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).
Meteorological scales
Cyclogenesis
Cyclogenesis | Meteorological scales
It  covers a portion of a continent, such as extratropical cyclones, with dimensions of across Synoptic scale systems cover a portion of a continent, such as extratropical cyclones, with dimensions of across. It covers a portion of a continent, such as extratropical cyclones, with dimensions of across Synoptic scale systems cover a portion of a continent, such as extratropical cyclones, with dimensions of across.
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
It is the opposite of cyclolysis
assistant
which scaled are used to measure it?
user
The macroscale, the synoptic scale, the mesoscale, and the microscale
assistant
what does the first one do?
user
It deals with systems with global size, such as the Madden–Julian oscillation
assistant
who invented the second one?
user
Sorry. I cannot find the answer based on the context.
assistant
what is the function of the third one?
user
It deals with  the study of weather systems smaller than synoptic scale systems but larger than microscale and storm-scale cumulus systems
assistant
is the fourth one the opposite of the first one?
user
Yes, it is smallest of the meteorological scales
assistant
what results does the second one give?
user
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
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
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
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
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
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
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
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
The opposite of cyclogenesis is cyclolysis.
Cyclogenesis | Introduction
Such upward motions decrease the mass of local atmospheric columns of air, which lower surface pressure.
Cyclogenesis | Modes of development
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
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
These warm core cyclones tend to form over the oceans between 10 and 30 degrees of the equator.
Cyclogenesis | Tropical cyclones
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
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
The majority of extratropical cyclones tend to restrengthen after completing the transition period.
Tropical cyclogenesis | Middle latitudes
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
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
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
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
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
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
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
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
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
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 synoptic scale in meteorology (also known as large scale or cyclonic scale) is a horizontal length scale of the order of 1000 kilometers (about 620 miles) or more. This corresponds to a horizontal scale typical of mid-latitude depressions (e.g., extratropical cyclones). Most high- and low-pressure areas seen on weather maps (such as surface weather analyses) are synoptic-scale systems, driven by the location of Rossby waves in their respective hemisphere. Low-pressure areas and their related frontal zones occur on the leading edge of a trough within the Rossby wave pattern, while high-pressure areas form on the back edge of the trough.
Synoptic scale meteorology | Introduction
Subtropical cyclones are of intermediate size. Cyclogenesis can occur at various scales, from the microscale to the synoptic scale. Larger-scale troughs, also called Rossby waves, are synoptic in scale. Shortwave troughs embedded within the flow around larger scale troughs are smaller in scale, or mesoscale in nature. Both Rossby waves and shortwaves embedded within the flow around Rossby waves migrate equatorward of the polar cyclones located in both the Northern and Southern hemispheres. All 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 lowers surface pressure.
Low-pressure area | Formation
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
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
Two of these storms reached tropical storm and subtropical storm intensity in August 2002 and September 2005 respectively.
Tropical cyclogenesis | Mediterranean and Black Seas
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
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
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
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 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
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
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
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
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
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
A case study of the Manual of Synoptic Satellite Meteorology featured by the Austrian Meteorological Institute (ZAMG) identified an area of secondary cyclogenesis which brought gusts in excess of 90 km/h to Northern France, Belgium and Southwestern Germany. The system formed in the wake of Lothar, and crossed Europe before the arrival of the later Cyclone Martin. The identification of this secondary area and its frontal systems contrasts with the analysis of the German Weather Service which suggested that solely a 'trough line' crossed Germany.
Cyclone Lothar | Lothar successor
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
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
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
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
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
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
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
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
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 the system. When pressures fall more than 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 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 is best. The stronger the upper level divergence over the cyclone, the deeper the cyclone can become.
Extratropical cyclone | Cyclogenesis
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
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
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
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 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
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
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
Kerry Emanuel created a mathematical model around 1988 to compute the upper limit of tropical cyclone intensity based on sea surface temperature and atmospheric profiles from the latest global model runs. Emanuel's model is called the "maximum potential intensity", or MPI. Maps created from this equation show regions where tropical storm and hurricane formation is possible, based upon the thermodynamics of the atmosphere at the time of the last model run. This does not take into account vertical wind shear.
Tropical cyclogenesis | Role of Maximum Potential Intensity (MPI)
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
Meteorological & Geoastrophysical Abstracts is a scholarly bibliographic database that covers meteorology, climatology, atmospheric chemistry and physics, astrophysics, hydrology, glaciology, physical oceanography and environmental sciences.
