The planet Earth is surrounded by a gaseous envelope, it is the atmosphere!
There is no defined boundary between the Earth's atmosphere and the solar atmosphere,except by the observation of the behavior of gaseous molecules.
The more these gaseous molecules are removed from the Earth and the less and less they are attracted to and by it!
The atmosphere is thus divided into different layers which are classified according to their altitude and the behavior of the temperature!
The Earth's atmosphere is the gaseous envelope surrounding the Earth called "air".
The dry air consists of 78.087 % of diazote, 20.95 % of dioxygen, 0.93 % of argon, 0.04 % of carbon dioxide and traces of other gases.
The atmosphere protects life on Earth by absorbing ultraviolet solar radiation,
By reheating the surface by retaining heat with the greenhouse effect
and reducing the temperature differences between day and night!
The lower layer of the atmosphere is called the troposphere.
It rises between 8 km at the poles and 16km over the Equator.
The boundary between the troposphere and the stratosphere is the tropopause.
The tropopause is delimited by stabilizing temperatures.
The temperature decreases with the altitude increasing by 0.60 degrees C every 100 m, on average, due to the scarcity
Of the air and the progressive removal of the substrate!
The troposphere is the densest of the four layers of the atmosphere and contains up to 75 % of the mass of the earth's atmosphere!
It consists mainly of nitrogen ( 78 %) and oxygen( 21 %) with only small concentrations of other gases.
Almost all water vapor or atmospheric moisture is found in the troposphere.
The troposphere is covered by the tropopause, a region where the température is stable.
The temperature of the air then begins to rise in the stratosphere.
Such an increase in temperature prevents mass convection of air beyond the tropopause, and consequently most climatic phenomena.
Clouds carrying storms, cumulonimbus, are confined to the troposphere.
It is the most troubled layer, constantly agitated by vertical and horizontal movements.
Vertical turbulence is due to the vicinity of the surface of the globe, which déterminés on the one hand mechanical(by friction) and on the other hand thermal ascension,instability and thermoconvection.
The circulation of the atmosphere depends on various factors.
Cosmic factors with solar radiation.
Planetary factors related to the states of the atmosphere, to the rotation of the Earth around its axis, but also related to the temperature and the salinity of the oceans.
Geographical factors related to the distribution of continents and seas, but also related to vegetation cover and freeze- up.
The circulation of the atmosphere is translated by movements in longitude, latitude, ascending and descending!
Concerning atmospheric pressure....
Air is a gas that has weight.
Atmospheric pressure is the weight of a column of air that extends from a given altitude to the top of the atmosphere and this weight applies to all objects on the surface of the Earth.
It is measured with a
Barometer by counter balancing the weight of the air with mercury.
This method is so widespread that the pressure is often expressed by the height of a column of mercury.
The pressure can therefore be measured in millimeters or in inches of mercury, or in kilopascal or hectopascal or finally in millibar.
At sea level, the pressure is 101.32 kPa or 1013.20 hPa or 1013.20 mb.
When the pressure is greater than 1013 hPa this corresponds to an anticyclone
but when the pressure is less than 1013 hPa it is a low pressure and the lower it is the wind.
An increase in air pressure generally favors good weather while a drop in pressure is often associated with bad weather.
Finally and if the air pressure goes down very fast either 4hPa or more during the last 6 hours, a storm approach!
In France, the highest pressure measured was 1050 hPa in Paris on 6 February 1821.
The lowest measured pressure was 947 hPa at Boulogne-sur-Mer on December 25, 1821.
Worldwide, the highest pressure measured is 1086.8 hPa at Tosontsengel, Khöusgöl( Mongolia)on 20 January 2010.
The lowest pressure measured was 870 hPa at the center of typhoon Juan in the Philippines on 14 October 1970 and also on 12 October 1979 at the heart of TyphoonTip in the Pacific.
Atmospheric pressure is the vital élément in predicting the weather;
Even if the atmospheric pressure "foresees" the weather to 80 %, it remains 20 % devoted to other elements of meteorology!
The stratosphere is the second main layer of the atmosphere.
It lies above the troposphere and is separated from it by the tropopause.
It occupies the region of the atmosphereabout 12 to 50 km, although its lower limit is higher at the equator and lower at the poles
The stratosphere defines a layer in which temperatures rise with increasing altitude.
At the top of the stratosphere, thin air can reach temperatures close to 0 degrees C.
This rise in temperature is caused by the absorption of the ultraviolet (UV) rays of the Sun by the ozone layer.
Such a temperature profile creates very stable atmospheric conditions.
The stratosphere has much less air turbulence, while we find so much turbulence in the troposphere.
As a result, the stratosphere is almost totally cloud-free!
The stratosphere provides some advantages for long-distance flight because it is above stormy weather and has strong, regular and horizontal winds.
The stratosphere is separated from the mesosphere, which lies above it, by the stratopause.
And what about ozone?
The ozone layer is a layer of ozone particles dispersed between 19 and 30 km altitude in the stratosphere.
