Atmosphere air masses. Air circulation
Movement of air masses
All the Earth's air continuously circulates between the equator and the poles. The air heated at the equator rises, is divided into two parts, one part begins to move towards north pole, the other part - to the south pole. Reaching the poles, the air cools. At the poles it twists and falls down.
Figure 1. The principle of air swirling
It turns out two huge vortices, each of which covers an entire hemisphere, the centers of these vortices are located at the poles.
Having descended at the poles, the air begins to move back to the equator; at the equator, the heated air rises. Then it moves towards the poles again.
In the lower layers of the atmosphere, movement is somewhat more complicated. In the lower layers of the atmosphere, air from the equator, as usual, begins to move towards the poles, but at the 30th parallel it falls down. One part of it returns to the equator, where it rises again, the other part, falling down at the 30th parallel, continues to move towards the poles.
Figure 2. Air movement in the northern hemisphere
Wind concept
Wind – the movement of air relative to the earth’s surface (the horizontal component of this movement), sometimes they speak of an ascending or descending wind, taking into account its vertical component.
Wind speed
Estimation of wind speed in points, the so-called Beaufort scale, according to which the entire range of possible wind speeds is divided into 12 gradations. This scale relates the strength of the wind to its various effects, such as the degree of rough seas, the swaying of branches and trees, the spread of smoke from chimneys, etc. Each gradation on the Beaufort scale has a specific name. Thus, zero on the Beaufort scale corresponds to calm, i.e. complete absence of wind. Wind at 4 points, according to Beaufort called moderate and corresponds to a speed of 5–7 m/sec; at 7 points - strong, with a speed of 12-15 m/sec; at 9 points - a storm, with a speed of 18-21 m/sec; finally, a wind of 12 points on Beaufort is already a hurricane, with a speed of over 29 m/sec . At the earth's surface, we most often have to deal with winds whose speeds are on the order of 4–8 m/sec and rarely exceed 12–15 m/sec. But still, in storms and hurricanes of moderate latitudes, speeds can exceed 30 m/sec, and in some gusts reach 60 m/sec. In tropical hurricanes, wind speeds reach up to 65 m/sec, and individual gusts – up to 100 m/sec. In small-scale vortices (tornadoes, blood clots), speeds of more than 100 m/sec are possible. In the so-called jet currents in the upper troposphere and lower stratosphere, the average wind speed over a long time and over large area can reach up to 70–100 m/sec . Wind speed at the earth's surface is measured by anemometers of various designs. Instruments for measuring wind at ground stations are installed at a height of 10–15 m above the earth's surface.
| Table 1. WIND STRENGTH. | |||
| Beaufort scale for determining wind force | |||
| Points | Visual signs on land | Wind speed, km/h | Wind power terms |
| Calmly; smoke rises vertically | Less than 1.6 | Calm | |
| The direction of the wind is noticeable by the deflection of the smoke, but not by the weather vane. | 1,6–4,8 | Quiet | |
| The wind is felt by the skin of the face; leaves rustle; ordinary weather vanes turn | 6,4–11,2 | Easy | |
| Leaves and small twigs are in constant movement; light flags flutter | 12,8–19,2 | Weak | |
| The wind raises dust and pieces of paper; thin branches sway | 20,8–28,8 | Moderate | |
| The leafy trees sway; ripples appear on land bodies of water | 30,4–38,4 | Fresh | |
| Thick branches sway; you can hear the wind whistling in the electrical wires; difficult to hold umbrella | 40,0–49,6 | Strong | |
| Tree trunks sway; it's hard to go against the wind | 51,2–60,8 | Strong | |
| Tree branches break; It's almost impossible to go against the wind | 62,4–73,6 | Very strong | |
| Minor damage; the wind tears off smoke hoods and tiles from roofs | 75,2–86,4 | Storm | |
| Rarely happens on land. Trees are uprooted. Significant damage to buildings | 88,0–100,8 | Heavy storm | |
| It happens very rarely on land. Accompanied by destruction over a large area | 102,4–115,2 | Fierce Storm | |
| Severe disruption (Scores 13–17 were added by the US Weather Bureau in 1955 and are used in the US and UK scales) | 116,8–131,2 | Hurricane | |
| 132,8–147,2 | |||
| 148,8–164,8 | |||
| 166,4–182,4 | |||
| 184,0–200,0 | |||
| 201,6–217,6 | |||
Direction of the wind
Wind direction refers to the direction from which it blows. You can indicate this direction by naming either the point on the horizon from where the wind is blowing, or the angle formed by the direction of the wind with the meridian of the place, i.e. its azimuth. In the first case, there are eight main directions of the horizon: north, northeast, east, southeast, south, southwest, west, northwest. And eight intermediate points between them: north-northeast, east-northeast, east-southeast, south-southeast, south-southwest, west-southwest, west-northwest, north -northwest. Sixteen points of reference, indicating the direction from which the wind blows, have abbreviations:
| Table 2. ABBREVIATIONS FOR RUMBERS | |||||||
| WITH | N | IN | E | YU | S | W | |
| CCB | NNE | ESE | ESE | SSW | SSW | WNW | W.N.W. |
| C.B. | NE | SE | S.E. | SW | S.W. | NW | NW |
| BCB | ENE | SSE | SSE | WSW | WSW | CVD | NNW |
| N – north, E – east, S – south, W – west |
Atmospheric circulation
Atmospheric circulation - meteorological observations of the state of the air envelope globe- the atmosphere - show that it is not at rest at all: with the help of weather vanes and anemometers, we constantly observe in the form of wind the transfer of air masses from one place to another. The study of winds in different areas of the globe has shown that the movements of the atmosphere in those lower layers that are accessible to our observation have a very different character. There are areas where wind phenomena, like other weather features, have a very clearly expressed character of stability, a known desire for constancy. In other areas, the winds change their character so quickly and often, their direction and strength change so sharply and suddenly, as if there was no legality in their rapid changes. With the introduction of the synoptic method for studying non-periodic weather changes, it became possible, however, to notice some connection between the distribution of pressure and the movements of air masses; further theoretical studies by Ferrel, Guldberg and Mohn, Helmholtz, Betzold, Oberbeck, Sprung, Werner Siemens and other meteorologists explained where and how air currents originate and how they are distributed over the earth's surface and in the mass of the atmosphere. A careful study of meteorological maps depicting the state of the lower layer of the atmosphere - the weather at the very surface of the earth - showed that atmospheric pressure is distributed rather unevenly over the earth's surface, usually in the form of areas with lower or higher pressure than in the surrounding area; according to the system of winds that arise in them, these areas represent real atmospheric vortices. Areas of low pressure are usually called barometric lows, barometric depressions or cyclones; region high blood pressure are called barometric highs or anticyclones. All the weather in the area they occupy is closely connected with these areas, which is sharply different for areas of low pressure from the weather in areas of relatively high pressure . Moving along the earth's surface, the mentioned areas carry with them the characteristic weather that is characteristic of them, and with their movements they cause its non-periodic changes. Further study of these and other areas led to the conclusion that these types of atmospheric pressure distribution may also have a different character in their ability to maintain their existence and change their position on the earth’s surface, and are characterized by very different stability: there are barometric minimums and maximums, temporary and permanent. While the first - vortices - are temporary and do not show sufficient stability and more or less quickly change their place on the earth's surface, now strengthening, now weakening and, finally, completely disintegrating in relatively short periods of time, areas of constant maxima and minima have extremely stable and remain in the same place for a very long time, without significant changes. The different stability of these regions is, of course, closely related to the stability of the weather and the nature of the air currents in the area they occupy: constant highs and lows will correspond to constant, stable weather and a definite, unchanging system of winds, remaining for months at the place of their existence; temporary vortices, with their rapid, constant movements and changes, cause extremely changeable weather and a very unstable wind system for a given area. Thus, in the lower layer of the atmosphere, near the earth’s surface, atmospheric movements are highly diverse and complex, and in addition, they do not always and not everywhere have sufficient stability, especially in those areas where temporary vortices predominate. What will be the movements of air masses in slightly higher layers of the atmosphere, ordinary observations do not say anything; Only observations of the movements of clouds allow us to think that there, at a certain height above the surface of the earth, all general movements of air masses are somewhat simplified, have a more defined and more uniform character. Meanwhile, there is no shortage of facts indicating the enormous influence of the high layers of the atmosphere on the weather in the lower ones: it is enough, for example, to point out that the direction of movement of temporary vortices is, apparently, directly dependent on the movement of the high layers of the atmosphere. Therefore, even before science began to have a sufficient number of facts to solve the question of the movements of the high layers of the atmosphere, some theories had already appeared that tried to combine all the individual observations of the movements of the lower layers of air and create a general scheme of the central air. atmosphere; This, for example, was the theory of the central atmosphere given by Mori. But until a sufficient number of facts were collected, until the relationship between air pressure at given points and its movements was fully clarified, until then such theories, based more on hypotheses than on actual data, could not give a real idea of what can actually happen and is happening in the atmosphere. Only towards the end of the last XIX century. Enough facts have accumulated for this and the dynamics of the atmosphere have been developed to such an extent that it has become possible to give a real, and not a fortune-telling, picture of the color of the atmosphere. The honor of solving the problem of the general circulation of air masses in the atmosphere belongs to the American meteorologist William Ferrel- a solution so general, complete and correct that all later researchers in this area only developed details or made further additions to Ferrel’s basic ideas. The main reason for all movements in the atmosphere is the uneven heating of various points on the earth's surface by the sun's rays. Uneven heating entails the appearance of a pressure difference over differently heated points; and the result of the pressure difference will always and invariably be the movement of air masses from places of higher to places of higher low pressure. Therefore, due to the strong heating of the equatorial latitudes and the very low temperature of the polar countries in both hemispheres, the air adjacent to the earth's surface must begin to move. If, according to available observations, we calculate the average temperatures different latitudes, then the equator will be on average 45° warmer than the poles. To determine the direction of movement, it is necessary to trace the distribution of pressure on the earth's surface and in the mass of the atmosphere. To eliminate the uneven distribution of land and water over the earth's surface, which greatly complicates all calculations, Ferrel made the assumption that both land and water are evenly distributed along the parallels, and calculated the average temperatures of various parallels, the decrease in temperature as one rises to a certain height above the earth's surface, and the pressure at the bottom; and then, using these data, he already calculated the pressure at some other altitudes. The following small plate presents the result of Ferrel's calculations and gives the average pressure distribution over latitudes on the surface of the earth and at altitudes of 2000 and 4000 m.
