American English

Definition of ionosphere noun from the Oxford Advanced American Dictionary

 

ionosphere

 noun
noun
NAmE//aɪˈɑnəˌsfɪr//
 
the ionosphere [singular]
 
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a layer of the earth's atmosphere between about 50 and  600 miles above the surface of the earth, that reflects radio waves around the earth compare stratosphere
See the Oxford Advanced Learner's Dictionary entry: ionosphere