yläilman

Yläilman is a Finnish term meaning the upper air, referring to the portion of the Earth's atmosphere located above the planetary boundary layer. In meteorology and atmospheric sciences, yläilma encompasses the troposphere above the boundary layer as well as the stratosphere, mesosphere and higher layers. The lower boundary of the upper air is not fixed; it generally lies above the surface in a zone where surface effects become weak, typically a few kilometers up, depending on conditions such as surface heating and moisture.

Observation and data collection for yläilman conditions are obtained through radiosonde soundings, aircraft measurements, and satellite atmospheric sounders, supplemented by ground-based remote sensing. Key variables recorded include temperature, humidity, wind speed and direction, and geopotential height, which are used to produce vertical profiles and to feed numerical weather prediction models and climate simulations. International networks coordinated by the World Meteorological Organization (WMO) ensure routine upper-air observations, including radiosonde launches and satellite retrievals.

Applications of yläilman data are central to weather forecasting and climate research. In forecasting, upper-air information helps characterize atmospheric stability, moisture transport, and jet streams, which influence storm development and wind patterns. In climate science, upper-air measurements contribute to studies of temperature trends, ozone distribution, and the response of the atmosphere to greenhouse gases. Aviation also relies on upper-air data for flight planning and turbulence forecasts.

Etymology and usage: the term is formed from Finnish ylä- meaning “upper” and ilma meaning “air.” The genitive form yläilman appears in phrases such as yläilman lämpötilat (upper-air temperatures) or yläilman olosuhteet (upper-air conditions).

See also: Lower atmosphere, Troposphere, Stratosphere, Radiosonde, Atmospheric sounding.