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80-557: The Great Arctic Cyclone , or "Great Arctic Cyclone of 2012" , was a powerful extratropical cyclone that was centered on the Arctic Ocean in early August 2012. Cyclones of this magnitude are rare in the Arctic summer, although common in the winter. The Great Arctic Cyclone was the strongest summer storm in the Arctic and the 13th-strongest storm observed at any time in the Arctic, since satellite observations began in 1979. Although

160-466: A category 5 hurricane . In the Arctic , the average pressure for cyclones is 980 millibars (28.94 inHg) during the winter, and 1,000 millibars (29.53 inHg) during the summer. Tropical cyclones often transform into extratropical cyclones at the end of their tropical existence, usually between 30° and 40° latitude, where there is sufficient forcing from upper-level troughs or shortwaves riding

240-430: A cold air airmass, the atmosphere becomes increasingly stable and the centre of gravity of the system lowers. As the occlusion process extends further down the warm front and away from the central low, more and more of the available potential energy of the system is exhausted. This potential energy sink creates a kinetic energy source which injects a final burst of energy into the storm's motions. After this process occurs,

320-400: A continent, such as extratropical cyclones , with dimensions of 1,000–2,500 km (620–1,550 mi) across. The mesoscale is the next smaller scale, and often is divided into two ranges: meso-alpha phenomena range from 200–2,000 km (120–1,240 mi) across (the realm of the tropical cyclone ), while meso-beta phenomena range from 20–200 km (12–124 mi) across (the scale of

400-454: A cyclone occludes, a tr ough o f w arm air al oft—or "trowal" for short—will be caused by strong southerly winds on its eastern periphery rotating aloft around its northeast, and ultimately into its northwestern periphery (also known as the warm conveyor belt), forcing a surface trough to continue into the cold sector on a similar curve to the occluded front. The trowal creates the portion of an occluded cyclone known as its comma head , due to

480-406: A definitive lower to mid-level warm core structure. A warm seclusion, the result of a baroclinic lifecycle, occurs at latitudes well poleward of the tropics. As latent heat flux releases are important for their development and intensification, most warm seclusion events occur over the oceans ; they may impact coastal nations with hurricane force winds and torrential rain . Climatologically,

560-415: A favorable quadrant of a maximum in the upper level jetstream known as a jet streak. The favorable quadrants are usually at the right rear and left front quadrants, where divergence ensues. The divergence causes air to rush out from the top of the air column. As mass in the column is reduced, atmospheric pressure at surface level (the weight of the air column) is reduced. The lowered pressure strengthens

640-413: A frontal boundary, eventually occluding and reaching a barotropically cold environment. It was developed completely from surface-based weather observations, including descriptions of clouds found near frontal boundaries. This theory still retains merit, as it is a good description for extratropical cyclones over continental landmasses. A second competing theory for extratropical cyclone development over

720-471: A highest recorded wind of 220 km/h (140 mph), resulting in the loss of 19 lives, 15 million trees, widespread damage to homes and an estimated economic cost of £ 1.2 billion ( US$ 2.3 billion). Although most tropical cyclones that become extratropical quickly dissipate or are absorbed by another weather system, they can still retain winds of hurricane or gale force. In 1954, Hurricane Hazel became extratropical over North Carolina as

800-486: A moderate cumulus, or as significant as a thunderstorm . Waterspouts normally develop as their parent clouds are in the process of development, and it is theorized that they spin up as they move up the surface boundary from the horizontal wind shear near the surface, and then stretch upwards to the cloud once the low level shear vortex aligns with a developing cumulus or thunderstorm. Weak tornadoes, known as landspouts, across eastern Colorado have been witnessed to develop in

880-661: A nor'easter caused at least 286 deaths in the Northeastern United States, one of the deadliest nor'easters on record. 62 years later in 2022 , a winter storm caused $ 8.5 billion in damages and 106 deaths across the United States and Canada. In September 1954, the extratropical remnants of Typhoon Marie caused the Tōya Maru to run aground and capsize in the Tsugaru Strait . 1,159 out of

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960-642: A pressure of 915 mbar (27.0 inHg), with the possibility of a pressure between 912–913 mbar (26.9–27.0 inHg), lower than the Braer Storm. The most intense extratropical cyclone across the North Pacific Ocean occurred in November 2014, when a cyclone partially related to Typhoon Nuri reached a record low pressure of 920 mbar (27 inHg). In October 2021, the most intense Pacific Northwest windstorm occurred off

