What is a cyclone? Almost everyone is interested in the weather - they look 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. In this article we will try to figure out what they are.
What is a cyclone?
A cyclone is a low-pressure zone covered by a system of circular winds. Simply put, it is a grandiose flat atmospheric vortex. Moreover, the air in it moves in a spiral around the epicenter, gradually approaching it. The reason for this phenomenon is considered to be low pressure in the central part. Therefore, warm, moist air masses rush upward, revolving around the center of the cyclone (eyes). This causes the accumulation of high density clouds. Strong winds are rampant in this zone, the speed of which can reach 270 km / h. In the Northern Hemisphere, air rotates counterclockwise with some swirl towards the center. In anticyclones, on the contrary, air swirls 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, a southern cyclone enters Europe from the Balkans; areas of the Mediterranean, Black and Caspian seas.
The mechanism of cyclone formation - the first phase
What is a cyclone and how is it formed? At the fronts, that is, in the contact zones of warm and cold air masses, cyclones arise and develop. This natural phenomenon is formed when a mass of cold polar air meets a mass of warm moist. At the same time, warm air masses burst into an array of cold ones, forming in them something like a tongue. This is the beginning of the initiation of the cyclone. Sliding relative to each other, these flows with different temperatures and air densities create a wave on the front surface, and therefore on the front line itself. It turns out a formation resembling an arc turned by concavity towards warm air masses. Its segment, located in the front eastern part of the cyclone, is a warm front. The western part, which is located at the rear of the atmospheric phenomenon, is a cold front. In between, zones of good weather are often found in the cyclone, which usually lasts only a few hours. Such a deflection of the front line is accompanied by a decrease in pressure at the wave apex.
Cyclone Evolution: Phase Two
Atmospheric cyclone continues to evolve further. The formed wave, moving, as a rule, to the east, northeast or southeast, is gradually deformed. The tongue of warm air penetrates further north, forming a well-defined warm sector of the cyclone. In its front part, warm air masses float on colder and denser. During the rise, steam condensation occurs and the formation of thick cumulus rain clouds, which leads to rainfall (rain or snow) that lasts a long time. The width of the zone of such frontal precipitation is in the summer about 300, and in winter - 400 km. At a distance of several hundred kilometers in front of a warm front near the earth's surface, the upward air flow reaches a height of 10 km or more, at which moisture condensation occurs with the formation of ice crystals. White cirrus clouds form from them . Therefore, it is precisely from them that one can predict the approach of the warm cyclone front.
The third phase of the formation of atmospheric phenomena
Further characteristic of the cyclone. The moist warm air of the warm sector, passing over the colder surface of the Earth, forms low layered clouds, fogs, drizzle. After passing through the warm front, warm cloudy weather with southerly winds sets in. Signs of this are often the appearance of haze and light fog. Then comes the cold front. The cold air passing along it swims under the warm air and forces it up. 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 precipitation zone of the cold front is about 70 km. Over time, the back of the cyclone replaces. It brings strong winds, cumulus clouds and cool weather. Over time, cold air pushes warmer east. After that, clear weather sets in.
How cyclones form: fourth phase
As the tongue of warm air penetrates into the mass of cool, it turns out to be more and more surrounded by cold air masses, and it is forced out upward. This creates a low pressure zone in the center of the cyclone, where the surrounding air masses rush. In the Northern Hemisphere, under the influence of Earth's rotation, they turn counterclockwise. As mentioned above, southern cyclones have opposite directions of rotation of the air masses. 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 tangentially to the circle around it. In the process of cyclone development, they intensify.
Fifth phase of cyclone evolution
Cool air in an atmospheric phenomenon moves at a faster speed than warm. Therefore, the cold front of the cyclone gradually merges with the warm one, forming the so-called front of occlusion. The Earth’s surface no longer has a warm zone. Only cold air masses remain there.
Warm air rises, where it is gradually cooled and freed from moisture reserves that fall on 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 uniformity in these air masses. Following this cyclone, a second one arises near the front on the crest of a new wave. These atmospheric phenomena always occur in series, with each following being somewhat south of the previous one. The height of the cyclone vortex often reaches the stratosphere, that is, rises to a height of 9-12 km. Especially large can be found at altitudes of 20-25 km.
Cyclone speed
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 a distance of 1000-1500 km or more in 24 hours. Sometimes they move at a speed of 70-80 km per hour and even more, passing 1800-2000 km per day. At this pace, the cyclone that was rampaging today in the region of England, after 24 hours, may already be in the region of Leningrad or Belarus, causing a sharp change in the weather. As the center of the atmospheric phenomenon approaches, the pressure drops. There are various names for cyclones and hurricanes. One of the most famous is Katrina, which caused serious damage to the United States.
Atmospheric fronts
What are cyclones, we have already figured out. Next, we will talk about their structural components - atmospheric fronts. What causes huge masses of moist air in a cyclone to rise high? To get an answer to this question, we first need to figure out 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 the cold air masses of temperate latitudes. Since the properties of warm and cool air are sharply different, it is natural that their masses cannot immediately mix. At the meeting point of air masses of different temperatures, a distinct band appears - a transitional zone between air fronts with different physical properties, which in meteorology is called the frontal surface. The zone separating the air masses of temperate and tropical latitudes is called the polar front. And the frontal surface between temperate and arctic latitudes is called arctic. Since the density of warm air masses is less than that of cold masses, the front is an inclined plane that always leans toward the cold massif at an extremely small angle to the surface. Cool air, as thicker, when meeting with warm raises the latter up. When imagining the front between the air masses, you must always bear in mind that this is an imaginary surface, tilted above the ground. The atmospheric front line, which is formed when this surface intersects the earth, is marked on weather maps.
Typhoon
I wonder if there is anything prettier in nature than a phenomenon like a typhoon? A clear calm sky over a well made of insane whirlwind, pierced by zigzags of lightning, walls two Everests high? However, big troubles threaten anyone who is at the bottom of this well ...
Originating in equatorial latitudes, typhoons head west, and then (in the Northern Hemisphere) turn 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. Typhoon speed increases as you move north. If near the equator and towards the west they move at a speed of only 17-20 km / h, then after turning to the northeast, their speed can reach 100 km / h. However, there are cases when, suddenly deceiving all forecasts and calculations, typhoons either completely stop, or madly rush forward.
Eye of the Hurricane
The eye is a bowl with convex walls of clouds, in which a relatively weak wind or a complete calm is observed. The sky is clear or partially covered by clouds. Pressure is 0.9 of 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 an eye is 35-55 km, while in a developed one, it decreases to 18-3 km. In the dying stage of the typhoon, the eye grows again. The sharper it is outlined, the more powerful the typhoon. In such hurricanes, the winds are stronger at the center. Closing all the flows around the eye, the winds spin at a speed of up to 425 km / h, gradually slowing down as they move away from the center.