What is a cyclone? Tropical cyclone in the Southern Hemisphere. Cyclones and anticyclones - characteristics and names
An air mass moving over a warmer underlying surface is called cold; moving over a colder underlying surface - warm; in thermal equilibrium with environment - local.
The air mass that forms in the Arctic is called arctic air, which is strongly cooled throughout the thickness, has low absolute and high relative humidity, carrying with it fogs and haze. IN temperate latitudes formed polar air. In winter, the masses of such air are close in their properties to the Arctic; in summer, the polar air is heavily dusty and has low visibility. Formed in the subtropics and tropics tropical air very warm, dusty, characterized by high absolute humidity, often causing opalescence phenomena (a reddish sun and distant objects in a blue haze). Continental tropical air is unstable during the day (convection, dust whirlwinds and storms, tornadoes). Visibility is reduced.
Equatorial air has in general the same properties as tropical air, but some of them are even more pronounced.
Fronts. The point of contact between two air masses with different physical properties, is called the interface (front). The line of intersection of such a surface with the underlying surface (sea or land) is called the front line. Fronts are divided into mobile and stationary.
The main arctic front separates the arctic air from the polar air; main polar front - polar air from tropical; the main tropical front is tropical air from the equatorial one.
warm front occurs when a warm air mass overflows onto a cold one. The pressure in front of such a front drops. Cirrus clouds in the form of "claws" also serve as a harbinger of a warm front. Pre-frontal fogs are observed ahead of a warm front. Crossing the zone of a warm front, the ship enters a wide band of heavy rain or snow with reduced visibility.
cold front occurs when cold air masses wedged under warm air. It comes with a "wall" of shower clouds. The pressure ahead of the front drops significantly. When meeting with a cold front, the ship enters the zone of showers, thunderstorms, squalls and heavy seas. However, if the wedge of cold air "cuts" the warm masses slowly, then behind the line of such a cold front the ship enters the zone of heavy precipitation.
Front of occlusion occurs when two masses of air - warm and cold - interact. If the overtaking mass has a temperature lower than the one in front, then the front is called the front of cold occlusion; if the overtaking mass has a temperature higher than the one in front, it is a warm occlusion front. Passing occlusion fronts, the ship can get into conditions of reduced visibility, precipitation, strong wind, accompanied by waves.
Cyclones. The cyclone originates as an area reduced pressure at the boundary of two masses of air different temperatures. Usually this is a wave disturbance on frontal surface. With a length of more than 1000 km, the wave becomes unstable and they say that the cyclone "deepens": between cold and warm fronts a sector is formed warm air linguistic form. With further development cold front, moving faster than warm, catches up with it; the closure of the warm and cold fronts eliminates the warm sector, forming an occlusion front.
The diameter of the cyclone ranges from several hundred to 5000 km; average travel speed 30-60 km/h. Careful observations of clouds, wind, changes in atmospheric pressure and air temperature allow us to draw important conclusions for navigation:
If individual small cumulus clouds are moving in the same direction as the wind below, the observer is at the rear of the cyclone and an improvement in weather can be expected;
If the direction of movement of the clouds does not coincide with the direction of the wind below, the observer is in front of the cyclone, and in one or two days one should expect prolonged precipitation and temperature changes (lowering it in summer and increasing it in winter);
If the wind increases and its direction changes according to the sun, the observer of the northern hemisphere (southern hemisphere) is in the right (left) half of the cyclone; if, the direction of the increasing wind changes against the sun, the reverse conclusion should be drawn;
If the wind direction does not change, the observer is on the path of the center of the cyclone and one should expect a temporary lull, and then an increase in the wind from the opposite side.
Tropical cyclones. Unlike cyclones originating in temperate latitudes, cyclonic disturbances that occur between the tropics are called tropical cyclones. In the West Indies they are called hurricanes; east of Asia - by typhoons; in the Indian Ocean - cyclones; in the southern part indian ocean- arcana. Tropical cyclones are typically less than 100-300 miles across with a center section 20-30 miles in diameter. The baric gradient in a tropical cyclone sometimes exceeds 40 mb, and the wind speed reaches 100 km / h, and these indicators, unlike cyclones of temperate latitudes, persist in almost the entire region of a hurricane (typhoon, etc.).
Rice. 114.