1040-525: A similar manner. An outbreak occurred in the Great Lakes in late September and early October 2003 along a lake effect band. September is the peak month of landspout and waterspout occurrence around Florida and for waterspout occurrence around the Great Lakes . Cyclogenesis is the opposite of cyclolysis, which concerns the weakening of surface cyclones. The term has an anticyclonic (high-pressure system) equivalent— Anticyclogenesis , which deals with

1120-526: A strong Category 3 storm. The Columbus Day Storm of 1962 , which evolved from the remains of Typhoon Freda, caused heavy damage in Oregon and Washington , with widespread damage equivalent to at least a Category 3. In 2005, Hurricane Wilma began to lose tropical characteristics while still sporting Category 3-force winds (and became fully extratropical as a Category 1 storm). In summer, extratropical cyclones are generally weak, but some of

1200-536: A strong baroclinic system and achieved warm seclusion status at maturity (or lowest pressure). Extratropical cyclones are generally driven, or "steered", by deep westerly winds in a general west to east motion across both the Northern and Southern hemispheres of the Earth. This general motion of atmospheric flow is known as "zonal". Where this general trend is the main steering influence of an extratropical cyclone, it

1280-468: A tropical cyclone. The Joint Typhoon Warning Center uses the extratropical transition (XT) technique to subjectively estimate the intensity of tropical cyclones becoming extratropical based on visible and infrared satellite imagery . Loss of central convection in transitioning tropical cyclones can cause the Dvorak technique to fail; the loss of convection results in unrealistically low estimates using

1360-547: Is an idealized formation model of cold-core cyclonic storms developed by Norwegian meteorologists during the First World War . The main concept behind this model, relating to cyclogenesis, is that cyclones progress through a predictable evolution as they move up a frontal boundary, with the most mature cyclone near the northeast end of the front and the least mature near the tail end of the front. A preexisting frontal boundary, as defined in surface weather analysis ,

1440-427: Is associated with the warm front is often extensive. In mature extratropical cyclones, an area known as the comma head on the northwest periphery of the surface low can be a region of heavy precipitation, frequent thunderstorms , and thundersnows . Cyclones tend to move along a predictable path at a moderate rate of progress. During fall , winter, and spring, the atmosphere over continents can be cold enough through

1520-675: Is at about 10,000 feet (3,048 meters) altitude. Cyclone phase diagrams are used to tell whether a cyclone is tropical, subtropical, or extratropical. There are two models of cyclone development and life cycles in common use: the Norwegian model and the Shapiro–Keyser model. Of the two theories on extratropical cyclone structure and life cycle, the older is the Norwegian Cyclone Model, developed during World War I . In this theory, cyclones develop as they move up and along

1600-406: Is best. The stronger the upper level divergence over the cyclone, the deeper the cyclone can become. Hurricane-force extratropical cyclones are most likely to form in the northern Atlantic and northern Pacific oceans in the months of December and January. On 14 and 15 December 1986, an extratropical cyclone near Iceland deepened to below 920 millibars (27 inHg), which is a pressure equivalent to

1680-415: Is known as "lee cyclogenesis" since the low forms on the leeward side of the mountains. Mesoscale convective systems can spawn surface lows which are initially warm core. The disturbance can grow into a wave-like formation along the front and the low will be positioned at the crest. Around the low, flow will become cyclonic, by definition. This rotational flow will push polar air equator-ward west of

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1760-560: Is known as a " zonal flow regime ". When the general flow pattern buckles from a zonal pattern to the meridional pattern, a slower movement in a north or southward direction is more likely. Meridional flow patterns feature strong, amplified troughs and ridges, generally with more northerly and southerly flow. Changes in direction of this nature are most commonly observed as a result of a cyclone's interaction with other low pressure systems , troughs , ridges , or with anticyclones . A strong and stationary anticyclone can effectively block

1840-475: Is known as the cold sector, while the area equatorward and east of its associated cold and warm fronts is known as the warm sector. The wind flow around an extratropical cyclone is counterclockwise in the northern hemisphere, and clockwise in the southern hemisphere, due to the Coriolis effect (this manner of rotation is generally referred to as cyclonic ). Near this center, the pressure gradient force (from