| Table 3. PRESSURE DISTRIBUTION BY LATITUDE AT THE GROUND TERRAIN AND AT ALTITUDES 2000 AND 4000 M | ||||||||
| Average pressure in the Northern Hemisphere | ||||||||
| At latitude: | 80 ○ | 70 ○ | 60 ○ | 50 ○ | 40 ○ | 30 ○ | 20 ○ | 10 ○ |
| At sea level | 760,5 | 758,7 | 758,7 | 760,07 | 762,0 | 761,7 | 759,2 | 757,9 |
| At an altitude of 2000 m | 582,0 | 583,6 | 587,6 | 593,0 | 598,0 | 600,9 | 600,9 | 600,9 |
| At an altitude of 4000 m | 445,2 | 446,6 | 451,9 | 457,0 | 463,6 | 468,3 | 469,9 | 470,7 |
| Average pressure in the Southern Hemisphere | ||||||||
| At latitude: | (equator) | 10 ○ | 20 ○ | 30 ○ | 40 ○ | 50 ○ | 60 ○ | 70 ○ |
| At sea level | 758,0 | 759,1 | 761,7 | 763,5 | 760,5 | 753,2 | 743,4 | 738,0 |
| At an altitude of 2000 m | 601,1 | 601,6 | 602,7 | 602,2 | 597,1 | 588,0 | 577,0 | 569,9 |
| At an altitude of 4000 m | 471,0 | 471,1 | 471,1 | 469,3 | 463,1 | 453,7 | 443,9 | 437,2 |
If we leave aside for now the lowest layer of the atmosphere, where the distribution of temperature, pressure, and also currents is very uneven, then at a certain height, as can be seen from the tablet, due to the ascending current of heated air near the equator, we find increased pressure above this latter, uniformly decreasing towards the poles and here reaching its smallest value. With such a distribution of pressure at these heights above the earth's surface, a colossal flow should form, covering the entire hemisphere and carrying masses of warm, heated air rising near the equator to the centers of low pressure - to the poles. If we also take into account the deflecting effect of the centrifugal force resulting from the daily rotation of the earth around its axis, which should deflect any moving body to the right from the original direction in the northern hemispheres, to the left - in the southern hemispheres, then at the considered altitudes in each hemisphere the resulting flow will obviously turn into , into a huge vortex that transports air masses in the direction from southwest to northeast in the northern hemisphere, from northwest to southeast in the southern hemisphere.
Observations of the movement of cirrus clouds and others support these theoretical conclusions. As the circles of latitude narrow, approaching the poles, the speed of movement of air masses in these vortices will increase, but to a certain limit; then it becomes more permanent. Near the pole, the inflowing masses of air should descend down, giving way to newly inflowing air, forming a downward flow, and then below they should flow back to the equator. Between both flows there must be a neutral layer of air at rest at a certain height. Below, however, such a correct transfer of air masses from the poles to the equator is not observed: the previous plate shows that in the lower layer of air the atmospheric pressure will be highest below, not at the poles, as it should be with its correct distribution corresponding to the upper one. Highest pressure in the lower layer it falls at a latitude of about 30°-35° in both hemispheres; therefore, from these centers of high pressure, the lower currents will be directed both to the poles and to the equator, forming two separate wind systems. The reason for this phenomenon, also theoretically explained by Ferrel, is as follows. It turns out that at a certain height above the earth's surface, depending on changes in the latitude of the place, the magnitude of the gradient and the coefficient of friction, the meridional component of the speed of movement of air masses can drop to 0. This is exactly what happens at latitudes of approx. 30°-35°: here at a certain altitude, not only is there therefore no movement of air towards the poles, but there is even, due to its continuous influx from the equator and from the poles, its accumulation, which leads to an increase in pressure below in these latitudes . Thus, at the very surface of the earth in each hemisphere, as already mentioned, two systems of currents arise: from 30° to the poles winds blow, directed on average from southwest to northeast in the north, from northwest to southeast in the southern hemisphere; from 30° to the equator the winds blow from NE to SW in the northern hemisphere, from SE to NW in the southern hemisphere. These last two systems of winds, blowing in both hemispheres between the equator and latitude 31°, form, as it were, a wide ring that separates both enormous vortices in the lower and middle layers of the atmosphere, carrying air from the equator to the poles (see also Atmospheric pressure). Where ascending and descending air currents form, lulls are observed; This is precisely the origin of the equatorial and tropical zones of silence; a similar belt of silence should, according to Ferrel, exist at the poles.
Where, however, does the reverse air flow spreading from the poles to the equator go? But it is necessary to take into account that as we move away from the poles, the sizes of circles of latitudes, and consequently the areas of belts of equal width occupied by spreading masses of air, quickly increase; that the speed of flows should decrease rapidly in inverse proportion to the increase in these areas; that at the poles, air, very rarefied in the upper layers, finally descends from top to bottom, the volume of which decreases very quickly as the pressure increases downwards. All these reasons fully explain why it is difficult, and even downright impossible, to follow these reverse lower flows at some distance from the poles. This is, in general terms, the scheme of the general circulation atmosphere, assuming a uniform distribution of land and water along parallels, given by Ferrel. Observations fully confirm it. Only in the lower layer of the atmosphere will air currents, as Ferrel himself points out, be much more complex than this scheme precisely due to the uneven distribution of land and water, and the difference in their heating by the sun's rays and their cooling in the absence or decrease of insolation; Mountains and hills also greatly influence the movements of the lowest layers of the atmosphere.
A careful study of atmospheric movements near the earth's surface generally shows that vortex systems represent the main form of such movements. Starting with the grandiose vortices, which, according to Ferrel, embrace each entire hemisphere, vortices, what can they be called? first order near the earth's surface one has to observe vortex systems successively decreasing in size, up to and including elementary small and simple vortices. As a result of the interaction of flows of different speeds and directions in the region of first-order vortices, near the earth's surface, second order vortices- the permanent and temporary barometric maxima and minima mentioned at the beginning of this article, which in their origin are, as it were, a derivative of previous vortices. The study of the formation of thunderstorms led A.V. Klossovsky and other researchers to the conclusion that these phenomena are nothing more than similar in structure, but incomparably smaller in size compared to the previous ones, third order vortices. These vortices appear to arise on the outskirts of barometric minima (second-order vortices) in exactly the same way as small, very quickly spinning and disappearing whirlpools are formed around a large depression formed in the water by an oar with which we row when sailing a boat. In exactly the same way, barometric minima of the second order, which are powerful air gyres, during their movement form smaller air vortices, which, in comparison with the minimum that forms them, are very small in size.
If these vortices are accompanied by electrical phenomena, which can often be caused by the corresponding conditions of temperature and humidity in the air flowing to the center of the barometric minimum at the bottom, then they appear in the form of thunderstorm vortices, accompanied by the usual phenomena of electrical discharge, thunder and lightning. If conditions are not favorable for the development of thunderstorm phenomena, we observe these third-order vortices in the form of quickly passing storms, squalls, showers, etc. There are, however, full reason to think that the vortex movements of the atmosphere are not exhausted by these three categories, so different in scale of the phenomenon. The structure of tornadoes, blood clots, and other phenomena shows that in these phenomena we are also dealing with real vortices; but the sizes of these fourth order vortices even less, even more insignificant, than thunderstorm whirlwinds. The study of atmospheric movements leads us, therefore, to the conclusion that the movements of air masses occur primarily - if not exclusively - through the formation of vortices. Arising under the influence of purely temperature conditions, first-order vortices, covering each entire hemisphere, give rise to smaller vortices near the earth's surface; these, in turn, cause the emergence of even smaller vortices. There seems to be a gradual differentiation of larger vortices into smaller ones; but the basic character of all these vortex systems remains absolutely the same, from the larger ones to the smallest in size, even in tornadoes and blood clots.
Regarding second-order vortices - permanent and temporary barometric maxima and minima - the following remains to be said. The studies of Hoffmeyer, Teisserand de Bor and Hildebrandson indicated a close connection between the occurrence and especially the movement of temporary maxima and minima with the changes undergone by permanent maxima and minima. The very fact that these latter, with all kinds of weather changes in the areas surrounding them, very little change their boundaries or contours, indicates that here we are dealing with some permanent causes that lie above the influence of ordinary weather factors. According to Teisserant de Bor, pressure differences caused by uneven heating or cooling various parts the earth's surface, summed up under the influence of a continuous increase in the primary factor over a more or less long period of time, give rise to large barometric maxima and minima. If the primary cause acts continuously or for a sufficiently long time, the result of its action will be permanent, stable vortex systems. Having reached known sizes and sufficient intensity, such constant maxima and minima are already determinants or regulators of weather over vast areas in their circumference. Such large, constant highs and lows were obtained in Lately, when their role in the weather phenomena of the countries around them became clear, the name centers of atmospheric action. Due to the invariance in the configuration of the earth's surface and the consequent continuity of the influence of the primary cause causing their existence, the position of such maxima and minima on the globe is quite definite and unchangeable to a certain extent. But, depending on various conditions, their boundaries and their intensity can vary within certain limits. And these changes in their intensity and their outlines, in turn, should affect the weather not only of neighboring, but sometimes even quite distant countries. Thus, Teisserant de Bor's research has fully established the dependence of weather in Europe on one of the following centers of action: anomalies negative character, accompanied by a decrease in temperature compared to normal, are caused by the intensification and expansion of the Siberian High or the intensification and advance of the Azores High; anomalies of a positive nature - with an increase in temperature compared to normal - are directly dependent on the movement and intensity of the Icelandic minimum. Hildebrandson went even further in this direction and quite successfully tried to connect changes in the intensity and movements of the two named Atlantic centers with changes not only in the Siberian High, but also in pressure centers in the Indian Ocean.
Air masses
Weather observations became quite widespread in the second half of the 19th century. They were necessary for the compilation of synoptic maps showing the distribution of air pressure and temperature, wind and precipitation. As a result of the analysis of these observations, an idea of air masses was formed. This concept made it possible to combine individual elements, identify various conditions weather and give its forecasts.
Air mass called large volume air, having horizontal dimensions of several hundred or thousand kilometers and vertical dimensions of the order of 5 km, characterized by approximately uniform temperature and humidity and moving as a single system in one of the currents of the general circulation of the atmosphere (GCA)
The uniformity of the properties of the air mass is achieved by forming it over a homogeneous underlying surface and under similar radiation conditions. In addition, such circulation conditions are necessary under which the air mass would linger for a long time in the area of formation.
