What is the movement of air masses definition. The movement of air masses in the atmosphere, the role of precipitation, weather, climate and climatic zonality in geological processes.31. How long does a vapor molecule stay in the atmosphere
Atmospheric circulation diagram
Air in the atmosphere is in constant motion. It moves both horizontally and vertically.
The primary reason for the movement of air in the atmosphere is the uneven distribution of solar radiation and the heterogeneity of the underlying surface. They cause uneven air temperature and, accordingly, atmospheric pressure above the earth's surface.
The pressure difference creates a movement of air that moves from areas of high to areas of low pressure. In the process of moving, air masses are deflected by the force of the rotation of the Earth.
(Remember how bodies move in the northern and southern hemispheres deviate.)
Of course, you have noticed how a light haze forms over the asphalt on a hot summer day. This is heated, light air rising up. A similar but much larger picture can be seen at the equator. Very hot air constantly rises, forming updrafts.
Therefore, a constant low-pressure belt is formed near the surface here.
The air that has risen above the equator in the upper layers of the troposphere (10-12 km) spreads to the poles. Gradually, it cools and begins to descend approximately above 30 t ° north and south latitude.
Thus, an excess of air is formed, which contributes to the formation of a tropical high-pressure belt in the surface layer of the atmosphere.
In the circumpolar regions, the air is cold, heavy and descends, causing downward movements. As a result, high pressure is formed in the near-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 upwards, causing updrafts.
As a result, a surface low-pressure belt is formed in temperate latitudes.
Map of the Earth's climate zones
If the earth's surface were uniform, atmospheric pressure belts would spread in continuous bands. However, the surface of the planet is an alternation of water and land, which have different properties. The land quickly heats up and cools down.
The ocean, on the contrary, heats up and releases its heat slowly. That is why 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, high and low pressure belts naturally alternate. High pressure - at the poles and near the tropics, low - at the equator and in temperate latitudes.
Types of atmospheric circulation
There are several powerful links in the circulation of air masses in the Earth's atmosphere. All of them are active and inherent in certain latitudinal zones. Therefore, they are called zonal types of atmospheric circulation.
Near 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 deviate to the right in the Northern Hemisphere and to the left in the Southern.
This is how constant powerful winds are formed - trade winds. In the Northern Hemisphere, the trade winds blow in the direction from the northeast, and in the Southern Hemisphere - from the southeast. So, the first zonal type of atmospheric circulation - trade wind.
Air moves from the tropics to temperate latitudes. Deviating under the influence of the force of the rotation of the Earth, they begin to gradually move from west to east. It is 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.
The movement of air from the subpolar belts of high pressure to temperate latitudes, where the pressure is low, is also regular.
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 various types of zonal air circulation dominate.
Due to the uneven heating of the land and ocean, the zonal pattern of movement of air masses is violated. For example, in the east of Eurasia in temperate latitudes, the western air transfer operates only for half a year - in winter. In summer, when the mainland heats up, the air masses move to land with the coolness of the ocean.
This is how the monsoon air transport occurs. The change in the direction 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- the 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, western air transport and eastern circumpolar air mass flow. Monsoonal air transport disrupts the general scheme of atmospheric circulation and is an azonal type of circulation.
General circulation of the atmosphere (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
By 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 that determine the general circulation of the atmosphere
3. Cyclones and anticyclones.
4. Winds affecting the general circulation of the atmosphere
5. Hair dryer effect
6. Scheme of the general circulation "Planet Machine"
Conclusion
List of used literature
Introduction
On the pages of scientific literature recently, the concept of general circulation of the atmosphere is often encountered, the meaning of which each specialist understands in his own way. This term is systematically used by specialists involved in geography, ecology, and the upper part of the atmosphere.
Increasing interest in the general circulation of the atmosphere is shown by meteorologists and climatologists, biologists and physicians, hydrologists and oceanologists, botanists and zoologists, and of course ecologists.
There is no consensus on whether this scientific direction has emerged recently or research has been going on here for centuries.
Below are the definitions of the general circulation of the atmosphere, as a set of sciences, and the factors influencing it are listed.
A certain list of achievements is given: hypotheses, developments and discoveries that mark certain milestones in the history of this set of sciences and give a certain idea of the range of problems and tasks considered by it.
The distinctive features of the general circulation of the atmosphere are described, as well as the simplest scheme of the general circulation called the "planetary machine" is presented.
1. General information about atmospheric circulation
The general circulation of the atmosphere (lat. Circulatio - rotation, Greek atmos - steam and sphaira - ball) is a set of large-scale air currents in the tropo- and stratospheres. As a result, there is an exchange of air masses in space, which contributes to the redistribution of heat and moisture.
The general circulation of the atmosphere is called the circulation of air on the globe, leading to its transfer from low latitudes to high latitudes and vice versa.
The general circulation of the atmosphere is determined by zones of high atmospheric pressure in the subpolar regions and tropical latitudes and zones of low pressure in temperate and equatorial latitudes.
The movement of air masses occurs both in latitudinal and meridional directions. In the troposphere, the circulation of the atmosphere 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 deviating effect on air flows of the Earth's rotation.
The main patterns of atmospheric circulation are constant.
In the lower stratosphere, jet streams of air in temperate and subtropical latitudes are predominantly western, and in tropical latitudes - eastern, and they go at a speed 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 in geographical zones.
In polar latitudes, easterly winds; in temperate - western with frequent disturbance by cyclones and anticyclones, trade winds and monsoons are most stable in tropical latitudes.
Due to the diversity of the underlying surface, regional deviations - local winds - appear on the form of the general circulation of the atmosphere.
2. Factors that determine the general circulation of the atmosphere
- Uneven distribution of solar energy over the earth's surface and, as a result, uneven distribution of temperature and atmospheric pressure.
- Coriolis forces and friction, under the influence of which air flows acquire a latitudinal direction.
– The influence of the underlying surface: the presence of continents and oceans, the heterogeneity of the relief, etc.
The distribution of air currents in the earth's surface has a zonal character. In the equatorial latitudes - calm or weak variable winds are observed. The trade winds dominate the tropical zone.
The trade winds are constant winds blowing from 30 latitudes to the equator, having a northeasterly direction in the northern hemisphere, and a southeasterly direction in the southern hemisphere. At 30-35? with. and y.sh. - calm zone, so-called. "horse latitudes".