1920-431: Is no longer used. The windfield of an extratropical cyclone constricts with distance in relation to surface level pressure, with the lowest pressure being found near the center, and the highest winds typically just on the cold/poleward side of warm fronts, occlusions, and cold fronts , where the pressure gradient force is highest. The area poleward and west of the cold and warm fronts connected to extratropical cyclones

2000-585: Is possible. Although tornadoes can form anywhere on Earth, the greatest number occur in the Great Plains in the United States, because downsloped winds off the north–south oriented Rocky Mountains , which can form a dry line, aid their development at any strength . Explosive development of extratropical cyclones can be sudden. The storm known in Great Britain and Ireland as the " Great Storm of 1987 " deepened to 953 millibars (28.14 inHg) with

2080-469: Is required for the development of a mid-latitude cyclone. The cyclonic flow begins around a disturbed section of the stationary front due to an upper level disturbance, such as a short wave or an upper-level trough, near a favorable quadrant of the upper-level jet. However, enhanced along-frontal stretching rates in the lower troposphere can suppress the growth of extratropical cyclones. Cyclogenesis can only occur when temperature decreases polewards (to

2160-407: Is still not fully understood, there are six main requirements for tropical cyclogenesis: sea surface temperatures that are warm enough, atmospheric instability, high humidity in lower to middle levels of the troposphere , enough Coriolis force to develop a low pressure center, a pre-existing low level focus or disturbance, and low vertical wind shear . These warm core cyclones tend to form over

2240-403: Is strong enough, temperature advection will increase, driving more vertical motion. This increases the overall strength of the system. Shearwise updrafts are the most important factor in determining cyclonic growth and strength. A surface low can have a variety of causes for forming. Topography can force a surface low to form when an existing baroclinic wave moves over a mountain barrier; this

2320-824: Is the extratropical cyclone. The descriptor extratropical signifies that this type of cyclone generally occurs outside the tropics and in the middle latitudes of Earth between 30° and 60° latitude. They are termed mid-latitude cyclones if they form within those latitudes, or post-tropical cyclones if a tropical cyclone has intruded into the mid latitudes. Weather forecasters and the general public often describe them simply as " depressions " or "lows". Terms like frontal cyclone, frontal depression, frontal low, extratropical low, non-tropical low and hybrid low are often used as well. Extratropical cyclones are classified mainly as baroclinic , because they form along zones of temperature and dewpoint gradient known as frontal zones . They can become barotropic late in their life cycle, when

2400-529: The Bergen School of Meteorology , largely observed cyclones at the tail end of their lifecycle and used the term occlusion to identify the decaying stages. Warm seclusions may have cloud-free, eye -like features at their center (reminiscent of tropical cyclones ), significant pressure falls, hurricane-force winds, and moderate to strong convection . The most intense warm seclusions often attain pressures less than 950 millibars (28.05 inHg) with

2480-1018: The Northern Hemisphere and 71,289–74,229 extratropical cyclones in the Southern Hemisphere were detected between 1979 and 2018 based on reanalysis data. A study of extratropical cyclones in the Southern Hemisphere shows that between the 30th and 70th parallels , there are an average of 37 cyclones in existence during any 6-hour period. A separate study in the Northern Hemisphere suggests that approximately 234 significant extratropical cyclones form each winter. Extratropical cyclones form along linear bands of temperature/dew point gradient with significant vertical wind shear , and are thus classified as baroclinic cyclones. Initially, cyclogenesis , or low pressure formation, occurs along frontal zones near

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2560-463: The Westerlies for the process of extratropical transition to begin. During this process, a cyclone in extratropical transition (known across the eastern North Pacific and North Atlantic oceans as the post-tropical stage), will invariably form or connect with nearby fronts and/or troughs consistent with a baroclinic system. Due to this, the size of the system will usually appear to increase, while

2640-410: The comma -like shape of the mid-tropospheric cloudiness that accompanies the feature. It can also be the focus of locally heavy precipitation, with thunderstorms possible if the atmosphere along the trowal is unstable enough for convection. Extratropical cyclones slant back into colder air masses and strengthen with height, sometimes exceeding 30,000 feet (approximately 9 km) in depth. Above

2720-521: The mesocyclone ). The microscale is the smallest of the meteorological scales, with a size under two kilometers (1.2 miles) (the scale of tornadoes and waterspouts ). These horizontal dimensions are not rigid divisions but instead reflect typical sizes of phenomena having certain dynamic characteristics. For example, a system does not necessarily transition from meso-alpha to synoptic scale when its horizontal extent grows from 2,000 to 2,001 km (1,242.7 to 1,243.4 mi). The Norwegian cyclone model

