Cyclones are always moving. By movement we mean the movement of the cyclone as a whole, regardless of the winds blowing in it, which have different speeds and directions in different parts of the cyclone. The movement of a cyclone as a single system is characterized by the movement of its center.
Cyclones move in the direction of the general air transport in the middle and upper troposphere (they also say: in the direction of the leading flow). This general air transfer most often occurs from west to east. Therefore, cyclones most often move from the western half of the horizon to the eastern half.
But it also happens that high, slow-moving cyclones and anticyclones, extending throughout the entire thickness of the troposphere, are located in such a way that isobars and currents at heights deviate from the zonal direction. Then the mobile cyclones, following this non-zonal upper transport, move with a large component to the south or north. In rare cases, the direction of the leading flow is even eastern; then the cyclone moves anomalously, from east to west.
In some cases, the paths of cyclones turn out to be very diverse, and even typical paths over a particular area present a rather complex picture. But on average, cyclones move from west to east with a component directed towards high latitudes. Therefore, the deepest cyclones are observed, as mentioned above, in subpolar latitudes: in the northern hemisphere - in the north of the Atlantic and Pacific oceans, in the southern hemisphere - near the continent of Antarctica.
The speed of movement of the cyclone is 25-35% less than the speed of the leading flow. On average, it is of the order of magnitude 30-40 km/h. In some cases it can be up to 80 km/h or more. In the late stage of a cyclone's life, when it is already filling, the speed of movement decreases, sometimes very sharply.
Although the speeds of cyclones are small, within a few days of its existence a cyclone can move a considerable distance, on the order of several thousand kilometers, changing the weather regime along the way.
As a cyclone passes, the wind increases and its direction changes. If a cyclone passes through a given place with its southern part, the wind changes from south to southwest and northwest. If a cyclone passes through its northern part, the wind changes from southeast to east, northeast and north. Thus, in the front (eastern) part of the cyclone, winds with a southern component are observed, in the rear (western) part - with a northern component. Temperature fluctuations during the passage of a cyclone are also associated with this.
Finally, cyclonic areas are characterized by increased cloudiness and precipitation. In the front part of the cyclone, precipitation is blanket, ascending sliding, falling from the clouds of a warm front or an occlusion front. In the rear part, precipitation is showery, from cumulonimbus clouds, characteristic of a cold front, but mainly of cold air masses flowing in the rear of the cyclone to low latitudes. In the southern part of the cyclone, drizzling precipitation of a warm air mass is sometimes observed.
The approach of a cyclone can often be seen by the drop in pressure and the first clouds appearing on the western horizon. These are frontal cirrus clouds moving in parallel bands. At a glance, due to perspective, these stripes appear to diverge from the horizon. They are followed by cirrostratus clouds, then denser altostratus clouds and, finally, nimbostratus clouds with accompanying nimbostratus clouds. Then, in the rear of the cyclone, pressure increases, and cloudiness takes on a rapidly changing character: cumulus and cumulonimbus clouds often give way to clearings.
Short-term processes of wind formation
Short-term processes also lead to the formation of winds, which, unlike the prevailing winds, are not regular, but occur chaotically, often during a certain season. Such processes are education cyclones, anticyclones and similar phenomena of a smaller scale, in particular thunderstorms.
Cyclone Katarina in the South Atlantic. March 26, 2004
Cyclones And anticyclones are called areas of low or, respectively, high atmospheric pressure, usually those that occur over a space measuring more than several kilometers. On Earth, they form over most of the surface and are characterized by their typical circulation structure. Due to the influence of the Coriolis force, in the Northern Hemisphere the air movement around the cyclone rotates counterclockwise, and around the anticyclone - clockwise. In the Southern Hemisphere, the direction of movement is reversed. When there is friction on a surface, there is a component of movement towards or away from the center, resulting in air moving in a spiral towards an area of low pressure or away from an area of high pressure.
Cyclone
Cyclone (from ancient Greek κυκλῶν - “rotating”) is an atmospheric vortex of huge (from hundreds to several thousand kilometers) diameter with low air pressure in the center.
Air movement (dashed arrows) and isobars (continuous lines) in a cyclone in the northern hemisphere
Air in cyclones circulates counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. In addition, in air layers at a height from the earth's surface to several hundred meters, the wind has a component directed towards the center of the cyclone, along the baric gradient (in the direction of decreasing pressure). The magnitude of the term decreases with height.
Schematic representation of the process of cyclone formation (black arrows) due to the rotation of the Earth (blue arrows)
A cyclone is not just the opposite of an anticyclone; they have a different mechanism of occurrence. Cyclones are constantly and naturally produced by the rotation of the Earth, thanks to the Coriolis force. A consequence of Brouwer's fixed point theorem is the presence of at least one cyclone or anticyclone in the atmosphere.
There are two main types of cyclones - extratropical And tropical. The first are formed in temperate or polar latitudes and have a diameter of from a thousand kilometers at the beginning of development, and up to several thousand in the case of the so-called central cyclone. Among extratropical cyclones, southern cyclones are distinguished, forming on the southern border of temperate latitudes (Mediterranean, Balkan, Black Sea, South Caspian, etc.) and moving to the north and northeast. Southern cyclones have enormous reserves of energy; It is with southern cyclones in central Russia and the CIS that the heaviest precipitation, winds, thunderstorms, squalls and other weather phenomena are associated.
Tropical cyclones form in tropical latitudes and have smaller sizes (hundreds, rarely more than a thousand kilometers), but larger baric gradients and wind speeds, reaching storm speeds. Such cyclones are also characterized by the so-called The “eye of the storm” is a central region with a diameter of 20-30 km with relatively clear and calm weather. Tropical cyclones can become extratropical during their development. Below 8-10° northern and southern latitudes, cyclones occur very rarely, and in the immediate vicinity of the equator they do not occur at all.
Cyclones in the atmosphere of Saturn. Photo of the Cassini probe
Cyclones arise not only in the atmosphere of the Earth, but also in the atmospheres of other planets. For example, in the atmosphere of Jupiter, the so-called Big red spot which is, apparently, a long-lived anticyclone. However, cyclones in the atmospheres of other planets have not been studied enough.
The Great Red Spot in the atmosphere of Jupiter (photo by Voyager 1)
The Great Red Spot is a giant anticyclone hurricane, measuring 24-40 thousand km in length and 12-14 thousand km in width (significantly larger than the Earth). The size of the spot is constantly changing, the general tendency is to decrease; 100 years ago, the BKP was approximately 2 times larger and much brighter. However, it is the largest atmospheric vortex in the Solar System.
Color animation of the movement of the BKP
Large dark spot in Neptune's atmosphere
A dark, elliptical spot (13,000 km × 6,600 km) was similar in size to the Earth. Around the spot, the wind speed reached 2400 km/h, which was the highest in the entire solar system. The spot is believed to be a hole in Neptune's methane clouds. A large dark spot constantly changes its shape and size.