One of the signs of the approach of a typhoon is the appearance of a swell coming from the wrong direction from which the wind blows or blew before. The swell developed by the wind can be detected already at a distance of 400-600 miles from the center of the typhoon. By the direction of the swell, one can judge the position of the center of the typhoon, and by changing this direction, one can judge the direction of its movement.
As the center of the typhoon approaches Atmosphere pressure drops sharply, cirrus clouds give way to a heap of shower clouds; there is a pre-storm calm with suffocating heat. Then the air temperature drops rapidly, it starts to rain, turning into a tropical downpour.
A simplified diagram of a tropical cyclone for the northern hemisphere is shown in fig. 114. As can be seen from the figure, the winds in the typhoon area are deviated from the direction to its center to the right by an average of 60°. Therefore, for an observer standing with his back to the wind, the center of the typhoon will be ahead, approximately 60° to the left of the wind direction. When approaching the center of the typhoon, the angle of wind deviation from the radius increases and reaches 90° in close proximity to the center. In the center of the typhoon, light winds and even calm are observed with rough seas. After passing through the center of the typhoon ("eye of the storm"), the wind very quickly increases to a hurricane. Wind force 12 points is maintained at a distance of 30-35 miles from the center and more. Then she gradually weakens. So, at a distance of 50-75 miles from the center of the typhoon, the wind force is 10 points; at a distance of 100-150 miles - 8-9 points. And only at a distance of 200-250 miles the wind force decreases to 6-7 points. Using the model of a tropical cyclone (see Fig. 114), it is not difficult to establish the position of the vessel relative to the path of movement of the center of the tropical cyclone: if the direction of the wind changes clockwise, then the right half of the cyclone passes through the vessel; if the direction of the wind changes counterclockwise - the left half; if the wind direction does not change - the center of the cyclone. In this way,
Rice. 115.
to choose the right course when meeting a tropical cyclone, you must be guided by the following rules:
1) when sailing in the northern hemisphere (Fig. 115, a): when passing the right half of a tropical cyclone, you need to lie in the sidewind of the right tack (bring the wind to the right cheekbone) and maintain this course until the barometer starts to rise;
When passing the left half of a tropical cyclone, you need to lie on the backstay of the starboard tack (bring the wind to the stern on the right) and keep this course until you leave the zone of the tropical cyclone; being on the path of the center of a tropical cyclone, they also lie on the backstay of the starboard tack (Fig. 115, a) and hold on as indicated earlier;
2) when swimming in the southern hemisphere (Fig. 115, b):
When passing the left half of a tropical cyclone, stay in the port side haul, keeping the course until the barometer begins to rise;
When passing the right half of a tropical cyclone, lie down on the left tack backstay and hold as indicated earlier; while on the path of a hurricane, also bring the wind back to the backstay of the port tack and so rule until the exit from the hurricane zone.
Anticyclones- areas of high atmospheric pressure are, like cyclones, stationary and mobile.
An anticyclone penetrating from the north brings a drop in temperature, clear weather and good visibility during the cold season; in the warm season - thunderstorms, the anticyclone coming from the south, in the cold season brings long cloudy weather; in warm weather - rains with thunderstorms, and at night - dew and ground fogs. a clear sign anticyclonic weather is drastic daily course air temperature, humidity and other meteorological elements.
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The weather on our planet is determined by certain atmospheric formations. Modern man so arranged that he is used to planning his affairs, regardless of weather conditions, but entire areas of its activity are completely dependent on the weather situation. Rainy weather, according to modern meteorologists, is brought by cyclones. What is a cyclone and what is its nature?
Modern ideas about the cyclone
A cyclone is a huge atmospheric vortex, a kind of funnel very large sizes. Its size is determined by the size of the diameter - from hundreds to thousands of hundreds of kilometers. It is formed due to the action of the so-called Coriolis forces. The emergence of such a vortex occurs when a humid and warm tropical air mass collides with a dry and cool Arctic one. The latter is slightly displaced by warm air currents, and they, in turn, begin to rotate along an elliptical trajectory - this is how a vortex is obtained. In its movement, it increases in size by capturing nearby air layers.
If you look at the schematic representation of a cyclone, you can see a low pressure area inside, and a high one closer to the periphery. Therefore, the air in such a formation will move from outside to inside - a huge funnel is formed, which moves at a speed of over fifty kilometers per hour.
What are cyclones?
Climatologists and meteorologists believe that there are two main types:
- tropical
- extratropical.
