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 the formation of surface high pressure systems.
Related terms
Cyclogenesis
Cyclogenesis | Related terms
It is the opposite of cyclolysis Cyclogenesis is the opposite of cyclolysis, which concerns the weakening of surface cyclones. The term has an anticyclonic equivalent Anticyclogenesis, which deals with the formation of surface high pressure systems. Cyclolysis and Anticyclogenesis The term has an anticyclonic equivalent, "Anticyclogenesis" which deals with the formation of surface high pressure systems.
we would expect what with low pressure in the northern hemisphere
user
234 significant extratropical cyclones form each winter
assistant
how does a low pressure area form?
user
Cyclogenesis is the development and strengthening of cyclonic circulations
assistant
what does the first word mean?
user
It  is the development and strengthening of cyclonic circulations in the atmosphere results in the formation of low pressure area
assistant
how is this associated with the weather?
user
Sorry. I cannot find the answer based on the context.
assistant
what are some of its related terms?
user
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 the formation of surface high pressure systems.
Cyclogenesis | Related terms
Climate cycles such as ENSO and the Madden–Julian oscillation modulate the timing and frequency of tropical cyclone development. There is a limit on tropical cyclone intensity which is strongly related to the water temperatures along its path.
Tropical cyclogenesis | Introduction
These warm core cyclones tend to form over the oceans between 10 and 30 degrees of the equator.
Cyclogenesis | Tropical cyclones
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 .
Cyclogenesis | Meteorological scales
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 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. The anticyclonic equivalent, the process of formation of high pressure areas, is anticyclogenesis.
Cyclogenesis | Introduction
Such upward motions decrease the mass of local atmospheric columns of air, which lower surface pressure.
Cyclogenesis | Modes of development
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, 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, the occluded parent low will fill as the secondary low deepens into the main weathermaker.
Cyclogenesis | Maturity
Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which temperate cyclogenesis occurs. Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment. Tropical cyclogenesis requires six main factors: sufficiently warm sea surface temperatures (at least ), atmospheric instability, high humidity in the 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. Tropical cyclones tend to develop during the summer, but have been noted in nearly every month in most basins.
Tropical cyclogenesis | Introduction
In a moist atmosphere, this lapse rate is 6.5 °C/km, while in an atmosphere with less than 100% relative humidity, the required lapse rate is 9.8 °C/km. At the 500 hPa level, the air temperature averages −7 °C (18 °F) within the tropics, but air in the tropics is normally dry at this level, giving the air room to wet-bulb, or cool as it moistens, to a more favorable temperature that can then support convection. A wetbulb temperature at 500 hPa in a tropical atmosphere of −13.2 °C is required to initiate convection if the water temperature is 26.5 °C, and this temperature requirement increases or decreases proportionally by 1 °C in the sea surface temperature for each 1 °C change at 500 hpa.
Tropical cyclogenesis | Warm waters, instability, and mid-level moisture
A preexisting frontal boundary, as defined in surface weather analysis, 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 | Precursors for development
The majority of extratropical cyclones tend to restrengthen after completing the transition period.
Tropical cyclogenesis | Middle latitudes
Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere. Cyclogenesis is an umbrella term for several different processes that all result in the development of some sort of cyclone. It can occur at various scales, from the microscale to the synoptic scale. Extratropical cyclones begin as waves along weather fronts before occluding later in their life cycle as cold-core systems. However, some intense extratropical cyclones can become warm-core systems when a warm seclusion occurs. Tropical cyclones form as a result of significant convective activity, and are warm core. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation.
Cyclone | Formation
Under a cold cyclone, 500 hPa temperatures can fall as low as −30 °C, which can initiate convection even in the driest atmospheres. This also explains why moisture in the mid-levels of the troposphere, roughly at the 500 hPa level, is normally a requirement for development. However, when dry air is found at the same height, temperatures at 500 hPa need to be even colder as dry atmospheres require a greater lapse rate for instability than moist atmospheres. At heights near the tropopause, the 30-year average temperature (as measured in the period encompassing 1961 through 1990) was −77 °C (−105 °F).
Tropical cyclogenesis | Warm waters, instability, and mid-level moisture
A recent example of a tropical cyclone that maintained itself over cooler waters was Epsilon of the 2005 Atlantic hurricane season.
Tropical cyclogenesis | Warm waters, instability, and mid-level moisture
Maturity is after the time of occlusion when 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 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.
Cyclogenesis | Maturity
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 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.
Cyclogenesis | Mesocyclones
Tropical cyclogenesis in the Northwestern Pacific is suppressed west of 150°E in the year following an El Niño event.