Great Dark Spot
Extratropical cyclone
Cyclones that form outside the tropical zone are known as extratropical. Of the two types of large-scale cyclones, they are larger in size (classified as synoptic cyclones), are the most common, and occur over most of the earth's surface. It is this class of cyclones that is most responsible for weather changes day after day, and their prediction is the main goal of modern weather forecasts.
According to the classical (or Norwegian) Bergen School model, extratropical cyclones form predominantly near the polar front in areas of particularly strong high-altitude jet streams and gain energy from the significant temperature gradient in the area. During the formation of a cyclone, a stationary atmospheric front breaks into sections of warm and cold fronts, moving towards each other with the formation of an occlusion front and the twisting of the cyclone. A similar picture emerges from the later Shapiro-Keyser model, based on observations of ocean cyclones, with the exception of the long-term movement of the warm front perpendicular to the cold one without the formation of an occlusion front.
Norwegian and Shapiro-Keyser models of extratropical cyclone formation
Once formed, a cyclone usually lasts for several days. During this time, it manages to advance over a distance of several hundred to several thousand kilometers, causing sharp changes in winds and precipitation in some areas of its structure.
Although large extratropical cyclones are usually associated with fronts, smaller cyclones can form within a relatively homogeneous air mass. A typical example is cyclones that form in polar air currents at the beginning of the formation of a frontal cyclone. These small cyclones have a name polar and often occur over the polar regions of the oceans. Other small cyclones arise on the leeward side of the mountains under the influence of westerly winds of temperate latitudes.
Extratropical cyclone - a cyclone that forms throughout the year in the extratropical latitudes of each hemisphere. There can be many hundreds of them in 12 months. The size of extratropical cyclones is very significant. A well-developed cyclone can have a diameter of 2-3 thousand km. This means that it can simultaneously cover several regions of Russia or provinces of Canada and determine the weather regime over this vast territory.
Propagation of an extratropical cyclone
The vertical extent (vertical power) of a cyclone changes as it develops. At first, the cyclone is noticeably pronounced only in the lower part of the troposphere. The temperature distribution in the first stage of a cyclone's life is, as a rule, asymmetrical relative to the center. In the front part of the cyclone, with the influx of air from low latitudes, temperatures are elevated; in the rear, with the influx of air from high latitudes, on the contrary, they are lowered. Therefore, with altitude, the isobars of the cyclone open up: a ridge of high pressure is found above the warm front part at altitudes, and a trough of low pressure is found above the cold rear part. With height, this wave formation, curvature of isobars or isohypses becomes more and more smoothed out.
Video showing the development of an extratropical cyclone
But with subsequent development, the cyclone becomes high, that is, closed isobars are found in it and in the upper half of the troposphere. In this case, the air temperature in the cyclone generally decreases, and the temperature contrast between the front and rear parts is more or less smoothed out: a high cyclone is generally a cold region of the troposphere. It is also possible for a cyclone to penetrate the stratosphere.
The tropopause above a well-developed cyclone is bent downward in the form of a funnel; First, this decrease in the tropopause is observed over the cold rear (western) part of the cyclone, and then, when the cyclone becomes cold throughout its entire area, the decrease in the tropopause is observed over the entire cyclone. The temperature of the lower stratosphere above the cyclone is increased. Thus, in a well-developed high cyclone, a low-beginning warm stratosphere is observed above the cold troposphere.
Temperature contrasts in the cyclone area are explained by the fact that the cyclone arises and develops on the main front (polar and arctic) between air masses of different temperatures. Both of these masses are drawn into the cyclonic circulation.
In the further development of the cyclone, warm air is pushed into the upper part of the troposphere, above the cold air, and itself undergoes radiation cooling there. The horizontal temperature distribution in the cyclone becomes more uniform, and the cyclone begins to fade.
The pressure in the center of the cyclone (the depth of the cyclone) at the beginning of its development does not differ much from the average: it can be, for example, 1000-1010 mb. Many cyclones do not deepen to more than 1000-990 mb. Relatively rarely, the depth of a cyclone reaches 970 mb. However, in especially deep cyclones, the pressure drops to 960-950 mb, and in some cases 930-940 mb was observed (at sea level) with a minimum of 925 mb in the northern hemisphere and 923 mb in the southern hemisphere. The deepest cyclones are observed at high latitudes. Over the Bering Sea, for example, in one third of all cases, the depth of cyclones in winter is from 961 to 980 mb.
As the cyclone deepens, the wind speeds in it increase. Winds sometimes reach storm speeds over large areas. This happens especially often in cyclones in the southern hemisphere. Individual wind gusts in cyclones can reach 60 m/sec, as was the case on December 12, 1957 on the Kuril Islands.
The life of a cyclone lasts several days. In the first half of its existence, the cyclone deepens, in the second it fills up and, finally, disappears completely (fades out). In some cases, the existence of a cyclone turns out to be long, especially if it combines with other cyclones, forming one common deep, extensive and inactive low pressure area, the so-called central cyclone. In the northern hemisphere, they most often form in the northern parts of the Atlantic and Pacific oceans. Climatological maps in these areas show well-known centers of action - the Icelandic and Aleutian depressions.
Having already filled in the lower layers, the cyclone can remain for some time in the cold air of the upper layers of the troposphere in the form high altitude cyclone.
tropical cyclone
Tropical cyclone diagram
Cyclones that form in the tropical zone are somewhat smaller than extratropical ones (they are classified as mesocyclones) and have a different mechanism of origin. These cyclones are powered by the upward movement of warm, moist air and can only exist over warm ocean regions, giving them the name warm-core cyclones (as opposed to extratropical cold-core cyclones). Tropical cyclones are characterized by very strong winds and significant amounts of precipitation. They develop and gain strength over the surface of the water, but quickly lose it over land, which is why their destructive effect usually manifests itself only on the coast (up to 40 km inland).
For the formation of a tropical cyclone, an area of very warm water surface is required, the heating of the air above which leads to a decrease in atmospheric pressure by at least 2.5 mm Hg. Art. Moist, warm air rises, but because of its adiabatic cooling, significant amounts of trapped moisture condense at high altitudes and fall as rain. The drier and thus denser air that has just been freed from moisture sinks down, forming zones of higher pressure around the cyclone's core. This process has a positive feedback, as a result of which, as long as the cyclone is over a fairly warm water surface, which supports convection, it continues to intensify. Although tropical cyclones most often form in the tropics, sometimes another type of cyclone takes on the characteristics of a tropical cyclone later in its life, as happens with subtropical cyclones.
tropical cyclone - a type of cyclone, or low-pressure weather system that occurs over a warm sea surface and is accompanied by powerful thunderstorms, heavy rainfall and gale force winds. Tropical cyclones get their energy by raising moist air, condensing water vapor in the form of rain, and sending the drier air that is produced in this process down. This mechanism is fundamentally different from that of extratropical and polar cyclones, from which tropical cyclones are classified as "warm-core cyclones".
