The atmospheric pressure refers to a differential, one imaginary air column which is measured weight on a given point on the earth 's surface. This column exerts pressure on the point, yielding a value. This is basically atmospheric pressure. The calculation is carried out as follows: the lower the weight of the column, the lower the pressure exerted and vice versa. Everything will depend on the amount and concentration of the molecules.
When the air is very cold, the atmosphere is stable, presenting stable atmospheric pressure levels, but when the air drastically changes its temperature, sudden pressure changes can occur, which leads to cyclones and hurricanes that disturb the atmosphere. For example, there are currents of hot air that reach a stable atmosphere causing a mixture of temperature, these cause the pressure to decrease creating instability, if this happens at low altitude, on the contrary, when it happens at a higher altitude, instability of the atmosphere will be regulated by the processes.
Atmospheric pressure is measured by means of a measuring instrument called a barometer. The average value of the pressure of the earth's atmosphere is 1013.25 hectopascals or millibars at sea level, which is measured at a latitude of 45 °.
The creation of the Barometer is due to the studies of Evangelista Torricelli. Torricelli's statement says textually: “If it happens that the height of the living silver is lower at the top of the mountain than below, it will necessarily be deduced that gravity and pressure of the air are the only cause of this suspension of living silver, and not the horror of emptiness, because it is true that there is much more air than despite the foot of the mountain than at its vertex "
