Why do air masses move north and south throughout the year?

In the process of moving air masses, water vapor is transported above the surface of the earth, under certain conditions it condenses and falls to the ground in droplet-liquid (rain) or solid (snow) form.  

The third reason for the movement of air masses is dynamic, which contributes to the formation of areas high pressure. Due to the fact that in equatorial zone The most heat comes, and air masses rise up to 18 km here. Therefore, intense condensation and precipitation in the form of tropical showers are observed. In the so-called horse latitudes (about 30 N and 30 S) cold, dry air masses, descending and adiabatically heating, intensively absorb moisture. Therefore, the main deserts of the planet naturally form in these latitudes.  

Solar energy causes planetary movements of air masses as a result of their uneven heating. Grandiose processes arise atmospheric circulation which are rhythmic in nature.  

This is a ventilation system in which the movement of air masses is carried out due to the resulting pressure difference outside and inside the building. The pressure difference is caused by the difference in the densities of the external and internal air and the wind pressure acting on the building. When the wind acts on the surfaces of a building on the leeward side, excess pressure is formed, and on the windward side - a vacuum. Natural ventilation is realized in the form of infiltration and aeration.  

Within the East European Plain, the movement of air masses is predominantly latitudinal: from the west, from the side Atlantic Ocean, to the east, deep into the continent. This is of great importance for the climate of the region, especially its western part, as it ensures the distribution of heat brought by the Gulf Stream over a wide area. The latitudinal circulation is especially pronounced in winter time of the year. Warm air, coming from the ocean, gradually cools as it moves over the plain, so the eastern regions of the country at this time are always colder than the western ones. IN summer time the opposite relationship is usually observed, since sea ​​air colder than continental. As the influence of the Atlantic Ocean weakens in east direction The continentality of the climate also increases noticeably. In accordance with these general patterns, the climate of the East European Plain changes from marine in the coastal regions of the Baltic states to continental, and in some places sharply continental in the Urals and the Caspian region. With air masses coming to the territory of the East European Plain from the Atlantic, and to Ukraine also from the side Mediterranean Sea, the bulk of moisture arrives, so the climate of the western regions is more humid than the eastern ones.  

Atmospheric circulation in the United States causes air masses to move from the Midwest to the Northeast. Along with the air, contamination with SO2 and the products of its interaction with other substances is also carried.  

According to observations of the formation and movement of air masses meteorological stations weather maps, or synoptic maps, are compiled. Such maps are used for weather forecasting, which has great value for a wide variety of industries National economy (Agriculture, air Transport etc. Accurate assessment of atmospheric conditions and weather forecasts are also important for hydrogeological research.  

Vortexes that arise in the atmosphere due to the movement of air masses relative to each other (tornadoes) rest on the surface of the earth or water.  

As is known, the reason for the formation of wind flows and the movement of air masses is uneven heating of different areas earth's surface associated with pressure changes. The wind flow is directed towards lower pressure, but the rotation of the Earth also affects the circulation of air masses in on a global scale.  

The movement of air masses should lead, first of all, to the smoothing of baric and temperature gradients. However, on our rotating planet with different heat capacity properties of the earth’s surface, different heat reserves of land, seas and oceans, the presence of warm and cold ocean currents, polar and continental ice the processes are very complex and often the contrasts in the heat content of various air masses not only do not smooth out, but, on the contrary, increase.[...]

The movement of air masses over the Earth's surface is determined by many reasons, including the rotation of the planet, the uneven heating of its surface by the Sun, the formation of zones of low (cyclones) and high (anticyclones) pressure, flat or mountainous terrain and much more. In addition, at different altitudes the speed, stability and direction of air flows are very different. Therefore, the transport of pollutants entering different layers of the atmosphere occurs at different speeds and sometimes in other directions than in the ground layer. With very strong emissions associated with high energies, pollution entering high, up to 10-20 km, layers of the atmosphere can move thousands of kilometers within a few days or even hours. Thus, volcanic ash ejected by the explosion of the Krakatoa volcano in Indonesia in 1883 was observed in the form of peculiar clouds over Europe. Radioactive fallout of varying intensity after testing particularly powerful hydrogen bombs fell on almost the entire surface of the Earth.[...]