In temperate latitudes, westerly winds prevail (southwest in the northern hemisphere, northwest in the southern hemisphere). In the polar latitudes, easterly (in the northern hemisphere northeast, in the southern hemisphere - southeast) winds blow.
In reality, the system of winds over the earth's surface is much more complicated. In the subtropical belt, the trade winds are disrupted in many areas by the summer monsoons.
In temperate and subpolar latitudes, cyclones and anticyclones have a great influence on the nature of air currents, and on the eastern and northern coasts - monsoons.
In addition, local winds are formed in many areas, due to the characteristics of the territory.
3. Cyclones and anticyclones.
The atmosphere is characterized by eddy movements, the largest of which are cyclones and anticyclones.
A cyclone is an ascending atmospheric vortex with reduced pressure in the center and a system of winds from the periphery to the center, directed against 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 more than 3000 km. Depth (pressure in the center) - 1000-970 hPa or less. Strong winds blow in the cyclone, usually up to 10-15 m/s, but can reach 30 m/s and more.
The average speed of the cyclone is 30-50 km/h. Most often, cyclones move from west to east, but sometimes they move from the north, south, and even east. The zone of the greatest frequency of cyclones is the 80th latitude of the northern hemisphere.
Cyclones bring cloudy, rainy, windy weather, in summer - cooling, in winter - warming.
Tropical cyclones (hurricanes, typhoons) form in tropical latitudes; this is one of the most formidable and dangerous natural phenomena. Their diameter is several hundred kilometers (300-800 km, rarely more than 1000 km), but a large difference in pressure between the center and the periphery is characteristic, which causes strong hurricane-force winds, tropical showers, and severe thunderstorms.
An anticyclone is a descending 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 dimensions 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 cloudy, rainless weather, 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 the ocean to the land, in winter - from the land to the ocean. The reason for the formation is the uneven heating of land and water in seasons. Depending on the zone of formation, monsoons are divided into tropical and extratropical.
Extratropical monsoons are especially pronounced on the eastern margin 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 cloudiness, precipitation, softens the summer heat, winter - 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.
Breeze (light wind-FR) - winds along the shores of the seas, large lakes and rivers, twice a day changing direction to the opposite: the daytime breeze blows from the reservoir to the shore, the night breeze - from the coast to the reservoir. Breezes are caused by the diurnal 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 the continents in tropical latitudes, washed by cold currents and cold water rising off the coast in the upwelling zone.
There it invades inland for tens of kilometers and produces a strong climatic effect: it reduces the temperature, especially in summer by 5-70 C, and in West Africa up to 100 C, increases the relative humidity of the air to 85%, contributes to the formation of fogs 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 there are "heat spots" 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, when the air descends and the air heats up adiabatically, the cloudiness disappears.
Glacial winds are cold winds that constantly blow from mountain glaciers down slopes and valleys. They are caused by the 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 the slope winds.
General circulation of the atmosphere
1) Due to the tilt of the Earth's axis and the sphericity of the Earth, the equatorial regions receive more solar energy than the polar regions.
2) At the equator, the air heats up → expands → rises up → a low pressure area is formed. 3) At the poles, the air cools down → condenses → sinks down → a high pressure area forms.
4) Due to the difference in atmospheric pressure, air masses begin to move from the poles to the equator.
Wind direction and speed are also affected by:
- properties of air masses (humidity, temperature…)
- underlying surface (oceans, mountain ranges, etc.)
- rotation of the globe around its axis (Coriolis force) 1) a general (global) system of air currents above the earth's surface, the horizontal dimensions of which are commensurate with the continents and oceans, and the thickness is from several kilometers to tens of kilometers.
trade winds - These are constant winds blowing from the tropics to the equator.
The reason: the equator is always low pressure (updrafts) and the tropics are always high pressure (downdrafts).
Due to the action of the Coriolis force: the trade winds of the Northern Hemisphere have a northeasterly 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 flows move from the poles to temperate latitudes and, under the influence of the Coriolis force, deviate to the west. Western winds are winds that blow from the tropics to temperate latitudes, predominantly 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 V.D region moves to the H, D, region. When moving under the influence of the Coriolis force, air currents deviate to the east.
Westerly winds bring warm and humid air to Estonia. air masses are formed 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:
summer- rainy and cold
winter- with thaws and snowfalls.
Anticyclone is an area of high atmospheric pressure with a maximum in the center.
air in an 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; with anticyclones, clear calm weather is established:
summer is hot
in winter it is frosty.
Atmospheric circulation
Definition 1
Circulation It is a system for the movement of air masses.
Circulation can be general on the scale of the entire planet and local circulation, which occurs over individual 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 at certain times and in certain places can be superimposed on the currents of the general circulation. With the general circulation of the atmosphere, huge waves and whirlwinds 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 action of centers of atmospheric pressure, the territories 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 formed under the influence of 3 main factors:
These factors complicate the general circulation of the atmosphere.
If the earth were uniform and not rotating around its axis - then the temperature and pressure at the earth's surface would correspond to thermal conditions and be of a latitudinal nature. This means that the decrease in temperature would occur from the equator to the poles.
With this distribution, warm air rises at the equator, while cold air sinks at the poles. 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 reduced.
At altitude, the air would flow 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 cause is the first cause of atmospheric circulation - different temperatures lead to different pressures at different latitudes. In reality, pressure is low at the equator, and high at the poles.
On a uniform rotating Earth in the upper troposphere and lower stratosphere, the winds during their outflow 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, winds flowing from the poles towards the equator and deviating would become easterly in the northern hemisphere, and southeasterly in the southern hemisphere. The second reason for the circulation of the atmosphere is clearly visible - dynamic. The zonal component of the general circulation of the atmosphere is due to the rotation of the Earth.
The underlying surface with an uneven distribution of land and water has a significant impact on the general circulation of the atmosphere.
Cyclones
The lower layer of the troposphere is characterized by eddies that appear, develop and disappear. Some eddies are very small and go unnoticed, while others have a great influence 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 the cyclone moves counterclockwise, in the Southern Hemisphere - clockwise. Cyclonic activity in middle 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, the occurrence of cyclones occurs on atmospheric fronts.
