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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Atmosphere and its movement. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Alternative energy sources The earth is surrounded by a thick layer of air - the atmosphere. With height, the air becomes more and more rarefied, less dense. At the surface of the Earth, at sea level, one cubic meter of air weighs about 0 kilograms at 1,3 degrees; and at an altitude of 25 kilometers above the earth's surface, a cubic meter of air already weighs more than thirty times less. Although the thickness of the earth's atmosphere reaches many hundreds of kilometers, but compared to the volume of the globe, it is not at all large. The lower layer of the atmosphere, ranging from 9 to 18 kilometers above the Earth's surface, is called the troposphere. This layer contains more than 3/4 by weight of air. The upper layers are called the stratosphere and ionosphere. Air, like all objects, has weight; it presses on the Earth and on all who live on it with great force; this force at the surface of the Earth is equal to approximately one kilogram for every square centimeter of body area. Air pressure gradually decreases with altitude. But even at the surface of the Earth, as we will see later, atmospheric pressure is never constant, it always changes. Air pressure equal to the pressure exerted at 0 degrees by a mercury column 760 millimeters high is called normal atmospheric pressure. This pressure is equal to 1,0336 kilograms per square centimeter. In meteorology, air pressure is usually measured in millibars. One millibar is approximately equal to the pressure exerted by one gram on the surface of one square centimeter. Normal atmospheric pressure is about 1000 millibars. Meteorology is the science of the atmosphere and the phenomena occurring in it, mostly physical. In a narrower sense, it is the science of the weather and its changes. The atmosphere is never at rest. Everywhere - at the poles and under the tropics, below, at the surface of the Earth, and above, where clouds float - the air is in motion. The movement of air around the earth is called the wind. What causes the movement of air in the atmosphere? Why do the winds blow? To better understand the cause of the wind, remember the well-known phenomenon. When in winter you open the door from a heated room to the street or to a colder room, cold air rushes from below into the warm room. At the same time, warm room air will come out from above. It is easy to verify this. Light a candle or a match and place it at the open door - first at the bottom, at the threshold, and then at the top (Fig. 1). At the bottom, the candle flame will be noticeably deflected by the flow of cold air into the room, and at the top, on the contrary, the flow of warm air coming from the room will deflect the candle flame outward, out of the room.
Why is this happening? Here's why. If we take two identical volumes of air, but differently heated, then the colder volume of air will always be denser, and therefore heavier. When heated, air, like all bodies, expands, becomes less dense and lighter. When we open the door to the street, the colder and denser outside air rushes into the warm room, displacing the less dense and lighter indoor air upwards. As heavier, outside air enters the room from below, is located in the room in the lower layers, near the floor. Displaced by cold heavy air, warm air rises and leaves the room outside through the top of the open doors. This example will allow us to understand the reasons for the movement of air in the atmosphere. The heat of the sun falling on the Earth primarily heats its surface. The atmosphere absorbs only a small part of solar thermal energy. From the heated surface of the globe, the lower layers of air that are in contact with it are heated. Warm layers of air mix with cold ones, give them their heat; this is how the air is heated. Thus, the more the earth's surface is heated by the Sun, the more the air lying above it also heats up. But how is the surface of the Earth heated by the Sun? Far from the same. This is primarily due to the fact that at different times of the year and in different climatic zones.
Earth The sun rises above the horizon in different ways. The higher the Sun is above the horizon, the more solar heat falls on the same area of the Earth's surface (Fig. 2). Due to the spherical shape of the Earth at the equator and near it, the rays of the Sun fall steeply, at noon almost vertically. In countries with a temperate climate, the sun's rays fall on the earth's surface much more gently. And in the polar countries and at the poles, the sun's rays only seem to glide over the earth's surface - the Sun rises relatively low above the horizon. Moreover, in winter the Sun does not appear above the horizon at all: there is a long polar night. For the same reason, the temperature of the Earth's surface changes during the day. During the day, when the Sun is high in the sky, the surface of the Earth is heated the most, in the evening, when the Sun goes below the horizon, the Earth begins to cool, and at night and in the morning its temperature drops even lower.