The term “tropical” means both the geographic area where such cyclones overwhelmingly occur, that is, tropical latitudes, and the formation of these cyclones in tropical air masses.
In the Far East and Southeast Asia, tropical cyclones are called typhoons, and in North and South America - hurricanes(Spanish) huracán, English hurricane), named after the Mayan wind god Huracan. It is generally accepted, according to the Beaufort scale, that storm goes into Hurricane at a wind speed of more than 117 km/h.
Tropical cyclones can cause not only extreme downpours, but also large waves on the sea surface, storm surges and tornadoes. Tropical cyclones can arise and maintain their strength only over the surface of large bodies of water, while over land they quickly lose strength. That is why coastal areas and islands suffer the most from the destruction they cause, while areas inland are relatively safe. However, heavy rainfall caused by tropical cyclones can cause significant flooding further inland, up to 40 km. Although the effect of tropical cyclones on humans is often very negative, significant amounts of water can break droughts. Tropical cyclones transfer large amounts of energy from tropical latitudes towards temperate latitudes, making them an important component of global atmospheric circulation processes. Thanks to them, the difference in temperature on different parts of the Earth's surface is reduced, which allows the existence of a more moderate climate over the entire surface of the planet.
Many tropical cyclones form under favorable conditions from weak atmospheric disturbances, the occurrence of which is influenced by such effects as like Madden-Julian oscillation, El Niño And North Atlantic Oscillation.
Madden-Julian oscillation - fluctuations in the circulation properties of the tropical atmosphere with a period of 30-60 days, which is the main factor of interseasonal variability in the atmosphere on this time scale. These oscillations take the form of a wave that moves east at a speed of 4 to 8 m/s over the warm regions of the Indian and Pacific Oceans.
Long wavelength radiation pattern showing Madden-Julian oscillation
The movement of the wave can be seen in various manifestations, most clearly in changes in the amount of precipitation. The changes first appear in the western Indian Ocean, gradually shift towards the central Pacific Ocean, and then fade away as they move towards the cold eastern regions of this ocean, but sometimes reappear with reduced amplitude over the tropical regions of the Atlantic Ocean. In this case, first there is a phase of increasing convection and precipitation, followed by a phase of decreasing precipitation.
The phenomenon was discovered by Ronald Madden and Paul Julian in 1994.
El Niño (Spanish) El Niño- baby, boy) or Southern Oscillation - fluctuations in the temperature of the surface layer of water in the equatorial part of the Pacific Ocean, which has a noticeable effect on the climate. In a narrower sense, El Niño is a phase of the Southern Oscillation in which an area of heated surface water moves eastward. At the same time, trade winds weaken or stop altogether, and upwelling slows down in the eastern part of the Pacific Ocean, off the coast of Peru. The opposite phase of oscillation is called La Niña(Spanish) La Nina- baby, girl). The characteristic oscillation time is from 3 to 8 years, but the strength and duration of El Niño in reality varies greatly. Thus, in 1790-1793, 1828, 1876-1878, 1891, 1925-1926, 1982-1983 and 1997-1998, powerful phases of El Niño were recorded, while, for example, in 1991-1992, 1993, 1994 this phenomenon , often repeating, was weakly expressed. El Niño 1997-1998 was so strong that it attracted the attention of the world community and the press. At the same time, theories about the connection of the Southern Oscillation with global climate change spread. Since the early 1980s, El Niño also occurred in 1986–1987 and 2002–2003.
El Niño 1997 (TOPEX)
Normal conditions along the western coast of Peru are determined by the cold Peruvian Current, which carries water from the south. Where the current turns to the west, along the equator, cold and plankton-rich waters rise from deep depressions, which contributes to the active development of life in the ocean. The cold current itself determines the aridity of the climate in this part of Peru, forming deserts. Trade winds drive the heated surface layer of water into the western zone of the tropical Pacific Ocean, where the so-called tropical warm pool (TTB) is formed. In it, the water is heated to depths of 100-200 m. The Walker atmospheric circulation, manifested in the form of trade winds, coupled with low pressure over the Indonesian region, leads to the fact that in this place the level of the Pacific Ocean is 60 cm higher than in its eastern part . And the water temperature here reaches 29-30°C versus 22-24°C off the coast of Peru. However, everything changes with the onset of El Niño. The trade winds are weakening, the TTB is spreading, and water temperatures are rising across a vast area of the Pacific Ocean. In the region of Peru, the cold current is replaced by a warm water mass moving from the west to the coast of Peru, upwelling weakens, fish die without food, and westerly winds bring humid air masses and rainfall to the deserts, even causing floods. The onset of El Niño reduces the activity of Atlantic tropical cyclones.
North Atlantic Oscillation — climate variability in the north Atlantic Ocean, which manifests itself primarily in changes in sea surface temperature. The phenomenon was first described in 2001 by Goldenberg and co-workers. Although there is historical evidence for the existence of this oscillation over a long period of time, accurate historical data on its amplitude and relationship with surface temperatures in tropical ocean regions is lacking.
Time dependence of fluctuations in the period 1856-2013
Other cyclones, particularly subtropical ones, are capable of acquiring the characteristics of tropical cyclones as they develop. Once formed, tropical cyclones move under the influence of prevailing winds; if conditions remain favorable, the cyclone gains strength and forms a characteristic vortex structure with eye in the center. If conditions are unfavorable or if the cyclone moves inland, it dissipates fairly quickly.
Structure
Tropical cyclones are relatively compact storms with a fairly regular shape, usually about 320 km in diameter, with spiraling winds converging around a central area of very low atmospheric pressure. Due to the Coriolis force, the winds deviate from the direction of the pressure gradient and spin counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Structure of a tropical cyclone
According to its structure, a tropical cyclone can be divided into three concentric parts. The outer part has an inner radius of 30-50 km; in this zone, the wind speed uniformly increases as it approaches the center of the cyclone. The middle part, which has a name wall eyes, characterized by high wind speeds. The central part with a diameter of 30-60 km is called eyes, here the wind speed decreases, the air movement is predominantly downward, and the sky often remains clear.
Eye
The central part of the cyclone, in which the air falls down, has the name eyes. If the cyclone is strong enough, the eye is large and characterized by calm weather and clear skies, although sea waves can be exceptionally large. The eye of a tropical cyclone is usually a regular round shape, and its size can range from 3 to 370 km in diameter, but most often the diameter is approximately 30-60 km. The eye of large mature tropical cyclones sometimes widens noticeably at the top, a phenomenon called the “stadium effect”: when observed from inside the eye, its wall resembles the shape of a stadium bleacher.
Hurricane Isabel of 2003, photograph from the ISS - the eye, eye wall, and surrounding rain bands characteristic of tropical cyclones can be clearly seen
The eye of tropical cyclones is characterized by very low atmospheric pressure, and it was here that the lowest atmospheric pressure was recorded at the earth's surface (870 hPa in Typhoon Type). In addition, unlike other types of cyclones, the air in the eye of tropical cyclones is very warm, always warmer than at the same altitude outside the cyclone.
