An official website of the United States government.

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Concept Breadcrumbs

Preferred Term:


Region of the atmosphere between the troposphere and mesosphere, having a lower boundary about 8 km. at the poles to 15 km. at the equator and an upper boundary of about 50 km.
Concept Schemes:
Broader Concept:
Narrower Concepts:
Download this Concept:
RDF/XMLCreated 2014-03-20, last modified 2014-11-17