Two air masses of opposite temperature, separated by a front, are drawn into a cyclone. Warm air at the interface intrudes into the cold air region and is deflected to high latitudes.
The balance is disturbed, and the cold air in the rear is forced to penetrate into low latitudes. There is a cyclonic bend of the front, which is a huge wave moving from west to east.
The wave stage is first stage cyclone development.
Warm air rises and slides over the frontal surface at the front of the wave. The resulting waves with a length of $1000$ km and more are unstable in space and continue to develop.
At the same time, the cyclone moves to the east at a speed of $100$ km per day, the pressure continues to fall, and the wind becomes stronger, the wave amplitude increases. This is second stage is the stage of a young cyclone.
On special maps, a young cyclone is outlined by several isobars.
With the advancement of warm air to high latitudes, a warm front forms, and the advancement of cold air into tropical latitudes forms a cold front. Both fronts are part of a single whole. A warm front moves more slowly 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 is third stage cyclone development - the stage of occlusion.
Fourth stage– its completion is final. The final displacement of warm air upwards and its cooling occurs, temperature contrasts disappear, the cyclone becomes cold over its entire area, slows down its movement and finally fills up. From inception to filling, the life of a cyclone lasts from $5$ to $7$ days.
Remark 1
Cyclones bring cloudy, cool and rainy weather in summer and thaws in winter. Summer cyclones move at a speed of $400-$800 km per day, winter - up to $1000 km per day.
Anticyclones
Cyclonic activity is associated with the emergence and development of frontal anticyclones.
Definition 3
Anticyclone- This is a huge atmospheric vortex with high pressure in the center.
Anticyclones are formed 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 circulation of the atmosphere
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 in time or recurring more often than others, are revealed by averaging meteorological elements over long periods of time. long-term observation periods,
On fig. 8, 9 shows the average long-term wind distribution near the earth's surface in January and July. In January, i.e.
in winter, in the Northern Hemisphere, giant anticyclonic eddies are clearly visible over North America and a particularly intense eddy over Central Asia.
In summer, anticyclonic eddies over the land are destroyed due to the heating of the continent, and over the oceans, such eddies are significantly enhanced and propagate to the north.
Surface pressure in millibars and prevailing air currents
Due to the fact that in the troposphere the air in the equatorial and tropical latitudes is warmed up much more intensively than in the polar regions, the 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 velocity of 2p/86400 radians per second. Air particles, moving from low latitudes to high latitudes, retain large linear velocities relative to the earth's surface, acquired at low latitudes, and therefore deviate as they move to the east. A west-east air transport is formed in the troposphere, which is reflected in Fig. ten.
However, such a correct regime of currents is observed only on maps of average values. "Snapshots" of air currents provide very diverse, each time new, non-repeating positions of cyclones, anticyclones, air currents, zones of meetings of warm and cold air, i.e., atmospheric fronts.
Atmospheric fronts play an important role in the general circulation of the atmosphere, since significant transformations of the energy of air masses from one type to another take place in them.
On fig. 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 eddies are born, powerful clouds and precipitation zones are formed, and wind intensifies.
When an atmospheric front passes through a given point, a noticeable cooling or warming is usually clearly observed, and the whole 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 the warm half of the year, the situation is just the opposite, at the poles the air is relatively warmer here, and at the equator it is cold.
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 transport 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, consequently, the highest kinetic energy of air are observed in jet streams.
Figuratively speaking, jet streams are air rivers in the atmosphere, rivers flowing near 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 "backward".
Average location of jet stream axes in the Northern Hemisphere in summer
The length of the jet streams reaches several thousand kilometers. Below the jet streams in the troposphere, there are wider and slower air "rivers" - planetary high-altitude frontal zones, which also play an important role in the general circulation of the atmosphere.
The occurrence of high wind speeds in jet streams and in planetary high-altitude frontal zones is due to the presence here of a large difference in 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. The theory shows that this increase is proportional to the horizontal temperature gradient of the considered air layer.
In the stratosphere, due to the reversal of the meridional air temperature gradient, the intensity of jet streams decreases and they disappear.
Despite the great 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. Most often and sharply, temperature contrasts are manifested in the polar front, which separates air from temperate latitudes from tropical air.
The position of the axis of the high-altitude frontal zone with a slight meridional exchange of air masses
Planetary high-altitude frontal zones and jet streams often occur in the polar front system. Although, on average, 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. On fig.
13, 14 show the positions of the axes of the high-altitude frontal zones in cases of stable west-east transport and in cases of developed meridional exchange of air masses.
An essential 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 multilayer structure of the wind field changes here at certain, but not exactly coinciding time intervals, which can also serve as some 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 temperate and high latitudes, then it becomes clear how complex and whimsically those atmospheric processes that directly affect the weather regime in temperate latitudes.
The position of the axis of the high-altitude frontal zone with a significant meridional exchange of air masses
Of great importance for the formation of atmospheric processes on a large scale is the state of the underlying surface, especially the state of the upper active water layer of the World Ocean. The surface of the World Ocean is almost 3/4 of the entire surface of the Earth (Fig. 15).
sea currents
Due to the high heat capacity and the 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 with sea currents is carried far to the north and warms nearby areas.
The heat capacity of water is several times greater than the heat capacity of the soil and rocks that make up the land. The heated water mass serves as a heat accumulator with which it supplies the atmosphere. At the same time, it should be noted that the 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 the 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 receives only 1/3 of all incoming energy directly from the Sun.
The remaining 2/3 of the energy it receives 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. First, a large amount 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 heats the surrounding layers of air. Secondly, the underlying surface gives off heat to the atmosphere through turbulent (i.e., vortex, disordered) heat transfer. 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 where cold air invades the warm ocean surface, reaches 5 km or more. In those cases when 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 cold air intrusion, the thickness of its layer, which is affected by the ocean, depends primarily on the magnitude of the water-air temperature difference. If the water is warmer than the air, then powerful convection develops, i.e., disordered ascending air movements, 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 water, then convection does not occur and the air changes its properties only in the lowest layers. Over the warm Gulf Stream in the Atlantic Ocean, with the intrusion of very cold air, the heat transfer of 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. The change in the properties of the air that hits a warm or cold oceanic surface occurs quite quickly - such changes can be noticed at a level of 3 or 5 km already a day after the start of the invasion.
