thermosphere

Atmospheric shell extending from the top of the mesosphere to outer space. It is a region of more or less steadily increasing temperature with height, starting at $70$ or $80 km$ . It includes the exosphere and most or all of the ionosphere (not the D region).

Source:

PAC, 1990, 62, 2167 (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2217