troposphere

[trop-uh-sfeer, troh-puh-]
noun Meteorology.
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.

Origin:
1905–10; tropo- + sphere

tropospheric [trop-uh-sfer-ik, -sfeer-, troh-puh-] , adjective
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World English Dictionary
troposphere (ˈtrɒpəˌsfɪə)
 
n
the lowest atmospheric layer, about 18 kilometres (11 miles) thick at the equator to about 6 km (4 miles) at the Poles, in which air temperature decreases normally with height at about 6.5°C per km
 
tropospheric
 
adj

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Etymonline
Word Origin & History

troposphere
1914, from Fr. troposphère, lit. "sphere of change," coined by Fr. meteorologist Philippe Teisserenc de Bort (1855-1913) from Gk. tropos "a turn, change" (see trope) + sphaira "sphere."
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
troposphere  [%PREMIUM_LINK%]     (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.

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Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary
troposphere [(troh-puh-sfeer, trop-uh-sfeer)]

The lowest layer of the atmosphere of the Earth, extending from ground level to an altitude of seven to ten miles.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Example sentences
Thank you troposphere for so vividly reminding us how much disdain is still out
  there against the ideal of equality.
All agreed that the troposphere should be getting warmer.
If he does become a star, he may finally be able to get the backing to blast
  into the troposphere.
The troposphere warms, the stratosphere cools, which is what you would expect
  from an enhanced greenhouse effect.
Image for troposphere
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