2800-468: The sea surface temperature is the greatest, leading to the greatest potential for instability. On rare occasions, an extratropical cyclone can transform into a tropical cyclone if it reaches an area of ocean with warmer waters and an environment with less vertical wind shear. An example of this happening is in the 1991 Perfect Storm . The process known as "tropical transition" involves the usually slow development of an extratropically cold core vortex into

2880-574: The 1,309 on board were killed, making it one of the deadliest typhoons in Japanese history . In July 2016, a cyclone in Northern China left 184 dead, 130 missing, and caused over $ 4.96 billion in damages. Cyclogenesis Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low-pressure area ). Cyclogenesis is an umbrella term for at least three different processes, all of which result in

2960-501: The Dvorak scale and is applied in the same way, except that "XT" is used instead of "T" to indicate that the system is undergoing extratropical transition. Also, the XT technique is only used once extratropical transition begins; the Dvorak technique is still used if the system begins dissipating without transition. Once the cyclone has completed transition and become cold-core , the technique

3040-472: The Dvorak technique. The system combines aspects of the Dvorak technique, used for estimating tropical cyclone intensity, and the Hebert-Poteat technique, used for estimating subtropical cyclone intensity. The technique is applied when a tropical cyclone interacts with a frontal boundary or loses its central convection while maintaining its forward speed or accelerating. The XT scale corresponds to

3120-519: The Great Arctic Cyclone did not cause the record melting of sea ice which occurred in 2012, turbulence from the storm is believed to have contributed to melting of sea ice, due to mechanical ice breakup and the rise of warmer saltier water from below ; however the main oceanic heat source, associated with inflowing Atlantic water, remained isolated from the turbulence. On August 2, 2012, an extratropical low formed over Siberia . During

3200-404: The Great Arctic Cyclone of 2012 was the strongest summer Arctic storm on record, since the beginning of records in 1979. Afterward, the storm slowly began to weaken, while drifting towards Canada . On August 12, the cyclone made landfall in the northern Canadian Arctic Archipelago , and slowly moved eastward across land, while rapidly weakening. Late on August 14, the Arctic cyclone dissipated over

3280-515: The Northern Hemisphere sees warm seclusions during the cold season months, while the Southern Hemisphere may see a strong cyclone event such as this during all times of the year. In all tropical basins, except the Northern Indian Ocean, the extratropical transition of a tropical cyclone may result in reintensification into a warm seclusion. For example, Hurricane Maria (2005) and Hurricane Cristobal (2014) each re-intensified into

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3360-524: The RFD reaching the ground. Waterspouts exist on the microscale. While some waterspouts are strong (tornadic) like their land-based counterparts, most are much weaker and caused by different atmospheric dynamics. They normally develop in moisture-laden environments with little vertical wind shear along lines of convergence, such as land breezes , lines of frictional convergence from nearby landmasses, or surface troughs. Their parent cloud can be as innocuous as

3440-702: The Southern Ocean with a pressure under 915 mbar (27.0 inHg). In the North Atlantic Ocean, the most intense extratropical cyclone was the Braer Storm , which reached a pressure of 914 mbar (27.0 inHg) in early January 1993. Before the Braer Storm, an extratropical cyclone near Greenland in December 1986 reached a minimum pressure of at least 916 mbar (27.0 inHg). The West German Meteorological Service marked

3520-436: The atmosphere), the two may combine to become a binary cyclone, where the vortices of the two cyclones rotate around each other (known as the " Fujiwhara effect "). This most often results in a merging of the two low pressure systems into a single extratropical cyclone, or can less commonly result in a mere change of direction of either one or both of the cyclones. The precise results of such interactions depend on factors such as

3600-783: The coast of Oregon , peaking with a pressure of 942 mbar (27.8 inHg). One of the strongest nor'easters occurred in January 2018 , in which a cyclone reached a pressure of 950 mbar (28 inHg). Extratropical cyclones have been responsible for some of the most damaging floods in European history. The Great storm of 1703 killed over 8,000 people and the North Sea flood of 1953 killed over 2,500 and destroyed 3,000 houses. In 2002, floods in Europe caused by two genoa lows caused $ 27.115 billion in damages and 232 fatalities,