Tropical cyclogenesis | Influence of ENSO
Due to the initial cold temperatures aloft, sea surface temperatures usually need to reach at least for this initial round of thunderstorms. The initial thunderstorm activity moistens up the environment around the low, which destabilizes the atmosphere by reducing the lapse rate needed for convection. When the next shortwave or upper level jet streak (wind maximum within the jet stream) moves nearby, convection reignites closer to the center and the system develops into a true subtropical cyclone. The average sea surface temperature that helps lead to subtropical cyclogenesis is . If the thunderstorm activity becomes deep and persistent, allowing its initial low level warm core to deepen, tropical cyclogenesis is possible.
Subtropical cyclone | Formation
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 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.
Cyclogenesis | Mesocyclones
Cyclogenesis can only occur when temperature decreases polewards (to 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 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.
Cyclogenesis | Vertical motion affecting development
Cyclogenesis is the development and strengthening of cyclonic circulations, or low-pressure areas, within the atmosphere. Cyclogenesis is the opposite of , and has an anticyclonic (high-pressure system) equivalent which deals with the formation of high-pressure areas—anticyclogenesis. Cyclogenesis is an umbrella term for several different processes, all of which result in the development of some sort of cyclone. Meteorologists use the term "cyclone" where circular pressure systems flow in the direction of the Earth's rotation, which normally coincides with areas of low pressure. The largest low-pressure systems are cold-core polar cyclones and extratropical cyclones which lie on the synoptic scale. Warm-core cyclones such as tropical cyclones, mesocyclones, and polar lows lie within the smaller mesoscale.
Low-pressure area | Formation
The opposite of cyclogenesis is cyclolysis.
Cyclogenesis | Introduction
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 the RFD reaching the ground.
Cyclogenesis | Tornadoes
There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to sustain a low pressure center, a preexisting low level focus or disturbance, and low vertical wind shear. While these conditions are necessary for tropical cyclone formation, they do not guarantee that a tropical cyclone will form.
Tropical cyclogenesis | Requirements for tropical cyclone formation
Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear. Cyclolysis is the opposite of cyclogenesis, and is the high-pressure system equivalent, which deals with the formation of high-pressure areas—Anticyclogenesis.
Cyclone | Formation
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 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.
Cyclogenesis | Waterspouts
Since 1984, Colorado State University has been issuing seasonal tropical cyclone forecasts for the north Atlantic basin, with results that are better than climatology. The university has found several statistical relationships for this basin that appear to allow long range prediction of the number of tropical cyclones. Since then, numerous others have followed in the university's steps, with some organizations issuing seasonal forecasts for the northwest Pacific and the Australian region. The predictors are related to regional oscillations in the global climate system: the Walker circulation which is related to the El Niño-Southern Oscillation; the North Atlantic oscillation (NAO); the Arctic oscillation (AO); and the Pacific North American pattern (PNA).
Tropical cyclogenesis | Seasonal forecasts
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 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.
Cyclogenesis | Tropical cyclones
Tornadoes exist on 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 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.
Cyclogenesis | Tornadoes
Minima in the wind pattern aloft are favorable for tropical cyclogenesis. Maxima in the wind pattern at various levels of the atmosphere show locations of jet streams. Areas colder than indicate a lack of significant icing, as long as there is no active thunderstorm activity.
Weather map | Constant pressure charts
Areas within approximately ten degrees latitude of the equator do not experience a significant Coriolis Force, a vital ingredient in tropical cyclone formation. However, a few tropical cyclones have been observed forming within five degrees of the equator.
Tropical cyclogenesis | Near the Equator
In general, westerly wind increases associated with the Madden–Julian oscillation lead to increased tropical cyclogenesis in all basins. As the oscillation propagates from west to east, it leads to an eastward march in tropical cyclogenesis with time during that hemisphere's summer season. There is an inverse relationship between tropical cyclone activity in the western Pacific basin and the north Atlantic basin, however. When one basin is active, the other is normally quiet, and vice versa. The main cause appears to be the phase of the Madden–Julian oscillation, or MJO, which is normally in opposite modes between the two basins at any given time.
Tropical cyclogenesis | Influence of the MJO
The Norwegian cyclone model 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.
Cyclogenesis | Norwegian cyclone model
Two of these storms reached tropical storm and subtropical storm intensity in August 2002 and September 2005 respectively.
Tropical cyclogenesis | Mediterranean and Black Seas
There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the 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. While these conditions are necessary for tropical cyclone formation, they do not guarantee that a tropical cyclone will form. Normally, an ocean temperature of 26.5 °C (79.7 °F) spanning through a depth of at least is considered the minimum to maintain the special mesocyclone that is the tropical cyclone. These warm waters are needed to maintain the warm core that fuels tropical systems.