The eye of a weak tropical cyclone may be partially or completely covered by clouds, which are called central dense cloud cover. This zone, unlike the eye of strong cyclones, is characterized by significant thunderstorm activity.
Eye of the Storm, or ofo, Bulls-eye - an area of clearing and relatively calm weather in the center of a tropical cyclone.
A typical eye of a storm has a diameter of 20 to 30 km, in rare cases up to 60 km. In this space, the air has a higher temperature and lower humidity than in the surrounding area of wind and rain clouds. As a result, stable temperature stratification occurs.
The wall of wind and rain serves as an insulator for the very dry and warmer air that descends into the center of the cyclone from the upper layers. Along the periphery of the eye of the storm, some of this air mixes with air from the clouds and, due to the evaporation of droplets, is cooled, thereby forming a powerful cascade of relatively cold air descending along the inside of the clouds.
Eye of Typhoon Odessa (1985)
At the same time, the air in the clouds rises rapidly.This construction forms the kinematic and thermodynamic basis of a tropical cyclone.
In addition, near the axis of rotation, the horizontal linear wind speed decreases, which for an observer, when entering the center of the cyclone, gives the impression of a ceased storm, in contrast to the surrounding space.
Wall of the eye
Wall of eyes called the ring of dense thunderclouds that surrounds the eye. Here the clouds reach the greatest height within the cyclone (up to 15 km above sea level), and precipitation and winds at the surface are the strongest. However, the maximum wind speed is achieved at a slightly higher altitude, usually about 300 m. It is during the passage of the eye wall over a certain area that the cyclone causes the greatest destruction.
The most severe cyclones (usually Category 3 or greater) are characterized by several eyewall replacement cycles during their lifetime. At the same time, the old eye wall narrows to 10-25 km, and it is replaced by a new one of larger diameter, which gradually replaces the old one. During each eyewall replacement cycle, the cyclone weakens (that is, the winds within the eyewall weaken and the temperature of the eye decreases), but with the formation of a new eyewall, it quickly gains strength to its previous values.
Outer zone
External part A tropical cyclone is organized into rainbands - bands of dense thunderclouds that slowly move towards the center of the cyclone and merge with the eye wall. At the same time, in the rain stripes, as in the eye wall, the air rises, and in the space between them, free from low clouds, the air descends. However, the circulation cells formed on the periphery are less deep than the central one and reach a lower height.
When a cyclone reaches land, instead of rain bands, air currents become more concentrated within the eyewall due to increased surface friction. At the same time, the amount of precipitation increases significantly, which can reach 250 mm per day.
Tropical cyclones also form cloud cover at very high altitudes (near the tropopause) due to the centrifugal movement of air at that altitude. This cover consists of high cirrus clouds that move from the center of the cyclone and gradually evaporate and disappear. These clouds may be thin enough that the sun can be seen through them and may be one of the first signs of an approaching tropical cyclone.
Dimensions
One of the most common definitions of cyclone size, which is used in various databases, is the distance from the center of circulation to the outermost closed isobar, this distance is called radius of the outer closed isobar. If the radius is less than two degrees latitude, or 222 km, the cyclone is classified as "very small" or "dwarf". A radius from 3 to 6 degrees latitude, or from 333 to 667 km, characterizes a “medium-sized” cyclone. “Very large” tropical cyclones have a radius greater than 8 degrees latitude, or 888 km. According to this system of measures, the largest tropical cyclones on Earth occur in the Pacific Northwest, approximately twice the size of the Atlantic tropical cyclones.
Other methods for determining the size of tropical cyclones are the radius at which tropical storm force winds exist (approximately 17.2 m/s) and the radius at which the relative wind speed curl is 1×10−5 s−1.
Comparative sizes of Typhoon Type, Cyclone Tracy with the territory of the United States
Mechanism
The main source of energy for a tropical cyclone is evaporation energy, which is released when water vapor condenses. In turn, evaporation of ocean water occurs under the influence of solar radiation. Thus, a tropical cyclone can be thought of as a large heat engine, the operation of which also requires the rotation and gravity of the Earth. In meteorology, a tropical cyclone is described as a type of mesoscale convection system that develops in the presence of a powerful source of heat and moisture.
Directions of convection currents in a tropical cyclone
Warm, moist air rises primarily within the cyclone's eye wall, as well as within other rain bands. This air expands and cools as it rises, its relative humidity, already high at the surface, increases even more, as a result of which most of the accumulated moisture condenses and falls as rain. The air continues to cool and lose moisture as it rises to the tropopause, where it loses almost all moisture and stops cooling with altitude. The cooled air sinks down to the ocean surface, where it is re-humidified and rises again. Under favorable conditions, the energy involved exceeds the cost of maintaining this process; excess energy is spent on increasing the volume of upward flows, increasing wind speeds and accelerating the condensation process, that is, leading to the formation of a positive feedback. For conditions to remain favorable, a tropical cyclone must be located over a warm ocean surface that provides the necessary moisture; when a cyclone passes a piece of land, it does not have access to this source and its strength quickly decreases. The Earth's rotation adds twist to the convection process as a result of the Coriolis effect - the deviation of the wind direction from the pressure gradient vector.
Drop in ocean surface temperature in the Gulf of Mexico with the passage of Hurricanes Katrina and Rita
The mechanism of tropical cyclones differs significantly from the mechanism of other atmospheric processes in that it requires deep convection, that is, one that covers a large range of altitudes. At the same time, rising currents cover almost the entire distance from the ocean surface to the tropopause, with horizontal winds limited primarily to the surface layer up to 1 km thick, while most of the remaining 15 km of the troposphere in tropical regions is used for convection. However, the troposphere is thinner at higher latitudes and the amount of solar heat there is less, limiting the zone of favorable conditions for tropical cyclones to the tropical belt. Unlike tropical cyclones, extratropical cyclones receive their energy primarily from horizontal air temperature gradients that pre-existed them.
The passage of a tropical cyclone over an area of the ocean leads to a significant cooling of the near-surface layer, both due to heat loss through evaporation and due to the active mixing of warm near-surface and cold deep layers and the production of cold rainwater. Cooling is also affected by dense cloud cover, which blocks the ocean surface from sunlight. As a result of these effects, over the few days during which the cyclone passes a certain area of the ocean, the surface temperature there drops significantly. This effect creates a negative feedback that can cause a tropical cyclone to lose strength, especially if its movement is slow.
The total amount of energy that is released in a medium-sized tropical cyclone is about 50-200 exajoules (10 18 J) per day or 1 PW (10 15 W). This is about 70 times more than humanity's total energy consumption, 200 times more than global electricity production, and equals the energy that would be released from the explosion of a 10-megaton hydrogen bomb every 20 minutes.