Meteorological &amp; Geoastrophysical Abstracts | Introduction
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
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
Misoscale is an unofficial scale of meteorological phenomena that ranges in size from 40 meters to about 4 kilometers. This scale was proposed by Ted Fujita, the father of the Fujita scale, to classify phenomenon of the order of the rotation within a thunderstorm, the scale of the funnel cloud of a tornado, and the size of the swath of destruction of a microburst. It is a subdivision of the microscale.
Misoscale meteorology | Introduction
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
This effect can take up to a century to set in and its strength is dependent on the exact pattern of ocean mixing. It is also subject to positive feedback, as the warming of the eastern Pacific in turn increases tropical cyclone activity; eventually a climate state featuring a permanent El Niño and a weaker El Niño Southern Oscillation can arise. During the mid-Piacenzian where carbon dioxide concentrations were close to present-day levels, Earth was about warmer than present and simulations indicate that tropical cyclones were more intense; the modelled distribution of tropical cyclones however was different from the one reconstructed for other stages of the Pliocene.
Cyclonic Niño | Computer simulations concerning the Pliocene
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
A majority of Mediterranean tropical cyclones (tropical cyclogenesis) form over two separate regions. The first, more conducive for development than the other, encompasses an area of the western Mediterranean bordered by the Balearic Islands, southern France, and the shorelines of the islands of Corsica and Sardinia. The second identified region of development, in the Ionian Sea between Sicily and Greece and stretching south to Libya, is less favorable for tropical cyclogenesis. An additional two regions, in the Aegean and Adriatic seas, produce fewer medicanes, while activity is minimal in the Levantine region. The geographical distribution of Mediterranean tropical-like cyclones is markedly different from that of other cyclones, with the formation of regular cyclones centering on the Pyrenees and Atlas mountain ranges, the Gulf of Genoa, and the island of Cyprus in the Ionian Sea.
Mediterranean tropical-like cyclone | Climatology
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
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
The database is produced by the American Meteorological Society, and is published by DIALOG and Cambridge Scientific Abstracts.
Meteorological &amp; Geoastrophysical Abstracts | Production and Access
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 minimum distance of 500 km (300 mi) from the equator is normally needed for tropical cyclogenesis. Whether it be a depression in the Intertropical Convergence Zone (ITCZ) or monsoon trough, a broad surface front, or an outflow boundary, a low level feature with sufficient vorticity and convergence is required to begin tropical cyclogenesis. About 85 to 90 percent of Pacific typhoons form within the monsoon trough. 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. Vertical wind shear of less than 10 m/s (20 kn, 33 ft/s) between the ocean surface and the tropopause is required for tropical cyclone development.
Typhoon | Genesis
In the second week of June, a large cyclonic gyre developed in the western Caribbean Sea during a positive phase of the Madden–Julian oscillation. Convection was enhanced by two tropical waves, with the first emerging into the Atlantic Ocean from the west coast of Africa on June 4 and reached the gyre between June 14 and June 15. As early as June 13, the National Hurricane Center (NHC) anticipated that a broad low pressure area would develop in the northwestern Caribbean Sea, which had the potential for tropical cyclogenesis. The second tropical wave began interacting with the gyre on June 17, resulting in the development of a broad low pressure area later that day.
Tropical Storm Cindy (2017) | Meteorological history
1. Holton, J. R. (2004). An introduction to dynamic meteorology. (4 ed., Vol. 88, pp. 269–276). San Diego, CA: Academic Press. 2. Hoskins, B. J., & Bretherton, F. P. (1972). Atmospheric frontogenesis models: Mathematical formulation and solution. J. Atmos. Sci., 29, 11-13. 3. Martin, J. E. (2006). Mid-latitude atmospheric dynamics. (1 ed., pp. 189–194). England: Wiley.
Frontogenesis | References
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
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
However, the MJO also influences these conditions that facilitate or suppress tropical cyclone formation. The MJO is monitored routinely by both the USA National Hurricane Center and the USA Climate Prediction Center during the Atlantic hurricane (tropical cyclone) season to aid in anticipating periods of relative activity or inactivity.
Madden–Julian oscillation | Influence on tropical cyclogenesis
Cyclonic Niño is a climatological phenomenon that has been observed in climate models where tropical cyclone activity is increased. Increased tropical cyclone activity mixes ocean waters, introducing cooling in the upper layer of the ocean that quickly dissipates and warming in deeper layers that lasts considerably more, resulting in a net warming of the ocean. In climate simulations of the Pliocene, this net warming is then transported by ocean currents and part of it ends up in the Eastern Pacific, warming it relative to the Western Pacific and thus creating El Niño-like conditions. Reconstructed temperatures in the Pliocene have shown an El Niño-like pattern of ocean temperatures that may be explained by increased tropical cyclone activity and thus increased temperatures in the Eastern Pacific.