Typhoon | Genesis
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 the warm air mass is pushed upwards into a trough of warm air aloft, which is also known as a trowal (a trough of warm air aloft). All developing low pressure areas share one important aspect, that of upward vertical motion within the troposphere.
Cyclogenesis | Modes of development
Tropical activity is also extremely rare in the Great Lakes. However, a storm system that appeared similar to a subtropical or tropical cyclone formed in 1996 on Lake Huron. The system developed an eye-like structure in its center, and it may have briefly been a subtropical or tropical cyclone.
Tropical cyclogenesis | Elsewhere
Extratropical cyclones form along linear bands of temperature/dewpoint gradient with significant vertical wind shear, and are thus classified as baroclinic cyclones. Initially, cyclogenesis, or low pressure formation, occurs along frontal zones near 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 the cyclone (a low pressure system).
Extratropical cyclone | Cyclogenesis
Tropical cyclones are known to form even when normal conditions are not met. For example, cooler air temperatures at a higher altitude (e.g., at the 500 hPa level, or 5.9 km) can lead to tropical cyclogenesis at lower water temperatures, as a certain lapse rate is required to force the atmosphere to be unstable enough for convection. In a moist atmosphere, this lapse rate is 6.5 °C/km, while in an atmosphere with less than 100% relative humidity, the required lapse rate is 9.8 °C/km. At the 500 hPa level, the air temperature averages −7 °C (18 °F) within the tropics, but air in the tropics is normally dry at this height, giving the air room to wet-bulb, or cool as it moistens, to a more favorable temperature that can then support convection.
Sea surface temperature | Tropical cyclones
Normally, an ocean temperature of 26.5 °C (79.7 °F) spanning through at least a 50-metre depth is considered the minimum to maintain a tropical cyclone. These warm waters are needed to maintain the warm core that fuels tropical systems. This value is well above 16.1 °C (60.9 °F), the global average surface temperature of the oceans. Tropical cyclones are known to form even when normal conditions are not met. For example, cooler air temperatures at a higher altitude (e.g., at the 500 hPa level, or 5.9 km) can lead to tropical cyclogenesis at lower water temperatures, as a certain lapse rate is required to force the atmosphere to be unstable enough for convection.
Tropical cyclogenesis | Warm waters, instability, and mid-level moisture
A 2015 simulation of tropical cyclogenesis did not show increased tropical cyclone genesis in the Pliocene, although the simulation did not obtain a decreased East-West Pacific temperature gradient and it did obtain increased tropical cyclone activity in the parts of the Central Pacific most critical for the occurrence of Cyclonic Niño effects. A 2018 simulation implied that adding tropical cyclone mixing induced climate phenomena to simulations of mid-Piacenzian climate can in some aspects improve and in others reduce the match between the modelled climate and the climate reconstructed from paleoclimate data. A 2019 study concluded that tropical cyclone activity in the Western Pacific is correlated to El Niño-associated temperature anomalies months later.
Cyclonic Niño | Subsequent findings
Whether it be a depression in the intertropical convergence zone (ITCZ), a tropical wave, a broad surface front, or an outflow boundary, a low level feature with sufficient vorticity and convergence is required to begin tropical cyclogenesis. Even with perfect upper level conditions and the required atmospheric instability, the lack of a surface focus will prevent the development of organized convection and a surface low. Tropical cyclones can form when smaller circulations within the Intertropical Convergence Zone merge.
Tropical cyclogenesis | Low level disturbance
The existence of a significant Coriolis force allows the developing vortex to achieve gradient wind balance. This is a balance condition found in mature tropical cyclones that allows latent heat to concentrate near the storm core; this results in the maintenance or intensification of the vortex if other development factors are neutral.
Tropical cyclogenesis | Coriolis force
Areas farther than 30 degrees from the equator (except in the vicinity of a warm current) are not normally conducive to tropical cyclone formation or strengthening, and areas more than 40 degrees from the equator are often very hostile to such development. The primary limiting factor is water temperatures, although higher shear at increasing latitudes is also a factor. These areas are sometimes frequented by cyclones moving poleward from tropical latitudes. On rare occasions, such as Pablo in 2019, Alex in 2004, Alberto in 1988, and the 1975 Pacific Northwest hurricane, storms may form or strengthen in this region. Typically, tropical cyclones will undergo extratropical transition after recurving polewards, and typically become fully extratropical after reaching 45–50˚ of latitude.
