Martin Jarvis of the British Antarctic Survey has authored a report published in the September issue of the Journal of Geophysics--Atmosphere regarding his team's findings based on tracking the fluctuations of the ionosphere. They think that the outer boundary of the thermosphere, which rises and falls daily, has gone into a long-term retreat of five miles closer to the earth.
I am sure that you can find at least an abstract of the article on the journal website, but the traffic has been heavy this morning and I could not get through myself.
http://www.agu.org/publs/agu-jour.html
Kathryn Aegis