Climate zones and atmospheric pressure
Atmospheric pressure depends on climatic zones of illumination and humidity, on the heating of the Earth by the rays of the Sun.
The reason for the appearance of atmospheric pressure belts is the difference in temperature of the air masses themselves, due to heating from the earth's surface. Due to the spherical shape of the Earth, different areas are heated unevenly by the Sun. This affects the formation of different weathering zones. What does the air temperature and low and high pressure zones have to do with it? How does cold air differ from warm air? What atmospheric pressure belts exist?
The density of cold air masses is greater than warm ones. And the higher the density, the heavier the air. The polar regions are cold, even in summer. Cold air is dense and heavy. Therefore, there is high atmospheric pressure there. In other words, the Arctic and Antarctic polar zones are the Earth's high pressure belts. It is always hot in equatorial regions. Warm air is light. Therefore, at the equator there is a low pressure belt of the Earth.
Pressure belts on earth
In tropical areas it is also hot, but at the same time a tropical zone of high atmospheric pressure is formed. What is the reason for this discrepancy in hot and dry tropics?
It's simple. At the equator, warm air rises to the upper limits of the troposphere and has a certain density, which gradually changes as the air cools. Spreading from the equator to the tropical zones, the same air masses, but with a different density and cold, descend to the Earth’s surface from the troposphere (see “Earth’s moisture belts”).
Between the two high pressure belts (between tropical and polar) lies a zone of low pressure. That is, the alternation is performed:
- Equator – low atmospheric pressure;
- Tropics – high atmospheric pressure;
- Temperate zones - n.d.;
- Polar – E.D.
- Dry climate - Arctic and Antarctic, Tropical - belts of high atmospheric pressure.
- Humid climate – Temperate and Equatorial – belts of low atmospheric pressure.
Atmosphere pressure
Atmospheric pressure is the force with which the atmosphere presses on the earth's surface.
At each point it is determined by the weight of the air placed above.
Thus, atmospheric pressure per 1 cm2 is 1 kg 33 g. Pressure is also measured in mm of mercury. Normal atmospheric pressure is 760 mm. rt. Art.., this value is fixed at an altitude of 0 meters (sea level) at a latitude of 45° and is the standard.
With altitude, atmospheric pressure decreases by 100 mmHg. Art. for every 1 km of ascent and is measured barometer or mercury barometer.
Atmospheric pressure is affected by temperature: when heated, air expands and rises, creating an area of low pressure; during cooling, on the contrary, it drops and creates an area of high pressure.
The distribution of atmospheric pressure over the earth's surface is zonal. This is due to uneven heating of the earth's surface, and, consequently, changes in pressure. The formation of atmospheric pressure belts near the earth's surface is influenced by the uneven distribution of solar heat and the rotation of the Earth. Depending on the time of year, both hemispheres of the Earth are heated by solar heat differently. This causes some movement of the atmospheric pressure belts: in summer - to the north, in winter - to the south.
On the globe there are three zones with a predominance of low atmospheric pressure (minimums) and four zones with a predominance of high atmospheric pressure (maxima).
At equatorial latitudes, the Earth's surface warms up greatly. Heated air expands, becomes lighter and therefore rises. As a result, low atmospheric pressure is established near the earth's surface near the equator.
In tropical latitudes, the continents are always warmer than the oceans , and the pressure above them is lower. Thus, there are maxima over the oceans throughout the year: North Atlantic (Azores), North Pacific, South Atlantic, South Pacific and South Indian. The lines that connect points with the same atmospheric pressure on a climate map are called isobars. The closer the isobars are to each other, the faster the atmospheric pressure changes over a distance. The amount of change in atmospheric pressure per unit distance (100 km) is called the baric gradient.