The former are formed in tropical latitudes, are relatively small in size, but bring with them strong, sometimes hurricane-like, winds and precipitation. Extratropical ones often form in northern and temperate latitudes. They are larger than tropical ones (up to several thousand kilometers), but the speed of air mixing in them is much less. The most energetic among this type are the so-called southern extratropical cyclones. It is with their arrival in a certain territory that heavy rains, winds, thunderstorms.
Cyclones on other planets
Because in our solar system Most planets have an atmosphere atmospheric vortices, similar to the terrestrial, are fixed often. For example, in the atmosphere of Venus, scientists often record storms over south pole, and artificial satellites have repeatedly transmitted images of cyclones from this planet. A long-lived giant cyclone has been recorded in the atmosphere of Jupiter.
Its study is included in the program of the station "Junon", which recently reached this planet.
Anticyclones - an area of high atmospheric pressure with closed concentric isobars at sea level and with air circulation from the center clockwise in the northern hemisphere and counterclockwise in the southern.
The pressure at the center of the anticyclone sometimes reaches 1060–1070 hPa (over Asia in winter), but usually it is lower. Often the anticyclone is multicenter. Horizontal baric gradients in anticyclones are, as a rule, smaller than in cyclones. This is explained by the large horizontal (up to 4000 km) sizes of anticyclones. The central parts of anticyclones are characterized by calm weather. However, in the northern part of the Pacific Ocean, anticyclones in the autumn-winter period can have strong (up to storm) winds.
There are intermediate anticyclones between cyclones of cyclonic series and final anticyclones between cyclonic series. The speed of movement of mobile anticyclones is usually 30–40 km/h. Moving generally from west to east, anticyclones deviate (separate from cyclones) to low latitudes. Usually a mobile anticyclone with a cold front (eastern) periphery and a warm rear (western) "part, warming up and intensifying, turns over time into a warm, high and inactive anticyclone. This process most often occurs in low latitudes, where powerful, high and warm subtropical anticyclones Stabilization of anticyclones occurs both in middle and high latitudes.
In this case, high blocking anticyclones disrupt the general west-east transport. It is stable, inactive anticyclones that are the most important centers of air mass formation.
Features of the structure of the anticyclone.
At the center of the baric maximum there is one or more points with the highest pressure. Usually it is in the range from 1000 to 1035 hPa. There were cases when the pressure rose to 1080 hPa. The dimensions of the baric maximum are measured by the greatest distance between points located on the outer closed isobar. Most often it is 2-3, but it can be up to 4 or more thousand km. As a rule, in anticyclones, the distances between isobars are greater than in cyclones. In the central parts of anticyclones, the pressure gradient is small, correspondingly, the wind speeds are small there. Baric gradients increase towards the periphery of the anticyclone.
Unlike cyclones, fronts on the surface map do not pass through the center of anticyclones. As you know, anticyclones are areas of divergence of air currents. Air flows in all directions from the center of the anticyclone. This eliminates the possibility of convergence of various air masses. The front line can pass only along the edge of the anticyclone or cross its crest approximately perpendicular to the axis of the crest.
11. Stages of anticyclone development.
The emergence and development of anticyclones is closely related to the development of cyclones, i.e. The mechanism of development of anticyclones is also closely related to the process of cyclogenesis. In essence, this is a single process associated with long waves at a stationary front.
Anticyclones originate in the crests of ultralong atmospheric waves on a sedentary front. An analysis of synoptic situations shows that intermediate anticyclones originate in a cold air mass behind the cold front of the last cyclone in a series. In the central parts of anticyclones, atmospheric fronts cannot pass, although some temperature asymmetry remains in them. At the periphery of anticyclones, lines of atmospheric fronts can pass.
The final anticyclone, unlike the intermediate ones, goes through all stages of development: the initial (appearance or origin), the young anticyclone, the stage of maximum development and the stage of destruction. In the first two stages, the anticyclone on the surface weather map is a ridge behind the cold front, in the central part of which closed isobars appear. It is a low cold baric formation. Warm advection is observed in its rear part, and cold advection is observed in its anterior part.
The area of pressure growth near the earth's surface covers the central and front parts of the anticyclone. These factors (advection of heat and cold, and increase in pressure) contribute to the continuation of anticyclogenesis. At the stage of maximum development, the anticyclone near the earth's surface is already outlined by several closed isobars. At the same time, in the first three stages, the anticyclone moves with the leading flow to the east. Anticyclones in the northern hemisphere deviate to the south (in the southern hemisphere - to the north). They invade lower latitudes behind cyclone lines behind cold fronts. At first, this movement is quite fast, but as it ages, the anticyclone decreases.