Life cycle
Formation
Map of the path of all tropical cyclones for the period 1985-2005
In all areas of the world where tropical cyclone activity occurs, it peaks in late summer, when the temperature difference between the ocean surface and the deep ocean is greatest. However, seasonal patterns differ somewhat depending on the basin. Globally, May is the least active month, September the most active, and November is the only month when all basins are active at the same time.
Important Factors
The formation process of tropical cyclones is still not fully understood and is the subject of intensive research. Typically, there are six factors necessary for the formation of tropical cyclones, although in some cases a cyclone can form without some of them.
Formation of trade wind convergence zones, which leads to atmospheric instability and contributes to the formation of tropical cyclones
In most cases, for a tropical cyclone to form, a surface ocean water temperature of at least 26.5°C at a depth of at least 50 m is required; This water temperature is the minimum sufficient to cause instability in the atmosphere above it and support the existence of a thunderstorm system.
Another necessary factor is the rapid cooling of air with height, which allows the release of condensation energy, the main source of energy of a tropical cyclone.
Also, for the formation of a tropical cyclone, high air humidity in the lower and middle layers of the troposphere is required; With a large amount of moisture in the air, more favorable conditions are created for the formation of instability.
Another characteristic of favorable conditions is a low vertical wind gradient, since a high wind gradient leads to a break in the cyclone's circulation pattern.
Tropical cyclones usually occur at a distance of at least 550 km, or 5 degrees latitude, from the equator - only there the Coriolis force is strong enough to deflect the wind and spin the vortex.
Finally, the formation of a tropical cyclone usually requires a pre-existing area of low pressure or disturbance weather, albeit without the circulation behavior associated with a mature tropical cyclone. Such conditions can be created by low-level and low-latitude flares that are associated with the Madden-Julian oscillation.
Formation areas
Most tropical cyclones in the world form within the equatorial belt (intertropical front) or its extension under the influence of the monsoon - a monsoon low pressure zone. Areas favorable for tropical cyclone formation also occur within tropical wave zones, where about 85% of intense Atlantic cyclones and most eastern Pacific tropical cyclones occur.
The vast majority of tropical cyclones form between 10 and 30 degrees latitude in both hemispheres, with 87% of all tropical cyclones forming within 20 degrees latitude of the equator. Due to the lack of Coriolis force in the equatorial zone, tropical cyclones very rarely form closer than 5 degrees from the equator, but it does happen, for example with tropical storm Wamei of 2001 and Cyclone Agni of 2004.
Tropical Storm Wamei before landfall
Tropical Storm Wamei, sometimes known as Typhoon Wamei, is a tropical cyclone known for forming closer to the equator than any other tropical cyclone on record. Wamei formed on December 26 as the last tropical cyclone of the 2001 Pacific typhoon season at 1.4°N latitude in the South China Sea. It quickly intensified and made landfall in southwest Malaysia. It virtually dissipated over the island of Sumatra on December 28, and its remnants later reorganized over the Indian Ocean. Although the tropical cyclone is officially designated as a tropical storm, its intensity is disputed, with some agencies classifying it as a typhoon based on wind speeds of 39 m/s and the presence of an eye.The storm caused floods and landslides in eastern Malaysia, causing US$3.6 million in damage (at 2001) and five victims.
Movement
Interaction with trade winds
The movement of tropical cyclones along the Earth's surface depends primarily on the prevailing winds resulting from global circulation processes; tropical cyclones are carried along by these winds and move with them. In the zone of occurrence of tropical cyclones, that is, between the 20 parallels of both hemispheres, they move westward under the influence of eastern winds - trade winds.
Global atmospheric circulation diagram
In the tropical regions of the North Atlantic Ocean and the northeast Pacific Ocean, trade winds form tropical waves starting from the African coast and passing through the Caribbean Sea, North America and fading in the central regions of the Pacific Ocean. These waves are where most of the tropical cyclones in these regions originate.
Coriolis effect
Due to the Coriolis effect, the rotation of the Earth not only causes tropical cyclones to spin, but also affects the deflection of their movement. Because of this effect, a tropical cyclone that moves west under the influence of trade winds in the absence of other strong air currents is deflected towards the poles.
Infrared image of Cyclone Monica, showing the twisting and rotation of the cyclone
Since easterly winds are applied to the cyclonic air movement on its polar side, the Coriolis force is stronger there, and as a result the tropical cyclone is pulled poleward. When a tropical cyclone reaches a subtropical ridge, temperate westerlies begin to reduce air speed on the polar side, but the difference in distance from the equator between different parts of the cyclone is large enough that the net Coriolis force is directed poleward. As a result, tropical cyclones in the Northern Hemisphere are deflected to the north (before turning to the east), and tropical cyclones of the Southern Hemisphere are deflected to the south (also before turning to the east).
Interaction with westerly winds of temperate latitudes
When a tropical cyclone crosses a subtropical ridge, which is an area of high pressure, its path usually deviates into a low pressure area on the polar side of the ridge. Once in the zone of westerly winds of the temperate zone, a tropical cyclone tends to move with them to the east, passing the moment of change of course (eng. recurvature). Typhoons moving west across the Pacific Ocean to the shores of Asia often change course off the coast of Japan to the north and then to the northeast, captured by southwesterly winds from China or Siberia. Many tropical cyclones are also deflected due to interaction with extratropical cyclones moving west to east in these areas. An example of a tropical cyclone changing course is Typhoon Yoke 2006, which moved along the described trajectory.
The path of Typhoon Yoke, which changed course off the Japanese coast in 2006
Landfall
Formally, a cyclone is considered to pass over land if this happens to its center of circulation, regardless of the state of the peripheral regions. Stormy conditions typically begin over a specific area of land several hours before the center of the cyclone makes landfall. During this period, that is, before the tropical cyclone formally makes landfall, the winds can reach their greatest strength - in this case they speak of a “direct impact” of the tropical cyclone on the coast. Thus, the moment a cyclone makes landfall actually marks the middle of the storm period for the areas where it happens. Safety measures should be taken before the winds reach a certain speed or before the rain reaches a certain intensity, and not be associated with the moment the tropical cyclone makes landfall.
Interaction of cyclones
When two cyclones approach each other, their centers of circulation begin to rotate around a common center. In this case, two cyclones approach each other and eventually merge. If the cyclones are different sizes, the larger one will dominate this interaction, and the smaller one will orbit around it. This effect is called Fujiwara effect, in honor of the Japanese meteorologist Sakuhei Fujiwara.
This image shows Typhoon Melor and Tropical Storm Parma, and their interaction in southeast Asia. This example shows how the strong Melor pulls the weaker Parma towards him
Satellites capture twin cyclones dancing over Indian Ocean
On January 15, 2015, two tropical cyclones formed over the central Indian Ocean. None of them threatened populated areas due to their low intensity and low chances of making landfall. Meteorologists were confident that Diamondra and Eunice would weaken and dissipate in the coming days. The close proximity of tropical cyclones enabled satellites to take stunning photographs of the dance of vortex systems over the ocean.