The values of meteorological elements within the air mass change slightly - their continuity remains, horizontal gradients are small. When analyzing meteorological fields, as long as we remain in a given air mass, linear graphical interpolation can be used with sufficient approximation when conducting, for example, isotherms.
A sharp increase in horizontal gradients of meteorological values, approaching an abrupt transition from one value to another, or at least a change in the magnitude and direction of gradients occurs in the transition (frontal zone) between two air masses. The pseudopotential air temperature, which reflects both the actual air temperature and its humidity, is taken as the most characteristic feature of a particular air mass.
Pseudopotential air temperature - the temperature that the air would take during an adiabatic process if first all the water vapor contained in it condensed at an infinitely decreasing pressure and fell out of the air and the released latent heat went to heat the air, and then the air was brought under standard pressure.
Since a warmer air mass is usually also more humid, the difference in pseudopotential temperatures of two neighboring air masses can be significantly greater than the difference in their actual temperatures. However, the pseudopotential temperature varies slowly with height within a given air mass. This property helps determine the layering of air masses one above the other in the troposphere.
Scales of air masses
Air masses are of the same order as the main currents of the general circulation of the atmosphere. The linear extent of air masses in the horizontal direction is measured in thousands of kilometers. Vertically, air masses extend up several kilometers of the troposphere, sometimes to its upper boundary.
With local circulations, such as, for example, breezes, mountain-valley winds, hair dryers, the air in the circulation flow is also more or less separated in properties and movement from surrounding atmosphere. However, in this case it is impossible to talk about air masses, since the scale of the phenomena here will be different.
For example, a strip covered by a breeze may be only 1-2 tens of kilometers wide, and therefore will not receive sufficient reflection on the synoptic map. The vertical power of the breeze current is also several hundred meters. Thus, with local circulations we are not dealing with independent air masses, but only with a disturbed state within the air masses over a short distance.
Objects arising as a result of the interaction of air masses - transition zones (frontal surfaces), frontal cloud systems of cloudiness and precipitation, cyclonic disturbances, have the same order of magnitude as the air masses themselves - comparable in area to large parts of continents or oceans and their time existence - more than 2 days ( table 4):
An air mass has clear boundaries that separate it from other air masses.
Transition zones between air masses with different properties are called front surfaces.
Within the same air mass, graphical interpolation can be used with sufficient approximation, for example, when drawing isotherms. But when moving through the frontal zone from one air mass to another, linear interpolation will no longer give a correct idea of the actual distribution of meteorological elements.
Centers for the formation of air masses
The air mass acquires clear characteristics at the source of formation.
The source of air mass formation must meet certain requirements:
The homogeneity of the underlying surface of water or land, so that the air in the hearth is subjected to sufficiently similar influences.
Homogeneity of radiation conditions.
Circulation conditions that promote stationary air in a given area.
The formation centers are usually areas where air descends and then spreads in the horizontal direction - anticyclonic systems meet this requirement. Anticyclones are more likely than cyclones to be low-moving, so the formation of air masses usually occurs in extensive low-moving (quasi-stationary) anticyclones.
In addition, the requirements of the source are met by slow-moving and diffuse thermal depressions that arise over heated land areas.
Finally, the formation of polar air occurs partly in the upper atmosphere in slow-moving, extensive and deep central cyclones at high latitudes. In these pressure systems, the transformation (transformation) of tropical air drawn into high latitudes in the upper layers of the troposphere into polar air occurs. All of the listed pressure systems can also be called centers of air masses, not from a geographical, but from a synoptic point of view.
Geographic classification of air masses
Air masses are classified, first of all, according to the centers of their formation, depending on their location in one of the latitude zones - Arctic, or Antarctic, polar, or temperate latitudes, tropical and equatorial.
According to geographical classification, air masses can be divided into main geographical types according to the latitudinal zones in which their foci are located:
Arctic or Antarctic air (AV),
Polar or temperate air (MF or HC),
Tropical Air (TV). These air masses are, in addition, divided into marine (m) and continental (k) air masses: mAV and kAV, muv and kUV (or mPV and kPV), mTV and kTV.
Equatorial air masses (EA)
As for equatorial latitudes, convergence (convergence of flows) and air rise occur here, so air masses located above the equator are usually brought from the subtropical zone. But sometimes independent equatorial air masses emerge.
Sometimes, in addition to foci in the strict sense of the word, areas are identified where in winter air masses are transformed from one type to another as they move. These are areas in the Atlantic south of Greenland and in the Pacific over the Bering and Okhotsk Seas where the cPV turns into mPV, areas over southeastern North America and south of Japan in the Pacific Ocean where the cPV turns into mPV during the winter monsoon, and area in southern Asia where the Asian CP turns into tropical air (also in the monsoon flow)
Transformation of air masses
When circulation conditions change, the air mass as a whole moves from the source of its formation to neighboring areas, interacting with other air masses.
When moving, the air mass begins to change its properties - they will depend not only on the properties of the source of formation, but also on the properties of neighboring air masses, on the properties of the underlying surface over which the air mass passes, as well as on the length of time that has passed since the formation of the air mass. masses.
These influences can cause changes in the moisture content of the air, as well as changes in air temperature as a result of the release of latent heat or heat exchange with the underlying surface.
The process of changing the properties of an air mass is called transformation or evolution.
The transformation associated with the movement of the air mass is called dynamic. The speed of movement of the air mass at different heights will be different, the presence of a velocity shift causes turbulent mixing. If the lower layers of air are heated, instability occurs and convective mixing develops.
Atmospheric circulation diagram
Air in the atmosphere is in constant motion. It moves in both horizontal and vertical directions.
The root cause of air movement in the atmosphere is the uneven distribution solar radiation and heterogeneity of the underlying surface. They cause uneven air temperature and, accordingly, atmospheric pressure over the earth's surface.
The pressure difference creates air movement, which moves from areas of high to low pressure. As they move, air masses are deflected by the force of the Earth's rotation.
(Remember how bodies moving in the Northern and Southern Hemispheres are deflected.)
You, of course, have noticed how on a hot summer day a light haze forms over the asphalt. This heated, light air rises. A similar, but much larger scale picture can be observed at the equator. Very hot air constantly rises, forming updrafts.
Therefore, a constant low pressure belt is formed here near the surface.
The air rising above the equator in the upper layers of the troposphere (10-12 km) spreads towards the poles. It gradually cools and begins to fall above approximately 30 t° north and south latitudes.
This creates an excess of air, which contributes to the formation of a tropical high-pressure zone in the surface layer of the atmosphere.
In the polar regions, the air is cold, heavy and sinks, causing downward movements. As a result, high pressure is formed in the surface layers of the polar belt.
Active atmospheric fronts form between the tropical and polar high-pressure belts in temperate latitudes. Massively colder air displaces warmer air upward, causing updrafts.
As a result, a surface low pressure belt is formed in temperate latitudes.
Map of Earth's climate zones
If the earth's surface were homogeneous, the atmospheric pressure belts would spread in continuous stripes. However, the planet's surface is an alternation of water and land, which have different properties. Sushi heats up and cools down quickly.
The ocean, on the contrary, heats up and releases its heat slowly. This is why the atmospheric pressure belts are torn into separate sections - areas of high and low pressure. Some of them exist throughout the year, others - in a certain season.
On Earth, belts of high and low pressure regularly alternate. High pressure is at the poles and near the tropics, low pressure is at the equator and in temperate latitudes.
Types of atmospheric circulation
In the Earth's atmosphere there are several powerful links in the circulation of air masses. All of them are active and inherent in certain latitudinal zones. Therefore, they are called zonal types of atmospheric circulation.
At the Earth's surface, air currents move from the tropical high pressure belt to the equator. Under the influence of the force arising from the rotation of the Earth, they are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
This is how constant powerful winds are formed - trade winds. In the Northern Hemisphere, trade winds blow from the northeast, and in the Southern Hemisphere, from the southeast. So, the first zonal type of atmospheric circulation is trade wind.
From the tropics, air moves to temperate latitudes. Deflected by the force of the Earth's rotation, they begin to gradually move from west to east. It is precisely this flow from the Atlantic that covers the temperate latitudes of all of Europe, including Ukraine. Western air transport in temperate latitudes is the second zonal type of planetary atmospheric circulation.
It is also natural for air to move from the circumpolar high pressure zones to the temperate latitudes, where the pressure is low.
Under the influence of the deflecting force of the Earth's rotation, this air moves from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere. The eastern subpolar flow of air masses forms the third zonal type of atmospheric circulation.
On the atlas map, find the latitudinal zones where different types of zonal air circulation prevail.
Due to uneven heating of land and ocean, the zonal pattern of movement of air masses is disrupted. For example, in the east of Eurasia in temperate latitudes, westerly air transport operates only for six months - in winter. In summer, when the continent warms up, air masses with the coolness of the ocean move to land.
This is how monsoon air transfer occurs. Changing the directions of air movement twice a year is a characteristic feature of the monsoon circulation. The winter monsoon is a flow of relatively cold and dry air from the mainland to the ocean.
Summer monsoon- movement of moist and warm air in the opposite direction.
Zonal types of atmospheric circulation
There are three main zonal type of atmospheric circulation: trade wind, westerly air transport and eastern subpolar flow of air masses. Monsoon air transport disrupts the general atmospheric circulation pattern and is an azonal type of circulation.
General atmospheric circulation (page 1 of 2)
Ministry of Science and Education of the Republic of Kazakhstan
Academy of Economics and Law named after U.A. Dzholdasbekova
Faculty of Humanities and Economics Academy
Discipline: Ecology
On the topic: “General circulation of the atmosphere”
Completed by: Tsarskaya Margarita
Group 102 A
Checked by: Omarov B.B.
Taldykorgan 2011
Introduction
1. General information about atmospheric circulation
2. Factors determining the general circulation of the atmosphere
3. Cyclones and anticyclones.
4. Winds affecting the general circulation of the atmosphere
5. Hair dryer effect
6. General circulation diagram “Planet Machine”
Conclusion
List of used literature
Introduction
On the pages scientific literature Recently, the concept of general circulation of the atmosphere has often come up, the meaning of which is understood by each specialist in his own way. This term is systematically used by specialists involved in geography, ecology, and the upper part of the atmosphere.
Meteorologists and climatologists, biologists and doctors, hydrologists and oceanologists, botanists and zoologists, and of course ecologists are showing increasing interest in the general circulation of the atmosphere.
There is no consensus whether this is scientific direction emerging recently or research here has been going on for centuries.
Below we propose definitions of the general circulation of the atmosphere as a set of sciences and list the factors influencing it.
