ilmakehän

Ilmakehän, the Finnish term for the atmosphere, refers to the gaseous envelope surrounding Earth. Held in place by gravity, it is essential for life, weather, and climate, and it shields the surface from much of space radiation while contributing to the planet’s temperature balance through the greenhouse effect. Note that ilmakehän is the Finnish possessive form of ilmakehä, commonly used in Finnish sources.

Earth’s atmosphere is dominated by nitrogen (about 78%) and oxygen (about 21%), with argon, carbon dioxide, neon, methane and other trace gases making up the rest. Water vapor varies widely by location and season, influencing humidity and weather. The average surface pressure is about 1013 hPa, and the atmosphere’s total mass is roughly 5.15 × 10^18 kilograms.

Structurally, the atmosphere is layered by temperature: troposphere (~8–15 km), stratosphere (~12–50 km), mesosphere (~50–85 km), thermosphere (~85–600+ km), and exosphere beyond that. The troposphere contains most weather and cools with height; the stratosphere contains the ozone layer and warms with altitude; higher layers are progressively thinner and are heated by solar radiation.

Key functions include supporting weather and climate, regulating surface temperatures, and protecting life from ultraviolet radiation through the ozone layer. Human activities alter atmospheric composition, affecting radiative balance and climate. The greenhouse effect helps keep Earth habitable, while aerosols and clouds modify energy transfer in complex ways.

Atmospheric data are collected by weather stations, radiosondes, satellites and ground-based instruments, enabling weather forecasting, climate monitoring, and studies of atmospheric chemistry.