On January 28, 2015, geostationary satellites belonging to EUMETSAT and the Japan Meteorological Agency, provided data to create the composite image (top). Radiometer (VIIRS) on board the satellite Suomi NPP took three photographs of the twin cyclones, which were combined to create the image below.
The two systems were at a distance of about 1.5 thousand kilometers from each other on January 28, 2015. Eunice, the stronger of the two cyclones, was located to the east of Diamondra. The maximum speed of stable winds of “Yunis” reached almost 160 km/h, while the maximum speed of winds of “Diamondra” did not exceed 100 km/h. Both cyclones moved in a southeast direction.
Typically, if two tropical cyclones approach each other, they begin to rotate cyclonically around an axis connecting their centers. Meteorologists call this phenomenon the Fujiwara effect. Such double cyclones can even merge into one if their centers converge close enough.
“But in the case of Eunice and Diamondra, the centers of the two vortex systems were too far apart,” explains Brian McNoldy, a meteorologist at the University of Miami. — From experience, the centers of cyclones must be at a distance of at least 1350 kilometers in order to begin to rotate around each other. According to the latest forecasts from the Joint Typhoon Warning Center, both cyclones are moving southeast at about the same speed, so they will likely not come closer to each other."
(To be continued)
Some time ago, before the advent of meteorological satellites, scientists could not even think that about one hundred and fifty cyclones and sixty anticyclones form in the Earth’s atmosphere every year. Previously, many cyclones were unknown because they occurred in places where there were no meteorological stations that could record their occurrence.
In the troposphere, the lowest layer of the Earth's atmosphere, vortices constantly appear, develop and disappear. Some of them are so small and unnoticeable that they pass by our attention, others are so large-scale and have such a strong influence on the Earth’s climate that they cannot be ignored (primarily this applies to cyclones and anticyclones).
Cyclones are areas of low pressure in the Earth's atmosphere, in the center of which the pressure is much lower than at the periphery. An anticyclone, on the contrary, is an area of high pressure that reaches its highest levels in the center. While over the northern hemisphere, cyclones move counterclockwise and, obeying the Coriolis force, try to move to the right. While the anticyclone moves clockwise in the atmosphere and deviates to the left (in the Southern Hemisphere of the Earth everything happens the other way around).
Despite the fact that cyclones and anticyclones are absolutely opposite vortices in their essence, they are strongly interconnected with each other: when pressure decreases in one region of the Earth, its increase is necessarily recorded in another. Also, cyclones and anticyclones have a common mechanism that causes air currents to move: non-uniform heating of different parts of the surface and the rotation of our planet around its axis.
Cyclones are characterized by cloudy, rainy weather with strong gusts of wind that arise due to the difference in atmospheric pressure between the center of the cyclone and its edges. An anticyclone, on the contrary, in the summer is characterized by hot, windless, partly cloudy weather with very little precipitation, while in the winter, thanks to it, clear but very cold weather sets in.
Snake Ring
Cyclones (gr. “snake ring”) are huge vortices, the diameter of which can often reach several thousand kilometers. They are formed in temperate and polar latitudes, when warm air masses from the equator collide with dry, cold currents moving towards them from the Arctic (Antarctica) and form a boundary between themselves, which is called an atmospheric front.
Cold air, trying to overcome the warm air flow remaining below, in some area pushes part of its layer back - and it comes into collision with the masses following it. As a result of the collision, the pressure between them increases and part of the warm air turned back, yielding to the pressure, is deflected to the side, beginning an ellipsoidal rotation.
This vortex begins to capture the layers of air adjacent to it, draws them into rotation and begins to move at a speed of 30 to 50 km/h, while the center of the cyclone moves at a lower speed than its periphery. As a result, after some time the diameter of the cyclone ranges from 1 to 3 thousand km, and the height – from 2 to 20 km.
Where it moves, the weather changes sharply, since the center of the cyclone has low pressure, there is a lack of air inside it, and cold air masses begin to flow in to make up for it. They displace warm air upward, where it cools, and the water droplets in it condense and form clouds, from which precipitation falls.
The lifespan of a vortex is usually from several days to weeks, but in some regions it can last about a year: usually these are areas of low pressure (for example, the Icelandic or Aleutian cyclones).
It is worth noting that such vortices are not typical for the equatorial zone, since the deflecting force of the planet’s rotation, necessary for the vortex-like movement of air masses, does not act here.
The southernmost, tropical cyclone, forms no closer to the equator than five degrees and is characterized by a smaller diameter, but higher wind speed, often transforming into a hurricane. According to their origin, there are such types of cyclones as the temperate cyclone and the tropical cyclone, which generates deadly hurricanes.
Vortexes of tropical latitudes
In the 1970s, tropical cyclone Bhola hit Bangladesh. Although the wind speed and strength were low and it was assigned only the third (out of five) hurricane category, due to the huge amount of precipitation that fell on the ground, the Ganges River overflowed its banks and flooded almost all the islands, washing away all settlements from the face of the earth.
The consequences were catastrophic: during the rampant disaster, from three hundred to five hundred thousand people died.
A tropical cyclone is much more dangerous than a vortex from temperate latitudes: it is formed where the temperature of the ocean surface is not lower than 26 °, and the difference between air temperatures exceeds two degrees, as a result of which evaporation increases, air humidity increases, which contributes to the vertical rise of air masses.
Thus, a very strong draft appears, capturing new volumes of air that have heated up and gained moisture above the ocean surface. The rotation of our planet around its axis gives the rise of air the vortex-like movement of a cyclone, which begins to rotate at enormous speed, often transforming into hurricanes of terrifying force.
A tropical cyclone is formed only over the ocean surface between 5-20 degrees north and south latitudes, and once on land, it fades out quite quickly. Its dimensions are usually small: the diameter rarely exceeds 250 km, but the pressure at the center of the cyclone is extremely low (the lower, the faster the wind moves, so the movement of cyclones is usually from 10 to 30 m/s, and wind gusts exceed 100 m/s) . Naturally, not every tropical cyclone brings death with it.
There are four types of this vortex:
- Disturbance – moves at a speed not exceeding 17 m/s;
- Depression - the movement of the cyclone is from 17 to 20 m/s;
- Storm - the center of the cyclone moves at a speed of up to 38 m/s;
- Hurricane - a tropical cyclone moves at a speed exceeding 39 m/s.
The center of this type of cyclone is characterized by a phenomenon called the “eye of the storm” - an area of calm weather. Its diameter is usually about 30 km, but if a tropical cyclone is destructive, it can reach up to seventy. Inside the eye of the storm, the air masses have a warmer temperature and less humidity than in the rest of the vortex.
Calm often reigns here; at the border, precipitation abruptly stops, the sky clears, the wind weakens, thereby deceiving people who, deciding that the danger has passed, relax and forget about precautions. Since a tropical cyclone always moves from the ocean, it drives huge waves in front of it, which, when they hit the coast, sweep everything out of the way.
Scientists are increasingly recording the fact that every year the tropical cyclone becomes more dangerous and its activity is constantly increasing (this is due to global warming). Therefore, these cyclones are found not only in tropical latitudes, but also reach Europe at an atypical time of year for them: they usually form in late summer/early autumn and never occur in spring.
Thus, in December 1999, France, Switzerland, Germany, and the UK were hit by Hurricane Lothar, so powerful that meteorologists could not even predict its appearance due to the fact that the sensors either went off scale or did not work. “Lotar” turned out to be the cause of the death of more than seventy people (they were mainly victims of road accidents and falling trees), and in Germany alone, about 40 thousand hectares of forest were destroyed in a few minutes.
Anticyclones
An anticyclone is a vortex in the center of which there is high pressure and low pressure at the periphery. It is formed in the lower layers of the Earth's atmosphere when cold air masses invade warmer ones. An anticyclone occurs in subtropical and subpolar latitudes, and its movement speed is about 30 km/h.
An anticyclone is the opposite of a cyclone: the air in it does not rise, but descends. It is characterized by the absence of humidity. An anticyclone is characterized by dry, clear, and windless weather, hot in summer and frosty in winter. Significant temperature fluctuations during the day are also characteristic (the difference is especially strong on the continents: for example, in Siberia it is about 25 degrees). This is explained by the lack of precipitation, which usually makes the temperature difference less noticeable.
Names of vortices
In the middle of the last century, anticyclones and cyclones began to be given names: this turned out to be much more convenient when exchanging information about hurricanes and cyclone movements in the atmosphere, since it made it possible to avoid confusion and reduce the number of errors. Behind each name of a cyclone and anticyclone there was hidden data about the vortex, down to its coordinates in the lower layer of the atmosphere.
Before making the final decision on the name of this or that cyclone and anticyclone, a sufficient number of proposals were considered: they were proposed to be designated by numbers, letters of the alphabets, names of birds, animals, etc. This turned out to be so convenient and effective that after a while Over time, all cyclones and anticyclones received names (at first they were female, and in the late seventies tropical vortices began to be called by male names).
Since 2002, a service has appeared that offers anyone who wants to name a cyclone or anticyclone by their name. The pleasure is not cheap: the standard price for a cyclone to be named after a customer is 199 euros, and an anticyclone costs 299 euros, since anticyclones occur less frequently.
In the 8th grade geography course, a number of topics are studied on various processes in the atmosphere. They need to be studied and understood, as they reveal the reasons and methods for the formation and change of weather, its prediction, which is of practical value for every person.
What are cyclones and anticyclones
One of the most interesting mechanisms is a kind of “air pumps” - atmospheric vortices of enormous size, the main role of which is the formation of weather over large areas of the earth's surface.
Their height is up to 20 km, and their diameter can reach 4-5 thousand km.
Rice. 1. A giant atmospheric vortex.
In this case, a cyclone is an air vortex that collects and throws air upward from its own center. An anticyclone, on the contrary, draws in air from the upper layers of the atmosphere and distributes it near the surface.
This happens because a cyclone is an area of low pressure, air rushes to where the pressure is lowest, that is, to the center of the cyclone. Rising air currents form there.
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An anticyclone is an atmospheric vortex characterized by high pressure. On the contrary, it “accelerates” air masses from its own center, drawing them in from higher layers of the atmosphere. In its center, downward flows are formed, which spiral from the center and are distributed over the earth's surface.
Atmospheric vortices often form in areas of atmospheric fronts; the main reason for their formation is the rotation of the Earth.
Rice. 2. Scheme of the structure of a cyclone and anticyclone.
Similar phenomena are observed in the atmosphere of other planets. An extraterrestrial long-lived cyclone is the Little Dark Spot in the atmosphere of Neptune, and an anticyclone is the Great Red Spot on Jupiter.
Comparison of features of atmospheric vortices
Cyclones and anticyclones have differences and similarities. Their similarities are:
- vortex structure;
- important role in weather formation over large regions.
The appearance of an anticyclone is influenced by the formation of cyclones nearby - excess air emitted by a low-pressure vortex accumulates and provokes the development of an area of high pressure, anticyclones.
The differences between atmospheric vortices are presented in the table of comparative characteristics:
|
Cyclone |
Anticyclone |
|
|
Place of formation |
More often over the oceans, it can form everywhere except the equatorial region, where the Coriolis force associated with the rotation of the Earth does not act |
In the tropics, over oceans and over ice fields |
|
Size (diameter) |
||
|
Movement |
Constant, speed 30-60 km/h, tropical storm typhoons are much faster |
Inactive or has a speed of 20-40 km/h |
|
Pressure |
In the center it is low, at the periphery it is high |
High in the center, low in the periphery |
|
Direction of rotation |
In the Northern Hemisphere they rotate counterclockwise, in the Southern Hemisphere they rotate counterclockwise. |
In the Northern Hemisphere the rotation is clockwise, and vice versa in the Southern Hemisphere. |
|
Brings the weather |
Wind, clouds, precipitation |
Clear or partly cloudy, calm, no precipitation |
On synoptic maps, letters are used to designate cyclones and anticyclones: H - means an area of low pressure, B - an area of high pressure.
Rice. 3. Synoptic map.
Types of cyclones and anticyclones
There are several types of cyclones, named after the place of formation:
- Arctic;
- temperate latitudes;
- southern extratropical;
- tropical.
Most of the cyclones passing through the territory of Russia are formed over the Atlantic, move from west to east and are classified as arctic or temperate. These are large-area atmospheric vortices.
Tropical cyclones are the most dangerous - they are characterized by relatively small sizes of only hundreds of kilometers, abnormally low pressure in the center, and therefore very high wind speeds, reaching storm speeds. It is these cyclones that cause the greatest destruction in the coastal countries of Asia and North America. They appear only over the sea and quickly fade when moving to land.
Anticyclones and cyclones have an average lifespan of 3-10 days until the atmospheric pressure equalizes. However, there are also permanent ones that exist for years, for example: the Icelandic and Aleutian cyclones, the Indian and Siberian anticyclones.
What have we learned?
The formation of atmospheric vortices depends on the distribution of air pressure in the atmosphere and the Coriolis forces that arise during the rotation of the Earth. Despite some similarities, they differ from each other in many ways: they rotate in different directions, provide different weather, and arise in different conditions.
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The weather in our country is unstable. This is especially evident in the European part of Russia. This occurs due to the fact that different air masses meet: warm and cold. Air masses differ in properties: temperature, humidity, dust content, pressure. Atmospheric circulation allows air masses to move from one part to another. Where air masses of different properties come into contact, atmospheric fronts.
Atmospheric fronts are inclined to the Earth's surface, their width reaches from 500 to 900 km, and their length extends to 2000-3000 km. In the frontal zones, an interface between two types of air appears: cold and warm. Such a surface is called frontal. As a rule, this surface is inclined towards the cold air - it is located under it, as it is heavier. And warm air, lighter, is located above the frontal surface (see Fig. 1).