Movement of air masses - wind resulting from differences in temperature and pressure in different regions planet, affects not only the physical and chemical properties of the air itself, but also the intensity of heat exchange, changes in humidity, pressure, chemical composition of the air, reducing or increasing the amount of pollution.[...]

The movement of air masses can be in the form of their passive movement of a convective nature or in the form of wind - due to the cyclonic activity of the Earth's atmosphere. In the first case, the dispersal of spores, pollen, seeds, microorganisms and small animals is ensured, which have special devices for this - anemochores: very small sizes, parachute-like appendages, etc. (Fig. 2.8). This entire mass of organisms is called aeroplankton. In the second case, the wind also transports aeroplankton, but over much longer distances, and can also transport pollutants to new zones, etc. [...]

Movement of air masses (wind). As is known, the reason for the formation of wind flows and the movement of air masses is the uneven heating of different parts of the earth's surface associated with pressure changes. The wind flow is directed towards lower pressure, but the rotation of the Earth also affects the circulation of air masses on a global scale. In the surface layer of air, the movement of air masses influences all meteorological factors environment, i.e., on climate, including regimes of temperature, humidity, evaporation from the surface of land and sea, as well as plant transpiration.[...]

ABNORMAL MOVEMENT OF THE CYCLONE. Movement of the cyclone in a direction sharply diverging from the usual one, i.e., from eastern half horizon to the west or along the meridian. A.P.C. is associated with the anomalous direction of the leading flow, which in turn is caused by the unusual distribution of warm and cold air masses in the troposphere.[...]

AIR MASS TRANSFORMATION. 1. A gradual change in the properties of the air mass as it moves due to changes in the conditions of the underlying surface (relative transformation).[...]

The third reason for the movement of air masses is dynamic, which contributes to the formation of areas of high pressure. Due to the fact that the most heat comes to the equatorial zone, air masses rise up to 18 km here. Therefore, intense condensation and precipitation in the form of tropical showers are observed. In the so-called “horse” latitudes (about 30° N and 30° S), cold dry air masses, sinking and adiabatically heating, intensively absorb moisture. Therefore, the main deserts of the planet naturally form in these latitudes. They were mainly formed in western parts continents. The westerly winds coming from the ocean do not contain enough moisture to transfer to the descending dry air. Therefore, there is very little rainfall here.[...]

The formation and movement of air masses, the location and trajectories of cyclones and anticyclones are of great importance for making weather forecasts. A visual representation of the weather conditions in this moment a synoptic map provides over a wide area.[...]

WEATHER CHANGE. The movement of certain weather conditions together with their “carriers” - air masses, fronts, cyclones and anticyclones.[...]

In a narrow boundary strip separating air masses, frontal zones (fronts) arise, characterized by an unstable state meteorological elements: temperature, pressure, humidity, wind direction and speed. Here, with exceptional clarity, the most important principle in physical geography of contrasting environments is manifested, expressed in a sharp activation of the exchange of matter and energy in the zone of contact (contact) of different properties. natural complexes and their components (F.N. Milkov, 1968). Active exchange of matter and energy between air masses during frontal zones manifests itself in the fact that it is here that the origin, movement with a simultaneous increase in power and, finally, the extinction of cyclones occur.[...]

Solar energy causes planetary movements of air masses as a result of their uneven heating. Grandiose processes of atmospheric circulation arise, which are rhythmic in nature.[...]

If in a free atmosphere with turbulent movements of air masses this phenomenon does not play a noticeable role, then in still or low-moving indoor air, this difference should be taken into account. In close proximity to the surface of various bodies we will have a layer with some excess of negative air ions, while ambient air will be enriched with positive air ions.[...]

Non-periodic weather changes are caused by the movement of air masses from one geographical area to another to common system atmospheric circulation.[...]

Due to the fact that at high altitudes the speed of movement of air masses reaches 100 m/sec, ions moving in a magnetic field can be displaced, although these displacements are insignificant compared to transport in the flow. What is important for us is the fact that polar zones ah, where are the power lines magnetic field The Earth is closed on its surface, the distortions of the ionosphere are very significant. The number of ions, including ionized oxygen, in the upper layers of the atmosphere of the polar zones is reduced. But the main reason low content ozone in the pole region - low intensity of solar radiation falling even during polar day at small angles to the horizon, and during the polar night, completely absent. The shielding role of the ozone layer in itself polar regions is not so important precisely because of the low position of the Sun above the horizon, which eliminates the high intensity of UV irradiation of the surface. However, the area of ​​polar “holes” in the ozone layer is a reliable indicator of changes in the total ozone content in the atmosphere.[...]