As a result of the fact that in the temperate latitudes of the Northern Hemisphere in winter the atmospheric pressure over the continents increases greatly, the low pressure belt is interrupted. It persists only over the oceans in the form of closed areas of low pressure - the Icelandic and Aleutian lows. On the contrary, winter maximums form over the continents: Asian and North American. In summer, in the temperate latitudes of the Northern Hemisphere, the belt of low atmospheric pressure is restored. A huge area of low atmospheric pressure centered in tropical latitudes—the Asian Low—forms over Asia.
In polar latitudes , under the influence of low temperatures, the air becomes heavier and sinks. Therefore, at the poles the atmospheric pressure is increased by 60-65° compared to the latitudes.
Relationship between pressure belts and precipitation.
In climate zones with low atmospheric pressure, precipitation in large quantities prevails. And, on the contrary, in climatic zones with high air pressure, precipitation is observed to a lesser extent. Why is that? Because the process of condensation of water vapor into liquid droplets occurs when warm air masses rise into the troposphere. This physical phenomenon is typical for climatic zones with low atmospheric pressure - equatorial and temperate zones.
Relationship between atmospheric pressure belts and precipitation
§12. Air pressure and precipitation at different latitudes
This I know
1. Why is atmospheric pressure low in the equator region near the Earth’s surface, and high in the upper layers of the troposphere?
In the region of the equator, the earth's surface receives a lot of heat. It heats the atmospheric air in the ground layers. Light warm air rises, so a low pressure area forms at the surface. Warm air with a lot of water vapor rises and cools. Rainfall occurs. The rising air enters the upper layers of the atmosphere already cooled, with increased pressure.
2. In what latitudes are belts of low atmospheric pressure located, and in which zones of high atmospheric pressure?
Low pressure belts form in equatorial and temperate latitudes. Increased pressure is observed at the poles and in tropical latitudes.
3. Name the main reason for the formation of atmospheric pressure belts.
The main reason for the formation of pressure belts is the uneven supply of heat to the earth's surface.
4. What is the distribution of cloudiness and precipitation on Earth related to?
Cloudiness and precipitation depend on the distribution of temperatures and pressure. In addition, precipitation is influenced by topography, winds, and ocean currents.
I can do this
5. Using the map in Figure 29, determine what the average annual precipitation is at the intersection of the Prime Meridian and the Tropic of the North. Compare with the average annual precipitation in your area.
The intersection of the Prime Meridian and the Tropic of the North is located in the Sahara Desert. Less than 100 mm of precipitation falls here per year. Most of Russia receives more precipitation than this indicator.
6. Comparing the map in Figure 29 and the physical map of the world, determine the areas where precipitation falls per year: less than 100 mm; from 500 to 1000 mm; 2000 mm or more. Explain how this relates to the distribution of atmospheric pressure belts.
Less than 100 mm of precipitation will fall in the tropics in northern Africa (Sahara Desert), on the western coasts in the tropical latitudes of Africa and South America, in the interior of Antarctica, in northern Greenland and the Canadian Arctic Archipelago, in most of the Arabian Peninsula, in the interior of Eurasia.
500-1000 mm: Atlantic coast of Eurasia, North America, South America; eastern coasts of Eurasia and Australia.
More than 2000 mm of precipitation per year falls in equatorial latitudes: in the Amazon, Ganges, on the coast of the Gulf of Guinea, on the islands of Indonesia, and the Philippines. In temperate latitudes, this amount of precipitation falls on the west coast of South America and on the coast of the Gulf of Alaska.
Normal atmospheric pressure
Normal atmospheric pressure is conventionally taken to be air pressure at sea level at a latitude of 45° and at a temperature of 0 °C. In this case, the atmosphere presses on every 1 cm 2 of the earth's surface with a force of 1.033 kg, and the mass of this air is balanced by a mercury column 760 mm high.
Torricelli experience
The value of 760 mm was first obtained in 1644 by Evangelista Torricelli (1608-1647) and Vincenzo Viviani (1622-1703) - students of the brilliant Italian scientist Galileo Galilei.