What increments of air temperature can be as a result of its transformation (change) above the underlying water surface? It turns out that in the cold half-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 of the Atlantic Ocean, i.e.
where the most intense transfer of heat from the ocean to the atmosphere occurs, the ocean gives off 10-30 times more heat than it receives from the atmosphere. Naturally, the heat reserves in the ocean are replenished by the influx of warm oceanic waters from tropical latitudes. Air currents distribute the heat received from the ocean for thousands of kilometers. The warming effect 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 of 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.
The northwestern part of the Pacific Ocean in winter is under the influence of the cold air of the Asian continent, the so-called winter monsoon, which propagates 1-2 thousand km deep into the ocean in the water layer and 3-4 thousand km in the middle troposphere (Fig. 16) .
Annual amounts of heat carried 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 in the direction of heat fluxes from the underlying surface to the atmosphere and back are very diverse and have a great influence on the change in the atmospheric processes themselves.
There are hypotheses according to which the features 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) 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 (baric ridge) is formed in the middle troposphere, along the eastern periphery of which the transfer of cold air masses from the Arctic begins, and in its western part - the transfer of warm air from tropical latitudes to the north. Such a situation can lead to the preservation of a long-term weather anomaly near the earth's surface in certain areas - dry and hot or rainy and cool in summer, frosty and dry or warm and snowy in 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 some kind of feedback: the nature of the circulation of the atmosphere affects the creation of cloud systems, and cloud systems, in turn, affect the change in circulation. We have listed only the most important of the studied "terrestrial" factors influencing 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 one should distinguish between changes in the circulation of air on the Earth in connection with changes in the total heat flux coming from the Sun to the Earth as a result of fluctuations in the value of the so-called solar constant. However, as recent studies show, in reality it is not a strictly constant value. The energy of the circulation of the atmosphere is continuously replenished due to the energy sent by the Sun. Therefore, if the total energy sent by the Sun fluctuates significantly, then this can affect the change in circulation and weather on Earth. This issue has not yet been sufficiently studied. As for the change in solar activity, 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 the corpuscular (i.e., consisting of charged particles, mainly protons) radiation from the Sun. Some meteorologists believe that the change in solar activity is associated with tropospheric processes in the Earth's atmosphere, that is, with the weather.
The latter statement needs more research, mainly due to the fact that the well-manifested 11-year cycle of solar activity is not clearly visible in the weather conditions on Earth.
It is known that there are whole schools of meteorologists-forecasters who quite successfully predict 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. The wind speed is determined by the difference in atmospheric pressure.
The influence of wind in navigation must be constantly taken into account, since it causes the ship to drift, storm waves, etc.
Due to the uneven heating of various parts of the globe, there is a system of atmospheric currents on a planetary scale (the general circulation of the atmosphere).
The air flow consists of separate vortices randomly moving in space. Therefore, the wind speed, measured at any point, continuously changes with time. The greatest fluctuations in wind speed are observed in the surface layer. In order to be able to compare wind speeds, a height of 10 meters above sea level was taken as a standard height.
Wind speed is expressed in meters per second, wind strength - in points. The ratio between them is determined by the Beaufort scale.
Beaufort scale
Wind speed fluctuations are characterized by the gust coefficient, which is understood as the ratio of the maximum speed of gusts of wind to its average speed obtained over 5-10 minutes.
As the average wind speed increases, the gust factor decreases. At high wind speeds, the gust factor is approximately 1.2 - 1.4.
The trade winds are winds that blow all year in one direction in the zone from the equator to 35 ° N. sh. and up to 30 ° S sh. Stable in direction: in the northern hemisphere - northeast, in the south - southeast. Speed - up to 6 m / s.
Monsoons are winds of temperate latitudes that blow 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, cloudy in summer, with rain and fog.
Breezes are caused by uneven heating of water and land during the day. In the daytime, there is a wind from the sea to the land (sea breeze). At night from the chilled coast - to the sea (coastal breeze). Wind speed 5 - 10 m/s.
Local winds arise in certain areas due to the features 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 that blows down a mountainside. Brings a significant chill.
It is observed in areas where a low mountain range borders the sea, during periods when atmospheric pressure increases over land and the temperature drops compared to pressure and temperature over the sea.
In the area of Novorossiysk Bay, bora acts in November - March with average wind speeds of about 20 m/s (individual gusts can be 50 - 60 m/s). The 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 wind of the central part of the Mediterranean Sea is 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 exist up to a quarter of a day and move at a speed of up to 30 knots. The wind speed inside the tornado can reach up to 100 m/s.
Storm winds occur mainly in areas with low atmospheric pressure. Tropical cyclones reach especially great force, at which the wind speed often exceeds 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 an atmospheric front. The passage of the front is accompanied by a sharp change in the weather.
The atmospheric front can be in a stationary state or in motion. Distinguish warm, cold fronts, as well as fronts of occlusion. 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 push against cold air masses. On weather maps, a warm front is marked with a solid line with semicircles along the front, indicating in the direction of colder air and the direction of movement.
As the warm front approaches, pressure begins to drop, clouds thicken, and heavy precipitation falls. In winter, when the front passes, low stratus clouds usually appear. The temperature and humidity of the air are slowly rising.
When a front passes, temperature and humidity usually increase rapidly, and the wind increases. After the passage of the front, the direction of the wind changes (the wind turns clockwise), the pressure drop stops and its weak growth begins, the clouds dissipate, and precipitation stops.
A cold front is formed when cold air masses advance on warmer ones (Fig. 18.2). On weather maps, a cold front is shown as a solid line with triangles along the front indicating warmer temperatures and direction of movement. The pressure in front of the front falls strongly and unevenly, the ship enters the zone of showers, thunderstorms, squalls and strong waves.
An occluded front is a front formed by the confluence of warm and cold fronts. Represented by a solid line with alternating triangles and semicircles.
Warm front section
cold front section
A cyclone is an atmospheric vortex of huge (hundreds to several thousand kilometers) diameter with reduced air pressure in the center. Air in a cyclone circulates counterclockwise in the northern hemisphere and clockwise in the southern.
There are two main types of cyclones - extratropical and tropical.
The first are formed in temperate or polar latitudes and have a diameter of thousands of 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 reduced atmospheric pressure in the center with storm wind speeds. Formed tropical cyclones move along with air masses from east to west, while gradually deviating to high latitudes.