Cyclonic Niño | Introduction
Modelling with the CAM3 general circulation model has indicated that the number of tropical cyclones was much larger than today and their occurrence more extensive owing to higher sea surface temperatures and a weaker atmospheric circulation (the Hadley cell and Walker circulation) which results in less wind shear. Also, tropical cyclones last longer and occur throughout the year rather than being tied to specific reasons. This expansion of tropical cyclone activity would bring tropical cyclones within reach of zones of the ocean where sea currents below the surface transport water towards the Eastern Pacific. Tropical cyclones induce mixing of the sea surface waters; with a tenfold increase in ocean mixing within two bands 8–40° north and south of the equator – especially mixing occurring in the Central Pacific where tropical cyclone activity is low under present-day climate – heat would be introduced into these sea currents and eventually lead to a warming of the central and eastern Pacific Ocean similar to El Niño and a warming of the upwelling regions, with a warming of about in the zone of the East Pacific cold tongue.
Cyclonic Niño | Computer simulations concerning the Pliocene
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 large storms seen on the gas giants are considered analogous to Earth cyclones. However, this is an imperfect metaphor as expected, due to the large differences in sizes, temperature, and composition between Earth and the gas giants, and even between gas giants. Polar vortices were observed on Venus and Saturn. In turn, Earth's thinner atmosphere shows weaker polar vorticity and effects.
Comparative planetary science | Storms and cyclonic activity
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
Sea surface temperature affects the behavior of the Earth's atmosphere above, so their initialization into atmospheric models is important. While sea surface temperature is important for tropical cyclogenesis, it is also important in determining the formation of sea fog and sea breezes. Heat from underlying warmer waters can significantly modify an air mass over distances as short as to . For example, southwest of Northern Hemisphere extratropical cyclones, curved cyclonic flow bringing cold air across relatively warm water bodies can lead to narrow lake-effect snow (or sea effect) bands. Those bands bring strong localized precipitation, often in the form of snow, since large water bodies such as lakes efficiently store heat that results in significant temperature differences—larger than —between the water surface and the air above.
Sea surface temperature | Importance to the Earth's atmosphere
A combination of wind shear and a lack of tropical disturbances from the Intertropical Convergence Zone (ITCZ) makes it very difficult for the South Atlantic to support tropical activity. At least 5 tropical cyclones have been observed here such as— a weak tropical storm in 1991 off the coast of Africa near Angola, Hurricane Catarina, which made landfall in Brazil in 2004 at Category 2 strength, a smaller storm in January 2004 located east of Salvador, Brazil, and Tropical Storm Iba in March 2019. The January storm is thought to have reached tropical storm intensity based on scatterometer wind measurements.
Tropical cyclogenesis | South Atlantic
With low wind shear and diffluence aloft, the JTWC remarked the system had a fair chance of developing. While the system was organizing, the center crossed the equator to reach about 0.5° S, thus becoming an anticyclonic circulation in the southern hemisphere. This was unusual, as the Coriolis effect is nonexistent along the equator—the Coriolis effect refers to planetary vorticity, which provides the spin in a cyclone. The JTWC later assessed the system as remaining in the northern hemisphere, reaching as far south as 0.7° N, or about 80 km (50 mi) from the equator. After the circulation organized further beneath the convection, the JTWC issued another TCFA at 0300 UTC on November 28.
Cyclone Agni | Meteorological history
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
On May 24, the NHC first discussed the possibility of tropical cyclogenesis due to a broad area of low pressure that was forecast to form off the coast of El Salvador and its associated tropical wave. The tropical wave tracked generally westward across the Caribbean Sea for several days: crossing over Panama and entering the Eastern Pacific basin on May 26. At this point, the NHC considered the disturbance to have a high chance of formation over the next 5 days. Low pressure developed within the disturbance a day later, in association with a broad cyclonic circulation that was enhanced by a Central American gyre on May 27.
Tropical Storm Amanda (2020) | Meteorological history
The possibility of tropical cyclogenesis from a tropical disturbance south of Mexico was first mentioned by the National Hurricane Center (NHC) on July 6. A westward-moving tropical wave crossed Central America and entered the Eastern Pacific on July 8. The next day, the wave spawned a weak area of low pressure while south of Guatemala. On July 10, the disturbance quickly organized, with convection, or thunderstorms, more concentrated near the center of the low. Early on July 11, satellite images showed that the disturbance was consolidating into a tropical depression. Consequently, at 12:00 UTC, the NHC declared the system Tropical Depression Five-E while located roughly 345 mi (555 km) south-southeast of Acapulco, Mexico.