Progressive horizontal movements water masses, associated with the movement of significant volumes of water over long distances, are called currents. Currents arise under the influence of various factors, such as wind (i.e. friction and pressure of moving air masses on the water surface), changes in the distribution of atmospheric pressure, uneven density distribution sea ​​water(i.e., horizontal pressure gradient of waters of different densities at the same depths), tidal forces of the Moon and the Sun. On the nature of the movement of water masses significant influence They also exert secondary forces, which do not themselves cause it, but appear only in the presence of movement. These forces include the force arising due to the rotation of the Earth - the Coriolis force, centrifugal forces, friction of water against the bottom and shores of continents, internal friction. Great influence on sea ​​currents influence the distribution of land and sea, the bottom topography and the outlines of the coasts. Currents are classified mainly by origin. Depending on the forces that excite them, currents are combined into four groups: 1) frictional (wind and drift), 2) gradient-gravitational, 3) tidal, 4) inertial.[...]

Wind turbines and sailing ships are propelled by the movement of masses of air due to the heating of it by the sun and the creation of air currents or winds. 1.[ ...]

TRAFFIC CONTROL. Formulation of the fact that the movement of air masses and tropospheric disturbances mainly occurs in the direction of isobars (isohypses) and, consequently, air currents of the upper troposphere and lower stratosphere.[...]

This, in turn, may lead to disruption of the movement of air masses near industrial areas located near such a park and increased air pollution.[...]

Most weather phenomena depend on whether air masses are stable or unstable. When the air is stable, vertical movements in it are difficult; when the air is unstable, on the contrary, they develop easily. The stability criterion is the observable temperature gradient.[ ...]

Hydrodynamic, closed type with adjustable air cushion pressure, with pulsation damper. Structurally, it consists of a body with a lower lip, a manifold with a tilting mechanism, a turbulator, upper lip with a mechanism for vertical and horizontal movement, mechanisms for precise adjustment of the profile of the outlet slot with the ability to automatically control the transverse profile of the paper web. The surfaces of the box parts in contact with the mass are thoroughly polished and electropolished.[...]

Potential temperature, in contrast to molecular temperature T, remains constant during dry adiabatic movements of the same air particle. If during the movement of the air mass its potential temperature changes, then an influx or outflow of heat is observed. Dry adiabatic is a line of equal value of potential temperature.[...]

Most typical case dispersion is the movement of a gas stream in a moving medium, i.e., during the horizontal movement of atmospheric air masses.[...]

The main reason for short-period OS oscillations, according to the concept put forward in 1964 by the author of the work, is the horizontal movement of the ST axis, directly related to the movement of long waves in the atmosphere. Moreover, the direction of the wind in the stratosphere above the observation site does not play a significant role. In other words, short-period oscillations of the OS are caused by changes in air masses in the stratosphere above the observation site, since these masses separate the ST.[...]

The state of the free surface of reservoirs due to large area their mirrors strong influence the wind is exerting. Kinetic energy air flow through frictional forces at the interface between two media, it is transferred to the masses of water. One part of the transferred energy is spent on the formation of waves, and the other goes to create a drift current, i.e. progressive movement of surface layers of water in the direction of the wind. In reservoirs of limited size, the movement of water masses by a drift current leads to a skew of the free surface. Near the windward coast the water level decreases - a wind surge occurs; near the leeward coast the level rises - a wind surge occurs. At the Tsimlyansk and Rybinsk reservoirs, level differences of 1 m or more were recorded at the leeward and windward shores. With prolonged wind, the distortion becomes stable. Masses of water that are supplied to the leeward coast by the drift current are discharged into reverse side bottom gradient current.[...]

The results obtained are based on solving the problem for stationary conditions. However, the terrain scales under consideration are relatively small and the time of movement of the air mass ¿ = l:/i is small, which allows us to limit ourselves to parametric consideration of the characteristics of the oncoming air flow.[...]

