record, with tropical storm-force winds 2,170 km (1,350 miles) in diameter. The smallest storm on record, Cyclone Tracy , was roughly 100 km (60 miles) wide before striking Darwin , Australia in 1974.79 Hurricane John is the longest-lasting tropical cyclone on record, lasting 31 days in 1994 . Prior to the advent of satellite imagery in 1961, however, many tropical cyclones were underestimated in their durations.80 John is the second longest-tracked tropical cyclone in the Northern Hemisphere on record, behind Typhoon Ophelia of 1960 which had a path of 8,500 miles (12,500 km). Reliable data for Southern Hemisphere cyclones is unavailable.81 LONG TERM ACTIVITY TRENDS See Also: Atlantic hurricane reanalysis While the number of storms in the Atlantic has increased since 1995, there is no obvious global trend; the annual number of tropical cyclones worldwide remains about 87 ± 10. However, the ability of climatologists to make long-term data analysis in certain basins is limited by the lack of reliable historical data in some basins, primarily in the Southern Hemisphere.82 In spite of that, there is some evidence that the intensity of hurricanes is increasing. Kerry Emanuel stated, "Records of hurricane activity worldwide show an upswing of both the maximum wind speed in and the duration of hurricanes. The energy released by the average hurricane (again considering all hurricanes worldwide) seems to have increased by around 70% in the past 30 years or so, corresponding to about a 15% increase in the maximum wind speed and a 60% increase in storm lifetime."83 Atlantic storms are becoming more destructive financially, since five of the ten most expensive storms in United States history have occurred since 1990. This can be attributed to the increased intensity and duration of hurricanes striking North America, and to a greater degree, the number of people living in susceptible coastal areas, following increased development in the region since the last surge in Atlantic hurricane activity in the 1960s. Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast may have gone unmeasured in some instances. The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect.84 The number and strength of Atlantic hurricanes may undergo a 50-70 year cycle, also known as the Atlantic Multidecadal Oscillation . Although more common since 1995, few above-normal hurricane seasons occurred during 1970-1994.85 Destructive hurricanes struck frequently from 1926-60, including many major New England hurricanes. A record 21 Atlantic tropical storms formed in 1933 , a record only recently exceeded in 2005 , which saw 28 storms. Tropical hurricanes occurred infrequently during the seasons of 1900-1925; however, many intense storms formed during 1870-1899. During the 1887 season, 19 tropical storms formed, of which a record 4 occurred after 1 November and 11 strengthened into hurricanes. Few hurricanes occurred in the 1840s to 1860s; however, many struck in the early 1800s, including an 1821 storm that made a direct hit on New York City . Some historical weather experts say these storms may have been as high as Category 4 in strength.86 These active hurricane seasons predated satellite coverage of the Atlantic basin. Before the satellite era began in 1960, tropical storms or hurricanes went undetected unless a ship reported a voyage through the storm or a storm hit land in a populated area. The official record, therefore, could miss storms in which no ship experienced gale-force winds, recognized it as a tropical storm (as opposed to a high-latitude extra-tropical cyclone, a tropical wave, or a brief squall), returned to port, and reported the experience. GLOBAL WARMING See Also: Global warming The U.S. National Oceanic And Atmospheric Administration Geophysical Fluid Dynamics Laboratory performed a simulation to determine if there is a Statistical Trend in the frequency or strength of cyclones over time. The simulation concluded "the strongest hurricanes in the present climate may be upstaged by even more intense hurricanes over the next century as the earth's climate is warmed by increasing levels of greenhouse gases in the atmosphere."87 In an article in '' Nature '', Kerry Emanuel stated that potential hurricane destructiveness, a measure combining hurricane strength, duration, and frequency, "is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multidecadal oscillations in the North Atlantic and North Pacific, and global warming." Emanuel predicted "a substantial increase in hurricane-related losses in the twenty-first century."88. Similarly, P.J. Webster and others published an article in '' Science '' examining the "changes in tropical cyclone number, duration, and intensity" over the last 35 years, the period when satellite data has been available. Their main finding was although the number of cyclones decreased throughout the planet excluding the