The earth's upper atmosphere
The layer is the highest region of the ionosphere (from 90 to 600 miles up) which contains the highest concentration of free electrons and is most useful for long-range radio transmission. It is the F region, named the Appleton-Barnett layer in honour of the work of English physicist Sir Edward Appleton and New Zealand physicist and meteorologist Miles Barnett, which determined in 1924 that radio waves reflect off the bottom edge of a layer of the atmosphere at about 60 miles altitude, thus confirming the hypothesis that a conducting layer surrounds Earth. This layer is now named the ionosphere and it is known to be composed of charged particles that react to solar variations, thus creating a space weather region around Earth. Appleton received the 1947 Nobel prize in Physics for "his investigations of the physics of the upper atmosphere especially for the discovery of the so-called Appleton layer".