Tropical cyclogenesis | Middle latitudes
Anticyclogenesis is the development or strengthening of an anticyclonic circulation in the atmosphere. It is the opposite of anticyclolysis (the dissolution or weakening of an anticyclone) and has a cyclonic equivalent known as cyclogenesis. Anticyclones are alternatively referred to as high pressure systems.
Anticyclogenesis | Introduction
In smaller systems, the development of a significant mesoscale convective complex in a sheared environment can send out a large enough outflow boundary to destroy the surface cyclone. Moderate wind shear can lead to the initial development of the convective complex and surface low similar to the mid-latitudes, but it must relax to allow tropical cyclogenesis to continue.
Tropical cyclogenesis | Weak vertical wind shear
Weak tornadoes, known as landspouts, across eastern Colorado have been witnessed to develop in 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 | Waterspouts
An inverse relationship exists between tropical cyclone activity in the western north Pacific basin and the north Atlantic basin, however. When one basin is active, the other is normally quiet, and vice versa. The main reason for this appears to be the phase of the MJO, which is normally in opposite modes between the two basins at any given time. While this relationship appears robust, the MJO is one of many factors that contribute to the development of tropical cyclones. For example, sea surface temperatures must be sufficiently warm and vertical wind shear must be sufficiently weak for tropical disturbances to form and persist.
Madden–Julian oscillation | Influence on tropical cyclogenesis
In the North Indian basin, storms are most common from April to December, with peaks in May and November. In the Southern Hemisphere, tropical cyclone activity generally begins in early November and generally ends on April 30. Southern Hemisphere activity peaks in mid-February to early March. Virtually all the Southern Hemisphere activity is seen from the southern African coast eastward, toward South America. Tropical cyclones are rare events across the south Atlantic Ocean and the far southeastern Pacific Ocean.
Tropical cyclogenesis | Times of formation
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 tend to be 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 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.
Extratropical cyclone | Cyclogenesis
Finally, looking at a cross section (y-z) through the confluent flow, using Q-vectors (Q pointing toward upward motion), on the warm side (bottom of confluent schematic), there is upward motion and on the other hand, the cold side (top of confluent schematic), there is downward motion. The cross-section points out convergence (arrows pointing towards each other) associated with tightening of horizontal temperature gradient. Conversely, divergence is noticed (arrows point away from each other), associated with stretching horizontal temperature gradient. Since the strength of the ageostrophic flow is proportional to temperature gradient, the ageostrophic tightening tendencies grow rapidly after the initial geostrophic intensification.
Frontogenesis | Elements of Frontogenesis
Cyclones have also been seen on extraterrestrial planets, such as Mars, Jupiter, and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream. Weather fronts mark the boundary between two masses of air of different temperature, humidity, and densities, and are associated with the most prominent meteorological phenomena.
Cyclone | Introduction
It has also been noted that when the monsoon trough lies near 20 degrees north latitude in the Pacific, the frequency of tropical cyclones is 2 to 3 times greater than when it lies closer to 10 degrees north.
Monsoon trough | In tropical cyclogenesis
If the associated jet stream is stronger than normal and there is colder than normal air in place in central Canada to provide a greater than normal temperature contrast with Gulf of Mexico moisture drawn northward by the developing panhandle low, surface cyclogenesis can be particularly energetic and cause a great swath of heavy snow to develop and blanket a large portion of the American Great Plains and upper-midwestern states in conjunction with very strong winds, the combination of which exceeds blizzard criteria. Over the Great Lakes, the interaction of these storms with the lakes can amplify windspeeds causing extreme heavy sometimes localized snowfall, thundersnow and often shoreline erosion.
Panhandle hook | Formation
Explosive cyclogenesis (also referred to as a weather bomb, meteorological bomb, explosive development, bomb cyclone or bombogenesis) is the rapid deepening of an extratropical cyclonic low-pressure area. The change in pressure needed to classify something as explosive cyclogenesis is latitude dependent. For example, at 60° latitude, explosive cyclogenesis occurs if the central pressure decreases by 24 mbar (hPa) or more in 24 hours. This is a predominantly maritime, winter event, but also occurs in continental settings, even in the summer. This process is the extratropical equivalent of the tropical rapid deepening. Although their cyclogenesis is totally different from that of tropical cyclones, bomb cyclones can produce winds of 74–95 mph, the same order as the first categories of the Saffir-Simpson scale and give heavy precipitation.