north Atlantic Ocean , there was a great increase in the number and proportion of very strong cyclones.89 The strength of the reported effect is surprising in light of modeling studies90 that predict only a one half category increase in storm intensity as a result of a ~2 °C global warming. Such an response would have predicted only a ~10% increase in Emanuel's potential destructiveness index during the twentieth century rather than the ~75-120% increase he reported. Secondly, after adjusting for changes in population and inflation, and despite a more than 100% increase in Emanuel's potential destructiveness index, no statistically significant increase in the monetary damages resulting from Atlantic hurricanes has been found.91 Both Emanuel and Webster et al. consider Sea Surface Temperatures to be vital in the development of cyclones. Though neither study can directly link hurricanes with global warming, the increase in sea surface temperatures is believed to be due to both global warming and nature variability, e.g. the hypothesized Atlantic Multidecadal Oscillation (AMO), though an exact attribution has not been defined. However, recent temperatures are the warmest ever observed for many ocean basins. In February 2007, the United Nations Intergovernmental Panel On Climate Change released its Fourth Assessment Report on Climate Change . The report noted many observed changes in the climate, including atmospheric composition, global average temperatures, ocean conditions, among others. The report concluded the observed increase in tropically intensity is larger than climate models predict. Additionally, the report considered that it is likely that storm intensity will continue to increase through the 21st century, and declared it more likely than not that there has been some human contribution to the increases in tropical cyclone intensity.92 However, there is no universal agreement about the magnitude of the effects anthropogenic global warming has on tropical cyclone formation, track, and intensity. For example, critics such as Chris Landsea assert that man-made effects would be "quite tiny compared to the observed large natural hurricane variability."93 A statement by the American Meteorological Society on February 1 , 2007 stated that trends in tropical cyclone records offer "evidence both for and against the existence of a detectable anthropogenic signal" in Tropical Cyclogenesis .94 Albeit many aspects of a link between tropical cyclones and global warming are still being "hotly debated", a point of agreement is that no individual tropical cyclone or season can be attributed to global warming.9596 RELATED CYCLONE TYPES in 2002 ]] See Also: Cyclone Extratropical cyclone Subtropical cyclone In addition to tropical cyclones, there are two other classes of cyclones within the spectrum of cyclone types. These kinds of cyclones, known as . An ''extratropical cyclone'' is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. 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;97 additionally, although not as frequently, an extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone. From space, extratropical storms have a characteristic " Comma -shaped" cloud pattern. Extratropical cyclones can also be dangerous when their low-pressure centers cause powerful winds and very high seas. 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 in a wide band of Latitude s, from the Equator to 50°. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm.98 From an operational standpoint, a tropical cyclone is usually not considered to become subtropical during its extratropical transition.99 TROPICAL CYCLONES IN POPULAR CULTURE See Also: Tropical cyclones in popular culture In Popular Culture , tropical cyclones have made appearances in different types of media, including Film s, Book s, Television , Music , and Electronic Game s. The media can have tropical cyclones that are entirely Fiction al, or can be based on real events.100 For example, George Rippey Stewart 's '' Storm '', a Best-seller published in 1941, is thought to have influenced meteorologists into giving female names to Pacific tropical cyclones.101 Another example is the hurricane in '' The Perfect Storm '', which describes the sinking of the '' Andrea Gail '' by the 1991 Halloween Nor'easter .102 Also, Hypothetical Hurricanes have been featured in parts of the plots of series such as '' The Simpsons '', '' Invasion '', '' Family Guy '', '' Seinfeld '', '' CSI Miami '', and '' Dawson's Creek ''. The 2004 film '' The Day After Tomorrow '' includes several mentions of actual tropical cyclones as well as featuring fantastical "hurricane-like" non-tropical arctic storms. SEE ALSO ;Annual seasons
;Forecasting and preparation
NOTES EXTERNAL LINKS ;Learning resources
;Regional specialised meteorological centers
;Past storms
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