Ilmakerros

Ilmakerros is a term used in meteorology and atmospheric science to describe a major layer of Earth's atmosphere defined by characteristic physical properties such as temperature profile, density, and chemical composition. The concept helps describe how the atmosphere changes with altitude, even though the boundaries between layers are gradual rather than abrupt.

The atmosphere is commonly divided into five principal ilmakerros: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The troposphere extends from the surface to about 8–12 kilometers and contains most of the atmospheric water vapor; weather phenomena occur there, and temperature generally decreases with height. The stratosphere reaches up to about 50 kilometers and contains the ozone layer; in this layer the temperature rises with altitude due to ozone absorbing ultraviolet radiation. The mesosphere lies up to roughly 85 kilometers, where temperatures fall again and meteoroids often burn up. The thermosphere starts around 85 kilometers and can extend hundreds of kilometers; temperatures rise with height because of intense solar heating, and this layer includes regions of ionized gas that affect radio communications. The exosphere is the outermost region, gradually thinning into space, and from about several hundred to thousands of kilometers above the surface the air becomes extremely tenuous.

Composition varies with height, but nitrogen and oxygen dominate the lower atmosphere, while water vapor, carbon dioxide, and trace gases play significant roles in different layers. The concept of ilmakerros emphasizes that boundaries are not sharp but reflect gradual changes in temperature gradients, density, and chemical processes. Measurement and study rely on radiosondes, satellites, lidar, and occultation techniques to observe temperature, composition, and dynamics across the layers.