troposphere

The lower layer of the atmosphere, extending from the Earth's surface - with which it is in contact - up to the tropopause, located around 11 km of altitude at mid-latitudes, although its thickness varies depending on meteorological conditions and latitude. Within it, temperature decreases fairly regularly with altitude, at a rate of 6.5°C/km (theoretical value, for the standard atmosphere), although in some stretches it presents inversions where that behavior is reversed. The troposphere contains approximately 80% of the total mass of the atmosphere and 99% of all water vapor. Atmospheric pressure, like temperature, decreases as one ascends through it, and it does so, moreover, very rapidly (exponential decrease). At about 5 km of altitude, pressure is approximately half that at sea level. From there upward, the scarcity of oxygen makes breathing difficult. Most meteorological phenomena occur in the troposphere (rain, storms, fronts, cyclones...), with vertical air movements taking place mainly linked to convection (ground heating) and orographic forcing. The agitation of the air, its constant movement, is one of the main hallmarks of this layer, whose name was proposed, in 1909, by the French meteorologist Léon P. Teisserenc de Bort (1855-1913), precisely in reference to its changeable nature. The word "troposphere" arises from the fusion of the Greek terms τροπος (tropos), meaning turn, and σϕαιρα (sphaira), sphere.