Explosive cyclogenesis | Introduction
Over the year, 45 cyclones on average in the Northern Hemisphere and 26 in the Southern Hemisphere develop explosively, mostly in the respective hemisphere's winter time. Less seasonality has been noticed in bomb cyclogenesis occurrences in the Southern Hemisphere.
Explosive cyclogenesis | Regions and motion
The climate is generally dry and mild, but with the exception of Naxos the soil is not very fertile; agricultural produce includes wine, fruit, wheat, olive oil, and tobacco. Lower temperatures are registered in higher elevations and these areas do not usually see wintry weather.
Cyclades | Geography
The term "weather bomb" is popularly used in New Zealand to describe dramatic or destructive weather events. Rarely are the events actual instances of explosive cyclogenesis, as the rapid deepening of low pressure areas is rare around New Zealand. This use of "bomb" may lead to confusion with the more strictly defined meteorological term. In Japan, the term is used both academically and commonly to refer to an extratropical cyclone which meets the meteorological "bomb" conditions. The term "bomb" may be somewhat controversial. When European researchers protested that it was a rather warlike term, Fred Sanders, the coauthor of the paper which introduced the meteorological usage quipped: "So why are you using the term 'front'?".
Explosive cyclogenesis | Other uses of "weather bomb"
Most studies based on anatomy have supported the vertebrate hypothesis, while most molecular phylogenies have supported the cyclostome hypothesis.
Cyclostomata | Possible external relationships
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 a continent, such as extratropical cyclones, with dimensions of across. The mesoscale is the next smaller scale, and often is divided into two ranges: meso-alpha phenomena range from across (the realm of the tropical cyclone), while meso-beta phenomena range from across (the scale of the mesocyclone). The microscale is the smallest of the meteorological scales, with a size under (the scale of tornadoes and waterspouts).
Cyclogenesis | Meteorological scales
This is based on the definition, standardised by Bergeron, for explosive development of a cyclone at 60°N as deepening by 24 mb in 24 hours. Sanders and Gyakum noted that an equivalent intensification is dependent on latitude: at the poles this would be a drop in pressure of 28 mb/24 hours, while at 25 degrees latitude it would be only 12 mb/24 hours. All these rates qualify for what Sanders and Gyakum called "1 bergeron".
Explosive cyclogenesis | History
Cyclomorphosis (also known as seasonal polyphenism) is the name given to the occurrence of cyclic or seasonal changes in the phenotype of an organism through successive generations. It occurs in small aquatic invertebrates that reproduce by parthenogenesis and give rise to several generations annually. It occurs especially in marine planktonic animals, and is thought to be caused by the epigenetic effect of environmental cues on the organism, thereby altering the course of their development.
Cyclomorphosis | Introduction
Except where noted otherwise, data relate to standard ambient temperature and pressure.
Cyclohexane (data page) | References
Cooler air temperatures at a higher altitude (e.g., at the 500 hPa level, or 5.9 km) can lead to tropical cyclogenesis at lower water temperatures than normal, as a certain lapse rate is required to force the atmosphere to be unstable enough for convection. In a moist atmosphere, this lapse rate is 6.5 °C/km (19 °F/mi), while in an atmosphere with less than 100% relative humidity, the required lapse rate is 9.8 °C/km (29 °F/mi). A recent example of a tropical cyclone that maintained itself over cooler waters was Alex of the 2016 Atlantic hurricane season, which became a hurricane over waters at only .
Cold-core low | Importance to tropical cyclones
A monsoon trough is a significant genesis region for tropical cyclones. Vorticity-rich low level environments, with significant low level spin, lead to a better than average chance of tropical cyclone formation due to their inherent rotation. This is because a pre-existing near-surface disturbance with sufficient spin and convergence is one of the six requirements for tropical cyclogenesis. There appears to be a 15- to 25-day cycle in thunderstorm activity associated with the monsoon trough, which is roughly half the wavelength of the Madden–Julian oscillation, or MJO. This mirrors tropical cyclone genesis near these features, as genesis clusters in 2–3 weeks of activity followed by 2–3 weeks of inactivity.
Monsoon trough | In tropical cyclogenesis
Cyclostratigraphy is the study of astronomically forced climate cycles within sedimentary successions. Astronomical cycles are variations of the Earth's orbit around the sun due to the gravitational interaction with other masses within the solar system. Due to this cyclicity, solar irradiation differs through time on different hemispheres and seasonality is affected. These insolation variations have influence on Earth's climate and so on the deposition of sedimentary rocks. The main orbital cycles are precession with at present main periods of 19 and 23 kyr, obliquity with at present main periods of 41 kyr, and 1.2 Myr, and eccentricity with at present main periods of around 100 kyr, 405 kyr, and 2.4 Myr.