Hurricane Dolores (2015) | Meteorological history
Even though only a minority of the bombs become so strong, some weaker ones have also caused significant damage.
Explosive cyclogenesis | Introduction
Synoptic scale meteorology predicts atmospheric changes at scales up to 1000 km and 10 sec (28 days), in time and space. At the synoptic scale, the Coriolis acceleration acting on moving air masses (outside of the tropics) plays a dominant role in predictions. The phenomena typically described by synoptic meteorology include events such as extratropical cyclones, baroclinic troughs and ridges, frontal zones, and to some extent jet streams. All of these are typically given on weather maps for a specific time. The minimum horizontal scale of synoptic phenomena is limited to the spacing between surface observation stations.
Meteorology | Synoptic scale
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 precipitation areas occur near frontal zones. The word "synoptic" is derived from the Greek word (""), meaning "seen together". The Navier–Stokes equations applied to atmospheric motion can be simplified by scale analysis in the synoptic scale. It can be shown that the main terms in horizontal equations are Coriolis force and pressure gradient terms; therefore, one can use geostrophic approximation. In vertical coordinates, the momentum equation simplifies to the hydrostatic equilibrium equation.
Synoptic scale meteorology | Introduction
The above equations are limited in many regards. For example, the geometry of the separator is not considered, the particles are assumed to achieve a steady state and the effect of the vortex inversion at the base of the cyclone is also ignored, all behaviours which are unlikely to be achieved in a cyclone at real operating conditions. More complete models exist, as many authors have studied the behaviour of cyclone separators., simplified models allowing a quick calculation of the cyclone, with some limitations, have been developed for common applications in process industries. Numerical modelling using computational fluid dynamics has also been used extensively in the study of cyclonic behaviour.
Cyclonic separation | Alternative models
An occluded front is formed during the process of cyclogenesis when a cold front overtakes a warm front. The cold and warm fronts curve naturally poleward into the point of occlusion, which is also known as the triple point in meteorology. It lies within a sharp trough, but the air mass behind the boundary can be either warm or cold. In a cold occlusion, the air mass overtaking the warm front is cooler than the cool air ahead of the warm front, and plows under both air masses. In a warm occlusion, the air mass overtaking the warm front is not as cool as the cold air ahead of the warm front, and rides over the colder air mass while lifting the warm air.
Surface weather analysis | Occluded front
The study of the atmosphere can be divided into distinct areas that depend on both time and spatial scales. At one extreme of this scale is climatology. In the timescales of hours to days, meteorology separates into micro-, meso-, and synoptic scale meteorology. Respectively, the geospatial size of each of these three scales relates directly with the appropriate timescale. Other subclassifications are used to describe the unique, local, or broad effects within those subclasses.
Meteorology | Spatial scales
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
Despite near normal water temperatures over the Arabian Sea, no storms developed in that portion of the basin. Convection was also lower than normal across the Bay of Bengal. The main factor against tropical cyclogenesis was persistently unfavorable wind shear. Overall, there were six depressions, five of which intensified into a cyclonic storm, which has maximum sustained winds of at least 65 km/h (40 mph).
2000 North Indian Ocean cyclone season | Season summary
At this point, despite vorticity lines being oriented in the vertical, the storm "can not" be considered a supercell, as the areas of rotation are "outside" of the main updraft. Due to the short time scale (scale analysis reveals the Coriolis acceleration in the vorticity equation is negligible on short time scales ), the areas of vorticity result in low pressure (perturbations) on the flanks of the convective updraft. Given favorable environmental thermodynamics (sufficient buoyancy and negligible convective inhibition {CIN}) these pressure perturbations will induce mass flux from below, initiating new convective updrafts. These new updrafts are now located "off" the hodograph, with one to the left and one to the right, both co-located with the previously mentioned pressure perturbations.
Splitting storm | Idealized example
For these reasons, only the frequency of storms can be reliably estimated from tree ring isotopic records, not their intensity. Speleothems, deposits formed in caves through the dissolution and redeposition of dolomite and limestone, can store isotope signatures associated with tropical cyclones, especially in fast growing speleothems, areas with thin soils and speleothems which have undergone little alteration. Such deposits have a high temporal resolution, and are also protected from many confounding factors although the extraction of annual layers has become possible only recently, with a two-week resolution (two separate layers correlated to two hurricanes that struck two weeks apart) achieved in one case.
Paleotempestology | Isotope ratios