But the icy Arctic causes complications in agriculture not only due to cold and long winters. Cold, and therefore dehydrated Arctic air masses do not warm up during the spring-summer movement. The higher the air temperature, the more pain! moisture is needed to saturate it. I.P. Gerasimov and K.K. Mkov noted that “at present, a simple increase in ice cover in the Arctic basin causes. . . zas; in Ukraine and the Volga region" 2.[...]

In 1889, a giant cloud of locusts flew from the coast of North Africa across the Red Sea to Arabia. The movement of insects lasted the whole day, and their mass amounted to 44 million tons. V.I. Vernadsky regarded this fact as evidence enormous power living matter, an expression of the pressure of life striving to take over the entire Earth. At the same time, he saw in this a biogeochemical process - the migration of elements included in the locust biomass, a completely special migration - through the air, over long distances, not consistent with normal mode movement of air masses in the atmosphere.[...]

Thus, the main factor determining the speed of katabatic winds is the temperature difference ice cover and atmosphere 0 and the angle of inclination of the ice surface. The movement of a cooled air mass down the slope of the Antarctic ice dome is enhanced by the effects of the fall of the air mass from the height of the ice dome and the influence of pressure gradients in the Antarctic anticyclone. Horizontal baric gradients, being an element of the formation of katabatic winds in Antarctica, contribute to increased air outflow to the periphery of the continent, primarily due to its supercooling at the surface of the ice sheet and the slopes of the ice dome towards the sea.[...]

The analysis of synoptic maps is as follows. Based on the information plotted on the map, the actual state of the atmosphere at the time of observation is established: the distribution and nature of air masses and fronts, the location and properties of atmospheric disturbances, the location and nature of cloudiness and precipitation, temperature distribution, etc. for given atmospheric circulation conditions. By compiling maps for different periods, you can use them to monitor changes in the state of the atmosphere, in particular the movement and evolution of atmospheric disturbances, the movement, transformation and interaction of air masses, etc. The representation of atmospheric conditions on synoptic maps provides a convenient opportunity for information about the state of the weather.[. ..]

Atmospheric macroscale processes studied using synoptic maps and causing weather patterns over large geographic areas. This is the emergence, movement and change in the properties of air masses and atmospheric fronts; the emergence, development and movement of atmospheric disturbances - cyclones and anticyclones, the evolution of condensation systems, intramass and frontal, in connection with the above processes, etc.[...]

Until aerial chemical treatment is completely excluded, it is necessary to make improvements in its use by carefully selecting objects, reducing the likelihood of “drifts” - movements of sawing air masses, controlled dosage, etc. For primary care in clearings by using herbicides, it is advisable to use typological diagnostics to a greater extent fellings Chemistry is a powerful means of caring for forests. But it is important that chemical care does not turn into poisoning of the forest, its inhabitants and visitors.[...]

In the nature around us, water is found in constant movement- and this is just one of many natural cycles of substances in nature. When we say “movement,” we mean not only the movement of water as a physical body (flow), not only its movement in space, but, above all, the transition of water from one physical condition to another. In Figure 1 you can see how the water cycle occurs. On the surface of lakes, rivers and seas, water is influenced by energy sun rays turns into water vapor - this process is called evaporation. In the same way, water evaporates from the surface of snow and ice cover, from plant leaves and from the bodies of animals and humans. Water vapor with warmer air currents rises to the upper layers of the atmosphere, where it gradually cools and turns back into a liquid or turns into a solid state - this process is called condensation. At the same time, water moves with the movement of air masses in the atmosphere (winds). From the resulting water droplets and ice crystals, clouds are formed, from which rain or snow eventually falls to the ground. Returned to earth as atmospheric precipitation water flows down slopes and collects in streams and rivers that flow into lakes, seas and oceans. Some of the water seeps through the soil and rocks and reaches underground and groundwater, which also, as a rule, flow into rivers and other bodies of water. Thus, the circle closes and can be repeated in nature endlessly.[...]