Cyclostratigraphy | Introduction
Trailing upper cyclones and upper troughs can cause additional outflow channels and aid in the intensification process. Developing tropical disturbances can help create or deepen upper troughs or upper lows in their wake due to the outflow jet emanating from the developing tropical disturbance/cyclone. There are cases where large, mid-latitude troughs can help with tropical cyclogenesis when an upper-level jet stream passes to the northwest of the developing system, which will aid divergence aloft and inflow at the surface, spinning up the cyclone. This type of interaction is more often associated with disturbances already in the process of recurvature.
Tropical cyclogenesis | Favorable trough interactions
Vertical wind shear of less than 10 m/s (20 kt, 22 mph) between the surface and the tropopause is favored for tropical cyclone development. A weaker vertical shear makes the storm grow faster vertically into the air, which helps the storm develop and become stronger. If the vertical shear is too strong, the storm cannot rise to its full potential and its energy becomes spread out over too large of an area for the storm to strengthen. Strong wind shear can "blow" the tropical cyclone apart, as it displaces the mid-level warm core from the surface circulation and dries out the mid-levels of the troposphere, halting development.
Tropical cyclogenesis | Weak vertical wind shear
The same process promotes the development of a low level jet to the east of the dryline. During the daytime, if heating and/or convergence are sufficient, the cap can be broken, resulting in convective clouds.
Dry line | Associated weather
Phylogeny based on the work of the following works
Cypriniformes | Phylogeny
Simulations using the CESM climate model conducted in 2018 showed a reduced temperature gradient between the East and West Pacific and a deeper thermocline in response to tropical cyclone driven mixing and anomalous eastward sea currents in the Pacific; this is accompanied by a cooling of the areas where mixing is strongest and a warming of the Eastern Pacific. There are also effects on the East Asian monsoon such as a stronger winter monsoon but in the simulations the background climate of the Piacenzian was more significant than the tropical cyclone effects.
Cyclonic Niño | Computer simulations concerning the Pliocene
Several studies, including and have compiled box and gravity cores in the North Pacific analyzing them for palynological content to determine the distribution of dinocysts and their relationships with sea surface temperature, salinity, productivity and upwelling. Similarly, and use a box core at 576.5 m of water depth from 1992 in the central Santa Barbara Basin to determine oceanographic and climatic changes during the past 40 kyr in the area.
Proxy (climate) | Dinoflagellate cysts
A minimum distance of from the equator (about 4.5 degrees from the equator) is normally needed for tropical cyclogenesis. The Coriolis force imparts rotation on the flow and arises as winds begin to flow in toward the lower pressure created by the pre-existing disturbance. In areas with a very small or non-existent Coriolis force (e.g. near the Equator), the only significant atmospheric forces in play are the "pressure gradient force" (the pressure difference that causes winds to blow from high to low pressure) and a smaller friction force; these two alone would not cause the large-scale rotation required for tropical cyclogenesis.
Tropical cyclogenesis | Coriolis force
"Surface Processes and Landforms", Don J. Easterbrook. Prentice Hall, New Jersey, 1999.
Cyclopean stairs | References
As pelagic creatures, cyclogygids were not bound to shallow waters surrounding continents and islands. At the time they lived, continents weren't blocking the exchange between different parts of the ocean, and this means they probably had large distributions, comprising one or more climate zones worldwide. "Cyclopyge" is well known from the Czech Republic, Morocco, England, Sweden, Canada (Newfoundland) and the United States.
Cyclopyge (trilobite) | Distribution
A reduction of temperature must at once occur, accompanied by the usual phenomena of showers. The chief agency in this transformation is agriculture. To be more concise. Rain follows the plow."
Charles Dana Wilber | Introduction
Tropical cyclogenesis is extremely rare in the far southeastern Pacific Ocean, due to the cold sea-surface temperatures generated by the Humboldt Current, and also due to unfavorable wind shear; as such, there are no records of a tropical cyclone impacting western South America. But in mid-2015, a rare subtropical cyclone was identified in early May relatively close to Chile. This system was unofficially dubbed "Katie" by researchers. Another subtropical cyclone was identified at 77.8 degrees longitude in May 2018, just off the coast of Chile. Vortices have been reported off the coast of Morocco in the past. However, it is debatable if they are truly tropical in character.
Tropical cyclogenesis | Elsewhere
Clutch size, hatching success, and egg production rate are negatively correlated with temperature. The proportion of breeding females is significantly related to the concentration of chlorophyll "a".