A certain list of achievements is given: hypotheses, developments and discoveries that mark well-known milestones in the history of this body of science and give a certain idea of the range of problems and tasks it considers.
The distinctive features of the general circulation of the atmosphere are described, and the simplest scheme of general circulation called the “planet machine” is presented.
1. General information about atmospheric circulation
The general circulation of the atmosphere (Latin Circulatio - rotation, Greek atmos - steam and sphaira - ball) is a set of large-scale air currents in the troposphere and stratosphere. As a result, air masses are exchanged in space, which contributes to the redistribution of heat and moisture.
The general circulation of the atmosphere is the circulation of air on the globe, leading to its transfer from low latitudes to high latitudes and back.
The general circulation of the atmosphere is determined by zones of high atmospheric pressure in the polar regions and tropical latitudes and zones of low pressure in temperate and equatorial latitudes.
The movement of air masses occurs in both latitudinal and meridional directions. In the troposphere, atmospheric circulation includes trade winds, westerly air currents of temperate latitudes, monsoons, cyclones and anticyclones.
The reason for the movement of air masses is the unequal distribution of atmospheric pressure and the heating by the Sun of the surface of land, oceans, ice at different latitudes, as well as the deflecting effect on the air flow of the Earth's rotation.
The main patterns of atmospheric circulation are constant.
In the lower stratosphere, jet air currents in temperate and subtropical latitudes are predominantly western, and in tropical latitudes - eastern, and they travel at speeds of up to 150 m/s (540 km/h) relative to the earth's surface.
In the lower troposphere, the prevailing directions of air transport differ across geographic zones.
In polar latitudes there are easterly winds; in temperate regions - western ones with frequent disruption by cyclones and anticyclones; trade winds and monsoons are the most stable in tropical latitudes.
Due to the diversity of the underlying surface, regional deviations - local winds - arise in the shape of the general circulation of the atmosphere.
2. Factors determining the general circulation of the atmosphere
– Uneven distribution of solar energy over the earth’s surface and, as a consequence, uneven distribution of temperature and atmospheric pressure.
– Coriolis forces and friction, under the influence of which air flows acquire a latitudinal direction.
– Influence of the underlying surface: the presence of continents and oceans, heterogeneity of relief, etc.
The distribution of air currents on the earth's surface is zonal. In equatorial latitudes there is a calm or weak variable winds are observed. Trade winds dominate in the tropical zone.
Trade winds are constant winds blowing from 30 latitudes to the equator, having a northeastern direction in the northern hemisphere and a southeastern direction in the southern hemisphere. At 30-35? With. and S. – calm zone, so-called. "horse latitudes".
In temperate latitudes, westerly winds predominate (southwest in the northern hemisphere, northwest in the southern hemisphere). In polar latitudes, easterly winds blow (in the northern hemisphere, northeasterly, in the southern hemisphere, southeasterly winds).
In reality, the wind system above the earth's surface is much more complex. IN subtropical zone In many areas, trade wind transport is disrupted by the summer monsoons.
In temperate and subpolar latitudes, cyclones and anticyclones have a huge influence on the nature of air currents, and on the eastern and northern coasts - monsoons.
In addition, in many areas local winds arise due to the characteristics of the territory.
3. Cyclones and anticyclones.
The atmosphere is characterized by vortex movements, the largest of which are cyclones and anticyclones.
A cyclone is an ascending atmospheric vortex with low pressure in the center and a system of winds from the periphery to the center, directed counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. Cyclones are divided into tropical and extratropical. Consider extratropical cyclones.
The diameter of extratropical cyclones is on average about 1000 km, but there are also more than 3000 km. Depth (pressure in the center) – 1000-970 hPa or less. Strong winds blow in a cyclone, usually up to 10-15 m/sec, but can reach 30 m/sec or more.
The average speed of the cyclone is 30-50 km/h. Most often, cyclones move from west to east, but sometimes they come from the north, south and even east. The zone of greatest frequency of cyclones is the 80th latitude of the northern hemisphere.
Cyclones bring cloudy, rainy, windy weather, cooling in summer, warming in winter.
Tropical cyclones (hurricanes, typhoons) form in tropical latitudes; they are one of the most formidable and dangerous natural phenomena. Their diameter is several hundred kilometers (300-800 km, rarely more than 1000 km), but they are characterized by a large difference in pressure between the center and the periphery, which causes strong hurricane winds, tropical showers, severe thunderstorms.
An anticyclone is a downward atmospheric vortex with increased pressure in the center and a system of winds from the center to the periphery, directed clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. The sizes of anticyclones are the same as those of cyclones, but in the late stage of development they can reach up to 4000 km in diameter.
Atmospheric pressure in the center of anticyclones is usually 1020-1030 hPa, but can reach more than 1070 hPa. The highest frequency of anticyclones is over the subtropical zones of the oceans. Anticyclones are characterized by partly cloudy weather without precipitation, with weak winds in the center, severe frosts in winter, and heat in summer.
4. Winds affecting the general circulation of the atmosphere
Monsoons. Monsoons are seasonal winds that change direction twice a year. In summer they blow from ocean to land, in winter - from land to ocean. The reason for its formation is unequal heating of land and water according to the seasons of the year. Depending on the zone of formation, monsoons are divided into tropical and extratropical.
Extratropical monsoons are especially pronounced on the eastern edge of Eurasia. The summer monsoon brings moisture and coolness from the ocean, while the winter monsoon blows from the mainland, lowering the temperature and humidity.
Tropical monsoons are most pronounced in the Indian Ocean basin. The summer monsoon blows from the equator, it is opposite to the trade wind and brings clouds, precipitation, softens the summer heat, the winter monsoon coincides with the trade wind, strengthens it, bringing dryness.
Local winds. Local winds have a local distribution, their formation is associated with the characteristics of a given territory - the proximity of water bodies, the nature of the relief. The most common are breezes, bora, foehn, mountain-valley and katabatic winds.
Breezes (light wind - fr) - winds along the shores of seas, large lakes and rivers, changing direction to the opposite twice a day: the daytime breeze blows from the reservoir to the shore, the night breeze - from the shore to the reservoir. Breezes are caused by the daily variation of temperature and, accordingly, pressure over land and water. They capture a layer of air 1-2 km.
Their speed is low - 3-5 m/s. A very strong daytime sea breeze is observed on the western desert coasts of continents in tropical latitudes, washed by cold currents and cold water, rising off the coast in the upwelling zone.
There it invades tens of kilometers inland and produces a strong climatic effect: it reduces the temperature, especially in summer by 5-70 C, and in western Africa up to 100 C, increases relative humidity air up to 85%, promotes the formation of fog and dew.
Phenomena similar to daytime sea breezes can be observed on the outskirts of large cities, where there is a circulation of colder air from the suburbs to the center, since “heat spots” exist over the cities throughout the year.
Mountain-valley winds have a daily periodicity: during the day the wind blows up the valley and along the mountain slopes, at night, on the contrary, the cooled air descends. The daytime rise of air leads to the formation of cumulus clouds over the slopes of the mountains; at night, as the air descends and adiabatically warms, the cloudiness disappears.
Glacial winds are cold winds that constantly blow from mountain glaciers down slopes and valleys. They are caused by cooling of the air above the ice. Their speed is 5-7 m/s, their thickness is several tens of meters. They are more intense at night, as they are amplified by slope winds.
General atmospheric circulation
1) Due to the tilt of the earth's axis and the sphericity of the earth, equatorial regions receive more solar energy than polar regions.
2) At the equator, the air heats up → expands → rises → a low pressure area is formed. 3) At the poles, the air cools → becomes denser → falls down → a high pressure area is formed.
4) Due to the difference in atmospheric pressure, air masses begin to move from the poles to the equator.
The direction and speed of winds are also influenced by:
- properties of air masses (humidity, temperature...)
- underlying surface (oceans, mountain ranges, etc.)
- rotation of the globe around its axis (Coriolis force)1) general (global) system of air currents over the earth's surface, the horizontal dimensions of which are comparable to the continents and oceans, and the thickness from several km to tens of km.
Trade winds - These are constant winds blowing from the tropics to the equator.
Reason: At the equator there is always low pressure (updrafts), and in the tropics there is always high pressure (downdrafts).
Due to the action of the Coriolis force: the trade winds of the Northern Hemisphere have a northeast direction (deviate to the right)
Southern Hemisphere trade winds - southeast (deviate to the left)
Northeast winds(in the Northern Hemisphere) and southeast winds(in the Southern Hemisphere).
Reason: air currents move from the poles to moderate latitudes and, under the influence of the Coriolis force, are deflected to the west. Western winds are winds blowing from the tropics to temperate latitudes mainly from west to east.
Reason: in the tropics there is high pressure, and in temperate latitudes it is low, so part of the air from the E.D. region moves to the N.D. region. When moving under the influence of the Coriolis force, air currents are deflected to the east.
Western winds bring warm and wet air, because air masses form over the waters of the warm North Atlantic Current.
The air in the cyclone moves from the periphery to the center;
In the central part of the cyclone, the air rises and
It cools, so clouds and precipitation form;
During cyclones, cloudy weather with strong winds prevails:
in summer– rainy and cool,
in winter– with thaws and snowfalls.
Anticyclone- This is an area of high atmospheric pressure with a maximum in the center.
the air in the anticyclone moves from the center to the periphery; in the central part of the anticyclone, the air descends and heats up, its humidity drops, the clouds dissipate; During anticyclones, clear, windless weather sets in:
in summer it’s hot,
in winter – frosty.
Atmospheric circulation
Definition 1
Circulation is a system of movement of air masses.
Circulation can be general on a planetary scale and local circulation that occurs over separate territories and water areas. Local circulation includes day and night breezes that occur on the coasts of the seas, mountain-valley winds, glacial winds, etc.
Local circulation in certain time and in certain places may be superimposed on general circulation currents. With the general circulation of the atmosphere, huge waves and vortices arise in it, which develop and move in different ways.
Such atmospheric disturbances are cyclones and anticyclones, which are characteristic features of the general circulation of the atmosphere.
As a result of the movement of air masses, which occurs under the influence of atmospheric pressure centers, areas are provided with moisture. As a result of the fact that air movements of different scales simultaneously exist in the atmosphere, overlapping each other, atmospheric circulation is a very complex process.
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The movement of air masses on a planetary scale is influenced by 3 main factors:
These factors complicate the general circulation of the atmosphere.
If the Earth were homogeneous and did not rotate around its axis - then the temperature and pressure at the surface of the earth would correspond to thermal conditions and be of a latitudinal nature. This means that the temperature decrease would occur from the equator to the poles.
