[trop-uh-sfeer, troh-puh-] 
| the lowest layer of the atmosphere, 6 mi. (10 km) high in some areas and as much as 12 mi. (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. |
| tro·po·sphere (trō'pə-sfîr', trŏp'ə-) n. The lowest region of the atmosphere between the earth's surface and the tropopause, characterized by decreasing temperature with increasing altitude. tro'po·spher'ic (-sfîr'ĭk, -sfěr'-) adj. |
The lowest layer of the atmosphere of the Earth, extending from ground level to an altitude of seven to ten miles.
| troposphere (trō'pə-sfîr', trŏp'ə-) Pronunciation Key
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 exosphere, mesosphere, stratosphere, thermosphere., See illustration at atmosphere. |
əˌsfɪər