THE atmosphere (from the greek atmospheres: gases and sphaira: sphere) is a layer of air formed by a mixture of gases that surrounds the earth's surface, in such a way as to be kept around the planet as a function of the force of gravity. It is one of the main elements responsible for the diffusion and maintenance of life forms on Earth.
It is predominantly composed of nitrogen, responsible for 78% of its volume, added to 21% oxygen and 1% of other gases, such as argon, helium, neon and carbon dioxide. The latter, as they are less abundant, are also called rare gases.
Atmosphere layers
Like Planet Earth itself, the atmosphere is divided into layers: troposphere, stratosphere, mesosphere, thermosphere and exosphere. Note the following illustration.
Diagram of division of atmospheric layers
THE Troposphere it is the most important layer for geographic studies and for human practices, as it is the most important layer of meteorological phenomena, such as rain and humidity variations. Its length is about 15 km.
Above the Troposphere is the Stratosphere, which extends up to 50 km in altitude. Its importance lies in the fact that it houses the Ozone Layer, whose composition is important in filtering the sun's rays.
Next comes the mesosphere, which extends up to 80 km in altitude. Because it is far from the Earth's average heat and relatively far from the sun's rays, it is the layer that has the lowest atmospheric temperatures.
After the Mesosphere comes the thermosphere, which reaches 500 km in altitude. Its importance for humans lies in the fact that it harbors ionized gases that help to reflect and propagate radio waves.
After the thermosphere to outer space, we finally have the exosphere, the layer where artificial satellites are usually positioned.
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Atmospheric pressure
To understand what exactly atmospheric pressure is, let us first understand the concept of Pressure.
Pressure is a force exerted on a certain area.. Thus, in Physics, it is calculated as follows:
p = F
THE
Formula representing atmospheric pressure
As force is always measured in N (newtons) and the area unit is usually in m2, the pressure measurement unit is N/m2, also called Pascal (Pan).
Knives can serve as an example of the relationship between force, pressure and area. The thinner the knife (that is, the sharper it is), the better the cut. This is because the contact surface (area) becomes smaller and, therefore, the force exerted by the pressure becomes greater.
Thus, considering that air has mass, we realize that it also exerts pressure on the surface, which we call atmospheric pressure. The only difference with the example explained above is that the atmosphere does not change its contact surface, remaining constant in regions with the same altitude.
However, as altitudes change, so does pressure. This is because the lower regions feel more the weight of the air and the higher regions feel less the weight of the air. Therefore, the higher the altitude, the lower the atmospheric pressure.
At sea level altitudes, the pressure is approximately 1.023pa, which, by convention, equates to 1 atm.
This explains, for example, why the higher regions are usually cooler, because the lower the pressure, the further away the molecules are and, consequently, the lower the temperatures.
The pressure difference between the different areas allows for atmospheric circulation and climatic variations throughout the year.
By Me. Rodolfo Alves Pena