Anticyclone(from Greek. anti - against, instead of; kyklon - swirling, rotating) is an area in the atmosphere, characterized by increased air pressure in the center.
The wind in the anticyclone blows, bending around the center in the Northern Hemisphere clockwise, in the Southern Hemisphere - counterclockwise, thereby forming a giant vortex.
A distinctive feature of anticyclones is a strictly defined wind direction. The wind is directed from the center to the periphery of the anticyclone, that is, in the direction of decreasing air pressure.
Another component of winds in an anticyclone is the effect of the Coriolis force due to the rotation of the Earth. In the Northern Hemisphere, this causes the moving stream to turn to the right. In the Southern Hemisphere, respectively, to the left. That is why the wind in the anticyclones of the Northern Hemisphere moves in a clockwise direction, and vice versa in the Southern Hemisphere. Cyclones are characterized by the reverse direction of the winds.
In a low anticyclone, cold, the isobars remain closed only in the lowest kilometers, and in the middle troposphere high blood pressure not found at all; the presence of a high-altitude cyclone above such an anticyclone is also possible. The high anticyclone is warm and preserves closed isobars with anticyclonic circulation even in the upper troposphere. Sometimes the anticyclone is multicenter.
On pressure distribution maps, an anticyclone is represented by concentric closed isobars (lines of equal pressure) of an irregular, approximately oval shape. highest pressure- in the center of the anticyclone and decreases towards the periphery.
The pressure in the center of the anticyclone at sea level rises to 1020-1040 mbar, and sometimes (for example, in winter in Asia) - up to 1080 mbar (with an average pressure at sea level of 1010-1015 mbar).
Anticyclones develop daily in the troposphere (lower part of the atmosphere) along with cyclones. Both of them are parts of the general circulation of the atmosphere, creating interlatitudinal air exchange. During the year, many hundreds of them arise over each hemisphere.
The duration of the existence of an individual anticyclone is several days, and sometimes weeks. Like cyclones, anticyclones move in the direction of the general transport of air in the troposphere, i.e. from west to east, deviating towards low latitudes.
The average speed of anticyclone movement is about 30 km/h in the Northern Hemisphere and about 40 km/h in the Southern Hemisphere, but often anticyclones take a long time in a sedentary state (blocking anticyclone).
blocking anticyclone - an almost motionless powerful anticyclone, which has the ability not to let other air masses into the territory occupied by itself. The average lifetime of such an anticyclone is from three to five days, only 1% of anticyclones last up to 15 days.
However, in 1972 and 2010, the anticyclone in summer time(on the European territory of Russia) existed in both cases for almost two months, causing a catastrophic drought and extreme heat, as well as forest fires (as a natural phenomenon).
Also on Earth there are constant anticyclones, these are:
- Azores anticyclone;
- Antarctic anticyclone;
- Bermuda anticyclone;
- Hawaiian anticyclone;
- Greenland anticyclone;
- Canadian anticyclone;
- North Pacific anticyclone;
- Siberian anticyclone;
- South Atlantic High;
- South Indian anticyclone;
- South Pacific anticyclone.
Above the so-called friction layer, i.e. above 1000 m on average, the wind in the anticyclone blows almost along isobars, but in the friction layer it deviates significantly from the isobars outward, at earth's surface at an angle close to 30°. This spreading of air from the area of the anticyclone in the lower layer is accompanied by its inflow into the anticyclone in the overlying layers of the atmosphere and its slow sinking - settling. When air settles, it heats up adiabatically and moves away from the saturation state. Therefore, the temperature of the troposphere in the anticyclone is increased (only over the land surface itself in winter it can be very low), there is little cloudiness, and precipitation, as a rule, is absent. The winds in the inner part of the anticyclone are weak, but intensify towards the periphery.
As the anticyclone develops and the temperature rises in it, the height of the anticyclone also increases: closed isobars are found at ever higher levels in the troposphere and even in the lower stratosphere. The stratosphere in an anticyclone begins at higher altitude than in a cyclone, and its temperature is lowered.
Signs of an anticyclone:
- clear or partly cloudy weather;
- lack of wind;
- lack of precipitation;
- stable nature of the weather (does not noticeably change in time while the anticyclone exists).
