ionopause

ionopause

(aɪˈɒnəˌpɔːz)
n
(Astronomy) the transitional zone in the atmosphere between the ionosphere and the exosphere, about 644 km (400 miles) from the earth's surface
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014