Introduction to Special Issue on “Long‐Term Changes and Trends in the Middle and Upper Atmosphere”

Abstract This special issue reports the latest results on long‐term variations and trends in the middle and upper atmosphere, in particular, in the mesosphere and thermosphere. The issue is based on selected papers from the 10th IAGA/ICMA/SCOSTEP workshop on Long‐term changes and trends in the atmosphere, held in Hefei, China, 14–18 May 2018. This introduction highlights recent progress in key science areas of long‐term changes in the upper atmosphere.