Rice. 1. Atmospheric fronts
The line of intersection of the frontal surface with the Earth's surface forms front line, which is also briefly called front.
Atmospheric front- a transition zone between two dissimilar air masses.
Warm air, being lighter, rises. As it rises, it cools and becomes saturated with water vapor. Clouds form in it and precipitation falls. Therefore, the passage of an atmospheric front is always accompanied by precipitation.
Depending on the direction of movement, moving atmospheric fronts are divided into warm and cold. Warm front formed when warm air flows into cold air. The front line moves towards the cold air. After the passage of a warm front, warming occurs. A warm front forms a continuous line of clouds hundreds of kilometers long. There are lingering drizzling rains and warming is setting in. The rise of air during the arrival of a warm front occurs more slowly compared to a cold front. Cirrus and cirrostratus clouds forming high in the sky are a harbinger of an approaching warm front. (see Fig. 2).
Rice. 2. Warm front ()
It is formed when cold air flows under warm air, while the front line moves towards warm air, which is forced upward. Typically, a cold front moves very quickly. This causes strong winds, heavy, often heavy rainfall with thunderstorms, and snowstorms in winter. Cooling occurs after the passage of a cold front (see Fig. 3).
Rice. 3. Cold front ()
Atmospheric fronts can be stationary or moving. If air currents do not move towards either cold or warm air along the front line, such fronts are called stationary. If air currents have a speed of movement perpendicular to the front line, and move either towards cold or towards warm air, such atmospheric fronts are called moving. Atmospheric fronts arise, move and collapse in about a few days. The role of frontal activity in climate formation is more pronounced in temperate latitudes, therefore most of Russia is characterized by unstable weather. The most powerful fronts arise when the main types of air masses come into contact: arctic, temperate, tropical (see Fig. 4).
Rice. 4. Formation of atmospheric fronts on the territory of Russia
Zones reflecting their long-term positions are called climate fronts. On the border between Arctic and temperate air, over the northern regions of Russia, a arctic front. Air masses of temperate latitudes and tropical ones are separated by a polar temperate front, which is located mainly south of the borders of Russia. The main climate fronts do not form continuous stripes of lines, but are divided into segments. Long-term observations have shown that the Arctic and polar fronts move south in winter and north in summer. In the east of the country, the Arctic front reaches the coast of the Sea of Okhotsk in winter. To the northeast of it, very cold and dry arctic air prevails. In European Russia, the Arctic front does not move so far. The warming effect of the North Atlantic Current is felt here. The branches of the polar climate front stretch over the southern territories of our country only in summer; in winter they lie over the Mediterranean Sea and Iran and occasionally cover the Black Sea.
Participate in the interaction of air masses cyclones And anticyclones- large moving atmospheric vortices that transport atmospheric masses.
An area of low atmospheric pressure with a specific system of winds blowing from the edges to the center and deviating counterclockwise.
An area of high atmospheric pressure with a specific system of winds blowing from the center to the edges and deviating clockwise.
Cyclones are of impressive size, extending into the troposphere to a height of up to 10 km and a width of up to 3000 km. In cyclones the pressure increases, and in anticyclones it decreases. In the northern hemisphere, winds blowing towards the center of cyclones are deflected under the influence of the force of the earth's axial rotation to the right (the air spins counterclockwise), and in the central part the air rises. In anticyclones, winds directed towards the outskirts also deviate to the right (the air swirls clockwise), and in the central part the air descends from the upper layers of the atmosphere downwards (see Fig. 5, Fig. 6).
Rice. 5. Cyclone
Rice. 6. Anticyclone
The fronts on which cyclones and anticyclones originate are almost never straight; they are characterized by wave-like bends (see Fig. 7).
Rice. 7. Atmospheric fronts (synoptic map)
In the resulting gulfs of warm and cold air, rotating tops of atmospheric vortices are formed (see Fig. 8).
Rice. 8. Formation of an atmospheric vortex
Gradually they separate from the front and begin to move and carry air on their own at a speed of 30-40 km/h.
Atmospheric vortices last 5-10 days before destruction. And the intensity of their formation depends on the properties of the underlying surface (temperature, humidity). Several cyclones and anticyclones form in the troposphere every day. Hundreds of them are formed throughout the year. Every day our country is under the influence of some kind of atmospheric vortex. Since air rises in cyclones, their arrival is always associated with cloudy weather with precipitation and winds, cool in summer and warm in winter. During the entire duration of the anticyclone, cloudless, dry weather prevails, hot in summer and frosty in winter. This is facilitated by the slow descent of air from higher layers of the troposphere. The descending air heats up and becomes less saturated with moisture. In anticyclones the winds are weak, and in their inner parts there is complete calm - calm(see Fig. 9).
Rice. 9. Air movement in an anticyclone
In Russia, cyclones and anticyclones are confined to the main climate fronts: polar and arctic. They also form on the border between marine and continental air masses of temperate latitudes. In western Russia, cyclones and anticyclones arise and move in the direction of the general air transport from west to east. In the Far East in accordance with the direction of the monsoons. When moving with westerly transport in the east, cyclones deviate to the north, and anticyclones - to the south (see Fig. 10). Therefore, the paths of cyclones in Russia most often pass through the northern regions of Russia, and anticyclones - through the southern regions. In this regard, the atmospheric pressure in the north of Russia is lower, there may be inclement weather for many days in a row, in the south there are more sunny days, dry summers and little snowy winters.
Rice. 10. Deviation of cyclones and anticyclones when moving from the west
Areas where intense winter cyclones pass: the Barents, Kara, Okhotsk Seas and the north-west of the Russian Plain. In summer, cyclones are most frequent in the Far East and in the west of the Russian Plain. Anticyclonic weather prevails all year round in the south of the Russian Plain, in the south of Western Siberia, and in winter over the entire Eastern Siberia, where the Asian maximum pressure is established.
The movement and interaction of air masses, atmospheric fronts, cyclones and anticyclones change the weather and influence it. Data on weather changes are plotted on special synoptic maps for further analysis of weather conditions in our country.
The movement of atmospheric vortices leads to changes in weather. Her condition for each day is recorded on special cards - synoptic(see Fig. 11).
Rice. 11. Synoptic map
Weather observations are carried out by an extensive network of weather stations. The observation results are then transmitted to hydrometeorological data centers. Here they are processed and weather information is plotted on synoptic maps. The maps show atmospheric pressure, fronts, air temperature, wind direction and speed, cloud cover and precipitation. The distribution of atmospheric pressure indicates the position of cyclones and anticyclones. By studying the patterns of atmospheric processes, we can predict the weather. Accurate weather forecasting is an extremely complex matter, since it is difficult to take into account the entire complex of interacting factors in their constant development. Therefore, even short-term forecasts of the hydrometeorological center are not always justified.
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Homework
- Why does precipitation occur in the zone of the atmospheric front?
- What is the main difference between a cyclone and an anticyclone?
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