In addition, the uneven heating of the earth's surface is explained by the fact that different parts of the surface are heated by the Sun and cooled differently. Of particular importance is the ability of water and land to heat up and cool down differently. The land quickly heats up to a higher temperature, but quickly cools down. Water, on the other hand (especially in the seas and oceans), due to constant mixing, heats up very slowly, but retains its heat much longer than land. This is explained by the fact that the heat capacity of water and land is different (heat capacity is the amount of heat required to heat the body by one degree). Different parts of the land are heated differently under the rays of the Sun. For example, black bare ground heats up much more than, say, a green field. Sand and stone are strongly heated by the Sun, forest and grass are much weaker. The ability of different parts of the earth to heat up differently under the rays of the sun also depends on what proportion of the rays incident on the surface is absorbed by the surface and what is reflected. Different bodies have different reflectivity. Thus, snow absorbs only 15 percent of solar energy, sand - 70 percent, and water reflects only 5 percent and absorbs 95 (Fig. 4). Differently heated parts of the globe heat up the air in different ways. How different the amount of heat received by air in different places can be seen from this example. In the desert, air receives 130 times more heat from heated sand than air receives from water in the sea, which is at the same latitude as the desert. But differently heated air has, as already mentioned, different densities. This creates different atmospheric pressure in different places: where the air is less heated and, therefore, denser, the atmospheric pressure is higher; on the contrary, where the air is heated more and therefore more rarefied, the air pressure is lower. And air with higher pressure always tends to move to where there is a lower atmospheric pressure, just as water always flows from a higher level to a lower one. This is how wind occurs in nature. The constant movement of air creates a difference in temperature and pressure in the atmosphere, which is associated with uneven heating of the globe by the Sun.
Thus, the wind in nature arises due to the energy of the sun's rays. In Figure 5 we present a simplified diagram of the main air currents. As can be seen from the diagram, even in its simplest form, the movement of air masses over the Earth is a rather complex picture. At the equator, due to the strong heating of the surface, a constant reduced air pressure is observed. Air streams flow here from the north and from the south and create constant winds - trade winds. These winds are deflected by the rotation of the Earth. In the northern hemisphere, if you look in the direction the trade wind blows, the wind deviates to the right, in the southern hemisphere - to the left. At an altitude of 3-7 kilometers, antitrade winds blow in these areas - winds of reverse directions. Near the equator there is a calm zone. As they move away from the equator, the antitrade winds deviate more and more from their direction towards the poles. At approximately 30 degrees latitude, there are calm bands on both sides of the equator; in these areas, the air masses flowing from the equator (antitrade winds) descend and create areas of high pressure. It is here that the trade winds are born. From here the winds blow towards the poles below. These winds are the prevailing westerlies; compared to the trade winds, they are much more variable. Old sailors call the areas between 30 and 60 degrees "western storms" areas. Calm zones around 30 degrees of latitude are sometimes called horse latitudes. Clear weather prevails here with high atmospheric pressure. This strange name has been preserved since the days when sailors sailed, and referred only to the area around Bermuda. Many ships carried horses from Europe to the West Indies. Once in a period of calm, sailboats lost the ability to move. At the same time, sailors often found themselves in difficult conditions. Water supplies were depleted, horses were the first to die from thirst. The corpses of horses thrown overboard were carried in waves for a long time. Winds blowing from the poles are often referred to as polar easterly winds (see Figure 5).
The picture of the main air currents above the Earth that we have described is further complicated by the constant winds that arise due to the uneven heating of water and land. We have already said that land heats up and cools faster than water. Due to this, during the day, the land has time to heat up much more than water: at night, on the contrary, water cools more slowly than land. Therefore, during the day over land, the air heats up more; heated air rises and increases the atmospheric pressure there. Air currents (at a height of approximately 1 km) rush to the water, and an increased atmospheric pressure is established above the water surface. As a result, a fresh wind, a breeze, begins to blow from the water below (Fig. 6).
But here comes the night. The land is rapidly cooling; the surrounding air is also cooled. Cold air, condensing, descends. Its pressure in the upper layers decreases. At the same time, the water remains warm for a long time and heats the air above it. It has been calculated that the cooling of 1 cubic meter of sea water by one degree gives such an amount of heat that is enough to heat more than 3 thousand cubic meters of air by one degree! When heated, the air rises and creates an increased atmospheric pressure there. As a result, the wind begins to blow on the coast above, and the continental breeze blows below - from land to water (Fig. 7).