SYNOPTIC METEOROLOGY. A meteorological discipline that took shape in the second half of the 19th century. and especially in the 20th century; the study of atmospheric macroscale processes and weather prediction based on their study. Such processes are the emergence, evolution and movement of cyclones and anticyclones, which are closely related to the emergence, movement and evolution of air masses and fronts between them. The study of these synoptic processes is carried out using a systematic analysis of synoptic maps, vertical sections of the atmosphere, aerological diagrams and other auxiliary means. The transition from synoptic analysis of circulation conditions over large areas of the earth's surface to their forecast and to the forecast of associated weather conditions still largely comes down to extrapolation and qualitative conclusions from the provisions of dynamic meteorology. However, in the last 25 years, numerical (hydrodynamic) forecasting of meteorological fields has been increasingly used by numerically solving the equations of atmospheric thermodynamics on electronic computers. See also weather service, weather forecast and a number of other terms. Common synonym: weather forecaster.[...]

The case of jet propagation that we have analyzed is not typical, since there are very few windless periods in almost any area. Therefore, the most typical case of scattering is the movement of a gas jet in a moving medium, i.e., in the presence of horizontal movement of atmospheric air masses. [...]

It is obvious that simply air temperature T is not a conservative characteristic of the heat content of air. Thus, with a constant heat content of an individual volume of air (turbulent mole), its temperature can vary depending on pressure (1.1). Atmosphere pressure, as we know, decreases with height. As a result, vertical movement of air leads to changes in its specific volume. In this case, the work of expansion is realized, which leads to changes in the temperature of air particles even in the case when the processes are isentropic (adiabatic), i.e. there is no heat exchange between an individual mass element and the space surrounding it. Changes in the temperature of the air moving vertically will correspond to dry-diabatic or moist-diabatic gradients, depending on the nature of the thermodynamic process.

Answering the question of what an air mass is, we can say that it is the human habitat. We breathe it, see it, feel it every day. Without the surrounding air, humanity would not be able to conduct its life activities.

The role of flows in the natural cycle

What is an air mass? This brings a change in weather conditions. Due to the natural movement of the environment, precipitation moves thousands of kilometers along to the globe. Snow and rain, cold and warmth come according to established patterns. Scientists can predict climate change by delving deeper into the patterns of natural disasters.

Let's try to answer the question: what is air mass? Its striking examples include cyclones that move continuously. With them comes warming or cooling. They move with a constant pattern, but in rare cases they deviate from the usual trajectory. As a result of such disturbances, disasters are discovered in nature.

So, in the desert snow falls from the encountered cyclones different temperatures or tornadoes and hurricanes are formed. This all relates to the answer to the question: what is an air mass? Its condition determines what the weather will be like, the saturation of the air with oxygen or moisture.

Change of heat and cold: reasons

Air masses are the main participant in the formation of climate on earth. Heating of the layers of the atmosphere occurs due to the energy received from the sun. Due to temperature changes, the density of the air changes. More sparse areas are filled with dense volumes.

Air masses are a collection of various conditions gaseous layers atmospheres that depend on the redistribution of heat due to the change of day and night. At night, the air cools, a wind appears, moving from more dense layers into sparse ones. The strength of the flow depends on the rate of temperature decrease, terrain, and humidity.

The movement of masses is affected by both horizontal and vertical temperature differences. During the day, the earth receives heat from the sun, beginning to release it to the lower layers of the atmosphere in the evening. This process continues all night, and the next morning water vapor is concentrated in the air. This causes precipitation: dew, rain, fog.

What are the different gaseous states?

The characteristics of air masses are a quantitative value with which one can describe certain states of gaseous layers and evaluate them.

There are three main indicators of the layers of the troposphere:

• Temperature provides information about the origin of mass displacement.
• Humidity is high in places located near seas, lakes and rivers.
• Transparency is defined externally. This parameter is affected by solid dust particles suspended in the air.

The following types of air masses are distinguished:

• Tropical - move to the side temperate latitudes.
• Arctic - cold masses, moving towards warm latitudes from the northern part of the planet.
• Antarctic - cold, moving from the south pole.
• Moderate, on the contrary, are warm air masses and move towards the cold poles.
• Equatorial regions are the warmest and disperse into areas with lower temperatures.

Subtypes

When air masses move, they transform from one geographical type to another. There are subtypes: continental, maritime. Accordingly, the former predominate on the land side, the latter bring moisture from the vast seas and oceans. There is a pattern of temperature differences in such masses depending on the season: in the summer the winds from the land are much warmer, and in the winter they warm the sea.