E. Torricelli sealed a long glass tube with divisions at one end, filled it with mercury and lowered it into a cup of mercury (this is how the first mercury barometer was invented, which was called the Torricelli tube). The mercury level in the tube dropped as some of the mercury spilled into the cup and settled at 760 millimeters. A void formed above the column of mercury, which was called the Torricelli void (Fig. 2).
E. Torricelli believed that the atmospheric pressure on the surface of the mercury in the cup is balanced by the weight of the mercury column in the tube. The height of this column above sea level is 760 mm Hg. Art.
Rice. 2. Torricelli experience
1 Pa = 10 -5 bar; 1 bar = 0.98 atm.
Air masses of Australia
This smallest continent of the planet is located in equatorial and tropical latitudes, which are characterized by high total solar radiation.
In addition, the Pacific Ocean and the existing system of trade wind air currents play an important role.
Note 1
The mainland lies in 3 climatic zones - subequatorial, tropical, subtropical, the island of Tasmania is in the temperate zone.
Near the equator in the eastern Pacific Ocean, the atmospheric circulation in winter and summer is more or less the same. To a large extent, the picture changes in the west of the continent and significant differences arise between seasons.
Figure 1. Air mass circulation over Australia. Author24 - online exchange of student work
In summer, the entire trade wind circulation shifts to the north. In the subequatorial climate zone, equatorial air masses dominate in winter, and tropical air masses dominate in summer.
In the tropical zone, which is divided into two regions - a humid climate in the east and a dry climate in the west, tropical air masses dominate throughout the year.
- Coursework 470 rub.
- Abstract 230 rub.
- Test work 200 rub.
The tropical climate zone in Australia occupies the largest area and is divided into three climatic regions:
- Mediterranean climate area in the southwest of the continent;
- area of continental climate in the central part;
- area of humid climate in the southeast.
In winter, tropical air masses are dominant in the tropical climate zone, and in summer they are replaced by temperate air of the Southern Hemisphere.
The island of Tasmania is influenced by moderate air masses throughout the year.
The shift in trade wind circulation creates a system of air flows from the Southern Hemisphere to the Northern Hemisphere towards Eurasia. Approaching Eurasia, the Northern Hemisphere trade wind deviates towards low pressure over the continent and turns into the summer southeast monsoon.
At this time, Australia and the islands receive very little precipitation. The extreme south of the continent, Tasmania and New Zealand receive a large amount of precipitation in July, because they are influenced by the circulation of temperate latitudes and moisture is brought by westerly winds.
Precipitation in the form of snow occurs in the highlands of south-eastern Australia.
Australia warms up the most in January, while Eurasia cools down at this time, resulting in a change in the distribution of air currents.
An area of low atmospheric pressure is formed over Australia, where air from both the Northern and Southern Hemispheres rushes.
Under the influence of the Coriolis force, the trade wind of the Northern Hemisphere deviates and changes its direction near the equator, after crossing which it takes a northwestern direction and, in the form of a humid equatorial monsoon, comes to the northern part of the mainland and the islands.
The action of the trade wind here is very intense, leaving a large amount of precipitation on the east coast and passing through the mountains of Eastern Australia, it transforms into a dry air flow.
The outlying parts of the mainland receive large amounts of precipitation in January.
The southern and southwestern parts of the continent at this time are under the influence of the eastern periphery of the South Indian High, and do not receive winds from the south and no precipitation.
Tasmania and New Zealand are influenced by westerly transport of air masses throughout the year. Air masses, thanks to the flat topography, can penetrate far into the interior without encountering any obstacles.
Climate zones of Australia
Between the equator and the mainland there are small islands and the northern part of New Guinea, located in the equatorial climate zone with dominant equatorial air masses and rising air currents.
The temperature here remains unchanged throughout the year and averages +24, +28 degrees.
The northern part of Australia, the south of New Guinea and a number of islands are located within the subequatorial belt, where the seasonality of the climate is clearly expressed. Winters are dry and summers are very wet.
