What is a cyclone? Tropical Cyclone in the Southern Hemisphere. Cyclones and anticyclones - characteristics and names

What is a cyclone? Almost every person is interested in the weather - looks at forecasts, summaries. At the same time he often hears about cyclones and anticyclones. Most people know that these atmospheric phenomena are directly related to the weather outside the window. In this article we will try to understand what they are.

What is a cyclone

The cyclone is a low-pressure zone, enclosed by a system of circular winds. Simply put, it is a grand flat atmospheric vortex. And the air in it moves in a spiral around the epicenter, gradually approaching it. The cause of this phenomenon is the reduced pressure in the central part. Therefore, warm moist air masses are carried upward, rotating around the center of the cyclone (eye). This causes the accumulation of clouds of high density. In this zone, strong winds are raging, the speed of which can reach 270 km / h. In the Northern Hemisphere, air rotation is counter-clockwise with some twist to the center. In anticyclones, on the contrary, the air turns clockwise. The tropical cyclone in the Southern Hemisphere works in much the same way. However, the directions are reversed. Cyclones can reach different sizes. Their diameter can be very large - up to several thousand kilometers. For example, a large cyclone is able to cover the entire European continent. As a rule, these atmospheric phenomena are formed at certain geographical points. For example, the southern cyclone comes to the territory of Europe from the Balkans; Areas of the Mediterranean, Black and Caspian Seas.

The mechanism of cyclone formation is the first phase

What is a cyclone and how is it formed? On the fronts, that is, in the areas of contact between warm and cold air masses, cyclones arise and develop. This natural phenomenon is formed when the mass of cold polar air meets a warm wet mass. At the same time, warm air masses break into an array of cold, forming in them something like a tongue. This is the beginning of the origin of the cyclone. Gliding relative to each other, these streams with different temperatures and air densities create a wave on the frontal surface, and consequently, on the front line itself. Obtained education, reminiscent of the arc, turned concavity in the direction of warm air masses. Its segment, located in the front eastern part of the cyclone, is a warm front. The western part, which is located from the rear of the atmospheric phenomenon, is a cold front. In the interval between them in a cyclone, there are often zones of good weather, which usually lasts only a few hours. Such a deflection of the front line is accompanied by a decrease in pressure at the top of the wave.

The evolution of the cyclone: the second phase

The atmospheric cyclone continues to evolve further. The formed wave, moving, as a rule, to the east, northeast or southeast, is gradually deformed. The language of warm air penetrates farther north, forming a well-pronounced warm sector of the cyclone. In its front, warm air masses float to colder and denser ones. When lifting, condensation of steam occurs and the formation of a powerful cumulus rain cloudiness, which leads to precipitation (rain or snow), which lasts a long time. The width of the zone of such frontal precipitation is about 300 in the summer and 400 km in winter. At a distance of several hundred kilometers in front of a warm front near the earth's surface, the ascending air stream reaches an altitude of 10 km or more, at which condensation of moisture occurs to form ice crystals. They form white cirrus clouds. Therefore, it is for them to predict the approach of the warm front of the cyclone.

The third phase of the formation of the atmospheric phenomenon

Further characterization of the cyclone. Wet warm air of the warm sector, passing over the cooler surface of the Earth, forms low layered clouds, fogs, drizzle. After the passage of the warm front, warm, cloudy weather sets in with the southern winds. Signs of this are often the appearance of haze and light mist. Then the cold front approaches. Cold air, passing along it, swims under the warm and pushes it upward. This leads to the formation of cumulonimbus clouds. They are the cause of downpours, thunderstorms, which are accompanied by a strong wind. The width of the zone of precipitation of the cold front is about 70 km. Over time, the rear part of the cyclone comes to replace. It brings strong winds, cumulus clouds and cool weather. Over time, cold air pushes warm to the east. After this, the weather is clear.

How cyclones form: the fourth phase

As the language of warm air penetrates into the cool mass, it is increasingly surrounded by cold air masses, and itself is forced outward. This creates a zone of low pressure in the center of the cyclone, where the surrounding air masses rush. In the Northern Hemisphere, under the influence of the Earth's rotation, they turn counter-clockwise. As already mentioned above, southern cyclones have opposite directions of rotation of air masses. It is due to the fact that the Earth turns around its axis, the winds are not directed to the center of the atmospheric phenomenon, but go along a tangent to the circle around it. During the development of the cyclone they are amplified.

