[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.
əˌsfɪər