Atmospheric pressure in the tropics
Between the main zones there are transitional climatic zones: subequatorial, subtropical, subarctic, subantarctic.
In the zone of low atmospheric pressure between 5-10° on both sides of the equator, the equatorial climate prevails - the climate of equatorial depression. In Eurasia, there is a decrease in precipitation across the territory from west to east.
In North America, the Cordillera mountain ranges are a natural boundary separating the maritime coastline from the continental inland areas.
Weather, unlike climate, is an instantaneous state of certain characteristics (temperature, humidity, atmospheric pressure).
Climate in the narrow sense - local climate - characterizes a given area due to its geographical location. Discrepancies with them in specific periods are considered deviations from these norms.
The most important element of climate, influencing its other characteristics, primarily temperature, is the radiant energy of the Sun.
In the troposphere, these include trade winds, monsoons, as well as air mass transfers associated with cyclones and anticyclones. In the hottest places, the heated air has a lower density and rises, thus forming a zone of low atmospheric pressure. Similarly, a zone of high pressure is formed in colder places.
Zonal-regional distribution of atmospheric pressure at sea level
Near the earth's surface, the pressure field is differentiated into belts and regions.
In the equatorial belt, approximately 10° latitude wide, there is low (1000-1008 mb) atmospheric pressure throughout the year - an equatorial depression. The driving force behind its formation is the latent heat of vaporization. Of the total mass of water evaporated in the tropical oceans in a strip 70° wide (from 35° N to 35° S), 75% enters the equatorial belt. Thermal energy generates enormous kinetic energy, lifting the air to 18 km altitude.
The equatorial minimum is not the monotonous continuous band of low pressure that it seemed to be until recently. Against the background of general depression, areas of high pressure continuously appear and disappear, although, of course, their intensity is not comparable with anticyclones of temperate latitudes. Changes in pressure are associated with changes in weather, thunderstorms, and wind squalls. The reason for pressure fluctuations in the equatorial belt is hydrothermal, associated with the release of latent heat of vaporization when air masses meet, at least slightly different from one another.
The winds in this band are random and short-lived, calm prevails, and the entire band is called calm.
During ascending convection, steam condenses, and moisture, both brought to the equator from tropical zones and evaporated locally, falls in heavy equatorial rains, which are called zenithal (based on the position of the Sun at the zenith).
In tropical latitudes, between 35 and 20° of both hemispheres, tropical or subtropical pressure maxima with descending air currents are located on the oceans: Azores and Hawaiian in the northern hemisphere, South Atlantic, South Pacific and South Indian in the southern. The pressure in them is 1022-1026 mb. They last all year.
Proponents of the classical atmospheric circulation scheme explained the formation of tropical pressure maxima by the lowering of air that rose above the equator and was transported to tropical latitudes in the upper troposphere (this transfer was called anti-trade winds, the existence of which has not been confirmed). Now, based on the analysis of maps of synoptic and baric topography, as well as data from high-tropospheric devices, it has been found that tropical highs are formed by the regeneration of anticyclones that have moved from mid-latitudes to the critical parallels of 35°, at which the value of the Coriolis force changes sharply. At the equator it is zero; anticyclones do not penetrate here, which is one of the reasons for the existence of the equatorial depression.
On continents, in accordance with their thermal regime, the pressure system changes from winter to summer. In the summer part of the year of each hemisphere, the pressure on land is normal or reduced (in Australia, South Africa); in the tropics of South Asia, as we have already seen, there is a deep (994 mb) Iran-Tara minimum. In the January part of the year, winter in the northern hemisphere, the Azores and Hawaiian highs merge with the Siberian (1040 mb) and North American (1022 mb), forming a continuous band of high pressure over the subtropical temperate latitudes of the entire northern hemisphere.
In the winter of the southern hemisphere (July part of the year), a minor Australian High (1020 mb) forms over the Australian mainland.