The fifth phase of the cyclone evolution

Cool air in the atmospheric phenomenon moves with a greater speed than warm. Therefore, the cold front of the cyclone gradually merges with the warm, forming the so-called occlusion front. Near the surface of the Earth there is no longer a warm zone. There remain only cold air masses.

Warm air rises upwards, where it gradually cools and is freed from moisture reserves that fall to the ground in the form of rain or snow. The difference between the temperature of cold and warm air is gradually leveled. In this case, the cyclone begins to fade. However, there is no complete homogeneity in these air masses. Following this cyclone, a second wave appears near the front on the crest of a new wave. These atmospheric phenomena always go in series, each following somewhat to the south of the previous one. The height of the cyclone vortex often reaches the stratosphere, that is, it rises to an altitude of 9-12 km. Especially large ones can be found at altitudes of 20-25 km.

Velocity of cyclones

Cyclones are almost always in motion. The speed of their movement can be very different. However, it decreases with the aging of the atmospheric phenomenon. Most often they move at a speed of about 30-40 km / h, passing for 24 hours a distance of 1000-1500 km or more. Sometimes they move with a speed of 70-80 km per hour and even more, passing for a day 1800-2000 km. At this rate, the cyclone that is rampaging today in the region of England can be in the area of Leningrad or Belarus in 24 hours, provoking a sharp change in the weather. As the center of the atmospheric phenomenon approaches, the pressure drops. There are different names for cyclones and hurricanes. One of the most famous is "Katrina", which caused serious damage to the territory of the United States.

Atmospheric fronts

What are the cyclones, we have already figured out. Then we will talk about their structural components - atmospheric fronts. What causes huge masses of moist air in the cyclone to rise high up? To get an answer to this question, we need to first understand what the so-called atmospheric fronts are. We have already said that warm tropical air moves from the equator to the poles and on its way meets cold air masses of temperate latitudes. Since the properties of warm and cool air differ sharply, it is natural that their arrays can not immediately mix. At the meeting point of air masses of different temperatures, a clearly defined band arises - a transition zone between air fronts with various physical properties, which in meteorology is called the frontal surface. The zone dividing the air masses of temperate and tropical latitudes is called the polar front. And the frontal surface between the temperate and arctic latitudes is called the Arctic. Since the density of warm air masses is less than that of cold air, the front is an inclined plane, which always tilts toward the cold mass at an extremely small angle to the surface. Cool air, as more dense, when meeting with a warm one, raises the last one up. When imagining a front between air masses, it must always be borne in mind that this is an imaginary surface inclined above the ground. The line of the atmospheric front, which is formed when this surface is crossed with the terrestrial one, is marked on the weather maps.

Typhoon

I wonder if there is anything more beautiful in nature than a typhoon? A clear, calm sky over a well made of a mad whirlwind, zigzag-pierced lightning, two heights of Everest? However, great trouble threatens anyone who finds himself at the bottom of this well ...

Emerging in equatorial latitudes, typhoons are sent to the west, and then (in the Northern Hemisphere) turn to the northwest, north or northeast. Although each of them does not exactly repeat the path of the other, most of them move along a curve that has the shape of a parabola. The speed of typhoons increases as you move northward. If near the equator and in the direction to the west they move at a speed of only 17-20 km / h, then after a turn to the northeast their speed can reach 100 km / h. However, there are cases when, suddenly deceiving all forecasts and calculations, typhoons then stop altogether, then they rush madly forward.

Eye of the Hurricane

The eye is a bowl with convex walls of clouds, in which there is a relatively weak wind or a complete calm. The sky is clear or partially covered with clouds. The pressure is 0.9 times the normal value. The eye of a typhoon can have a size of 5 to 200 km in diameter, depending on the stage of its development. In a young hurricane, the size of the eye is 35-55 km, and in the developed one it decreases to 18-20 km. In the stage of typhoon fading, the eye grows again. The more clearly it is outlined, the more powerful the typhoon. In such hurricanes winds are stronger at the center. Closing all the streams around the eye, the winds whirl at a speed of up to 425 km / h, gradually slowing down as you move away from the center.