Standard Atmosphere

Reference atmosphere adopted by ICAO (International Civil Aviation Organization), which aims to facilitate air navigation. It establishes, for mean sea level, an atmospheric pressure of 1013.25 hPa and a temperature of 15 ºC. It also considers that, between that level and the tropopause, temperature decreases at a rate of 0.65 ºC/100 m (vertical temperature gradient), treats air as a perfect gas, and assumes that the hydrostatic equation is satisfied. Based on these premises, pressure and temperature values can easily be calculated at any altitude of interest. The standard atmosphere is also known as the standard atmosphere or ISA, and its characteristics are based on the conditions that, on average, occur at temperate latitudes.