Such cyclones are also characterized by the so-called. "eye of the storm" - the central area with a diameter of 20 - 30 km with relatively clear and calm weather. About 80 tropical cyclones are observed annually in the world.
View of the cyclone from space
Tropical cyclone paths
In the Far East and Southeast Asia, tropical cyclones are called typhoons (from the Chinese tai feng - big wind), and in North and South America - hurricanes (Spanish huracán, named after the Indian god of the wind).
It is generally accepted that a storm turns into a hurricane at a wind speed of more than 120 km / h, at a speed of 180 km / h a hurricane is called a strong hurricane.
7. Wind. General circulation of the atmosphere
Lecture 7. Wind. General circulation of the atmosphere
Wind – this is the movement of air relative to the earth's surface, in which the horizontal component predominates. When an upward or downward wind movement is considered, the vertical component is also taken into account. The wind is characterized direction, speed and gust.
The reason for the occurrence of wind is the difference in atmospheric pressure at different points, determined by the horizontal baric gradient. The pressure is not the same, primarily due to the different degrees of heating and cooling of the air, and decreases with height.
To represent the distribution of pressure on the surface of the globe, pressure is applied to geographical maps, measured at the same time at different points and reduced to the same height (for example, to sea level). Points with the same pressure are connected by lines - isobars.
In this way, areas of increased (anticyclones) and low (cyclones) pressure are identified, as well as the direction of their movement for weather forecasting. Isobars can be used to determine how much pressure changes with distance.
In meteorology, the concept horizontal baric 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 complicated, 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, the air movement deviates from the baric gradient to the right in the northern hemisphere, 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 the wind speed and the 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 deviates the wind from the gradient over land by 45-55o, over the sea - by 70-80o.
With an increase in 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 / s, less often - in km / h and points. The direction is taken from where the wind blows, determined in rhumbs (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 the speed in field experiments.
Anemorumbometer allows you to remotely measure the direction and speed of the wind , anemorumbograph continuously records these indicators.
The diurnal variation of wind speed over the oceans is almost not observed and is well pronounced over land: at the end of the night - a minimum, in the afternoon - a maximum. The annual course is determined by the laws of the general circulation of the atmosphere and differs in regions of the globe. For example, in Europe in summer - the minimum wind speed, in winter - the maximum. In Eastern Siberia, the opposite is true.
The direction of the wind in a particular place changes often, but if we take into account the frequency of winds of different rhumbs, we can determine that some are more frequent. For such a study of directions, a graph called the wind rose is used. On each straight line of all points, the observed number of wind events for the desired period is plotted and the obtained values \u200b\u200bare connected on the points with lines.
The wind contributes to maintaining the constancy of the gas composition of the atmosphere, mixing the air masses, transports moist sea air deep into the continents, providing them with moisture.
The adverse effect of wind for agriculture can be manifested in increased evaporation from the soil surface, causing drought, and wind erosion of soils is possible at high wind speeds.
The speed and direction of the wind must be taken into account when pollinating fields with pesticides, when irrigating with sprinklers. The direction of the prevailing winds must be known when laying forest belts, snow retention.
local winds.
The local winds are called winds that are characteristic only for certain geographical areas. They are of particular importance in their influence on weather conditions, their origin is different.
breezes – winds near the coastline of the seas and large lakes, which have a sharp diurnal change in direction. Happy sea breeze blows ashore from the sea, and at night - coastal breeze blows from land to sea (Fig. 2).
They are pronounced in clear weather during 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 several hundred meters (up to 1-2 km), with an average speed of 3-5 m/s, and in the tropics - and more, penetrating tens of kilometers deep into land or sea.
The development of breezes is associated with the diurnal 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 is transferred from the sea to the land. At night, the land cools faster and stronger, 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 decrease by 10 ° C or more, and relative humidity can increase by 40%.
Breezes are also observed on the shores of large lakes: Ladoga, Onega, Baikal, Sevan, etc., as well as on large 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 periodicity. During the day, they blow up the valley and along the slopes of the mountains as a result of heating by the sun, and at night, when cooled, the air flows down the slopes. Nighttime air movement can cause frost, which is especially dangerous in the spring when gardens are in bloom.
Föhn –warm and dry wind blowing from the mountains to the valleys. At the same time, the temperature of the air 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.
Foehn is formed when an air current crosses a ridge. Since a vacuum is created on the leeward side, the air is sucked down in the form of a downward wind. The descending air heats up 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 would heat up to 22o, and the humidity would decrease to 17%. If the air rises up the windward slope, then water vapor condenses and clouds form, precipitation falls, and the descending air will be even drier.
The duration of hair dryers is from several hours to several days. A hair dryer can cause intense snowmelt and floods, dries up soils and vegetation until they die.
Bora–it is a strong, cold, gusty wind that blows from low mountain ranges towards warmer seas.
Bora is best known in the Novorossiysk Bay of the Black Sea and on the Adriatic coast near the city of Trieste. Similar to boron in origin and manifestation north in the region of
Baku, mistral on the Mediterranean coast of France, northser in the Gulf of Mexico.
Bora occurs 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 / s, while the temperature is greatly reduced, sometimes by more than 25 ° C. Bora fades a few kilometers from the coast, but sometimes it can capture a significant part of the sea.
In Novorossiysk, bora is observed about 45 days a year, more often from November to March, with a duration of up to 3 days, rarely up to a week.
General circulation of the atmosphere
General circulation of the atmosphere– it is a complex system of large air currents that carry very large masses of air over the globe.
In the atmosphere near the earth's surface in polar and tropical latitudes, eastward transport is observed, in temperate latitudes - westward.
The movement of air masses is complicated by the rotation of the Earth, as well as by the relief and the influence of areas of high and low pressure. The deviation of the winds from the prevailing directions is up to 70o.
In the process of heating and cooling of huge masses of air over the globe, areas of high and low pressure are formed, which determine the direction of planetary air currents. Based on long-term average values of pressure at sea level, the following regularities were revealed.
On both sides of the equator there is a low pressure zone (in January - between 15o north latitude and 25o south latitude, in July - from 35o north latitude to 5o south latitude). This area, called equatorial depression, extends more to the hemisphere where it is summer in a given month.