The ozone layer is essential for life on Earth because it absorbs the ultraviolet( UV ) radiation emitted by the Sun.
The unique physical properties of ozone allow the ozone layer to act as the sunscreen of our planet , providing an invisible filter to help protect all life forms from ultraviolet( UV ) rays emitted by the Sun.
Most of the UV radiation entering the atmosphere is absorbed by ozone, which prevents them from reaching the surface of the Earth.
Ozone is created in the stratosphere above the tropics and then the stratospheric winds vehicle them around the Earth.
Ozone( O3 ) is composed of three oxygen atoms O.
Ozone molecules are capable of absorbing ultraviolet rays and decompose into oxygen dioxide O2 and a free oxygen atom.
Then, when the highly energetic solar radiation strikes an oxygen molecule O2, it absorbs the UV rays and creates two oxygen atoms O by dividing into two.
If the latter comes into contact with another oxygen molecule O2, then they can regenerate an O3 molecule.
This process is known as photolysis.
Ozone would be also naturally decomposed in the stratosphere by sunlight and by a chemical reaction with various compounds containing nitrogen, hydrogen and chlorine.
These chemicals are all naturally found in the atmosphere in very small quantities!
Volcanic eruptions can alter the amount of ozone in the atmosphere, as was the case with the Pinatubo and Hudson eruptions in 1991.
Finally, solar activity also has an influence on the amount of stratospheric ozone!
Loss of ozone?
If the polar regions have a great loss of ozone in the spring, it is mainly due to the polar vortex!
The topography and circular form of the Antarctic is such that a stagnant vortex of stratospheric air, extremely cold, distinct from the rest of the atmosphere, which forms over the region during the long polar nights!
This temperature is around -100 degrees C in the stratosphere of Antarctica and is -80 degrees C in the Arctic stratosphere.
The polar vortex is established in the middle and low stratosphere above 16 km altitude.
The wind blowing around the polar vortex can reach the speed of 100 m/sec!
The air circulates in this polar vortex all winter, becoming cold enough to allow the formation of polar stratospheric clouds that would accelerate and increase the stratospheric destruction of the ozone layer when sunlight returns in early spring.
The vortex is generally very stable over Antarctica during the austral winter, as it is a fairly homogeneous continent, well centered at the South Pole.
Such a vortex also exists in the Arctic, but to a lesser extent.
The Arctic region is composed of many distinct land masses and islands that extend all around the North Pole, and so the air can not circulate as easily as in Antarctica.
This instability of the air causes the temperature there to be less than at the South Pole.
The polar vortex is what causes the winter depressions and the severity of winters.
It is also this polar vortex which determines the undulations of the polar jet!
The air in the upper stratosphere and the lower mesosphere descends into the polar vortex!
Above the equator, between 20 and 50 km above sea level, the stratospheric winds travel around the globe either in the east or in the west.
Every 15 to 20 months the direction is reversed.
This phenomenon is known as the Quasi Biennial Oscillation (QBO).
The winds in general change first the direction from west to east, and vice versa, at the top of the stratosphere at about 30 km altitude.
The change propagates downwards at a speed of 1 km per month but decreases when it reaches 23 km altitude.
This propagation is more regular with the east winds and the amplitude of this change is twice that of the west winds.
In 2015, scientists from the Max Planck Institute published an article on a large anomaly in this cycle,
Something that has never been observed since the measures have been in place for about 60years!
The question arises as to the influence of global warming on this oscillation!
The effects of the quasi-biennialoscillation allows the mixing of certain aerosols, including ozone depleters, atmospheric gases and in particular water vapor,
the stratospheric ozone that protects us from solar UV, And the modification of the precipitation zones of the monsoon.
It would also influences the atmospheric circulation of the northern hemisphere in winter, when the stratosphere warms up by the sudden reversal of the polar vortex.
It would influences the composition of the Antarctic vortex!
The mesosphere, literally the middle sphere is the third highest layer in our atmosphere.
The mesosphere occupies the region between 50 and 80 kilometers above the surface of the Earth, above the troposphere and stratosphere, and below the thermosphere.
It is separated from the stratosphere by the stratopause and the thermosphere by the mesopause.
Temperatures in the mesosphere fall with increasing altitude, up to about -100 degrees C.
The mésosphère would be the coldest of the atmospheric layers.
In fact it is colder than the lowest of the temperatures recorded in Antarctica.
It is cold enough to freeze water vapor into clouds of ice.
You can see these clouds if the sunlight strikes them after bedtime.
They are called "Noctilucent Clouds".
The visibility of these clouds is increased when the Sun is 4 to 16 degrees below the horizon.
The mesosphere is also the layer in which many meteors are consumed as they enter the atmosphere of the Earth.
From the Earth they are seen as shooting stars!
The highest layer of the atmosphere is the thermosphere.
The thermosphere begins at 90 -100 km and goes up to 1280 kilometers of altitude!
The pressure there is almost zero and the molecules of air are very rare.
Solar ultraviolet, very short wave lengths(between 100 and 200 nanometers) is absorbed by molecular oxygen at between 100 and 150 km of altitude.