With this distribution, warm air at the equator rises, and cold air at the poles sinks. As a result, it would accumulate at the equator in the upper part of the troposphere, and the pressure would be high, and at the poles it would be low.
At altitude, the air would flow out in the same direction and lead to a decrease in pressure over the equator and its increase over the poles. The outflow of air near the earth's surface would occur from the poles, where the pressure is high, towards the equator in the meridional direction.
It turns out that the thermal reason is the first reason for the circulation of the atmosphere - different temperatures lead to different pressures at different latitudes. In reality, the pressure is low above the equator and high at the poles.
On a uniform rotating On Earth in the upper troposphere and lower stratosphere, the winds, when they flow out to the poles, in the northern hemisphere should deviate to the right, in the southern hemisphere - to the left and at the same time become westerly.
In the lower troposphere, the winds, flowing from the poles towards the equator and deflecting, would become easterly in the northern hemisphere, and southeasterly in the southern hemisphere. The second reason for atmospheric circulation is clearly visible - dynamic. The zonal component of the general circulation of the atmosphere is determined by the rotation of the Earth.
The underlying surface with an uneven distribution of land and water has a significant influence on the general circulation of the atmosphere.
Cyclones
The lower layer of the troposphere is characterized by vortices that appear, develop and disappear. Some vortices are very small and go unnoticed, while others have a big impact on the planet's climate. First of all, this applies to cyclones and anticyclones.
Definition 2
Cyclone is a huge atmospheric vortex with low pressure in the center.
In the Northern Hemisphere, the air in a cyclone moves counterclockwise, in the Southern Hemisphere - clockwise. Cyclonic activity in mid-latitudes is a feature of atmospheric circulation.
Cyclones arise due to the rotation of the Earth and the deflecting force of Coriolis, and in their development they go through stages from inception to filling. As a rule, cyclones occur on atmospheric fronts.
Two air masses of opposite temperatures, separated by a front, are drawn into a cyclone. Warm air at the interface is injected into a region of cold air and deflected into high latitudes.
The balance is disrupted, and cold air in the rear part is forced to penetrate into low latitudes. A cyclonic bend of the front arises, which represents huge wave, moving from west to east.
The wave stage is first stage cyclone development.
Warm air rises and slides along the frontal surface at the front of the wave. The resulting waves with a length of $1000$ km or more are unstable in space and continue to develop.
At the same time, the cyclone moves east at a speed of $100$ km per day, the pressure continues to fall, and the wind becomes stronger, the amplitude of the wave increases. This second stage– stage of a young cyclone.
On special maps, a young cyclone is outlined by several isobars.
As warm air moves to high latitudes, it forms warm front, and the movement of cold air into tropical latitudes forms a cold front. Both fronts are parts of a single whole. A warm front moves slower than a cold front.
If a cold front catches up with a warm front and merges with it, a occlusion front. Warm air rises and twists in a spiral. This third stage cyclone development – occlusion stage.
Fourth stage– filling it out is final. The warm air is finally pushed upward and cooled, temperature contrasts disappear, the cyclone becomes cold over its entire area, slows down and finally fills. From inception to filling, the life of a cyclone lasts from $5$ to $7$ days.
Note 1
Cyclones bring cloudy, cool and rainy weather in summer and thaw in winter. Summer cyclones move at a speed of $400$-$800$ km per day, winter ones - up to $1000$ km per day.
Anticyclones
Cyclonic activity is associated with the emergence and development of frontal anticyclones.
Definition 3
Anticyclone is a huge atmospheric vortex with high pressure in the center.
Anticyclones form in the rear of the cold front of a young cyclone in cold air and have their own stages of development.
There are only three stages in the development of an anticyclone:
General atmospheric circulation
The objects of study of the general circulation of the atmosphere are moving cyclones and anticyclones of temperate latitudes with their rapidly changing meteorological conditions: trade winds, monsoons, tropical cyclones, etc. Typical features of the general circulation of the atmosphere, stable over time or repeating more often than others, are revealed by averaging meteorological elements over long periods of time. long-term observation periods,
In Fig. 8, 9 shows the average long-term distribution of wind at the earth's surface in January and July. In January, i.e.
In winter, in the Northern Hemisphere, giant anticyclonic vortices are clearly visible over North America and a particularly intense vortex over Central Asia.
In summer, anticyclonic eddies over land are destroyed due to the warming of the continent, and over the oceans such eddies intensify significantly and spread to the north.
Pressure at the Earth's surface in millibars and prevailing air currents
Due to the fact that in the troposphere the air in equatorial and tropical latitudes is heated much more intensely than in the polar regions, air temperature and pressure gradually decrease in the direction from the equator to the poles. As meteorologists say, the planetary gradient of temperature and pressure is directed in the middle troposphere from the equator to the poles.
(In meteorology, the gradient of temperature and pressure is taken in the opposite direction compared to physics.) Air is a highly mobile medium. If the Earth did not rotate around its axis, then in the lower layers of the atmosphere the air would flow from the equator to the poles, and in the upper layers it would return back to the equator.
But the Earth rotates at an angular speed of 2n/86400 radians per second. Air particles, moving from low to high latitudes, retain high linear velocities relative to the earth's surface, acquired at low latitudes, and therefore are deflected as they move east. A west-east air transfer is formed in the troposphere, which is reflected in Fig. 10.
However, such a regular current regime is observed only on maps of average values. “Snapshots” of air currents give very diverse, each time new, non-repeating positions of cyclones, anticyclones, air currents, zones of meeting warm and cold air, i.e., atmospheric fronts.
Atmospheric fronts play a large role in the general circulation of the atmosphere, since significant transformations of the energy of air masses from one type to another occur in them.
In Fig. Figure 10 schematically shows the position of the main frontal sections in the middle troposphere and near the earth's surface. Numerous weather phenomena are associated with atmospheric fronts and frontal zones.
Here cyclonic and anticyclonic vortices originate, thick clouds and precipitation zones form, and wind increases.
When an atmospheric front passes through a given point, a noticeable cooling or warming is usually clearly observed, and the entire character of the weather changes sharply. Interesting features are found in the structure of the stratosphere.
Planetary frontal zone in the middle troposphere
If heat is located in the troposphere near the equator; air masses, and at the poles - cold, then in the stratosphere, especially in warm half year, the situation is just the opposite, the air here is relatively warmer at the poles, and cold at the equator.
The temperature and pressure gradients are directed in the opposite direction with respect to the troposphere.
The influence of the deflecting force of the Earth's rotation, which led to the formation of west-east transfer in the troposphere, creates a zone of east-west winds in the stratosphere.
Average location of jet stream axes in the Northern Hemisphere in winter
The highest wind speeds, and therefore the highest kinetic energy of air, are observed in jet streams.
Figuratively speaking, jet streams are air rivers in the atmosphere, rivers flowing at the upper boundary of the troposphere, in the layers separating the troposphere from the stratosphere, i.e. in layers close to the tropopause (Fig. 11 and 12).
Wind speed in jet streams reaches 250 - 300 km/h - in winter; and 100 - 140 km/h - in summer. Thus, a low-speed aircraft, falling into such a jet stream, can fly “backwards”.
Average location of jet stream axes in the Northern Hemisphere in summer
The length of jet streams reaches several thousand kilometers. Below the jet streams in the troposphere, wider and less fast air “rivers” are observed - planetary high-altitude frontal zones, which also play a large role in the general circulation of the atmosphere.
The occurrence of high wind speeds in jet streams and in planetary high-altitude frontal zones occurs due to the presence here big difference air temperatures between neighboring air masses.
The presence of a difference in air temperature, or as they say, "temperature contrast", leads to an increase in wind with height. Theory shows that such an increase is proportional to the horizontal temperature gradient of the air layer in question.
In the stratosphere, due to the reversal of the meridional air temperature gradient, the intensity of jet streams decreases and they disappear.
Despite the large extent of planetary high-altitude frontal zones and jet streams, they, as a rule, do not encircle the entire globe, but end where horizontal temperature contrasts between air masses weaken. The most frequent and dramatic temperature contrasts occur in the polar front, which separates the air of temperate latitudes from the tropical air.
Position of the axis of the altitudinal frontal zone with insignificant meridional exchange of air masses
Planetary high-altitude frontal zones and jet streams often occur in the polar front system. Although on average the planetary high-altitude frontal zones have a direction from west to east, in specific cases the direction of their axes is very diverse. Most often in temperate latitudes they have a wave-like character. In Fig.
13, 14 show the positions of the axes of high-altitude frontal zones in cases of stable west-east transport and in cases of developed meridional exchange of air masses.
A significant feature of air currents in the stratosphere and mesosphere over the equatorial and tropical regions is the existence there of several layers of air with almost opposite directions of strong winds.
The emergence and development of this multi-layer structure of the wind field here changes at certain, but not entirely coincident, intervals of time, which can also serve as some kind of prognostic sign.
If we add to this that the phenomenon of sharp warming in the polar stratosphere, which regularly occurs in winter, is in some way connected with processes in the stratosphere occurring in tropical latitudes, and with tropospheric processes in moderate and high latitudes, then it will become clear how complex and whimsical those atmospheric conditions develop processes that directly affect the weather regime in temperate latitudes.
Position of the axis of the altitudinal frontal zone with significant meridional exchange of air masses
The state of the underlying surface, especially the state of the upper active layer of water in the World Ocean, is of great importance for the formation of large-scale atmospheric processes. The surface of the World Ocean makes up almost 3/4 of the entire surface of the Earth (Fig. 15).
Sea currents
Due to their high heat capacity and ability to mix easily, ocean waters store heat for a long time during encounters with warm air in temperate latitudes and throughout the year in southern latitudes. The stored heat is carried far to the north by sea currents and warms nearby areas.
The heat capacity of water is several times greater than the heat capacity of soil and rocks composing the land. The heated water mass serves as a heat accumulator, with which it supplies the atmosphere. It should be noted that land reflects the sun's rays much better than the surface of the ocean.
The surface of snow and ice reflects the sun's rays especially well; 80-85% of all solar radiation falling on snow is reflected from it. The surface of the sea, on the contrary, absorbs almost all the radiation that falls on it (55-97%). As a result of all these processes, the atmosphere directly from the Sun receives only 1/3 of all incoming energy.
It receives the remaining 2/3 of its energy from the underlying surface heated by the Sun, primarily from the water surface. Heat transfer from the underlying surface to the atmosphere occurs in several ways. Firstly, a large number of Solar heat is spent on the evaporation of moisture from the surface of the ocean into the atmosphere.