Such coastal winds are known to everyone who lives on the shores of large lakes or seas. Well known, for example, are the breezes on the Black, Azov, and Caspian Seas; so, in Sukhumi there are breezes all year round. Breezes also blow on large lakes, such as Sevan, Issyk-Kul, Onega and others. Breezes are also observed on the banks of large rivers, for example, on the Volga near Saratov, on its high right bank. The breezes don't travel far. These are purely local winds. Uneven heating of water and land in the coastal areas of the seas and oceans creates winds similar to breezes. These are the so-called monsoons. Monsoons are seasonal winds, they blow half a year in one direction, half a year in another. They blow due to the different heating and cooling of the seas and continents in winter and summer. In summer, the air over the mainland heats up much more than over the sea. On the contrary, in winter the air over the sea (ocean) is warmer than the air over the mainland. This is explained by the fact that in summer the continents heat up more and in winter they cool more than water, while the sea, which is colder in summer, becomes warmer than land in winter. The large heat capacity of water allows the ocean to store huge reserves of heat from summer. Thus, in summer, the continents, as it were, heat up the atmosphere, while the seas and oceans cool it. In winter, the situation changes: the seas become "atmospheric stoves", and the continents become "refrigerators". For this reason, the monsoons blow; in winter - from land to the sea, and in summer from the sea to the mainland. Monsoons are observed in all climatic zones, even on the shores of the Arctic Ocean. The direction of the monsoons is also affected by the rotation of the Earth. The monsoons are most pronounced in India. Finally, for a general description of air currents, it is necessary to say about atmospheric vortices - cyclones. The air currents that we talked about above are associated with the movement of huge volumes of air in the atmosphere - air masses. It is customary to call an air mass such volumes of air that retain their specific properties for some time. So, for example, the air mass coming from the Arctic brings with it a low temperature and dry, transparent air. The interface between two different air masses is called a front. On both sides of the front, air temperature, wind speed, etc. are often sharply different. Therefore, when a front passes over a place, the weather in this area usually changes dramatically. When two adjacent air masses with different temperatures (and hence different air densities) move at different speeds, or when they move relative to each other along the front (Fig. 8 above) on the boundary surface of air masses, due to the interaction of warm and cold masses of air, a wave disturbance arises - an air wave, as it were, forms at the front. In this case, cold air flows under warm air, and warm air, in turn, begins to push cold air. The air currents begin to swirl. The wave disturbance at the front grows, the interface between two air masses bends more and more steeply: thus, an increasingly strong vortex air movement - a cyclone - gradually arises (see Fig. 8).
There are three main fronts where cyclones occur: arctic, polar and tropical. The Arctic front is the dividing line between the Arctic and polar air (northern latitudes). The polar front separates the polar and tropical air (temperate latitudes). The tropical front is the dividing line between tropical and equatorial air (southern latitudes). Atmospheric pressure in a cyclone decreases towards its center. At the center of the cyclone, air pressure is lowest. If on the map of the area where the cyclone develops, all points with the same pressure are connected by lines - for example, one line connects all points with a pressure of 990 millibars, the other with a pressure of 995 millibars, etc., then it turns out that all such lines are in the cyclone areas will be closed curved lines (Fig. 9). Such lines are called isobars. The isobar at the center of this region will connect the lowest pressure points. Due to this distribution of pressures in the cyclone, the winds blow in it from the edges to the center, so that a circle of counterclockwise winds is formed.
The cyclone moves through the atmosphere; it brings with it a sudden change in wind direction and speed. The average speed of cyclones is 25-40 kilometers per hour. In addition to cyclones, i.e., in other words, areas with low pressure, areas with high pressure also appear in the atmosphere - anticyclones. Here the air pressure rises towards the center. Cyclones and anticyclones often capture very large areas stretching for thousands of kilometers. Therefore, these atmospheric disturbances have a noticeable effect on the general circulation of air in the atmosphere, complicating it even more. The emergence and change of various winds in temperate latitudes are mainly associated with the movement of cyclones and anticyclones. Very strong, hurricane-force winds arise in cyclonic disturbances that originate on the tropical front, over the southern seas. These cyclones are called tropical cyclones. Author: Karmishin A.V.
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