Atmosphere of Earth and balloons, and too low to permit orbital spacecraft. The mesosphere is mainly accessed by sounding rockets and rocket-powered aircraft. The stratosphere is the second-lowest layer of Earth's atmosphere. It lies above the troposphere and is separated from it by the tropopause. This layer extends from the top of the troposphere at roughly above Earth's surface to the stratopause at an altitude of about . The atmospheric pressure at the top of the stratosphere is roughly 1/1000 the pressure at sea level. It contains the ozone layer, which is the part of Earth's atmosphere that contains relatively high concentrations of
Mixed layer determining the mixed layer depth is to examine the profile of potential temperature, the temperature which the air would have if it were brought to the pressure found at the surface without gaining or losing heat. As such an increase of pressure involves compressing the air, the potential temperature is higher than the in-situ temperature, with the difference increasing as one goes higher in the atmosphere. The atmospheric mixed layer is defined as a layer of (approximately) constant potential temperature, or a layer in which the temperature falls at a rate of approximately 10 °C/km, provided it is free of