the lowest layer of the atmosphere, 6 miles (10 km) high in some areas and as much as 12 miles (20 km) high in others, within which there is a steady drop in temperature with increasing altitude and within which nearly all cloud formations occur and weather conditions manifest themselves.
1914, from French troposphère, literally "sphere of change," coined by French meteorologist Philippe Teisserenc de Bort (1855-1913) from Greek tropos "a turn, change" (see trope) + sphaira "sphere" (see sphere).
The lowest and densest region of the Earth's atmosphere, extending from the Earth's surface to the tropopause. The troposphere is characterized by temperatures that decrease with increasing altitude. At the top of this region, temperatures are close to -55°C (-67°F). The weather, major wind systems, and cloud formations occur mostly in the troposphere. See also exospheremesospherestratospherethermosphere. See illustration at atmosphere.