When this moisture condenses, heat is released, which warms the surrounding layers of air. Secondly, the underlying surface gives off heat to the atmosphere through turbulent (i.e., vortex, disordered) heat exchange. Thirdly, heat is transferred by thermal electromagnetic radiation. As a result of the interaction of the ocean with the atmosphere, important changes occur in the latter.
The layer of the atmosphere into which the heat and moisture of the ocean penetrates, in cases of invasion of cold air onto the warm ocean surface, reaches 5 km or more. In cases where warm air invades the cold water surface of the ocean, the height to which the influence of the ocean extends does not exceed 0.5 km.
In cases of invasion of cold air, the thickness of its layer, which is influenced by the ocean, depends primarily on the magnitude of the temperature difference between water and air. If the water is warmer than the air, then powerful convection develops, i.e., disordered upward movements of air, which lead to the penetration of heat and moisture into the high layers of the atmosphere.
On the contrary, if the air is warmer than the water, then convection does not occur and the air changes its properties only in the lowest layers. Above the warm Gulf Stream in the Atlantic Ocean, during the invasion of very cold air, heat transfer from the ocean can reach up to 2000 cal/cm2 per day and extends to the entire troposphere.
Warm air can lose 20-100 cal/cm2 per day over the cold ocean surface. Changes in the properties of air falling on a warm or cold ocean surface occur quite quickly - such changes can be noticed at a level of 3 or 5 km within a day after the start of the invasion.
What air temperature increments can occur as a result of its transformation (change) above the underlying water surface? It turns out that in the cold half of the year the atmosphere over the Atlantic warms up by 6° on average, and sometimes it can warm up by 20° per day. The atmosphere can cool by 2-10° per day. It is estimated that in the North Atlantic Ocean, i.e.
where the most intense heat transfer from the ocean to the atmosphere occurs, the ocean gives off 10-30 times more heat than it receives from the atmosphere. It is natural that the heat reserves in the ocean are replenished by the influx of warm ocean waters from tropical latitudes. Air currents distribute the heat received from the ocean over thousands of kilometers. The warming influence of the oceans in winter leads to the fact that the difference in air temperature between the northeastern parts of the oceans and continents is 15-20° at latitudes 45-60° near the earth's surface, and 4-5° in the middle troposphere. For example, the warming effect of the ocean on the climate of Northern Europe has been well studied.
In winter, the northwestern part of the Pacific Ocean is under the influence of the cold air of the Asian continent, the so-called winter monsoon, which extends 1-2 thousand km deep into the ocean in the surface layer and 3-4 thousand km in the middle troposphere (Fig. 16) .
Annual amounts of heat transferred by sea currents
In summer, it is colder over the ocean than over the continents, so the air coming from the Atlantic Ocean cools Europe, and the air from the Asian continent warms the Pacific Ocean. However, the picture described above is typical for average circulation conditions.
Day-to-day changes in the magnitude and direction of heat flows from the underlying surface to the atmosphere and back are very diverse and have a great influence on changes in the atmospheric processes themselves.
There are hypotheses according to which the peculiarities of the development of heat exchange between different parts of the underlying surface and the atmosphere determine the stable nature of atmospheric processes over long periods of time.
If the air warms up above the anomalously (above normal) warm water surface of one or another part of the World Ocean in the temperate latitudes of the Northern Hemisphere, then an area of high pressure (pressure ridge) forms in the middle troposphere, along the eastern periphery of which the transfer of cold air masses from the Arctic begins, and along its western part - the transfer of warm air from tropical latitudes to the north. This situation can lead to the persistence of a long-term weather anomaly at the earth's surface in certain areas - dry and hot or rainy and cool in the summer, frosty and dry or warm and snowy in the winter. Cloudiness plays a very significant role in the formation of atmospheric processes by regulating the flow of solar heat to the earth's surface. Cloud cover significantly increases the proportion of reflected radiation and thereby reduces the heating of the earth's surface, which, in turn, affects the nature of synoptic processes. It turns out to be somewhat similar feedback: the nature of atmospheric circulation influences the creation of cloud systems, and cloud systems, in turn, influence changes in circulation. We have listed only the most important of the studied “terrestrial” factors that influence the formation of weather and air circulation. The activity of the Sun plays a special role in the study of the causes of changes in the general CIRCULATION of the atmosphere. Here it is necessary to distinguish between changes in air circulation on Earth in connection with changes in the total flow of heat coming from the Sun to Earth as a result of fluctuations in the value of the so-called solar constant. However, as recent research shows, in reality it is not a strictly constant value. The atmospheric circulation energy is continuously replenished by the energy sent by the Sun. Therefore, if the total energy sent by the Sun fluctuates significantly, this can affect changes in circulation and weather on Earth. This issue has not yet been sufficiently studied. As for the change solar activity, then it is well known that various disturbances arise on the surface of the Sun, sunspots, torches, floccules, prominences, etc. These disturbances cause temporary changes in the composition of solar radiation, the ultraviolet component and corpuscular (i.e., consisting of charged particles, mainly protons) radiation from the Sun increases. Some meteorologists believe that changes in solar activity are associated with tropospheric processes in the Earth's atmosphere, i.e., with the weather.
This last statement requires further research, mainly due to the fact that the well-manifested 11-year cycle of solar activity is not clearly visible in weather conditions on Earth.
It is known that there are entire schools of meteorological forecasters who are quite successful in predicting the weather in connection with changes in solar activity.
Wind and general atmospheric circulation
Wind is the movement of air from areas of higher air pressure to areas of lower pressure. Wind speed is determined by the magnitude of the difference in atmospheric pressure.
The influence of wind in navigation must be constantly taken into account, since it causes ship drift, storm waves, etc.
Due to the uneven heating of different parts of the globe, there is a system of atmospheric currents on a planetary scale (general atmospheric circulation).
The air flow consists of individual vortices moving randomly in space. Therefore, the wind speed measured at any point changes continuously over time. The greatest fluctuations in wind speed are observed in the near-water layer. In order to be able to compare wind speeds, a height of 10 meters above sea level was taken as the standard height.
Wind speed is expressed in meters per second, wind force in points. The relationship between them is determined by the Beaufort scale.
Beaufort scale
Fluctuations in wind speed are characterized by the gustiness coefficient, which is understood as the ratio of the maximum speed of wind gusts to its average speed obtained over 5 - 10 minutes.
As the average wind speed increases, the gust factor decreases. At high wind speeds, the gustiness coefficient is approximately 1.2 - 1.4.
Trade winds are winds that blow all year round in one direction in the zone from the equator to 35° N. w. and up to 30° south. w. Stable in direction: in the northern hemisphere - northeast, in the southern hemisphere - southeast. Speed – up to 6 m/s.
Monsoons are winds of temperate latitudes, blowing from the ocean to the mainland in summer and from the mainland to the ocean in winter. Reach speeds of 20 m/s. Monsoons bring dry, clear and cold weather to the coast in winter, and cloudy weather with rain and fog in summer.
Breezes arise due to uneven heating of water and land during the day. During the daytime, wind arises from sea to land (sea breeze). At night from the chilled coast - to the sea (shore breeze). Wind speed 5 – 10 m/s.
Local winds arise in certain areas due to the characteristics of the relief and differ sharply from the general air flow: they arise as a result of uneven heating (cooling) of the underlying surface. Detailed information about local winds is given in sailing directions and hydrometeorological descriptions.
Bora is a strong and gusty wind directed down a mountain slope. Brings significant cooling.
It is observed in areas where a low mountain range borders the sea, during periods when atmospheric pressure increases over land and the temperature decreases compared to the pressure and temperature over the sea.
In the area of the Novorossiysk Bay, the bora operates in November - March with average wind speeds of about 20 m/s (individual gusts can be 50 - 60 m/s). Duration of action is from one to three days.
Similar winds are observed on Novaya Zemlya, on the Mediterranean coast of France (mistral) and off the northern shores of the Adriatic Sea.
Sirocco - hot and humid winds in the central Mediterranean Sea are accompanied by clouds and precipitation.
Tornadoes are whirlwinds over the sea with a diameter of up to several tens of meters, consisting of water spray. They last up to a quarter of a day and move at speeds of up to 30 knots. The wind speed inside a tornado can reach up to 100 m/s.
Storm winds occur predominantly in areas with low atmospheric pressure. Tropical cyclones reach especially great strength, with wind speeds often exceeding 60 m/s.
Strong storms are also observed in temperate latitudes. When moving, warm and cold air masses inevitably come into contact with each other.
The transition zone between these masses is called the atmospheric front. The passage of the front is accompanied by a sharp change in the weather.
An atmospheric front can be stationary or in motion. There are warm, cold fronts, and occlusion fronts. The main atmospheric fronts are: arctic, polar and tropical. On synoptic maps, fronts are depicted as lines (front line).
A warm front is formed when warm air masses attack cold ones. On weather maps, a warm front is marked by a solid line with semicircles along the front indicating the direction of colder air and the direction of movement.
As the warm front approaches, pressure begins to drop, clouds thicken, and heavy precipitation begins to fall. In winter, low stratus clouds usually appear when a front passes. The temperature and humidity are slowly increasing.
As a front passes, temperatures and humidity typically rise quickly and winds pick up. After the front passes, the wind direction changes (the wind turns clockwise), the pressure drop stops and its slight increase begins, the clouds dissipate, and precipitation stops.
A cold front is formed when cold air masses attack warmer ones (Fig. 18.2). On weather maps, a cold front is depicted as a solid line with triangles along the front indicating warmer temperatures and the direction of movement. The pressure ahead of the front drops strongly and unevenly, the ship finds itself in a zone of showers, thunderstorms, squalls and strong waves.
An occlusion front is a front formed by the merger of a warm and cold front. It appears as a solid line with alternating triangles and semicircles.
Section of a warm front
Cross section of a cold front
A cyclone is an atmospheric vortex of huge diameter (from hundreds to several thousand kilometers) with low air pressure in the center. The air in a cyclone circulates counterclockwise in the northern hemisphere and clockwise in the southern hemisphere.
There are two main types of cyclones – extratropical and tropical.
The first are formed in temperate or polar latitudes and have a diameter of a thousand kilometers at the beginning of development, and up to several thousand in the case of the so-called central cyclone.
A tropical cyclone is a cyclone formed in tropical latitudes; it is an atmospheric vortex with low atmospheric pressure in the center with storm-like wind speeds. Formed tropical cyclones move along with air masses from east to west, while gradually deviating towards high latitudes.
