[mez-uh-sfeer, mes-, mee-zuh-, -suh-] 
| 1. | (in the classification of the earth's atmosphere by chemical properties) the region between the ionosphere and the exosphere, extending from about 250–650 mi. (400–1050 km) above the surface of the earth. |
| 2. | (in the classification of the earth's atmosphere by thermal properties) the region between the stratosphere and the thermosphere, extending from about 20–50 mi. (32–80 km) above the surface of the earth. |
| mes·o·sphere (měz'ə-sfîr', měs'-) n. The portion of the atmosphere from about 30 to 80 kilometers (20 to 50 miles) above the earth's surface, characterized by temperatures that decrease from 10°C to -90°C (50°F to -130°F) with increasing altitude. mes'o·spher'ic (-sfîr'ĭk, -sfěr'-) adj. |
əˌsfɪər