Pseudocalanus elongatus | Life cycle and reproduction
Molecular and biochemical evidence suggests that mitochondria are related to Rickettsiales proteobacteria (in particular, the SAR11 clade, or close relatives), and that chloroplasts are related to nitrogen-fixing filamentous cyanobacteria.
Symbiogenesis | From endosymbionts to organelles
Tropical cyclones typically began to weaken immediately following and sometimes even prior to landfall as they lose the sea fueled heat engine and friction slows the winds. However, under some circumstances, tropical or subtropical cyclones may maintain or even increase their intensity for several hours in what is known as the brown ocean effect. This is most likely to occur with warm moist soils or marshy areas, with warm ground temperatures and flat terrain, and when upper level support remains conducive.
Tropical cyclogenesis | Inland intensification
Several curves are related to the cycloid. All these curves are roulettes with a circle rolled along another curve of uniform curvature. The cycloid, epicycloids, and hypocycloids have the property that each is similar to its evolute. If "q" is the product of that curvature with the circle's radius, signed positive for epi- and negative for hypo-, then the curve:evolute similitude ratio is 1 + 2"q". The classic Spirograph toy traces out hypotrochoid and epitrochoid curves.
Cycloid | Related curves
In meteorology, an occluded front is a weather front formed during the process of cyclogenesis, when a cold front overtakes a warm front. When this occurs, the warm air is separated (occluded) from the cyclone center at the Earth's surface. The point where the warm front and the occluded front meet (and consequently the nearest location of warm air to the center of the cyclone) is called the "triple point". The trowal (short for TROugh of Warm air ALoft) is the projection on the Earth's surface of the trough of warm air aloft formed during the occlusion process of the depression.
Occluded front | Introduction
Climate is sometimes modeled as a stochastic process but this is generally accepted as an approximation to processes that are otherwise too complicated to analyze.
Climatology | Methods
The cytological uniformity within each group, while providing circumstantial evidence that they descended from a single ancestor and simplifying interpretations of cladistic analyses, provides neither positive nor negative support for a possible role of polyploidy in evolving the giant-rosette growth-form.
Dendrosenecio | Cytological uniformity
The northwestern Mediterranean and the Gulf of Genoa in particular, are not only a transition area for passing cyclones, but are frequently areas of cyclogenesis. Low pressure areas move into or are formed as a result of North Atlantic air entering the Mediterranean Sea between the Alps and the Massif Central, via the Rhone Valley, or via the Carcassonne gap between the Pyrenees and Massif Central. This cold and moist air enters the Mediterranean basin, and is deflected by the high mountains of northwest Corsica, which divert the air mass to the northeast, triggering cool and wet Libeccio winds in response into the Ligurian Sea, which in turn hit the western Apennines located in the immediate vicinity of the sea.
Genoa low | Cyclogenesis
Even though only a minority of the bombs become so strong, some weaker ones have also caused significant damage.
Explosive cyclogenesis | Introduction
Worldwide, tropical cyclone activity peaks in late summer when water temperatures are warmest. Each basin, however, has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active. In the North Atlantic, a distinct hurricane season occurs from June 1 through November 30, sharply peaking from late August through October. The statistical peak of the North Atlantic hurricane season is September 10. The Northeast Pacific has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and a peak in early September.
Tropical cyclogenesis | Times of formation
Several atmospheric features and climate drivers which are typically conducive to tropical cyclogenesis were present in Australian longitudes during March 2018. In early- to mid-March, a monsoon trough developed to the north of Australia, stretching from the eastern Indonesian archipelago to the northern Coral Sea. Although associated convective activity decreased somewhat as the monsoon trough began to weaken, this was offset by the interaction of significant cross-equatorial flow from the Northern Hemisphere with a large area of strong southeasterly wind from the Australian continent. The convergence of these winds provided ample rotational energy for the development of any low-pressure systems in the region.
Cyclone Nora | Meteorological history
The phylogeny of Capitosauroidea according to Witzmann "et al." (2016). The phylogeny of the genus "Cyclotosaurus" according to Witzmann et al. (2016). See also alternative phylogenies from 2017 with the description of "C. naraserluki."
Cyclotosaurus | Phylogeny
Frontogenesis is a meteorological process of tightening of horizontal temperature gradients to produce fronts. In the end, two types of fronts form: cold fronts and warm fronts. A cold front is a narrow line where temperature decreases rapidly. A warm front is a narrow line of warmer temperatures and essentially where much of the precipitation occurs. Frontogenesis occurs as a result of a developing baroclinic wave. According to Hoskins & Bretherton (1972, p. 11), there are eight mechanisms that influence temperature gradients: horizontal deformation, horizontal shearing, vertical deformation, differential vertical motion, latent heat release, surface friction, turbulence and mixing, and radiation.