3680-419: The cooler air ahead of the system is denser , and therefore more difficult to dislodge. Later, the cyclones occlude as the poleward portion of the cold front overtakes a section of the warm front, forcing a tongue, or trowal , of warm air aloft. Eventually, the cyclone will become barotropically cold and begin to weaken. Atmospheric pressure can fall very rapidly when there are strong upper level forces on

3760-413: The core weakens. However, after transition is complete, the storm may re-strengthen due to baroclinic energy, depending on the environmental conditions surrounding the system. The cyclone will also distort in shape, becoming less symmetric with time. During extratropical transition, the cyclone begins to tilt back into the colder airmass with height, and the cyclone's primary energy source converts from

3840-422: The cyclone (a low pressure system). The lowered pressure acts to draw in air, creating convergence in the low-level wind field. Low-level convergence and upper-level divergence imply upward motion within the column, making cyclones cloudy. As the cyclone strengthens, the cold front sweeps towards the equator and moves around the back of the cyclone. Meanwhile, its associated warm front progresses more slowly, as

3920-439: The depth of the troposphere to cause snowfall. Squall lines, or solid bands of strong thunderstorms, can form ahead of cold fronts and lee troughs due to the presence of significant atmospheric moisture and strong upper level divergence, leading to hail and high winds. When significant directional wind shear exists in the atmosphere ahead of a cold front in the presence of a strong upper-level jet stream, tornado formation

4000-449: The development of some sort of cyclone , and at any size from the microscale to the synoptic scale . The process in which an extratropical cyclone undergoes a rapid drop in atmospheric pressure (24 millibars or more) in a 24-hour period is referred to as explosive cyclogenesis , and is usually present during the formation of a nor'easter . Similarly, a tropical cyclone can undergo rapid intensification . The anticyclonic equivalent,

4080-400: The distribution of heat around the cyclone becomes fairly uniform with its radius. Extratropical cyclones form anywhere within the extratropical regions of the Earth (usually between 30° and 60° latitude from the equator ), either through cyclogenesis or extratropical transition. In a climatology study with two different cyclone algorithms, a total of 49,745–72,931 extratropical cyclones in

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4160-437: The far northern reaches of Canada. The Great Arctic Cyclone of 2012 became the strongest Arctic storm in the summer on record, since records began in 1979. At its peak intensity of 962 mbar (28.4 inHg), the Great Arctic Cyclone was also the 13th-strongest Arctic storm overall, since reliable records began. Extratropical cyclone The term " cyclone " applies to numerous types of low pressure areas, one of which

4240-411: The ground with it. As the mesocyclone approaches the ground, a visible condensation funnel appears to descend from the base of the storm, often from a rotating wall cloud. As the funnel descends, the RFD also reaches the ground, creating a gust front that can cause damage a good distance from the tornado. Usually, the funnel cloud begins causing damage on the ground (becoming a tornado) within minutes of

4320-467: The growth period of the cyclone, or cyclogenesis, ends, and the low begins to spin down (fill) as more air is converging into the bottom of the cyclone than is being removed out the top since upper-level divergence has decreased. Occasionally, cyclogenesis will re-occur with occluded cyclones. When this happens a new low center will form on the triple-point (the point where the cold front, warm front, and occluded front meet). During triple-point cyclogenesis,

4400-477: The higher latitudes). The existence of such transients are also closely related to the formation of the Icelandic and Aleutian Low — the two most prominent general circulation features in the mid- to sub-polar northern latitudes. The two lows are formed by both the transport of kinetic energy and the latent heating (the energy released when water phase changed from vapor to liquid during precipitation) from

4480-428: The low via its trailing cold front, and warmer air will push poleward low via the warm front. Usually the cold front will move at a quicker pace than the warm front and "catch up" with it due to the slow erosion of higher density airmass located out ahead of the cyclone and the higher density airmass sweeping in behind the cyclone, usually resulting in a narrowing warm sector. At this point an occluded front forms where

4560-436: The lower part of the atmosphere spinning in invisible tube-like rolls. The convective updraft of a thunderstorm is then thought to draw up this spinning air, tilting the rolls' orientation upward (from parallel to the ground to perpendicular) and causing the entire updraft to rotate as a vertical column. As the updraft rotates, it may form what is known as a wall cloud. The wall cloud is a spinning layer of clouds descending from