Such cyclones are also characterized by the so-called The “eye of the storm” is a central area with a diameter of 20–30 km with relatively clear and windless weather. About 80 tropical cyclones are observed annually in the world.
View of a cyclone from space
Paths of tropical cyclones
In the Far East and South-East Asia tropical cyclones are called typhoons (from the Chinese tai feng - big wind), and in the North and South America– hurricanes (Spanish huracán, named after the Indian god of the wind).
It is generally accepted that a storm becomes a hurricane when wind speeds exceed 120 km/h; at speeds of 180 km/h, a hurricane is called a strong hurricane.
7. Wind. General atmospheric circulation
Lecture 7. Wind. General atmospheric circulation
Wind – This is the movement of air relative to the earth's surface, in which the horizontal component predominates. When upward or downward wind movement is considered, the vertical component is also taken into account. The wind is characterized direction, speed and impetuosity.
The cause of wind is the difference in atmospheric pressure at different points, determined by the horizontal pressure gradient. The pressure is not the same primarily due to different degrees of heating and cooling of the air and decreases with altitude.
To get an idea of the pressure distribution on the surface of the globe, on geographic Maps apply pressure measured at the same time at different points and normalized to the same height (for example, sea level). Points with the same pressure are connected by lines - isobars.
In this way, areas of high (anticyclones) and low (cyclones) pressure and the directions of their movement are identified for weather forecasting. Using isobars, you can determine the amount of pressure change with distance.
In meteorology, the concept is accepted horizontal pressure gradient is the change in pressure per 100 km along a horizontal line perpendicular to the isobars from high pressure to low pressure. This change is usually 1-2 hPa/100 km.
The movement of air occurs in the direction of the gradient, but not in a straight line, but more complexly, which is due to the interaction of forces that deflect the air due to the rotation of the earth and friction. Under the influence of the Earth's rotation, air movement deviates from the pressure gradient to the right in the northern hemisphere, and to the left in the southern hemisphere.
The largest deviation is observed at the poles, and at the equator it is close to zero. The friction force reduces both wind speed and deviation from the gradient as a result of contact with the surface, as well as inside the air mass due to different speeds in the layers of the atmosphere. The combined influence of these forces deflects the wind from the gradient over land by 45-55o, over the sea - by 70-80o.
With increasing altitude, the wind speed and its deviation increase up to 90° at a level of about 1 km.
Wind speed is usually measured in m/sec, less often in km/h and points. The direction is taken to be where the wind is blowing, determined in bearings (there are 16 of them) or angular degrees.
Used for wind observations vane, which is installed at a height of 10-12 m. A hand-held anemometer is used for short-term observations of speed in field experiments.
Anemorummeter allows you to remotely measure wind direction and speed , anemormbograph continuously records these indicators.
The diurnal variation of wind speed over the oceans is almost not observed and is well expressed over land: at the end of the night - a minimum, in the afternoon - a maximum. The annual cycle is determined by the patterns of general circulation of the atmosphere and differs among regions of the globe. For example, in Europe in summer there is a minimum wind speed, in winter it is maximum. IN Eastern Siberia- vice versa.
The direction of the wind in a particular place changes often, but if you take into account the frequency of winds of different directions, you can determine that some occur more often. To study directions in this way, a graph called a wind rose is used. On each straight line of all points of reference, the observed number of wind events for the required period is plotted and the obtained values on the points of reference are connected by lines.
The wind helps maintain the constancy of the gas composition of the atmosphere, mixing air masses, transporting moist sea air inland, providing them with moisture.
The unfavorable effect of wind on agriculture can manifest itself in increased evaporation from the soil surface, causing drought; wind erosion of soils is possible at high wind speeds.
Wind speed and direction must be taken into account when pollinating fields with pesticides and when irrigating with sprinklers. The direction of the prevailing winds must be known when laying forest strips and snow retention.
Local winds.
Local winds are called winds that are characteristic only of certain geographical areas. They are of particular importance in their influence on weather, their origin is different.
Breezes – winds coastline seas and large lakes that have a sharp diurnal change in direction. During the day sea breeze blows onto the shore from the sea, and at night - onshore breeze blows from land to sea (Fig. 2).
They are pronounced in clear weather in the warm season, when the overall air transport is weak. In other cases, for example during the passage of cyclones, breezes can be masked by stronger currents.
Wind movement during breezes is observed at a distance of several hundred meters (up to 1-2 km), with an average speed of 3 - 5 m/sec, and in the tropics - even more, penetrating tens of kilometers deep into land or sea.
The development of breezes is associated with the daily variation of land surface temperature. During the day, the land heats up more than the surface of the water, the pressure above it becomes lower and air transfer from the sea to the land is formed. At night, the land cools faster and more strongly, and air is transferred from land to sea.
The daytime breeze lowers the temperature and increases the relative humidity, which is especially pronounced in the tropics. For example, in West Africa When sea air moves to land, the temperature can drop by 10°C or more, and the relative humidity can increase by 40%.
Breezes are also observed on the coasts of large lakes: Ladoga, Onega, Baikal, Sevan, etc., as well as on big rivers. However, in these areas the breezes are smaller in their horizontal and vertical development.
Mountain-valley winds are observed in mountain systems mainly in summer and are similar to breezes in their daily frequency. During the day, they blow up the valley and along the mountain slopes as a result of heating by the sun, and at night, when cooled, the air flows down the slopes. Night air movement can cause frost, which is especially dangerous in the spring when gardens are blooming.
Föhn –a warm and dry wind blowing from the mountains to the valleys. At the same time, the air temperature rises significantly and its humidity drops, sometimes very quickly. They are observed in the Alps, in the Western Caucasus, on the southern coast of Crimea, in the mountains of Central Asia, Yakutia, on the eastern slopes of the Rocky Mountains and in other mountain systems.
A foehn is formed when an air current crosses a ridge. Since a vacuum is created on the leeward side, air is sucked down in the form of a downward wind. The descending air is heated according to the dry adiabatic law: by 1°C for every 100 m of descent.
For example, if at an altitude of 3000 m the air had a temperature of -8o and a relative humidity of 100%, then, having descended into the valley, it will heat up to 22o, and the humidity will drop to 17%. If the air rises along the windward slope, then water vapor condenses and clouds form, precipitation occurs, and the descending air will be even drier.
The duration of hair dryers ranges from several hours to several days. A hairdryer can cause intense snow melting and flooding, drying out soils and vegetation until they die.
Bora–it is a strong, cold, gusty wind that blows from low mountain ranges towards a warmer sea.
The most famous bora is in the Novorossiysk Bay of the Black Sea and on the Adriatic coast near the city of Trieste. Similar to bora in origin and manifestation north in the area of
Baku, mistral on the Mediterranean coast of France, Northser in the Gulf of Mexico.
Bora is created when cold air masses pass through the coastal ridge. The air flows down under the force of gravity, developing a speed of more than 20 m/sec, while the temperature drops significantly, sometimes by more than 25 ° C. Bora fades away a few kilometers from the coast, but sometimes it can cover a significant part of the sea.
In Novorossiysk, bora is observed about 45 days a year, most often from November to March, with a duration of up to 3 days, rarely up to a week.
General atmospheric circulation
General atmospheric circulation– this is a complex system of large air currents that transport very large masses of air over the globe.
In the atmosphere near the earth's surface in polar and tropical latitudes, eastern transport is observed, and in temperate latitudes - western transport.
The movement of air masses is complicated by the rotation of the Earth, as well as by topography and the influence of areas of high and low pressure. The deviation of winds from the prevailing directions is up to 70°.
In the process of heating and cooling huge masses of air above the globe, areas of high and low pressure are formed, which determine the direction of planetary air currents. Based on long-term average pressure values at sea level, the following patterns have been identified.
On both sides of the equator there is a low pressure zone (in January - between 15° north latitude and 25° south latitude, in July - from 35° north latitude to 5° south latitude). This zone, called equatorial depression, extends more to the hemisphere where in given month summer.
In the direction to the north and south of it, the pressure increases and reaches maximum values at subtropical high pressure zones(in January - at 30 - 32o northern and southern latitudes, in July - at 33-37o N and 26-30o S). From the subtropics to the temperate zones, the pressure drops, especially significantly in the southern hemisphere.
The minimum pressure is at two subpolar low pressure zones(75-65o N and 60-65o S). Further towards the poles the pressure increases again.
The meridional baric gradient is also located in accordance with pressure changes. It is directed from the subtropics on the one hand - to the equator, on the other - to the subpolar latitudes, from the poles to the subpolar latitudes. The zonal direction of winds is consistent with this.
Over the Atlantic, Pacific and Indian Oceans Northeast and southeast winds blow very often – trade winds. Western winds in the southern hemisphere, at latitudes 40-60o, go around the entire ocean.
In the northern hemisphere at temperate latitudes, westerly winds are constantly expressed only over the oceans, and over continents the directions are more complex, although westerlies also predominate.
Eastern winds of polar latitudes are clearly observed only along the outskirts of Antarctica.
In the south, east and north of Asia there is a sharp change in the direction of winds from January to July - these are areas monsoon. The causes of monsoons are similar to the causes of breezes. In summer, the Asian mainland heats up greatly and an area of low pressure spreads over it, where air masses from the ocean rush.
The resulting summer monsoon causes large amounts of precipitation, often of a torrential nature. In winter, high pressure sets over Asia due to more intense cooling of the land compared to the ocean and cold air moves towards the ocean, forming the winter monsoon with clear, dry weather. Monsoons penetrate more than 1000 km in a layer above land up to 3-5 km.
Air masses and their classification.
Air mass- this is a very large amount of air, which occupies an area of millions of square kilometers.
In the process of general circulation of the atmosphere, the air is divided into separate air masses, which remain for a long time over a vast territory, acquire certain properties and cause various types of weather.
Moving to other areas of the Earth, these masses bring with them their own weather patterns. The predominance of air masses of a certain type(s) in a particular area creates the characteristic climate regime of the area.
The main differences in air masses are: temperature, humidity, cloudiness, dust content. For example, in summer the air over the oceans is wetter, colder, and cleaner than over land at the same latitude.
The longer the air stays over one area, the more it undergoes changes, so air masses are classified according to geographical areas where they were formed.
There are main types: 1) Arctic (Antarctic), which move from the poles, from high pressure zones; 2) temperate latitudes“polar” – in the northern and southern hemispheres; 3) tropical– move from subtropics and tropics to temperate latitudes; 4) equatorial– are formed above the equator. Within each type, marine and continental subtypes are distinguished, differing primarily in temperature and humidity within the type. The air, being in constant motion, moves from the area of formation to neighboring ones and gradually changes properties under the influence of the underlying surface, gradually turning into a mass of a different type. This process is called transformation.