In summer, the anticyclone brings hot, cloudy weather. IN winter period anticyclone brings very coldy, sometimes frosty fog is also possible.
An important feature of anticyclones is their formation in certain areas. In particular, anticyclones form over ice fields. And the more powerful the ice cover, the more pronounced the anticyclone; that is why the anticyclone over Antarctica is very powerful, and over Greenland it is low-power, over the Arctic it is medium in severity. Powerful anticyclones also develop in the tropical zone.
An interesting example drastic changes Eurasia serves in the formation of various air masses. In the summertime over her central regions an area is formed low pressure where air is sucked in from neighboring oceans. This is especially pronounced in the South and East Asia: an endless string of cyclones carries moist warm air deep into the mainland.
In winter, the situation changes dramatically: an area forms over the center of Eurasia high pressure- Asian maximum, cold and dry winds from the center of which (Mongolia, Tyva, southern Siberia), diverging clockwise, carry the cold up to the eastern outskirts of the mainland and cause clear, frosty, almost snowless weather for Far East, in northern China. In the western direction, anticyclones influence less intensively. Sharp drops in temperature are possible only if the center of the anticyclone moves to the west of the observation point, because the wind changes direction from south to north. Similar processes are often observed in the East European Plain.
A cyclonic vortex in a horizontal section usually has a rounded or oval shape with a diameter from several hundred to 2-3 thousand km. Its height also varies widely: from 1-2 to 8-10 km and more.
The size of the cyclone depends on the age, i.e., on the duration of its existence, and on the conditions of development. The smallest cyclone in temperate latitudes is in the initial stage of development. The cyclone diameter at this stage is 300-500 km.
On a synoptic map, the area occupied by a cyclone is depicted by a system of circular isobars drawn every 5 or 2.5 mb.
Cyclones arise in the zone of contact between air masses of different properties, i.e., on the main and secondary atmospheric fronts. The formation of a cyclonic vortex is a rather complex process, but the simplest concept about it is as follows.
The parallel movement of two adjacent air masses along the front line at the same speed can continue long time without significant changes in the position of the front. However, if one of them begins to move at a different speed and in the opposite direction, then individual sections of the stationary front will necessarily begin to deform (curve), i.e., they will begin to move. The curvature of the front line, and hence the frontal surface, occurs due to differences in the speed and density of adjacent air masses interacting near the front. Often this is largely facilitated by the orography of a given geographical area (large uplands, ridges). The curved part of the front has the shape of a wave (first flat and then steep). Air flows in the place where the wave originates, violating the straightness, form a vortex: part of the cold air begins to wedge into the warm, and warm - into the cold. With such a movement of air masses, two mobile sections appear on the stationary front - cold and warm, - gradually lengthening as the vortex grows.
The swirling of air flows and the deformation of the stationary front usually occur in the area where greatest fall pressure. Therefore, the appearance of a wave-like curvature of the front is accompanied by the simultaneous formation of a region of low pressure, i.e., cyclone.
1) the stage of the wave, characterized by a weak wave-like curvature of the stationary front and the appearance of a small area of low pressure at the top of the wave;
2) the stage of a young cyclone, characterized by the formation of a clearly defined "warm sector", well-defined cold and warm fronts and a system of several concentrically closed circular isobars;
3) the stage of occlusion (the beginning of attenuation), characterized by a gradual closure of the cold and warm sections of the front, resulting in the formation of an occlusion front; the warm sector, due to the displacement of warm air into the upper layers, gradually narrows and, finally, completely disappears; the entire region in the lower layers becomes completely occupied by the same cold air, which, due to its greater density, causes a general increase in pressure. As a result of pressure equalization, the cyclone, filling up, finally disappears.
One of the important additional properties of each cyclone is that in its area (especially in the central one), as a result of the surface convergence of air flows, orderly ascending air movements develop. The latter, along with the fronts, play a very important role in the formation of weather in the area of the cyclone.
The emerging cyclones never stay in place. The average speed of their movement is 30-40 km/h, sometimes it increases to 70-100 km/h. Young cyclones have the highest translational speed, and old (occluded) cyclones have the lowest.
The duration of the existence of a cyclone ranges from 1 to 6-7 days. During this time, he manages to travel a distance of up to several thousand kilometers.
Cyclones on the fronts often appear in series (4-5 cyclones each), moving one after another in approximately the same direction.