In the direction to the north and south of it, the pressure increases and reaches its maximum values in subtropical high pressure zones(in January - at 30 - 32o north and south latitude, in July - at 33-37o N and 26-30o S). From the subtropics to temperate zones, the pressure drops, especially significantly in the southern hemisphere.
The minimum pressure is in two subpolar low pressure zones(75-65o N and 60-65o S). Further towards the poles, the pressure increases again.
In accordance with pressure changes, the meridional baric gradient is also located. It is directed from the subtropics on the one hand - to the equator, on the other - to subpolar latitudes, from the poles to subpolar latitudes. This is consistent with the zonal direction of the winds.
Over the Atlantic, Pacific and Indian Oceans, northeast and southeast winds very often blow - trade winds. Western winds in the southern hemisphere, at latitudes of 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 the continents, the directions are more complicated, although westerlies also predominate.
East winds of the 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 the winds from January to July - these are areas monsoons. The causes of monsoons are similar to those of breezes. In summer, the mainland of Asia heats up strongly and an area of low pressure spreads over it, where air masses rush from the ocean.
The resulting summer monsoon causes large amounts of precipitation, often showers. In winter, high pressure sets in over Asia due to the more intense cooling of the land, compared to the ocean, and cold air moves to the ocean, forming a 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 covers 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 regions of the Earth, these masses bring with them their own weather regime. The predominance of air masses of a certain type (types) in a particular area creates a characteristic climatic regime of the area.
The main differences between air masses are: temperature, humidity, cloudiness, dustiness. For example, in summer the air over the oceans is more humid, colder, cleaner than over land at the same latitude.
The longer the air is over one area, the more it undergoes changes, so air masses are classified according to the geographical zones where they 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 the subtropics and tropics to temperate latitudes; 4) equatorial- formed over the equator. In each type, marine and continental subtypes are distinguished, differing primarily in temperature and humidity within the type. The air, being in constant motion, passes from the area of formation to the neighboring ones and gradually changes its properties under the influence of the underlying surface, gradually turning into a mass of another type. This process is called transformation.
cold air masses are called those that move to a warmer surface. They cause a chill in the areas where they come.
When they move, they themselves warm up from the earth's surface, so large vertical temperature gradients arise inside the masses and convection develops with the formation of cumulus and cumulonimbus clouds and heavy rainfall.
Air masses moving to a colder surface are called warm masses. They bring warmth, but they themselves are cooled from below. Convection does not develop in them and stratus clouds predominate.
Neighboring air masses are separated from each other by transition zones, which are strongly inclined to the Earth's surface. These zones are called fronts.
10. Air masses
10.5. Transformation of air masses
When the circulation conditions change, the air mass as a whole moves from the center of its formation to neighboring areas, interacting with other air masses.
When moving, the air mass begins to change its properties - they will already 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, and also on the length of time that has elapsed since the formation of the air mass. masses.
These influences can cause changes in the moisture content of the air, as well as a change in air temperature as a result of the release of latent heat or heat exchange with the underlying surface.
i 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 speed shift causes turbulent mixing. If the lower layers of air are heated, then instability occurs and convective mixing develops.
Usually the process of transformation of the air mass lasts from 3 to 7 days. A sign of its end is the cessation of changes in air temperature from day to day both near the earth's surface and at heights - i.e. reaching the equilibrium temperature.
i The equilibrium temperature characterizes the temperature characteristic of a given
area at this time of the year.
The process of reaching the equilibrium temperature can be considered as the process of formation of a new air mass.
The transformation of air masses proceeds especially intensively when the underlying surface changes, for example, when the air mass moves from land to sea.
A striking example is the transformation of continental temperate air over the Sea of Japan in winter.
10. Air masses
When continental temperate air moves over the Sea of Japan, it transforms into air similar in properties to temperate marine air, which occupies the Pacific Ocean in winter.
Continental temperate air is characterized by low humidity and very low air temperatures. The transformation of cold continental air over the Sea of Japan proceeds very intensively, especially in cases of sudden intrusions, when the air mass is in the initial stage of transformation.
The main role in the thermal transformation of air in the surface layer is played by turbulent heat exchange between the air mass and the underlying sea surface.
The intensity of heating of cold air over the sea is directly proportional to the difference in water and air temperatures. According to empirical estimates, the value of thermal transformation of cold air near the sea surface is directly proportional to the product
(T-Tw) t,
where T is the temperature of the continental air, Tw is the temperature of the sea surface, t is the time (in hours) of movement of the continental air over the sea.
Since the temperature difference between the air of the continental monsoon and the temperature of the sea surface over the Sea of Japan exceeds 10-15 ° C off the coast of Primorye, the air warming near the sea surface occurs very quickly and depends on its path passed over the sea.
In addition, when cold air enters the warm underlying surface of the Sea of Japan, its instability increases. The value of the vertical temperature gradient in the surface layer (100-150 m) increases rapidly with height.
Note that with a weak wind, the air warms up more strongly than with a strong wind, but only a thin surface layer of the atmosphere warms up. In strong winds, a thicker layer of air, up to 1.5 km or more, is involved in mixing. Intense turbulent heat exchange, an indirect indicator of which is a significant frequency of moderate and strong winds over the sea, favors the rapid spread of warm air upwards. At the same time, cold advection increases with height, which leads to an increase in the instability of the air mass.
When moving over the sea, the continental air not only warms up, but is also enriched with moisture, which also increases its instability in accordance with a decrease in the level of condensation.
10. Air masses
When moist air rises as a result of condensation processes, the latent heat of vaporization is released. The released heat of condensation (latent heat of vaporization) is used to heat the air. When moist air rises, the temperature drops already according to the humid adiabatic law, i.e., more slowly than in the case of dry air.
As it moves over the sea, accompanied by heating and humidification, the air mass becomes unstable, at least in the lower 1.5-km layer of the atmosphere. It intensively develops not only dynamic, but also thermal convection. This is evidenced by the formation of cumulus clouds, which are deformed closed cells. These cells, under the influence of the wind, stretch in the form of chains from the coast of Primorye to the western coast of Japan, where their thickness increases and they give precipitation.
The formation of clouds over the sea and the change in cloudiness along the path of the air mass, in turn, leads to changes in air temperature. The resulting cloudiness shields the outgoing radiation and creates atmospheric counterradiation.