Cold Air masses are those that move to a warmer surface. They cause cooling in the areas where they come.
As they move, they are heated by the earth's surface, so large vertical temperature gradients arise within the masses and convection develops with the formation of cumulus and cumulonimbus clouds and rainfall.
Air masses moving towards a colder surface are called warm by the masses. They bring warming, but they themselves cool from below. Convection does not develop in them and stratus clouds predominate.
Neighboring air masses are separated from each other by transition zones that are strongly inclined to the Earth's surface. These zones are called fronts.
Air masses- large volumes of air in the lower part of the earth's atmosphere - the troposphere, having horizontal dimensions of many hundreds or several thousand kilometers and vertical dimensions of several kilometers, characterized by approximately uniform temperature and moisture content horizontally.
Kinds:Arctic or Antarctic air(AB), Temperate air(UV), tropical air(TV), Equatorial air(EV).
Air in ventilation layers can move in the form laminar or turbulent flow. Concept "laminar" means that the individual air flows are parallel to each other and move in the ventilation space without turbulence. When turbulent flow its particles not only move in parallel, but also perform transverse movement. This leads to vortex formation throughout the entire cross-section of the ventilation duct.
The condition of the air flow in the ventilation space depends on: Air flow speed, Air temperature, Cross-sectional area of the ventilation duct, Shapes and surfaces of building elements at the boundary of the ventilation duct.
IN earth's atmosphere air movements of the most varied scales are observed - from tens and hundreds of meters (local winds) to hundreds and thousands of kilometers (cyclones, anticyclones, monsoons, trade winds, planetary frontal zones).
The air is constantly moving: it rises - upward movement, falls - downward movement. The movement of air in a horizontal direction is called wind. The cause of wind is the uneven distribution of air pressure on the Earth's surface, which is caused by the uneven distribution of temperature. In this case, the air flow moves from places with high pressure to the side where the pressure is less.
When there is wind, the air does not move evenly, but in shocks and gusts, especially near the surface of the Earth. There are many reasons that influence the movement of air: friction of the air flow on the surface of the Earth, encountering obstacles, etc. In addition, air flows, under the influence of the rotation of the Earth, are deflected to the right in the northern hemisphere, and to the left in the southern hemisphere.
Invading areas with different surface thermal properties, air masses are gradually transformed. For example, temperate sea air, entering land and moving inland, gradually heats up and dries out, turning into continental air. The transformation of air masses is especially characteristic of temperate latitudes, into which warm and dry air from tropical latitudes and cold and dry air from subpolar latitudes invade from time to time.
- an important factor in climate formation. It is expressed by moving various types air masses
Air masses- these are moving parts of the troposphere that differ from each other in temperature and humidity. There are air masses sea And continental.
Marine air masses form over the World Ocean. They are more humid compared to continental ones that form over land.
In different climatic zones The Earth forms its own air masses: equatorial, tropical, temperate, arctic And Antarctic.
As air masses move, they retain their properties for a long time and therefore determine the weather of the places where they arrive.
Arctic air masses form over the Arctic Ocean (in winter, over the northern continents of Eurasia and North America). They are characterized by low temperature, low humidity and increased air transparency. Intrusions of Arctic air masses into temperate latitudes cause a sharp cooling. The weather is mostly clear and partly cloudy. When moving deeper into the continent to the south, Arctic air masses are transformed into dry continental air of temperate latitudes.
Continental Arctic air masses form over the icy Arctic (in its central and eastern parts) and over the northern coast of the continents (in winter). Their features are very low air temperatures and low moisture content. The invasion of continental Arctic air masses onto the mainland leads to severe cooling in clear weather.
Marine arctic air masses are formed in warmer conditions: over ice-free waters with higher air temperatures and higher moisture content - this is the European Arctic. Intrusions of such air masses onto the mainland in winter even cause warming.
The analogue of the Arctic air of the Northern Hemisphere in the Southern Hemisphere is Antarctic air masses. Their influence extends mostly to adjacent sea surfaces and rarely to the southern edge of the South American continent.
Moderate(polar) air is the air of temperate latitudes. Moderate air masses penetrate into polar, as well as subtropical and tropical latitudes.
Continental temperate air masses in winter usually bring clear weather with severe frosts, and in summer - fairly warm, but cloudy, often rainy, with thunderstorms.
Marine temperate air masses are transported to the continents by westerly winds. They are characterized by high humidity and moderate temperatures. In winter, maritime moderate air masses bring cloudy weather, heavy precipitation and thaws, and in summer - large clouds, rain and lower temperatures.
Tropical air masses are formed in tropical and subtropical latitudes, and in summer - in continental regions in the south of temperate latitudes. Tropical air penetrates into temperate and equatorial latitudes. High temperature is a common feature of tropical air.
Continental tropical air masses are dry and dusty, and maritime tropical air masses- high humidity.
equatorial air, occurring in the Equatorial Depression, very warm and humid. In summer in the Northern Hemisphere, equatorial air, moving north, is drawn into the circulation system of the tropical monsoons.
Equatorial air masses are formed in equatorial zone. They are characterized by high temperatures and humidity throughout the year, and this applies to air masses that form both over land and over the ocean. Therefore, equatorial air is not divided into marine and continental subtypes.
The entire system of air currents in the atmosphere is called general circulation of the atmosphere.
Atmospheric front
Air masses are constantly moving, changing their properties (transforming), but quite sharp boundaries remain between them - transition zones several tens of kilometers wide. These border zones are called atmospheric fronts and are characterized by an unstable state of temperature, air humidity,.
The intersection of such a front with the earth's surface is called line of the atmospheric front.
When an atmospheric front passes through any area above it, the air masses and, as a result, the weather change.
Temperate latitudes are characterized by frontal precipitation. In the zone of atmospheric fronts, extensive cloud formations thousands of kilometers long occur and precipitation occurs. How do they arise? The atmospheric front can be considered as the boundary of two air masses, which is inclined to the earth's surface at a very small angle. Cold air is located next to warm air and above it in the form of a flat wedge. In this case, warm air rises up the wedge of cold air and cools, approaching a state of saturation. Clouds appear from which precipitation falls.
If the front moves toward the retreating cold air, warming occurs; such a front is called warm. Cold front on the contrary, it advances into the territory occupied by warm air (Fig. 1).
Rice. 1. Types of atmospheric fronts: a - warm front; b - cold front
Condensation is a change in the state of a substance from gaseous to liquid or solid. But what is condensation in the mastaba of the planet?
At any given time, the atmosphere of planet Earth contains over 13 billion tons of moisture. This figure is practically constant, since losses due to precipitation are ultimately continuously replenished by evaporation.
The rate of moisture circulation in the atmosphere
The rate of moisture circulation in the atmosphere is estimated at a colossal figure - about 16 million tons per second or 505 billion tons per year. If all the water vapor in the atmosphere suddenly condensed and fell as precipitation, this water could cover the entire surface of the globe with a layer of about 2.5 centimeters, in other words, the atmosphere contains an amount of moisture equivalent to only 2.5 centimeters of rain.
How long does a vapor molecule stay in the atmosphere?
Since the average annual precipitation on Earth is 92 centimeters, it follows that moisture in the atmosphere is renewed 36 times, that is, 36 times the atmosphere is saturated with moisture and freed from it. This means that a molecule of water vapor remains in the atmosphere for an average of 10 days.
Path of the water molecule
Once evaporated, a molecule of water vapor usually drifts for hundreds and thousands of kilometers until it condenses and falls with precipitation on the Earth. Water falling as rain, snow or hail on the highlands of Western Europe travels approximately 3,000 km from the North Atlantic. Several physical processes occur between liquid water turning into vapor and precipitation falling on Earth.
From the warm surface of the Atlantic, water molecules enter warm, moist air, which then rises above the surrounding colder (more dense) and drier air.
If strong turbulent mixing of air masses is observed, then a layer of mixing and clouds will appear in the atmosphere at the boundary of two air masses. About 5% of their volume is moisture. Air saturated with steam is always lighter, firstly, because it is heated and comes from a warm surface, and secondly, because 1 cubic meter of pure steam is about 2/5 lighter than 1 cubic meter of clean dry air at the same temperature and pressure. It follows that moist air is lighter than dry air, and warm and humid air even more so. As we will see later, this is a very important fact for the processes of weather change.
Movement of air masses
Air can rise for two reasons: either because it becomes lighter as a result of heating and humidification, or because forces act on it, causing it to rise above some obstacles, such as over masses of colder and denser air or over hills and mountains.
Cooling
The rising air, having entered layers with lower atmospheric pressure, is forced to expand and cool at the same time. Expansion requires costs kinetic energy, which is taken from the thermal and potential energy of atmospheric air, and this process inevitably leads to a decrease in temperature. The cooling rate of a rising portion of air often changes if this portion is mixed with surrounding air.
Dry adiabatic gradient
Dry air, in which there is no condensation or evaporation, and no mixing, and does not receive energy in any other form, cools or warms by a constant amount (1 ° C every 100 meters) as it rises or falls. This quantity is called the dry adiabatic gradient. But if the rising air mass is moist and condensation occurs in it, then latent heat of condensation is released and the temperature of the steam-saturated air drops much more slowly.
Moist adiabatic gradient
This amount of temperature change is called the moist-adiabatic gradient. It is not constant, but changes with changes in the amount of latent heat released, in other words, it depends on the amount of condensed steam. The amount of steam depends on how much the air temperature drops. In the lower layers of the atmosphere, where the air is warm and humidity is high, the moist-adiabatic gradient is slightly more than half the dry-adiabatic gradient. But the wet-adiabatic gradient gradually increases with height and at very high altitudes in the troposphere is almost equal to the dry-adiabatic gradient.
The buoyancy of moving air is determined by the relationship between its temperature and the temperature of the surrounding air. Typically, in the real atmosphere, air temperature falls unevenly with height (this change is simply called a gradient).
If the air mass is warmer and therefore less dense than the surrounding air (and the moisture content is constant), then it rises upward in the same way as a child's ball immersed in a tank. Conversely, when the moving air is colder than the surrounding air, its density is higher and it sinks. If the air has the same temperature as neighboring masses, then their density is equal and the mass remains motionless or moves only with the surrounding air.
Thus, there are two processes in the atmosphere, one of which promotes the development of vertical air movement, and the other slows it down.
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