Frontogenesis | Introduction
The horizontal shear and horizontal deformation direct to concentrate the pole-equator temperature gradient over a large synoptic scale (1000 km). The quasi-geostrophic equations fail in the dynamics of frontogenesis because this weather phenomenon is of smaller scale compared to the Rossby radius; so semigeostrophic theory is used. Generally, Rossby number—ratio of inertial to coriolis terms—is used to formulate a condition of geostrophic flow. Across the front, the Rossby number is on the order of udu/dx/fv = (10 m/s)^2/(1000 km)/(1e-4 s-1)/(1 m/s) = 1; this shows we cannot ignore the inertial term (one must take into account the ageostrophic wind). Along the front, the Rossby number is on the order of udv/dx/fu = (10 m/s)/(1000 km)*(1e-4 s-1)*(10 m/s) = 0.01, which means it is in geostrophic and thermal wind balance.
Frontogenesis | Elements of Frontogenesis
During frontogenesis, the temperature gradient tightens and as a result, the thermal wind becomes imbalanced. To maintain balance, the geostrophic wind aloft and below adjust, such that regions of divergence/convergence form. Mass continuity would require a vertical transport of air along the cold front where there is divergence (lowered pressure). Although this circulation is described by a series of processes, they are actually occurring at the same time, observable along the front as a thermally direct circulation. There are several factors that influence the final shape and tilt of the circulation around the front, ultimately determining the type and location of clouds and precipitation.
Frontogenesis | Development of the Frontogenetical Circulation
Given the direction of the winds around an anticyclonic circulation and the fact that weather systems move from west to east: Surface ridges, just like highs, generate fair weather because they develop under wind convergence in the negative vorticity advection zone ahead of the upper level ridge. The vertical downward air motion then gives a divergence of the winds near the surface. The subsidence of the air causes a warming in the column compared to the previous environment and therefore a drying of it because its relative humidity decreases, which has the effect of clearing the sky.
Ridge (meteorology) | Related weather
A 2010 climate simulation indicated that increasing the average winds of tropical cyclones induced warming in the Eastern Pacific and cooling in the Western Pacific, consistent with an El Niño like response; there is also strengthening of the Hadley cell of the atmospheric circulation and some heat is transported out of the tropics by the western boundary currents. Similar East-West temperature changes were obtained in other 2010 and 2011 studies; in the latter high latitude temperatures warmed by about and a global warming by and the former indicated that the heat is transported at depths of about towards the Equatorial Undercurrent which then brings it into the Eastern Pacific.
Cyclonic Niño | Subsequent findings
This reaction shows a swelling in the related tissues, making fertilization evident. From these areas oogenesis occurs, followed by the maturation of the oocytes.
Chondrocladia lyra | Reproduction
But the consequence of atypical cell and nuclear morphology in other tissues is unknown.
Pleomorphism (cytology) | Introduction
Climate models, sea surface temperatures reconstructed with alkenones and sometimes even reconstructions from foraminifera in the same drill core have yielded conflicting results. Coral-based reconstructions have been used in a 2011 study to infer that the El Niño Southern Oscillation already existed during the Pliocene, including discrete El Niño events.
Cyclonic Niño | Pliocene
A cyclostationary process is a signal having statistical properties that vary cyclically with time. A cyclostationary process can be viewed as multiple interleaved stationary processes. For example, the maximum daily temperature in New York City can be modeled as a cyclostationary process: the maximum temperature on July 21 is statistically different from the temperature on December 20; however, it is a reasonable approximation that the temperature on December 20 of different years has identical statistics. Thus, we can view the random process composed of daily maximum temperatures as 365 interleaved stationary processes, each of which takes on a new value once per year.
Cyclostationary process | Introduction
The Eady Model yields stable and unstable modes. Unstable modes have height, vorticity, vertical velocity, and several other atmospheric parameters with contours that tilt westward with height, though temperature contours tilt eastward with height for unstable modes. A poleward heat flux is observed in unstable modes, yielding the positive feedback necessary for cyclogenesis. Low pressure, high vorticity regions are then “stretched”, and high pressure and low vorticity regions are “squashed”, yielding higher and lower vorticity, respectively. In contrast, the opposite is observed in decaying modes: height, vorticity, etc. contours tilt eastward with height, except temperature which tilts westward with height.
Eady Model | Results
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 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 the low via its trailing cold front, and warmer air will push poleward low via the warm front.
Cyclogenesis | Modes of development