In addition, downdrafts of air are formed along the periphery of the cloud cell. When lowered, the air is removed from the saturation state and adiabatically heated. The total downward flow over the sea can make a significant contribution to the change in air temperature over the sea.
In addition, the change in albedo plays a role in the direction of increasing air temperature: in winter, air moves from the continent, where snow cover prevails (albedo on average 0.7), to the open sea surface (albedo on average 0.2). These conditions can increase the air temperature by 5-10 °C.
The accumulation of warm air near the eastern shores of the Sea of Japan activates the formation of clouds and precipitation, which, in turn, affects the formation of the air temperature field.
10.6. Thermodynamic classification of air masses
From the point of view of the transformation of air masses, they can be classified into warm, cold and neutral. This classification is called thermodynamic.
10. Air masses
i Warm (cold) is an air mass that is warmer (colder)
its environment and in the given area gradually cools (heats up), trying to approach thermal equilibrium
The environment here refers to the nature of the underlying surface, its thermal state, as well as neighboring air masses.
Relatively warm (cold) is an air mass that is warmer (colder) than the surrounding air masses, and which continues to warm up (cool down) in a given area, i.e. is cold (warm) in the above sense.
To determine whether the air mass in a given area is cooling or warming up, one should compare the air temperature measured at the same time for several days, or the average daily air temperatures.
i Local (neutral) air mass is the mass located in
thermal equilibrium with its environment, i.e. day after day retaining its properties without significant changes.
Thus, the transforming air mass can be both warm and cold, and upon completion of the transformation, it becomes local.
On the OT 1000 500 map, a cold air mass corresponds to a hollow or a closed area of cold (cold center), and a warm air mass corresponds to a ridge or heat center.
An air mass can be characterized by both unstable and stable equilibrium. This separation of air masses takes into account one of the most important results of heat exchange - the vertical distribution of air temperature and the corresponding type of vertical equilibrium. Certain weather conditions are associated with stable (UVM) and unstable (NVM) air masses.
Neutral (local) air masses in any season can be both stable and unstable, depending on the initial properties and the direction of transformation of the air mass from which this air mass was formed. Over the continents, neutral air masses in summer are usually unstable, in winter
- stable. Over the oceans and seas, such masses are more often stable in summer and unstable in winter.
Condensation is the 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 the planet Earth contains over 13 billion tons of moisture. This figure is almost constant, as losses due to precipitation are eventually continuously replaced by evaporation.
Moisture cycle rate in the atmosphere
The rate of circulation of moisture in the atmosphere is estimated at a colossal figure - about 16 million tons per second or 505 billion tons per year. If suddenly all the water vapor in the atmosphere condensed and fell out as precipitation, then 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 on Earth an average of 92 centimeters falls per year, therefore, 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 water vapor molecule stays in the atmosphere for an average of 10 days.
Water molecule path
Once evaporated, a water vapor molecule usually drifts hundreds and thousands of kilometers until it condenses and falls to the Earth with precipitation. Water that falls as rain, snow or hail on the highlands of Western Europe travels about 3,000 km from the North Atlantic. Between the transformation of liquid water into steam and the precipitation on Earth, several physical processes take place.
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 in this case a strong turbulent mixing of air masses is observed, then a layer of mixing and clouds will appear in the atmosphere at the border of two air masses. About 5% of their volume is moisture. Steam-saturated air 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 is even more so. As we shall see later, this is a very important fact for weather change processes.
Movement of air masses
Air can rise for two reasons: either because it becomes lighter as a result of heating and moisture, or because forces act on it, causing it to rise above some obstacles, such as masses of colder and denser air, or over hills and mountains.
Cooling
Rising air, having fallen into layers with lower atmospheric pressure, is forced to expand and at the same time cool. Expansion requires the expenditure of 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 the surrounding air.
Dry adiabatic gradient
Dry air, in which there is no condensation or evaporation, as well as mixing, which does not receive energy in another form, cools or heats up by a constant amount (by 1 ° C every 100 meters) as it rises or falls. This value is called the dry adiabatic gradient. But if the rising air mass is moist and condensation occurs in it, then the latent heat of condensation is released and the temperature of the air saturated with steam falls much more slowly.
Wet adiabatic gradient
This amount of temperature change is called the wet-adiabatic gradient. It is not constant, but changes with the change 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 wet-adiabatic gradient is slightly more than half of the dry-adiabatic gradient. But the wet-adiabatic gradient gradually increases with height and at a very high altitude in the troposphere is almost equal to the dry-adiabatic gradient.
The buoyancy of moving air is determined by the ratio between its temperature and the temperature of the surrounding air. As a rule, in the real atmosphere, the temperature of the air falls unevenly with height (this change is simply called a gradient).
If the mass of air is warmer and therefore less dense than the surrounding air (and the moisture content is constant), then it rises 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 the neighboring masses, then their density is equal and the mass remains stationary or moves only together 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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Along with geographic latitude, an important climate-forming factor is atmospheric circulation, i.e., the movement of air masses.
air masses- significant volumes of air in the troposphere, which has certain properties (temperature, moisture content), depending on the characteristics of the region of its formation and moving as a whole.
The length of the air mass can be thousands of kilometers, and upwards it can extend to the upper limit of the troposphere.
Air masses are divided into two groups according to the speed of movement: moving and local. moving air masses, depending on the temperature of the underlying surface, are divided into warm and cold. Warm air mass - moving on a cold underlying surface, cold mass - moving on a warmer surface. Local air masses are air masses that do not change their geographical position for a long time. They can be stable and unstable depending on the season, as well as dry and wet.
There are four main types of air masses: equatorial, tropical, temperate, arctic (antarctic). In addition, each of the types is divided into subtypes: marine and continental, differing in humidity. For example, the maritime arctic mass is formed over the northern seas - the Barents and White Seas, is characterized, like the continental air mass, but with slightly increased humidity. (see fig. 1).
Rice. 1. Area of formation of Arctic air masses
The climate of Russia forms, to one degree or another, all air masses, with the exception of the equatorial one.