4640-456: The mesocyclone. The wall cloud tends to form closer to the center of the mesocyclone. The wall clouds do not necessarily need a mesocyclone to form and do not always rotate. As the wall cloud descends, a funnel-shaped cloud may form at its center. This is the first stage of tornado formation. The presence of a mesocyclone is believed to be a key factor in the formation of the strong tornadoes associated with severe thunderstorms. Tornadoes exist on

4720-417: The microscale or low end of the mesoscale gamma domain. The cycle begins when a strong thunderstorm develops a rotating mesocyclone a few miles up in the atmosphere, becoming a supercell. As rainfall in the storm increases, it drags with it an area of quickly descending air known as the rear flank downdraft (RFD). This downdraft accelerates as it approaches the ground, and drags the rotating mesocyclone towards

4800-764: The mid- latitude cyclones. The most intense extratropical cyclone on record was a cyclone in the Southern Ocean in October 2022. An analysis by the European Centre for Medium-Range Weather Forecasts estimated a pressure of 900.7 mbar (26.60 inHg) and a subsequent analysis published in Geophysical Research Letters estimated a pressure of 899.91 mbar (26.574 inHg). The same Geophysical Research Letters article notes at least five other extratropical cyclones in

4880-580: The most damaging flood in European since at least 1985. In late December 1999, Cyclones Lothar and Martin caused 140 deaths combined and over $ 23 billion in damages in Central Europe, the costliest European windstorms in history. In October 2012, Hurricane Sandy transitioned into an extratropical cyclone off the coast of the Northeastern United States . The storm killed over 100 people and caused $ 65 billion in damages,

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4960-580: The next few days, the storm slowly drifted into the Arctic Ocean, while gradually strengthening. On August 5, the storm reached the Arctic Ocean and began to rapidly intensify, while drifting closer to the North Pole . On August 6, the extratropical cyclone reached a peak intensity of 962 mbar (28.4 inHg), while centered about halfway between Alaska and the North Pole. At this point,

5040-407: The north, in the northern hemisphere), and pressure perturbation lines tilt westward with height. Cyclogenesis is most likely to occur in regions of cyclonic vorticity advection , downstream of a strong westerly jet. The combination of vorticity advection and thermal advection created by the temperature gradient and a low pressure center cause upward motion around the low. If the temperature gradient

5120-437: The occluded parent low will fill as the secondary low deepens into the main weathermaker. Tropical cyclones exist within a mesoscale alpha domain. As opposed to mid-latitude cyclogenesis, tropical cyclogenesis is driven by strong convection organised into a central core with no baroclinic zones, or fronts, extending through their center. Although the formation of tropical cyclones is the topic of extensive ongoing research and

5200-543: The oceans between 10 and 30 degrees of the equator. Mesocyclones range in size from mesoscale beta to microscale. The term mesocyclone is usually reserved for mid-level rotations within severe thunderstorms, and are warm core cyclones driven by latent heat of its associated thunderstorm activity. Tornadoes form in the warm sector of extratropical cyclones where a strong upper-level jet stream exists. Mesocyclones are believed to form when strong changes of wind speed and/or direction with height (" wind shear ") sets parts of

5280-467: The oceans is the Shapiro–Keyser model, developed in 1990. Its main differences with the Norwegian Cyclone Model are the fracture of the cold front, treating warm-type occlusions and warm fronts as the same, and allowing the cold front to progress through the warm sector perpendicular to the warm front. This model was based on oceanic cyclones and their frontal structure, as seen in surface observations and in previous projects which used aircraft to determine

5360-463: The part of the cold front ahead of the cyclone will develop into a warm front, giving the frontal zone (as drawn on surface weather maps ) a wave-like shape. Due to their appearance on satellite images, extratropical cyclones can also be referred to as frontal waves early in their life cycle. In the United States , an old name for such a system is "warm wave". In the northern hemisphere, once

5440-572: The path of an extratropical cyclone. Such blocking patterns are quite normal, and will generally result in a weakening of the cyclone, the weakening of the anticyclone, a diversion of the cyclone towards the anticyclone's periphery, or a combination of all three to some extent depending on the precise conditions. It is also common for an extratropical cyclone to strengthen as the blocking anticyclone or ridge weakens in these circumstances. Where an extratropical cyclone encounters another extratropical cyclone (or almost any other kind of cyclonic vortex in