Everywhere there are dominant air masses that constantly prevail due to established patterns. They determine the weather in a given area, and, as a result, this leads to differences in flora and fauna. IN Lately The transformation of air masses has changed significantly due to human activity.

The transformation of air masses manifests itself more clearly on the coasts, where currents from land and sea meet. In some areas the wind does not subside even for a second. More often it is dry and does not change direction long time.

How does flow transformation occur in nature?

Air masses become visible under certain conditions. Examples of such phenomena are clouds, clouds, fogs. They can be located both at an altitude of thousands of kilometers and directly above the ground. The latter are formed when the ambient temperature sharply decreases due to high humidity.

The sun is playing important role in the endless process of movement of air masses. The change of day and night causes the streams to rush upward, lifting particles of water with them. High in the sky they crystallize and begin to fall. IN summer season When it is warm enough, the ice has time to melt in flight, so precipitation is observed mainly in the form of rain.

And in winter, when cold streams pass over the ground, snow or even hail begins to fall. Therefore, in areas of equatorial and tropical latitudes, warm air spreads the crystals. In the regions of the northern regions, these precipitations occur almost every day. Cold currents are heated by the heated earth's surface, the rays of the sun pass through the air layers. But the heat given off at night causes the formation of clouds, morning dew, and fog.

How do you recognize a change in weather based on certain signs?

Even in the past, they learned to predict precipitation based on obvious signs:

• In the distance, white or ray-shaped areas become barely visible.
• A sharp increase in wind indicates the approach of cold masses. It may rain or snow.
• Clouds always gather in areas of low pressure. Exists the right way define this area. To do this, you need to turn your back to the stream and look a little to the left of the horizon. If condensations appear there, then this is a clear sign of inclement weather. Don't be confused: clouds on the right side are not a sign of worsening weather conditions.
• The appearance of a whitish veil when the sun begins to fog.

The wind subsides when cold area passes. Warmer currents fill the resulting vacuum, and it often becomes stuffy after rain.

Large volumes of air in the troposphere, having more or less the same properties, are called air masses. The air mass covers an area of ​​thousands and millions of square kilometers, extending upward for several kilometers and even reaching the boundary of the troposphere. It is characterized by a general direction of movement, but inside this volume of air there may be different winds. An air mass acquires its properties (temperature, humidity, dust content) in contact with the underlying surface over which it lingers. Moving over a surface with different properties, it heats up or cools, moisturizes or becomes drier and gradually turns into another air mass (transforms).

Stand out main (zonal) types of air masses , forming in latitudinal zones with different atmospheric pressure:

equatorial - warm and humid;

two tropical - warm and dry over continents;

two air masses temperate latitudes - less warm and more humid than tropical, but warmer and more humid than Arctic and Antarctic;

Arctic and Antarctic - cold and dry.

All zonal air masses, except the equatorial one, are divided into continental And maritime.

Since the high and low pressure belts shift throughout the year, the air masses also shift. In addition to the belts of their permanent presence, belts arise in which one air mass dominates in winter, and another in summer.

Properties of air masses

Atmospheric fronts

Atmospheric front called the division between air masses with different properties. The most important of these properties is temperature. Cold air, meeting warm air, always ends up at the bottom. It flows under the warm one, trying to push it upward. Warm air, on the contrary, flows onto cold air and if it presses against it, it itself rises along the interface plane. Depending on which air is more active and in which direction the front moves, it is called either warm or cold.

Warm front means the onset of warm air, slowly pushing aside cold air. It brings warming, preceded by precipitation from stratus clouds that form in rising warm air.

Cold front brings cold weather. Its arrival is accompanied by increased wind, and sometimes thunderstorms and tornadoes. Precipitation falls mainly after the front line passes.

Atmospheric processes associated with fronts are called frontal processes.

Warm and cold fronts usually occur in zones separating the main (zonal) types of air masses. These zones are called frontal zones , or climatological fronts . There are only five such fronts: arctic And Antarctic, two temperate (polar) and one tropical . The first two separate the Arctic (Antarctic) air from the air of temperate latitudes, the second two separate the air of temperate latitudes from the tropical air. A tropical front forms where tropical and equatorial air meet, differing in humidity rather than temperature. He is alone and is always in the hemisphere where it is summer.