Consider the properties of various masses circulating on the territory of our country. arctic the air mass is formed mainly over the Arctic in polar latitudes, characterized by low temperatures in winter and summer. It has low absolute humidity and high relative humidity. This air mass dominates all year round in the Arctic zone, and in winter it moves to the subarctic. Moderate the air mass is formed in temperate latitudes, where the temperature changes depending on the season: relatively high in summer, relatively low in winter. According to the seasons of the year, humidity also depends on the place of formation. This air mass dominates the temperate zone. Partly, on the territory of Russia is dominated by tropical air masses. They form in tropical latitudes and have a high temperature. Absolute humidity depends on the place of formation, and relative humidity is usually low (see Fig. 2).
Rice. 2. Characteristics of air masses
The passage of various air masses on the territory of Russia causes a difference in weather. For example, all the “cold waves” in our country coming from the north are Arctic air masses, and tropical air masses from Asia Minor or, sometimes, from northern Africa come to the south of the European part (they bring hot, dry weather).
Consider how air masses circulate through the territory of our country.
Atmospheric circulation is a system of motion of air masses. Distinguish between the general circulation of the atmosphere on the scale of the entire globe and the local circulation of the atmosphere over individual territories and water areas.
The process of circulation of air masses provides the territory with moisture, and also affects the temperature. Air masses move under the influence of atmospheric pressure centers, and the centers change depending on the season. That is why the directions of the prevailing winds, which bring air masses to the territory of our country, change. For example, European Russia and the western regions of Siberia are under the influence of constant westerly winds. With them come moderate sea air masses of temperate latitudes. They form over the Atlantic (See Fig. 3).
Rice. 3. Movement of marine moderate air masses
When the westerly transport weakens, the Arctic air mass comes with the northerly winds. It brings a sharp cold snap, early autumn and late spring frosts. (see Fig. 4).
Rice. 4. Movement of the Arctic air mass
Continental tropical air on the territory of the Asian part of our country comes from Central Asia or from Northern China, and it comes to the European part of the country from the peninsula of Asia Minor or even from North Africa, but more often such air is formed on the territory of North Asia, Kazakhstan, the Caspian lowland. These areas lie in the temperate climate zone. However, the air above them warms up very strongly in summer and acquires the properties of a tropical air mass. Continental moderate air mass prevails all year round in the western regions of Siberia, so winters are clear and frosty, and summers are quite warm. Even over the Arctic Ocean, Greenland has warmer winters.
Due to strong cooling over the Asian part of our country, an area of strong cooling is formed in Eastern Siberia (high pressure area - ). Its center is located in the regions of Transbaikalia, the Republic of Tyva and Northern Mongolia. Very cold continental air spreads from it in different directions. It extends its influence over vast territories. One of its directions is the northeast up to the Chukchi coast, the second - to the west through Northern Kazakhstan and the south of the Russian (East European) plain to about 50ºN. Clear and frosty weather sets in with a small amount of snow. In summer, due to warming, the Asian maximum (Siberian anticyclone) disappears and low pressure sets in. (See Fig. 5).
Rice. 5. Siberian anticyclone
The seasonal alternation of areas of high and low pressure forms the monsoon circulation of the atmosphere in the Far East. It is important to realize that, passing through certain territories, air masses can change depending on the properties of the underlying surface. This process is called transformation of air masses. For example, the Arctic air mass, being dry and cold, while passing through the territory of the East European (Russian) Plain, heats up and becomes very dry and hot in the region of the Caspian Lowland, which causes dry winds.
Asian High, or, as it is called, the Siberian anticyclone is an area of high pressure that forms over Central Asia and Eastern Siberia. It manifests itself in winter and is formed as a result of cooling of the territory in conditions of enormous size and hollow relief. In the central part of the maximum over Mongolia and South Siberia, the pressure in January sometimes reaches 800 mm Hg. Art. This is the highest pressure recorded on earth. In winter, the great Siberian anticyclone extends here, especially stable from November to March. The winter here is so windless that with little snowfall, the branches of the trees turn white for a long time from the “unshaken” snow. Frosts already from October reach -20 ... -30ºС, and in January it often reaches -60ºC. The average temperature per month drops to -43º, it is especially cold in the lowlands, where cold heavy air stagnates. When there is no wind, severe frosts are not so hard to bear, but at -50º it is already difficult to breathe, low fogs are observed. Such frosts make it difficult for planes to land.
Bibliography
- Geography of Russia. Nature. Population. 1 hour Grade 8 / V.P. Dronov, I.I. Barinova, V.Ya Rom, A.A. Lobzhanidze.
- V.B. Pyatunin, E.A. Customs. Geography of Russia. Nature. Population. 8th grade.
- Atlas. Geography of Russia. population and economy. - M.: Bustard, 2012.
- V.P. Dronov, L.E. Savelyeva. UMK (educational-methodical set) "SPHERES". Textbook “Russia: nature, population, economy. 8th grade". Atlas.
- Climate-forming factors and atmospheric circulation ().
- Properties of air masses that form the climate of Russia ().
- Western transfer of air masses ().
- Air masses ().
- Atmospheric circulation ().
Homework
- What kind of air mass transfer dominates in our country?
- What properties do air masses have, and what does it depend on?
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 an approximate horizontal uniformity of temperature and moisture content.
Kinds:Arctic or Antarctic air(AB), temperate air(UV), tropical air(TV) equatorial air(EV).
The air in the 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 move not only in parallel, but also make transverse motion. This leads to vortex formation over the entire cross section of the ventilation duct.
The state of the air flow in the ventilation space depends on: Air flow rates, Air temperatures, Cross-sectional areas of the ventilation duct, Forms and surfaces of building elements at the border of the ventilation duct.
In the earth's atmosphere, air movements of various 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 - an upward movement, it falls - a downward movement. The movement of air in a horizontal direction is called wind. The reason for the occurrence of wind is the uneven distribution of air pressure on the surface of the Earth, which is caused by an uneven distribution of temperature. In this case, the air flow moves from places with high pressure to the side where the pressure is less.
With the wind, the air does not move evenly, but in shocks, gusts, especially near the surface of the Earth. There are many reasons that affect the movement of air: the 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 deviate to the right in the northern hemisphere, and to the left in the southern hemisphere.
Invading areas with different thermal properties of the surface, the air masses are gradually transformed. For example, temperate marine air, entering the land and moving deep into the mainland, gradually heats up and dries up, turning into continental air. The transformation of air masses is especially characteristic of temperate latitudes, which from time to time are invaded by warm and dry air from tropical latitudes and cold and dry air from subpolar latitudes.