Geography lesson 8th grade Topic: Atmospheric fronts, cyclones. anticyclones

Updated July 20, 2021 Author: Dmitry Ivanetscu
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Cyclones and anticyclones are moving atmospheric vortices that move gigantic volumes of air masses and determine the nature of the weather over vast areas.

Their sizes are colossal: up to 3 thousand km in diameter and up to 16 km in height.

These powerful atmospheric formations have a similar formation mechanism, but in essence they are antipodes (this can be seen even by their name). Let's look at both of these phenomena in more detail.

What is a cyclone?

In the troposphere (lower atmospheric layer), atmospheric vortices constantly appear and disappear.
Many of them are quite small, but some are enormous in size and reach several thousand kilometers in diameter. If such a vortex moves counterclockwise in the northern hemisphere or clockwise in the southern hemisphere, and there is an area of ​​low pressure inside, then it is called a cyclone. It has a colossal supply of energy and leads to negative weather phenomena such as thunderstorms, strong winds, and squalls.

Depending on where they form, cyclones are classified as tropical or extratropical. The first ones appear in tropical latitudes and are small in size (several hundred kilometers in diameter). At their center there is usually an area with a diameter of 20–25 km with sunny weather, and storms and winds rage at the edges.

Extratropical cyclones, formed in polar and temperate latitudes, reach gigantic sizes and simultaneously cover large areas of the earth's surface. They are called differently in different areas: in America - hurricane, in Asia - typhoon, and in Australia - willy-willy. Each powerful cyclone gets its own name, for example Katrina, Sandy, Nancy.

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 forms 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.

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.

TOP 1 article that is read along with this

• 1. Atmospheric front, weather

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.

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.

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:

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.

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.

Colored lakes of Kelimutu volcano121144.750

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 a 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.