The boundaries of climate zones are associated with climatological fronts

Atmospheric pressure constantly changes over time. home the reason for this is uneven heating of the air. The change in pressure is predominantly non-periodic.

The distribution of pressure in the atmospheric layer can be clearly shown using surfaces drawn through points with the same pressure and called isobaric surfaces(Fig. 17).

The lines formed from the intersection of isobaric surfaces with the earth's surface are called isobars. Straight-line isobars arise from the intersection of the earth's surface by parallel isobaric surfaces at a certain angle. Closed isobars are formed when convex or concave isobaric surfaces intersect the earth's surface.

System of closed isobars With the reduced pressure in the center forms a barometric minimum, or cyclone, a system of closed isobars with increased pressure in the center - barometric maximum, or anticyclone. Unclosed systems of isobars form a pressure trough, a ridge And saddle (Fig. 18).

The density of isobars depends on the change in pressure per unit distance. This change towards decreasing pressure perpendicular to the isobar is called the pressure gradient.

An idea of ​​the distribution of pressure over the earth's surface over a certain period of time can be obtained from isobar maps (Fig. 19, 20). Analysis of the maps shows a pronounced zonality in the distribution of pressure throughout the year, especially over the ocean. There is an area of ​​low pressure above the equator. In the subtropics - zone high blood pressure, which breaks up into separate maxima over the ocean. In temperate latitudes there is a zone of low pressure, above the poles there is a zone of high pressure.

Depending on the season, high and low pressure zones shift to the north and south, and over the continents they, in addition, change their sign to the opposite.

Pressure highs and lows have big influence on weather and climate, that's why they are called centers of atmospheric action spheres.

A comparison of maps of pressure distribution at sea level with maps of pressure at different altitudes shows that unevenness in the distribution of pressure near the Earth's surface gradually smoothes out with height. The alternation of high and low pressure belts disappears; The area of ​​high pressure is located above the equator, the pressure decreases towards the poles.

Wind, or the horizontal movement of air, is characterized by speed and direction.

Wind speed is measured in meters

per second, in kilometers per hour and in Beaufort scale points (from 0 to 12 points). The Beaufort scale relates wind strength to various effects (sea roughness, swaying of trees and branches, etc.). The direction of the wind is determined by the position of the point on the horizon from which it blows. Wind direction can be expressed by azimuth or bearing. A visual representation of the frequency of a particular wind direction is given by

compass roses

(Fig. 21). A wind rose is constructed by plotting the percentage repeatability of the corresponding wind in the direction of the points and connecting the ends of the resulting segments. The direction of the wind depends on the direction of the pressure gradient, which deflects the effects of the Earth's rotation, friction, and when moving along curvilinear isobars - on centrifugal force. At the Earth's surface, the usual wind speed is about 4 - 8 m/sec and rarely exceeds 15 The direction of the wind depends on the direction of the pressure gradient, which deflects the effects of the Earth's rotation, friction, and when moving along curvilinear isobars - on centrifugal force. m/sec. m/sec In storms and hurricanes of moderate latitudes, speeds can exceed 30 and reach 60 in gusts In tropical hurricanes speeds reach 65 m/sec m/sec, and in some gusts up to 100

In the so-called jet streams in the upper troposphere and lower stratosphere, the average wind speed over a long time and over a large area can reach 70-100

m/sec. If you show the wind direction at different points on a map with short arrows, and then draw solid lines so that the arrows showing the wind direction are tangent to them, you get current lines. With rectilinear isobars, the current lines are straight. In cyclones they look like spirals converging in the center, in anticyclones they diverge from the center (Fig. 22).

If the movement of air occurs in a curvilinear manner, then centrifugal force also appears. Then, in the case of uniform motion, three forces acting on the air must be balanced - gradient, deflecting the rotation of the Earth and centrifugal. Let us assume that the motion trajectories are circles. Speed

at any point of the trajectory it is directed tangentially to the circle. The deflecting force is directed at right angles to the speed, i.e., along the radius of the circle to the right (in the northern hemisphere). The centrifugal force is also directed along the radius of the circular trajectory towards its convexity. The gradient force must balance the geometric sum of these two forces and lie on the same straight line with them, that is, on the radius of the circle. Since the tangent to the isobar lies at right angles to the gradient, the wind is directed along the isobar. This wind is called gradient(Fig. 23).

