Earth and Moon

Layers of the Earth's atmosphere

Layers of the Earth's atmosphere

The layers of the atmosphere they are the 5 regions in which the zone of gases that surrounds the Earth is divided, the outermost and least dense.

The mass of air surrounding the Earth is not homogeneous, but, as it rises, it changes in composition, density, temperature ... To study it, five layers are established: troposphere, stratosphere, mesosphere, thermosphere and exosphere.

These atmospheric layers are grouped into two regions that differ in their composition:

• »The lowest is the homosphere, which reaches up to 80 km high and covers the first three layers: troposphere, stratosphere and mesosphere. The composition of the air in this region is more or less constant, although not the density, which decreases as the height increases.

• »Above 80 km the region called upper atmosphere or heterosphere, which covers the two upper layers: thermosphere and exosphere. It is stratified in terms of composition. Molecular nitrogen abounds up to 400 km; above, up to 1,100 km, it is composed of atomic oxygen; from there to 3,500 km there is a layer of helium and above it is only hydrogen.

Let's see now five layers of the earth's atmosphere. We analyze them from the bottom up, but be careful: the side illustration is, of course, the other way around. All measurements are approximate.

Troposphere

The troposphere is the layer of the lowest atmosphere. It starts at ground level and reaches an upper limit, called tropopause, located about 7 km high at the poles and 18 km at the equator. It produces important vertical and horizontal movements of the air masses, the winds, and there is relative abundance of water.

It is the area of ​​clouds and climatic phenomena: rains, storms, anticyclones, fronts ... and it is also the most interesting layer for ecology: together with the marine waters and the surface layer of the earth's crust forms what we call environment where life develops

The temperature decreases, with variations, as it rises, and reaches -55 ° C (55 below zero) at its upper limit. The following table shows more detailed data:

Height (m)Pressure (mb)DensityTemperature (ºC)
010131,22615
1.000898,61,1128,5
2.000794,81,0072
3.000700,90,910-4,5
4.000616,20,820-11
5.0005400,736-17,5
10.000264,10,413-50
15.000120,30,194-56,5

Stratosphere

The stratosphere is the atmospheric layer that starts from the tropopause and reaches an upper limit, called stratopause, located about 50 km altitude. The temperature changes its tendency and increases until it reaches around 0 ºC in the stratopause.

In this part of the atmosphere, between 30 and 50 kilometers, is the famous ozone layer, the ozonosphere, important because it absorbs harmful solar radiation for living beings. Ultraviolet rays transform oxygen into ozone, and so the temperature increases.

Here there is almost no movement of the air in the vertical direction, but the horizontal winds frequently reach 200 km / h, which facilitates the rapid dispersion of any substance that reaches the stratosphere throughout the globe, as occurs with the gases that They destroy ozone.

Mesosphere

The mesosphere is the third in height between the layers of the Earth's atmosphere. It extends between 50 and 80 km high and ends at the mesopause. It contains only about 0.1% of the total air mass. It is important because of the ionization and the chemical reactions that occur in it.

In this intermediate layer the temperature drops to -80 ° C. Combined with the low air density, it determines the formation of turbulence and atmospheric waves that act at very large spatial and temporal scales.

The mesosphere is the layer where spacecraft that return to Earth begin to notice the structure of the background winds, and not just the aerodynamic brake. When meteoroids enter the atmosphere they usually disintegrate, causing the flashes we call Shooting Stars. This begins to occur in the ionosphere, continues in the mesosphere and is one of the most important functions of the Earth's atmosphere.

Thermosphere or Ionosphere

The thermosphere or ionosphere extends from a height of almost 80 km above the earth's surface to the thermopause, 700 km or more. At this point there is very little air. When the particles in the atmosphere are ionized by ultraviolet radiation, they tend to remain ionized due to the minimal collisions that occur between ions.

It is called a thermosphere because ionized gases can raise the temperature to 1,500 ° C, although with such a low density this heat is not transmitted, for example, to the International Space Station or the Hubble Space Telescope, which has its stable orbits in this layer. Here too the auroras when the solar wind hits the ions in the polar regions.

The ionosphere has a great influence on the propagation of radio signals. A part of the energy radiated by a transmitter to the ionosphere is absorbed by the ionized air and another is refracted, or diverted, back to the Earth's surface. This last effect allows the reception of radio signals at much greater distances than would be possible using the waves traveling at the height of the earth's surface.

Exosphere

The highest of the atmospheric layers, above the ionosphere, is called an exosphere (or exosphere) and extends to 10,000 km, which constitutes the upper limit of the atmosphere.

The gases gradually disperse in the exosphere until they have the same composition and density of the outer space, where they can easily escape, since the earth's gravity hardly acts. In this area there are many polar orbit meteorological satellites and GPS.

The upper part of this layer is part of the magnetosphere, a space located around the Earth in which the magnetic field of the planet dominates over the magnetic field of the interplanetary medium. Naturally, there is no defined limit to the layers of the Earth's atmosphere.

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