5520-471: The pressure at the center of the cyclone compared to the pressure outside the cyclone) and the Coriolis force must be in an approximate balance for the cyclone to avoid collapsing in on itself as a result of the difference in pressure. The central pressure of the cyclone will lower with increasing maturity, while outside of the cyclone, the sea-level pressure is about average. In most extratropical cyclones,

5600-463: The process of formation of high-pressure areas , is anticyclogenesis . The opposite of cyclogenesis is cyclolysis . There are four main scales, or sizes of systems, dealt with in meteorology: the macroscale, the synoptic scale, the mesoscale , and the microscale. The macroscale deals with systems with global size, such as the Madden–Julian oscillation . Synoptic scale systems cover a portion of

5680-475: The release of latent heat from condensation (from thunderstorms near the center) to baroclinic processes. The low pressure system eventually loses its warm core and becomes a cold-core system . The peak time of subtropical cyclogenesis (the midpoint of this transition) in the North Atlantic is in the months of September and October, when the difference between the temperature of the air aloft and

5760-489: The second costliest tropical cyclone at the time. Other extratropical cyclones have been related to major tornado outbreaks . The tornado outbreaks of April 1965 , April 1974 and April 2011 were all large, violent, and deadly tornado outbreaks related to extratropical cyclones. Similarly, winter storms in March 1888 , November 1950 and March 1993 were responsible for over 300 deaths each. In December 1960

5840-431: The size of the two cyclones, their strength, their distance from each other, and the prevailing atmospheric conditions around them. Extratropical cyclones can bring little rain and surface winds of 15–30 km/h (10–20 mph), or they can be dangerous with torrential rain and winds exceeding 119 km/h (74 mph), and so they are sometimes referred to as windstorms in Europe. The band of precipitation that

5920-406: The storm has completed strengthening and the cyclonic flow is at its most intense. Thereafter, the strength of the storm diminishes as the cyclone couples with the upper-level trough or upper-level low, becoming increasingly cold core. The spin-down of cyclones, also known as cyclolysis, can be understood from an energetics perspective. As occlusion occurs and the warm air mass is pushed upwards over

6000-441: The surface of the earth, the air temperature near the center of the cyclone is increasingly colder than the surrounding environment. These characteristics are the direct opposite of those found in their counterparts, tropical cyclones ; thus, they are sometimes called "cold-core lows". Various charts can be examined to check the characteristics of a cold-core system with height, such as the 700 millibars (20.67 inHg) chart, which

6080-499: The system. When pressures fall more than 1 millibar (0.030  inHg ) per hour, the process is called explosive cyclogenesis, and the cyclone can be described as a bomb . These bombs rapidly drop in pressure to below 980 millibars (28.94 inHg) under favorable conditions such as near a natural temperature gradient like the Gulf Stream , or at a preferred quadrant of an upper-level jet streak, where upper level divergence

6160-502: The systems can cause significant floods overland because of torrential rainfall. The July 2016 North China cyclone never brought gale -force sustained winds, but it caused devastating floods in mainland China , resulting in at least 184 deaths and ¥ 33.19 billion ( US$ 4.96 billion) of damage. An emerging topic is the co-occurrence of wind and precipitation extremes, so-called compound extreme events, induced by extratropical cyclones. Such compound events account for 3–5% of

6240-460: The total number of cyclones. In the classic analysis by Edward Lorenz (the Lorenz energy cycle ), extratropical cyclones (so-called atmospheric transients) acts as a mechanism in converting potential energy that is created by pole to equator temperature gradients to eddy kinetic energy. In the process, the pole-equator temperature gradient is reduced (i.e. energy is transported poleward to warm up

6320-554: The vertical structure of fronts across the northwest Atlantic. A warm seclusion is the mature phase of the extratropical cyclone life cycle. This was conceptualized after the ERICA field experiment of the late 1980s, which produced observations of intense marine cyclones that indicated an anomalously warm low-level thermal structure, secluded (or surrounded) by a bent-back warm front and a coincident chevron-shaped band of intense surface winds. The Norwegian Cyclone Model , as developed by

6400-412: The warm air mass is pushed upwards into a trough of warm air aloft, which is also known as a trowal (a tro ugh of w arm air al oft). All developing low-pressure areas share one important aspect, that of upward vertical motion within the troposphere. Such upward motions decrease the mass of local atmospheric columns of air, which lower surface pressure. Maturity is after the time of occlusion when

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