Centrifugal force under actual atmospheric conditions is generally less strength gradient. Therefore, to balance the acting forces, it is necessary that the deflecting force of the Earth's rotation be directed in the same way as the centrifugal force, and that they together balance the gradient force.

This means that the deflection force must also be directed outward, away from the center of the cyclone. The wind speed should deviate at a right angle from the deflecting force to the left (in the northern hemisphere). Therefore, the wind must be directed counterclockwise. In an anticyclone, reasoning in this way, one can prove that the wind will be directed clockwise. IN

lower layers

atmosphere, air movement is also influenced by friction. It slows down the movement of air and changes its direction. Let us imagine uniform rectilinear movement of air in the presence of friction force. In this case, three forces are balanced: gradient, deflection and friction (Fig. 24). Since the strength friction does not lie on the same straight line with the deflecting force, then the gradient force, which balances the sum of the other two forces, cannot lie on the same straight line with the deflecting force. It will make an acute angle with the wind speed. In other words, the wind speed will cross the isobars, deviating from the gradient to the right. In this case, the wind speed can be decomposed into two components - along the isobar and along the gradient. air in circular isobars in the presence of friction force, then the wind speed will also deviate from the isobars, having a component directed along the baric gradient. Drawing streamlines in the lower layers of the cyclone, we see that they are spirals, twisting counterclockwise and converging to the center of the cyclone. In the lower layers of the anticyclone, streamlines are spirals diverging clockwise from the center of the anticyclone (see Fig. 22).

Air masses and fronts.Air masses in their properties bear the imprint of the region of the Earth where they were formed. Moving to other areas, air masses transfer their weather patterns there. Predominance in a given area of ​​mass certain type creates a characteristic climate regime areas. By geographical principle Four types of air masses with different zonal positions of foci can be distinguished: Arctic (Antarctic), polar (temperate latitudes), tropical and equatorial. Each type is characterized by its own temperature range, its own humidity values, visibility range, etc. The main types of air masses are divided into marine and continental subtypes, which differ primarily in humidity.

Air masses moving from a colder surface to a warmer one are called cold; they cause cooling in the areas where they come. But along the way, the cold mass warms up from the earth's surface. Therefore, large vertical gradients temperatures and convection develops with cumulus and cumulonimbus clouds and rainfall. Air masses moving more cold surface, are called warm. They bring warming, but they themselves cool down below, which creates small vertical temperature gradients in their lower layers. Convection does not develop in them; they are dominated by stratus clouds and fogs.

Air masses are separated from each other by relatively narrow transition zones, strongly inclined to the Earth's surface (their angle of inclination is less than 1°). These zones are called fronts. The length of the fronts is thousands of kilometers, the width is tens of kilometers. Fronts can be traced upward for several kilometers, often up to the stratosphere.

The fronts between the above geographical types of air masses are called the main ones. Front between Arctic and polar air called Arctic, between polar and tropical - polar, between tropical and equatorialnom - tropical.

Fronts are associated with special weather events. Rising movements air in frontal zones lead to the formation of extensive cloud systems with precipitation. Atmospheric waves arising in air masses on both sides of the front lead to the formation of atmospheric disturbances - cyclones and anticyclones, which determine the wind regime and other weather features.

Fronts are constantly eroded and re-emerged due to the characteristics of atmospheric circulation. Together with them, air masses are formed, transformed and lose their individuality.

If air currents have a component perpendicular to the front, it shifts in one direction or another. According to this, fronts are divided into warm and cold. Warm front

moves towards cold air. In this case, warm air flows onto the retreating cold air, rising up along the interface. As cold air retreats, its lower layers, as a result of friction with the surface, lag somewhat behind, and the front rises very gently. When warm air slowly rises, typical cloud systems form. Cold front moves towards warm air. In this case cold air moves faster than the warm one, flowing under it and pushing it up. In this case, the lower layers of cold air lag behind the upper ones in their movement, and the frontal surface rises steeply above the earth's surface.

When warm and cold fronts meet,