The temperature increases with the altitude and remains at a level called "thermopause", located from 250 to 500 km depending on the activity of the sun.
After thermopause, the temperature varies between 300 and 1600 degrees C, depending on the energy received by the sun.
The temperatures are high, but since the density of matter is extremely low, it would be very cold for us since the few molecules of air are not enough to transfer us a suitable heat.
The thermosphere is the region where the northern and southern lights form near the poles!
The lower part of the thermosphere is called the ionosphere.
The ionosphere reflected short waves, radio waves.
These waves, emitted by a transmitter, rebound on the ionosphere and are sent back to Earth.
If they are rotated with a certain angle, they can almost circle the globe.
The ionosphere thus allows communication with very remote regions.
The ionosphere is immersed in the very thin upper layer of our atmosphere: the thermosphere.
It is a layer of ionized air in the atmosphere extending 50/60 km above the surface of the Earth at about 640 km altitude!
At the level of the magnetic equator there is a phenomenon known as an équatorial electrojet, which is reflected by large convective movements in the ionosphere
The motions of the ionosphere are complex and depend on many factors such as atmospheric conditions, solar activity, season...
The ionosphere is divided into four parts characterized by a relative maximum of electron density.
Area D extends from 50/60 km to 90 km altitude.
It behaves like a sponge facing the highfrequency waves that pass through it.
Much more present during the day, its ionization is directly proportional to the solar flux, it forms at daybreak and disappears immediately after the sun set.
It consists essentially of heavy ions, such as nitrogen oxides.
As its absorption is inverse proportional to the frequency, the bands of 160 and 80 meters are completely absorbed during short hours of sunshine.
Region E extends from 90 to 140 km altitude.
It is the lowest region used by radio waves to reflect on it.
It is a very special mirror that can be used under both sides, reflecting upwards and downwards.
It appears at dawn and disappears at bedtime.
This layer exhibits, during minimum solar activity, phenomena known as sporadic E which are observed at frequencies greater than 21 MhZ.
The F region is the most ionized mainly responsible for long distance communications
When the solar cycle is at its maximum, this creates more layer ionization, and allows the ionosphere to refract higher frequencies( 15, 12, 10 and even 6 meters) to the Earth for DX contacts.
Around the minimum of the cycle, the number of sunspots is so low that the higher frequencies pass through the ionosphere and disappear into space.
The large number of free electrons in the ionosphere allows the propagation of electromagnetic waves.
Radio signals(a form of electromagnetic radiation) can "bounce" back on the ionosphere allowing radio communication over long distances.
The F-layer is ionized at sunrise, reaches its maximum very rapidly, gradually decreasing at night and reaching its minimum just before daybreak.
During the day, region F splits into two!
The F1 region which extends from 140 to 200 km of altitude is not an important means of propagation, its formation is directly dependent on sunrise and sunset.
After sun set, layer F1 decreases sharply to leave room for layer F2.
The F2 region extends from 200 to 250-600 km depending on the solar activity.
This is the first layer that supports high frequency communications.
During the day it is relatively thin, but during the night, this layer doubles its dimensions, being directly under the influence of solar radiation.
This layer is very dense and allows communication over 1500 km in a single leap!
The energy and dynamics of the thermosphere are strongly coupled with that of the ionosphere as well as that of the lower layers of the atmosphere.
The ionosphere also plays a special role in the mechanisms of loss of atmospheric chemical species towards the interplanetary medium, coupled with the magnetosphere, and contributes to the chemical evolution of our atmosphere.
In this region of the atmosphere, the energy of the sun is so strong that it breaks the molecules and atoms of air, leaving ions(atoms with missing electrons) and freeelectrons to float!
The ionosphere is the region of the atmosphere where the aurora borealis occurs according to the activity of the sun.
They occur mostly in layer F.
The ionization of air molecules in the ionosphere is produced by ultraviolet radiation from the sun, and to a lesser degree by high energy particles from the sun and cosmic rays.
The ionization of the Earth's upper atmosphere is measured continuously in the visible spectrum by observing the number of spots that appear daily on the Sun.
Measurements are also made outside the visible band in the UV and X bands normally absorbed by the Earth's atmosphere.
Indication which is of great interest to the "amateur" radio operator and which indicates the degree of ionization of the upper atmosphere(measurement of the radio frequency flux Fs).
F is expressed in units of flux.
It can range from 65/66 in years when solar activity is minimum as in June 1986, with a flow unit of 66.
This measure is more than 300 units at a maximum of solar activity as on June 15, 1989 with 327 Flow Unit!
Above the ionosphere and up to the top of the atmosphere is the exosphere.
The exosphere is 640 km up to 10.000 km altitude!
It is the outer thermosphere, where the atmosphere merges with the space in the extremely thin air.
It is composed of atoms of hydrogen, helium and oxygen.
However, the rarefied particles virtually no longer collide and behave like independent bodies subjected to the action of gravity alone.
It is in this zone where there are many satellites that gravitate around the Earth!