heterosphere

heterosphere

[′hed·ə·rə‚sfir]
(meteorology)
The upper portion of a two-part division of the atmosphere (the lower portion is the homosphere) according to the general homogeneity of atmospheric composition; characterized by variation in composition, and in mean molecular weight of constituent gases; starts at 50-62 miles (80-100 kilometers) above the earth and therefore closely coincides with the ionosphere and the thermosphere.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

heterosphere

heterosphere
The upper portion of a two-part division of the atmosphere according to the general homogeneity of atmospheric composition; the layer above the homosphere. The heterosphere is characterized by variation in the composition and the mean molecular weight of constituent gases. This region starts at 50 to 60 miles (80–100 km) above the earth and, therefore, closely coincides with the ionosphere and the thermosphere.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved